Laboratory Testing for Optometry

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Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Introduction
A working knowledge of basic medical laboratory testing can be crucial in the event that a
systemic condition or infection is a suspect etiology of an ocular finding. The correct diagnosis
and appropriate referral to another health care provider can depend entirely on the results of a
laboratory test. This paper discusses indications for laboratory tests that are most useful for
optometry, including hematology, blood chemistry, urinalysis, serology, the PPD, and cytology
and how to interpret their results.
Optometrists should always communicate with the patient’s primary health care provider when
considering requesting a medical laboratory test. Primary health care providers may often
provide useful information regarding the patient’s health history and can often recommend
other useful tests to order. When in doubt of which medical laboratory test to request, always
consult with a primary care physician.
Blood Work
Blood work consists of three categories: hematology, blood chemistry, and serology. The
differences between these is described below:
Hematology
Hematology, the study of blood and its components, can be broken down into three specific
test groupings which will be discussed in detail:
•
•
•
The Complete Blood Count
Erythrocyte Sedimentation Rate
C-Reactive Protein
The Eight Components of the Complete Blood Count:
Red Blood Cell Count (RBC)
The RBC count tells the clinician the number of erythrocytes per cubic millimeter (mm3 or µL).
Normal ranges for a CBC can be seen in Table 1 below (1).
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Page 1 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
When the RBC count is below the normal range, the patient is diagnosed with anemia. Anemia
can be caused by blood loss, iron or vitamin B12 deficiency, or bone marrow dysfunction.
Conversely, when the RBC count is above the normal, called polycythemia, it may be due to
ominous causes like leukemia (2). Both anemia and polycythemia can lead to cotton-wool
spots and/or hemorrhages on the retina: including white centered retinal hemorrhages (Roth
Spots), mid-peripheral or peripheral retinal hemorrhages (3).
Hemoglobin (Hb)
Recall that hemoglobin (Hb) is the iron-containing protein that carries oxygen in the
bloodstream, as part of the RBC. Therefore, anemic conditions that reduce RBC count also
reduce Hb levels. Polycythemic conditions, like leukemia, can likewise elevate Hb levels, as can
lung disease. Elevated Hb levels are expected for patients who live at high altitudes, and might
also be seen in smokers (2). The normal range for Hb can be seen in Table 1.
Hematocrit (HCT)
HCT is also called the packed cell volume, and tells the clinician the percentage of the blood
volume occupied by red blood cells. The normal percentage of HCT is 42-52% of blood volume
for men and 37-47 % for women (1). Low HCT levels could mean the patient has anemia.
Higher HCT is associated with a disease called polycythemia vera (2). Polycythemia vera is a
myeloproliferative disorder that causes all of the red blood cell elements in the blood to be
over-produced. A stem cell defect is the theorized cause of this disorder. This rare condition
usually occurs in the sixth decade of life and most commonly affects Caucasian females of
Jewish descent (2).
Systemic symptoms of polycythemia vera are a result of the increased red blood cell mass in
the blood: headache, pruritis (itching), fatigue, and weight loss. The pruritis is exacerbated by
heat (showering or exercising) due to the increased amount of histamine from the red blood
cells. Ocular signs of polycythemia vera can include retinal vein thrombosis and occlusions, in
addition to cotton wool spots (3). Eventually 5-10% of patients with polycythemia vera will
develop acute leukemia (2).
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Page 2 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Mean Corpuscular Volume (MCV)
The average size of red blood cells is measured by the MCV. A low MCV can indicate that the
patient has iron deficiency anemia, while high MCV suggests vitamin B12 deficiency (pernicious
anemia). Overall, MCV is used to help diagnose anemia, but it call also occur with recent blood
loss, or poor bone marrow function, or folic acid deficiencies (2). Normal levels for the MCV is
80-90 fL (femtoliters) (1).
Folic acid plays a crucial role in DNA synthesis, including the DNA of rapidly dividing cells.
Erythrocytes, leukocytes, and platelet formation will be affected in folic acid deficiency,
resulting in abnormal cells. Vitamin B12 aids folic acid in DNA synthesis. Thus, a B12 deficiency
can also interfere with normal blood cell formation. It can result in an elevated MCV, called
macrocytic anemia (2).
Mean Corpuscular Hemoglobin (MCH)
The MCH is a test of the mass of the hemoglobin present in an average red blood cell. The
normal range for MCH is 27-31 picograms (see Table 1). Both low (hypochromic) and high
(hyperchromic) MCH values can be consistent with anemia. Hyperchromic anemias include folic
acid or vitamin B12 deficiency. Hypochromic anemias include iron deficiency and a disease
known as thalassemia (3).
Thalassemia is a family of congenital disorders that cause decreased production of normal
hemoglobin in red blood cells. Abnormal hemoglobin can lead to anemia, spleen disease,
infections, gallstones and bone deformities (most common in the face) (2).
Platelet Count (PLT)
Platelets, once called thrombocytes, are necessary for blood clotting and repairing damaged
blood vessels. A normal platelet count is between 150,000- 400,000 platelets/mm3 (see Table
1).
Expect PLT values to be elevated with chronic bleeding such as gastric ulcers, in patients who
smoke, or those with leukemia. Expect reduced PLT values from autoimmune
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Page 3 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
thrombocytopenia (resulting in the destruction of RBCs), blood loss, due to anticoagulant
medication side effects, like Warfarin (Coumadin). A low PLT can also indicate disease such as
an enlarged spleen, septicemia, bone marrow failure due to leukemia, or a condition called
myelofibrosis (2,3).
In myelofibrosis red blood cells have unregulated proliferation. The platelets that are formed
are giant, irregular or fragmented and cannot function normally (2,3).
Mean Platelet Volume (MPV)
The MPV can tell the clinician the average size of the platelets in a patient’s bloodstream.
Normal platelet volume is 7-11 fL (Table 1).
Decreased MPV is consistent with diseases like aplastic anemia. Recent research has shown
that a low MPV can also be associated with inflammatory bowel diseases, and high MPV may be
an independent risk factor for transient ischemic attack (stroke) and myocardial infarction (3).
An elevated MPV can also indicate idiopathic thrombocytopenic purpura. Thrombocytopenia
purpura is a blood disorder found in young children, two to four years old. The destruction of
platelets in this disorder is often followed by upper-respiratory infections. The cause of this
disorder is unknown, but causes children to easily bleed. This condition often will
spontaneously go into remission. A more chronic form of this condition can also occur (2).
White Blood Cell Count (WBC)
WBC count is the number of leukocytes per cubic millimeter (mm3 or µL). A normal WBC count
is 4,000-10,000/ mm3 (Table 1). A low WBC count is called leukopenia. Infection will classically
show the clinician an elevated WBC count. Leukemia (bone cancer) will grossly raise WBC count
as well (3)
Ocular signs of leukemia include white-centered retinal hemorrhages (Roth Spots) flame
hemorrhages and mid-peripheral retinal hemorrhages (75).
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Page 4 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Table 1: Blood Components
Complete Blood Count Component
Normal Adult Value Nice
Red Blood Cell (RBC) Count
Men: 4.7-6.1 million cells/uL
Women: 4.2-5.4 million cells/uL
Hemoglobin (Hb)
Men: 14-18g/dL or 8.7-11.2 mmol/L
Women: 12-16 g/dL or
7.4-9.9 mmol/L
Hematocrit (HCT)
Men: 42-52%
Women: 37-47 %
Mean Corpuscular Volume (MCV)
80-90 fL (femtoliters/µ3)
Mean Corpuscular Hemoglobin (MCH)
27–31 picograms (pg)
Platelet Count (PLT)
150,000- 400,000 platelets/mm3
Mean Platelet Volume (MPV)
7-11 fL (femtoliters)
White Blood Cell (WBC) Count
Men: 5,000-10,000 wbc/mcL3
Women:4,500-11,000 wbc/ mcL3
Source: http://www.webmd.com/a-to-z-guides/complete-blood-count-cbc?page=3
Note that all medical laboratory equipment and hospitals may use different criterion for the
norms of the laboratory testing values (though they are always similar). These norms are
known as “reference” values. If a test value is outside of the reference numbers, the laboratory
test will be flagged with an “L” for lower than normal values and an “H” for higher than normal
values. Table 2 below shows an example of a printout for a complete blood count with
differential test.
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Page 5 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Table 2: Example of CBC with Differntial Medical Laboratory Print Out Southwest Washington
Medical Center Test Patient
Complete Blood Count With Differential Components
A complete blood count should always be ordered with a differential component because it
implies which type of immune response is occurring and give clues to underlying pathology
including infection, autoimmune disease, blood disorders, and allergies.
Differential blood count (Diff) divides white blood cells into five different types. They are (in
order of incidence):
1. Neutrophils: These white blood cells work like a “vacuum cleaner”, by phagocytizing
microorganisms or particles. A higher than normal number of neutrophils are most often due to
bacterial infection, but can also arise from arthritis, surgery, trauma, or myocardial infarction.
Myeloproliferative disorders are a less likely cause (2,3).
2. Lymphocytes: these white blood cells make antibodies bind to pathogens to coordinate the
immune response. They come in three varieties: Cytotoxic (“Killer”), T-cells and B-cells. Expect
them to be elevated in patients with viral infections, active allergies and toxic reactions like
food poisoning. The lymphocyte count will be depressed in HIV positive patients, as the disease
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Page 6 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
selectively attacks and destroys the Helper T-cells (2,3).. Isolated retinal cotton wools spots can
be seen in HIV infection (75).
3. Monocytes fight infection by phagocytizing dead or damaged cells and pathogens not fought off
by neutrophils or leukocytes. A high count can indicate systemic bacteria, as in septicemia (3)..
4. Eosinophils: seen in response to allergies, parasitic infections, collagen vascular disease and
other extensive skin diseases, as well as Addison’s Disease. In the latter case, this is called
eosinophilia (2,3).
5. Basophils: this fifth type of white blood cell brings about allergic response to antigens, mainly
by releasing histamine to cause inflammation. Low numbers of basophils may precede the
onset of leukemia (2,3)
Table 3: White Blood Cells
White Blood Cell Type
Normal Values
% of total WBC count
Neutrophil
48 -80k/ mm3
40% to 60%
Lymphocyte
21-47k / mm3
20% to 40%
Monocyte
4 -8k / mm3
2% to 8%
Eosinophils
0-0.70k/ mm3
1% to 4%
Appearance
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Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Basophils
0-0.20k / mm3
0.5-1%
Source: 4,5
Please note again, that “normal values” or “reference values” will vary slightly from test
instrument to test instrument. Table 4 shows the laboratory print out with reference ranges.
Note that the printout includes the norm for the percentage of total WBC count.
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Page 8 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Table 4: Examples of CBC Differential of White Blood Cells
Medical Laboratory Print Out: Southwest Washington Medical Center Test Patient
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copyrighted by the Pacific University, or by the authors of the individual documents, and are provided for the
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Page 9 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Erythrocyte Sedimentation Rate (ESR or sed rate)
Abnormal blood plasma proteins from inflammatory disease stick to red blood cells and cause
them to settle to the bottom of a blood sample more quickly. The height of the RBC’s, in mm,
settled out of plasma per hour is called the erythrocyte sedimentation rate (ESR) (2).
The ESR test has excellent sensitivity but low specificity. In other words, it can detect even
subtle inflammation, but cannot tell the clinician which disease state is responsible (3). ESR is
elevated in inflammatory conditions including systemic lupus erythematosus, rheumatoid
arthritis, tuberculosis, myocardial infarction, polymyalgia rheumatica and hepatitis C, in
addition to temporal giant cell arteritis (GCA) (3).
If the patient is a suspect for GCA, the first blood test the clinician should order is an ESR (75).
Signs and symptoms of GCA include: optic neuritis, positive afferent pupillary defect, vision loss,
temporal headache, jaw claudication (muscular pain when chewing) and scalp tenderness. A
temporal artery biopsy should also be immediately ordered if temporal arteritis is strongly
suspected. The biopsy may be ordered while lab results are being processed. Sometimes, both
tests are needed because one test may have equivocal results.
The maximum normal ESR for men is equal to the patient’s age divided by two. The normal
maximum ESR for women is equal to (age + 10) divided by two (3,6). A sedimentation rate
greater than 50 mm/hr is suggestive of inflammation. Always order a CBC with an ESR, as
anemia can falsely increase the ESR. The Westergren ESR type is more commonly used (2).
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Page 10 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
The Erythrocyte Sedimentation Test
Source: 6
C- Reactive Protein (CRP)
Another marker of inflammation is C-Reactive Protein. This plasma protein rises dramatically in
systemic inflammation. In addition to CRP being an indicator of acute inflammation, it can also
be elevated in stress, trauma, surgery, neoplastic infection or myocardial infarction (7).
Clinicians use the CRP to check for inflammatory flare-ups, or to monitor the effectivity a
specific treatment regimen. Note that the CRP level is not always elevated by inflammation,
thus this test has some false negatives. When it is elevated, CRP levels have been associated
with increased risk for diabetes, hypertension and cardiovascular disease (7). Patients with CRP
levels of less than 1mg/L are considered low risk, while levels of greater than 3mg/L are
considered high risk for cardiovascular disease (76). The role of CRP in coronary artery disease is
still being investigated. It is possible that the CRP is not merely a marker of inflammation, but
instead plays an active role in inflammatory disease (3).
Blood Chemistry
Blood chemistry testing includes: glucose tests, lipid profiles, thyroid and kidney function
testing.
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Page 11 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Glucose Testing
Blood glucose testing should be run if diabetes is suspected. Diabetes is a disease that leads to
an inability of the body to correctly produce and/or use insulin. As a result, high levels of
glucose are present in the bloodstream. These high levels of glucose can eventually lead to
blood vessel damage and tissue hypoxia. Systemically, diabetes can lead to peripheral
neuropathy and kidney damage (3,8,9).
The well-known signs of diabetic eye disease include: fluctuations in visual acuity, cotton wool
spots, retinal/ or vitreal hemorrhages, and early onset nuclear sclerotic cataracts. Advanced
cases can show neovascularization of the iris, angle, retina, and/or optic nerve (75).
Neovascularization of the retina in diabetes. Photo Source: Dr. Nada Lingel
Fasting Plasma Glucose (FPG) or Blood Sugar (FBS)
Most clinicians use the fasting blood sugar to test for diabetes. As implied by the name, make
sure patients fast for at least 8 hours prior to the FPG. Two reading of elevated levels are
needed to diagnose diabetes. Physicians also use fasting glucose testing to determine the
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Page 12 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
presence of impaired glucose tolerance, a recently established “pre-diabetes” condition. Note
that in healthy patients, blood glucose levels should return to levels below 100 mg/dL relatively
quickly, even after meals. See Table 5 (9).
Random plasma glucose (RPG)
RPG is the glucose level measured without fasting. Normal levels can be seen in Table 5.
Diabetic patients will often have glucose testing kits that can help monitor the RPG at home.
These kits are widely available and can easily be used in office by eye health care practioners
should diabetic eye disease or out of control blood sugar be suspected. No special licensing is
necessary for home blood glucose monitoring kit usage.
Measurements of RPG in office will require some extra equipment in addition to just the blood
monitoring kit, to insure safety for both the practioner and the patient. A home blood
monitoring kit uses a lancet to puncture the skin and draw blood. As blood and sharp
instrumentation are involved in this testing process, universal precautions need to be taken.
The doctor (or technician) administering the test, should always be wearing a new set of latex
(or equivalent hypoallergenic) gloves to prevent disease transmission and should wash hands
immediately before and after the gloves are worn(10).
Used lancets will need to properly disposed of in a “sharps container” to prevent accidental
punctures. Sharps containers can be obtained through local buying groups or local medical
laboratories. A good resource for finding sharps container services can be found at:
http://www.safeneedledisposal.org/dispcenters (11).
Some sharps container services will replace full containers when needed or often times local
pharmacies will charge a small fee to dispose of the sharps.
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Page 13 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Source:http://web.princeton.edu/sites/ehs/biosafety/livevirusworker/decontamination.htm
In RPG testing a droplet of blood taken usually from a patient’s sterilized finger is squeezed
onto the end of a glucose blood test strip. The opposite end of the strip is then inserted into
the blood glucose monitor (each monitor will vary). Once the test results are read off of the
monitor, the test strip, gloves and any sterile cotton or paper products in contact with blood
will have to be properly disposed of to stop possible pathologic transmission. Again proper
hand washing following the procedure is a must (10). Similar to a sharps container, a medical
waste container can be obtained through waste disposal services. Each practioner should check
with his state occupational safety and health division for specific regulations. Links to proper
medical disposal procedures and services can be found at the Environmental Protection
Agencies Website, http://www.epa.gov/epaoswer/other/medical/index.htm (12).
Oral glucose tolerance test (OGTT)
Expectant mothers who develop gestational diabetes are often pre-diabetic before pregnancy.
The oral glucose tolerance test screens for gestational diabetes. Blood sugar is loaded with 75100 g of glucose solution, and serial blood glucose levels are measured. Thus, a glucose
metabolism curve is generated. Impaired ability to metabolize glucose could indicate
gestational diabetes (9).
The Glycosylated Hemoglobin Test (HbA1c or A1c)
Free glucose binds to hemoglobin on red blood cells. The HbA1c measures the
amount/percentage of this binding. As red blood cells live on average for 90 days, the HbA1c is
a measurement of blood sugar over an approximate three-month time period. It is often used
to check compliance with diabetic medications as well as the effectiveness of medical
management. In diabetic patients with poor compliance to diet and medications, including
insulin, the HbA1c is above 7% (8,9).
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www.pacificu.edu/optometry/ce
Page 14 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Table 5: Laboratory Glucose Testing
Glucose Tests
Intrepretations
Normal range: 65 to 99mg/dL
Fasting plasma glucose
(Fasting is defined as no caloric intake for atPre-Diabetes: 100 to 125mg/dL
Diabetes:
>126 mg/dL
least 8 hours.)
Random plasma glucose
Normal range: 65 to 200mg/dL
Diabetes: >200 mg/dL
Oral glucose tolerance test
Normal if: Fasting: <95mg/dL
(100g load)
1 hour: <180 mg/dL
2 hours: <155mg/dL
3 hours: <140 mg/dL
Two or more of the plasma glucose values
must be met or exceeded for a positive
diagnosis.
Glycosylated hemoglobin
Normal Glycemic control: 4% to 6%
(HbA1c or A1c)
Poor control: >9%
Sources: American Diabetic Association Standards of Care in Diabetes 2007(9)
Table 6: Example of an Hemoglobin A1c Medical Laboratory Print Out - Southwest
Washington Medical Center Test Patient
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Page 15 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
Kidney Function Tests
Kidney Function Tests should be ordered in the event that kidney problems are suspected.
Again, diabetics often have kidney failure.
Urea is the primary nitrogenous waste product of human metabolism. High values (>60mg/dL)
can indicate renal failure. If blood urea nitrogen (BUN) and creatinine values are high, this likely
indicates decreased kidney function. Pregnancy is also known to lower the BUN value (3).
The kidneys are also responsible for eliminating creatinine, a byproduct of muscle metabolism.
Patients with greater muscle mass will produce more creatinine. When creatinine levels are
high, the kidneys are likely to be responsible. A declining creatinine value indicates improving
kidney function. Normal levels for creatinine in women are 0.6-1.2mg/dL and for men are 0.51.1mg/dL (77).
Lipid Profile Testing : Serum lipids: cholesterol and triglycerides
A Lipid profile should be ordered in the event that vascular disease is suspected. Hollenhorst
arterial plaques, central/partial retinal vein, or arteriole occlusion, sudden/ transient vision loss,
amaurosis fugax and mid/peripheral retinal hemorrhages could point toward vascular disease
(14,15).
The three parts of total serum cholesterol are as follows:
1. High density lipoproteins: (HDL). The “good” cholesterol, protects against heart disease by
helping remove excess cholesterol deposited in arteries. Higher levels of this cholesterol type
are considered to be beneficial and cardio-protective (3,13).
2. Low density lipoproteins: (LDL). The “bad” cholesterol, LDL cholesterol deposits into arterial
walls when its levels are elevated (3,13).
3. Very-low density lipoproteins: (VLDL). The most dangerous form of cholesterol. VLDLs are
associated with arterial plaque formation (3,13).
Triglycerides are soluble fats that are found in the blood plasma and adipose tissue. Elevated
levels are associated with heart disease, hypertension and pancreatitis. High amount are due to
excess intake of fatty foods and carbohydrates (3,13).
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copyrighted by the Pacific University, or by the authors of the individual documents, and are provided for the
convenience of university faculty, students, and staff, with no warranty of accuracy or usability.
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Page 16 of 54
Laboratory Testing for Optometry
Author: Tracy Doll, OD
COPE #21399-PD
3 credits
If ocular ischemic syndrome is suspected in conjunction with amarosis fugax, carotid duplex
imaging should be ordered as well (14,15) (see imaging section below).
Table 7: Laboratory Glucose Testing
Lipid Type
Low Values
Normal values
High Values
Triglycerides
<150mg/dL (same as the<150mg/dL
>200 mg/dL
>500 mg is very high
normal range)
150-199 mg/dL is
borderline
40 - 59mg/dL
High-density
Men: <40/dL
>60 mg/dL is considered to
lipoproteins
Women: <50mg/dL
be cardio-protective
Low-density
lipoproteins
Very-low density
lipoproteins
<100mg/dL reduces risk130-159mg/dL
for heart disease
borderline
100 - 129mg/dL- near
optimal
<40mg/dL
>40mg/dL
is>160-189 mg/dL
>190mg/dL increases risk of
heart disease
N/A
Table Source: http://www.nhlbi.nih.gov/guidelines/cholesterol/atp3xsum.pdf (13).
An example of a lipid panel medical laboratory printout can be seen below in Table 8. Note that
in addition to a reference range, the printout also contains information that could be useful to
any primary care practioner (including optometrists): it includes optimal values for lipid levels.
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Table 8: Example of a Lipid Panel Medical Laboratory Print OutSouthwest Washington
Medical Center Test Patient
Thyroid Function Tests
The pituitary gland secretes Thyroid Stimulating Hormone (TSH), which stimulates the thyroid
to produce Triiodothyronine (T3) and Thyroxine (T4), the two main thyroid hormones in the
bloodstream (8,16)
The pituitary gland regulates the amount of TSH made by measuring the amounts of T3 and T4
already circulating in the blood stream. If high amounts of circulating T3 and T4 are detected,
the pituitary will decrease the amount of TSH secreted as there are already enough thyroid
hormones in the blood stream. Conversely, when T3 and T4 levels are low, TSH secretion
increases. See Table 5 for normal reference levels of thyroid hormones (8,16).
Elevated TSH can indicate congenital or primary hypothyroidism, while depressed TSH levels
indicate hyperthyroidism (8,16).
Elevated levels of T4 and T3 can be found in hyperthyroidism, acute thyroiditis and hepatitis.
Depressed levels of T4 and T3 are seen in hypothyroidism and with chronic thyroiditis (8).
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Levels of TSH are easier to measure and so are typically obtained first. It is also easier and less
expensive to measure T4, so T3 is usually not measured on screening tests
Many medications that can affect TSH measurements include: antithyroid medications, lithium,
potassium iodide, amiodarone, dopamine, and prednisone (17).
Thyroid Functioning Tests should be ordered if Graves Disease or another thyroid condition is
suspected. Lid retraction, proptosis (exopthalmometry values greater than 22mm or 3mm or
more asymmetry between the eyes), extraocular muscle restrictions, and dry eye could all
indicate Graves Disease (17).
Patients who have Graves’ Disease may be euthyroid at the time of diagnosis. Negative
laboratory tests do not exclude Graves’ disease (17). Orbital imaging studies may still be
necessary (see imaging section below).
Table 9: Thyroid Panel
Thyroid Hormone
Triiodothyronine (T3)/
Normal Levels
80 to 180ng/dL
2.1-6.3pmol/L
Thyroxine (T4)
4.6 to 12µg/dL
Thyroid stimulating hormone 0.4 to 4.0 mIU/L
Source: http://www.nlm.nih.gov/medlineplus/ency/article/003684.htm (5,16)
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Graves Exophthamos. Source: Dr. Richard London
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Table 8: Example of a Lipid Panel Medical Laboratory Print OutSouthwest Washington
Medical Center Test Patient
Urinalysis
Urinalysis can also be ordered in conjunction with blood testing to help confirm systemic
etiology to ocular conditions. This paper focuses on urinalysis correlating to kidney and liver
disease. Keep in mind when ordering urinalysis that the urine used for urinalysis should be
collected no more than two hours prior testing (18).
As previously noted, diabetes is a systemic disease that can affect the health of the kidneys (see
ocular signs of diabetes above under “glucose testing). The following components of urinalysis
can aid in the detection of diabetic kidney disease:
Urine Glucose
The kidneys will normally filter all of the glucose out of urine, thus any glucose in urine is
considered to be an abnormal finding. When excess glucose is present in the blood stream, as
in diabetes, the kidney will max out its capacity for re-absorption 180 to 200 mg per dL (18).
The excess glucose is then “spilled” into the urine where it can be detected by using a chemical
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“dipstick,” a color sensitive pad, containing chemical that react with glucose. The color change
will reflect the amount of glucose in the urine (19). Glucose can also be present in urine
secondary to other systemic conditions including Cushing's syndrome, liver and pancreatic
disease, and Fanconi's syndrome (18).
Urine Protein
In a healthy kidney, only very small particles (weight of less than 20,000 Daltons) can pass
through the kidney’s filtration system (18,20). In diabetic kidney disease, proteins such as
albumin, serum globulins, and proteins secreted by the nephron are allowed to pass into the
urine, as the kidney is damaged. Urine proteins in amounts larger than 50 mg per day (10 to 20
mg per dL) are indicative of renal disease (18). Excess amounts or the protein albumin, or
microalbuminuria (30 to 150 mg of protein per day), is a sign of early renal disease, particularly
in diabetic patients (18). As with urine glucose, urine protein is detected by “dip-stick” testing.
Other systemic conditions that can lead to proteinuria (high levels of urine protein) include:
congestive heart failure, dehydration, emotional stress, exercise, fever, seizures, focal
segmental glomerulonephritis, IgA nephropathy (i.e., Berger's disease), IgM
nephropathy.membranoproliferative glomerulonephritis, Membranous nephropathy, minimal
change disease, secondary glomerular causes, Alport's syndrome, amyloidosis, systemic lupus
erythematosus), Fabry's disease, infections, malignancies, sarcoidosis, ickle cell disease, Tubular
causes, aminoaciduria, Fanconi syndrome, heavy metal ingestion, hypertensive nephrosclerosis,
interstitial nephritis, multiple myeloma (18).
Urine Ketones
Ketones, like urine gluocose and protein are not normally found in urine. Ketones are
byproducts of body fat metabolism. As with the previous test the “dipstick method” is used for
ketone detection. Ketonuria also occurs most commonly is associated with uncontrolled
diabetes. Pregnancy, hyperthyroidism, carbohydrate-free diets, and starvation can also cause
Ketonuria (18,21).
In addition to urinalysis being able to detect kidney disease, it can also be an indicator of liver
disease.
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Bilirubin
Bilirubin is a yellowish pigment created by the death of red blood cells. The liver is responsible
for filtering and disposing of the deceased red blood cells into the gut. If the liver is not
functioning, too much bilirubin could be allowed into the blood stream and lead to a condition
known as jaundice, where the yellow pigment deposits in connective tissue. The main eye sign
of jaundice is yellowed conjunctiva. Bilirubin does not normally appear in urine, so urinalysis
detection of bilirubin can indicate liver disease (18,22,23).
Serological Testing
Serological testing identifies antibodies in the blood serum. If any autoimmune disease or
immune response is suspected to be the culprit for ocular findings, serological tests should be
ordered. Recall that ocular inflammation or infection can be caused by an antibody-mediated
immune response. Serological Testing includes the following tests:
Venereal Disease Research Laboratory/ Rapid Plasma Reagin (VDRL/RPR)
Fluorescent Treponemal Antibody Absorption Test (FTA-ABS)
The VDRL and RPR are the screening tests for Treponema pallidum, the bacterium that causes
syphilis while the FTA-ABS is a blood test used to confirm the presence of antibodies directed
against syphilis. Recall that syphilis is most commonly contracted as a sexually transmitted
disease (it can also be congential, passed on in utero from mother to child) (24).
Because of the expense of the FTA-ABS, many practioners first order a VDRL. If those results are
positive, then the FTA-ABS is ordered. Note that VDRL can be negative in latent syphilis or after
successful syphilis treatment. All 3 tests can get be falsely positive in pregnancy or systemic
lupus erythematosus (24).
Eye signs of syphilis infection include: acute and chronic anterior and posterior uveitis
(granulomatous in 50% of cases), interstitial keratitis, conjunctivitis, scleritis, chorioretinitis,
classic “salt and pepper fundus,” retinal periphlebitis, optic nerve head inflammation or pallor
and secondary cataract. Note that syphilis in known as the “great imitator,” as it mimics many
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ocular conditions. A good medical and social case history is essential in the differential diagnosis
of syphilis (24).
Angiotensin Converting Enzyme (ACE)
ACE is the main test used to screen for sarcoidosis. ACE is 75% sensitive for sarcoid and; it is
95% specific if combined with a gallium scan and chest x-ray (see imaging section below).
Sarcoidosis is a granulomatous disease that can affect any of the organs, but most commonly
affects the lungs. This condition is most common amongst races of color. It is also seen more
often in women, peaking in two different age groupings: 25-35 year olds and 45-65 year olds
(25).
Eye signs for sarcoidosis include: conjunctivitis, iris nodules, granulomatous uveitis, vitritis,
periphlebitis (candle wax drippings), and vasculitis. Tuberculosis, lymphoma, leprosy, diabetes,
hyperthyroidism, and alcoholic cirrhosis can all cause false negative results (26).
Periphlebitis in Sarcoidosis
http://www.uveitis.org/images/sarc8apost.png
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Rheumatoid factor (RF) test
Antibodies normally attach to pathogens or foreign material in the body, thus flagging them for
destruction by the body’s immune response. In autoimmune disease, the body will create
antibodies to the body’s own cells (27). The RF test looks for an autoantibody that specifically
binds to immunoglobulin G (IgG) in blood stream. RF test is the main serological test for
rheumatoid arthritis. Seventy percent of patients with RA are RF positive. Other autoimmune
diseases such as systemic lupus erythematosus and Sjögren’s syndrome are also RF positive
(27). RF is measured by using a blood titer, a measurement of the amount or concentration of a
substance in a solution. A titer is usually expressed as a ratio, the second number indication the
number of times a blood sample can be diluted and still detect the antibody (28, 29). RF is
considered positive, when the titer value is greater than 1:80 (see Table 10 below).
Table 10: Example of a Rheumatoid Factor Medical Laboratory Print Out Southwest
Washington Medical Center Test Patient
Please note that only 5% of Juvenile Rheumatoid Arthritis (JRA) patients are RF positive, so the
RF serology is not an effective test for JRA. The Erythrocyte Sedimentation Rate is also elevated
in RA patients and can be run in conjunction with the RF serology (78).
Rheumatoid arthritis is an autoimmune disease that affects the joints. Systemic
indications of rheumatoid arthritis are: polyarticular (multiple) joint stiffness and pain
(specifically hand, wrist, knee) even in the absence of activity. The proximal joints are the
involved, while the distal joints tend to be spared. Ulnar deviation (fingers pointing outward) is
common in later stages. Fever and malaise can also be seen (27). Common ocular signs of
rheumatoid arthritis include: dry eye, keratoconjunctivitis, episcleritis and scleritis (27).
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Ulnar Deviation of the fingers in Rheumatoid Arthritis
http://www.gutenberg.org/files/17921/17921-h/images/fig160.png
The Antinuclear Antibody test (ANA)
The ANA looks for the presence of autoantibodies aimed toward the cells own DNA. ANA is also
measured using a blood titer. Values greater than 1:20 to 1:40 are typically considered
significant (3,31).
Table 11: Example of a Rheumatoid Factor Medical Laboratory Print Out Southwest
Washington Medical Center Test Patient
ANA can have positive test results in 25% of patients with juvenile rheumatoid arthritis, 30% of
rheumatoid arthritis, 40-70% with Sjogren’s Syndrome, in 60-90% of patients with scleroderma,
and in 95% with systemic lupus erythematosus. Patients with syphilis, chronic infections,
sarcoidosis, and liver disease can also test ANA positive (30).
ANA is positive in 95% of lupus patients (31). Systemic lupus erythematosus usually occurs in
young to middle age adult women in races of color. The condition causes the body to make
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autoanibodies often against the body’s major organs. Renal failure is often the leading cause of
death. These antibodies can also attack the structures of the eye. The major ocular signs
include eyelid erythema, plaques and ulceration. Keratitis sicca, stromal/marginal infiltrates,
pannus formation, and ultimately, ulceration, or neovascularization can occur due to exposure.
Deep interstitial keratitis and kerato-endothelitis can also occur. Migraine headache, diffuse or
nodular scleritis, vitreoretinal / choroidal inflammation, subretinal neovascular membrane
formation, retinal vascular occlusion and multiple cotton-wool spots are a common retinopathy
can also be seen in ocular lupus (30). Systemically, a butterfly-shaped rash overlying the cheeks
and nose is often seen. Infiltration of the lungs by sarcoid granulomas can be observed with
chest x-ray imaging (see imaging section below) (30).
Systemic Lupus Butterfly Rash
Source: http://www.allaboutarthritis.com/AllAboutArthritis/layoutTemplates/html/en/
contentdisplay/printerfriendly_document.jsp?docID=condition/arthritis/clinicalArticle/Lupus.x
ml
Recall that Rheumatoid Factor is rarely positive in juvenile rheumatoid arthritis (only 5%), while
ANA is positive in 25% of children with JRA. Eye signs of juvenile rheumatoid arthritis are:
bilateral anterior uveitis (chronic or acute), usually non-granulomatous, band keratopathy,
small keratic precipitates, posterior senechiae, posterior subcapsular cataracts, vitritis (anterior
not uncommon), cystoid macular edema, hypotony, and maculopathy (82).
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Human leukocyte antigen test: (HLA)
HLA blood testing detects proteins that are present in high concentrations on the surface of
white blood cells, indicating autoimmunity (33). The subtypes of HLA are categorized by letters
numbers and can be indicative of pathology.
The HLA-B27 marker is found in 95% of patients who have ankylosing spondilitis and 70% of
those who have Reiter’s syndrome (Reactive Arthritis) (3).
The main eye signs of ankylosing spondylitis are uveitis with keratic precipitates,
posterior/anterior synechiae, posterior subcapsular cataracts, vitritis, retinal vasculitis,
epiretinal membrane (34). Chronic lower back stiffness and pain are the most common
systemic symptoms (35).
Source: http://hcd2.bupa.co.uk/images/factsheets/ankylosing_edit.gif
Reiter’s syndrome is an autoimmune disease that most commonly affects young (20-40 yearold) males. Eye signs for Reiter’s Syndrome include: conjunctivitis and uveitis. Systemically
common symptoms are urethritis and arthritis. A frequently mentioned way to remember the
systemic manifestation triad for Reiter’s is: “Can’t See. Can’t Pee. Can’t Dance with Me” (36,37).
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HLA- B5 indicates Behçet’s Disease. The major signs of Behçet’s disease, a multisystemic
disorder of unknown etiology, are oral and genital ulcers, skin lesions, and synovitis
(inflammation of the joints). Oral ulcers are the hallmark for this condition (38).
These systemic signs are very often accompanied by anterior/posterior uveitis. Other eye signs
include: retinal vasculitis, chorioretinitis, scleritis, keratitis, vitreous hemorrhage, optic neuritis,
conjunctivitis, retinal vein occlusion, and retinal neovascularization (38).
Other HLA types:
o
o
o
HLA-DR5 suggests Hashimotos Thyroiditis (79)
HLA -DR2 suggestes Lyme Disease (80).
HLA -DR2/3 suggests Systemic Lupus Erythematosus, though ANA testing is more routine
testing for SLE (81).
Enzyme Linked Immunosorbent Assay: (ELISA) and the Western Blot
The ELISA is a blood serum testing method, not a specific test for one kind of disease. Blood is
exposed to antibodies for specific diseases in the ELISA. If a disease is present, antibodies laced
with florescent markers will “stick to” the disease antigen in the serum, indicating an immune
response (8,39,40).
ELISA can be used to confirm Toxocarosis. This is useful in children with posterior
granulomatous uveitis, where toxocarosis can be a main cause. ELISA is also diagnostic in West
Nile and Epstein-Barr viruses, and anthrax (39,40).
The main use for ELISA, however, is as a screener for the Human Immunodeficiency Virus
(39,40).
The Western Blot (WB), like the ELISA is a laboratory testing method, not a specific disease test.
The WB testing separates the blood sample proteins out and then exposes these proteins to
specific disease antigens, leading to the detection of a disease agent (41). The WB can be used
to confirm Mad Cow Disease, Lyme disease and toxoplasmosis (42) along with many other
conditions. The WB’s main use is to confirm HIV after the ELISA screener. It is the confirmatory
test.
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The most common early sign of HIV in the eye can be secondary infections such as herpes
zoster ophthalmicus, Kaposi sarcoma of the conjunctiva, molluscum contagiosum, conjunctival
microvasculopathy, Herpes simplex keratitis or viral keratitis. HIV retinopathy is most
commonly seen as cotton wool spots. In later stages of the disease or progression to AIDS,
retinochorioditis, in addition to secondary infections such as cytomegalovirus, syphilis and
histoplasmosis can also be seen (43).
Cotton Wool Spots in HIV retinopathy
http://www.kellogg.umich.edu/theeyeshaveit/acquired/images/cottonwool.jpg
Kaposi’s Sarcoma
Source: http://medinfo.ufl.edu/year2/mmid/bms5300/images/b21.jpg
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PPD Sking Testing
Purified Protein Derivative (Mantoux test)
The PPD test indicates infection or exposure to Mycobacterium tuberculosis, which can lead to
granulomatous disease. It is also postive in the case the patient has received a TB vaccine (as is
sometimes given in the military or in European countries), or has successfully resisted the
disease and has a natural immune response (44).
0.1mL of tuberculin, a glycerine extract of the tubercule bacilli, is injected into the skin. An
immune response is expected in a person who has been previously exposed to the bacteria. The
reaction is read 48 to 72 hours later, by measuring the diameter of induration in millimeters.
Indurantion is a raised, hardened, palpable area, often reddened. If the PPD is positive, a chest
x-ray is indicated (see imaging section below) to confirm active infection.
Source: http://en.wikipedia.org/wiki/Image:Mantoux_tuberculin_skin_test.jpg
The amount of the induration considered to be positive can vary depending on the individual
(44).
5 mm or more is considered positive in patients with HIV or immunosupression, in those who
have had recent contact with persons with TB, patients with nodular or fibrotic changes on
chest x-ray consistent with old healed TB.
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10mm or more is considered positive in intravenous drug users, mycobacterology lab personal,
health care workers, residents, and employees of high risk highly populated close setting
settings such as prisons, homeless shelters and nursing homes. Recent arrivals (<5years) to this
country from high-prevalence countries, children less than four years old, or children and
adolencents exposed to adults are also in this high risk category.
15mm or more is considered positive in patients who have no known risk factors for TB.
Remember, risk factors can include vaccination or a vigorous natural immunity to the
bacterium.
Should the size of the induration increase 10mm or more within a two year peroid, this is
considered a conversion from inactive to active TB (44). Note that false positives are common
and can indicate exposure versus active infections.
Eye signs of tuberculosis are granulomatous conjunctivitis, scleritis, uveitis, vitritis with
snowball cellular aggregates, pars plana “snow banking” accumulation of cellular aggregates,
choroidal granulomas that could be isolated or mutlifocal and lead to scarring, cystoid macular
edema and optic nerve head inflammation (83).
75% of patients with active TB have pulmonary involvement, which can lead to symptoms of
chest pain, coughing, or coughing up of blood. Transmission of the disease is through airborne
droplets released when an infected individual coughs, sneezes, spits or speaks. Other
symptoms include general malaise, fever, chills, night sweats, and weight loss (83).
Imaging Studies
Imaging studies can often be used to aid in the diagnosis of systemic health conditions, in
addition to blood and serological testing. The Carotid Duplex, X-Ray, CAT Scan, and MRI are all
imaging studies with which the optometrist should become familiar.
The Carotid Duplex
The Carotid Duplex is an ultrasound that is used to look for plaques, blood clots, stenosis of the
blood vessels or other blood flow obstructions in the carotid arteries. Recall that the carotid
arteries are the major sources of the blood supply to both the brain and eyes. A duplex
ultrasound combines Doppler imaging with traditional ultrasound to form color images of the
carotid arteries by measuring how sound waves bounce of the body tissues. Red blood cells will
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bounce back the sound waves at a different frequency than the blood vessels and deposits such
as cholesterol. The velocity at which the blood is moving through the vessel is also picked up by
the duplex. By measuring this velocity at different locations and times, the amount of stenosis
can be calculated (46-48). A radiologist will record these velocities and interpret them. A chart,
such as the one seen below will be used to calculate the amount of internal carotid artery
stenosis (46-48).
Table 12: Carotid Artery Stenosis Criterion
Stenosis % Peak Systolic
Peak End Dyastolic Peak Systolic
Velocity in cm/sec Velocity in cm/sec Velocity Ratio
<50
<125
-<2
50-69
125-230
40-100
2-4
>70
>230
>110
>4
Near
May not be
--occlusion detectable
Total
May not be
--occlusion detectable
Source: http://razi.ams.ac.ir/AIM/0473/005.htm
-----
Appearance
No plaque or
thickening seen
Plaque or
thickening seen
Visible plaque
and/or lumen
narrowing
Lumen narrowing
No detectable
lumen
Recall that ocular ischemic syndrome (OIS) is a result of low blood supply to the eye. It usually
only occurs if there is 90% or greater stenosis of the carotid artery. This will lead to a 50% drop
in profusion to the central retinal artery. Common anterior segment findings include advanced
cataract, anterior segment inflammation, and iris neovascularization. Posterior segment signs
include narrowed retinal arteries, dilated but nontortuous retinal veins, mid-peripheral dotand-blot retinal hemorrhages, cotton-wool spots, optic nerve or retinal neovascularization and
spontaneous arterial pulsation. The main symptoms include ocular pain and abrupt (lasting 10
minutes or less) or gradual visual loss (14-15).
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Source: http://www.nlm.nih.gov/medlineplus/ency/imagepages/18051.htm
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Carotid Duplex Screen Image
Source: http://www.gehealthcare.com/usen/ultrasound/products/msucmecd.html
Mid peripheral Hemorrhages as seen in OIS
Source: http://www.revoptom.com/handbook/SECT44a.HTM
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X-Ray
X-Rays, also called Röntgen rays, are a type of electromagnetic radiation that can be used to
image bodily structures. The patient is placed between the X-ray emitting source and a
photographic receptor, called a plate. This plate produces shadows of the body’s internal
structures being X-rayed. X-rays can pass through soft tissues such as organs and muscles. The
X-Rays that pass will turn the receptor plate black when it is developed. Bone and other dense
tissues block X-rays and thus do not turn the plate black, appearing white on the plate. If a soft
tissue, such as a blood vessel needs to be imaged, radiopaque dyes can be injected to block Xrays, and thus will be seen as white on the scan, similar to the more dense body tissues (49).
The Chest X-Ray is often used to confirm granulomatous disease. The chest, lungs, heart, major
arteries, ribs, and diaphragm are all included in the final imaging photos. Below is a photo of a
healthy pair of lungs. Be sure to notice the black, empty space occupying the lungs: these are
areas where the X-rays passed, unblocked. The white spot to the lower left in the photo is the
heart (50).
Normal Chest X-Ray
Source: http://www.rctradiology.com/generalradiology.html
The lungs are common sites for granulomatous infiltration. Recall that sarcoidosis, tuberculosis,
and histoplasmosis (see below) are all granulomatous systemic diseases.
In Sarcoidosis, the infiltration will cause scarring, which can be seen as a diffuse granular
appearance or white spots in areas that should be normally black (50).
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Late sarcoidosis: white
scars
Early sarcoidosis: granular
Source: http://www.nlm.nih.gov/medlineplus/ency/article/003804.htm
In tuberculosis, the infiltration of the lungs by tubercules can cause scarring and death of the
lung tissue. The areas of infiltration are easily seen in the photo below as white areas and are
marked by arrows. A similar appearance can be seen in histoplasmosis (50).
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Advanced Tuberculosis
Side view
front view
Source:http://www.nlm.nih.gov/medlineplus/ency/article/003804.htm
Tuberculosis, in addition to causing lung disease, can have eye complications. Tuberculosis can
manifest in the eye as anterior or intermediate uveitis, chorioretinitis, panophthalmitis and
choroidal tumors (89).
Histoplasmosis capsulatum is a fungus endemic to the Ohio Mississippi River Valley. Bird and
bat droppings accumulate and create an environment perfect for Hisoplasmosis capsulatum.
When the fungus becomes airborne, it can be inhaled and deposits in the lungs, where it
causes infection. This infection can spread through the blood stream and take up residence in
the eye at the level of the choroid. The triad of ocular signs in histoplasmosis infection
includes: 1. Disseminated midperipheral choroiditis, which appears as yellow-white, punchedout lesions from infiltration and subsequent scarring. 2. Macular /paramacular subretinal
neovascular membrane, which is seen as a gray-green area surrounding the macula with or
without exudates, sub-retinal blood or scarring. 3. Peripapillary atrophy or scarring adjacent to
the optic nerve head(51,52).
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Histoplasmosis Triad: Choroiditis, Paramacular/papillary scarring
Source: http://www.revoptom.com/HANDBOOK/sect5o.htm
Computed Axial Tomography Scans
The Computed Axial Tomography (CT or CAT) uses combined x-ray scans from a circular x-ray
machine and computer to create cross-sectional and three-dimensional images of body
structures called tomograms. The tomogram images show slices through the body.
Occasionally contrast dyes, usually iodine-based dye or barium solution, can be injected into
the blood stream or taken orally to enhance the difference between bodily tissues (53,54).
Graves’ Ophthalmopathy is supported by positive CT Scan imaging. Recall that Grave’s eye
disease can cause infiltration of the orbital tissues. These are easily imaged with a CT scan. The
extraocular muscles will show enlargement at the center (often called the belly), while the
tendon insertions are spared (17). Prominent intraconal fat, as well as fat at the apex of the
orbit is often seen. A CT scan can show compression of the optic nerve and proptosis.
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Graves Ophthalmopathy- Infiltration of Extraocular Muscles
Source: http://www.learningradiology.com/caseofweek/caseoftheweekpix2/cow154lg.jpg
CT scans can also be useful in the identification of an orbital blowout fracture. When pressure
is applied to the orbital contents, as in blunt force trauma, the weakest point of the orbit can
fracture. This fracture of the orbital floor or walls saves the globe from rupture. In this process,
orbital fat and muscles can become entrapped. Signs and symptoms of entrapment include:
extraocular muscles restrictions, pain on movement and diplopia (especially in up or lateral
gaze). Other signs of orbital blowout fracture include enophthalmos, crepitus, rhinorrhea, and
periorbital lacerations or ecchymosis. A CT scan shows the best display of inferior orbital rims,
naso-ethmoid bones, and the maxillary sinuses. If air and fluid levels can be seen in the
maxillary sinus on CT scan, this could be indicative of fracture of the maxillary sinus, which lies
beneath the orbital floor (see photo below). In the event that a blowout fracture is suspected,
careful examination of the anterior segment for laceration or perforation should be preformed.
Blunt force trauma can also put the patient at higher risk for retinal detachment (55).
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Blow Out Fracture of Orbital Floor
Source: http://www.hawaii.edu/medicine/pediatrics/pemxray/v6c09.html
Orbital cellulitis is another ocular condition that can be confirmed through computed axial
tomography. An orbital infection (bacterial, viral, or fungal) posterior to the orbital septum
needs to be carefully differentially diagnosed. Orbital cellulitis is an emergent condition as
patients are at a high risk of infection spreading to the orbital contents, cavernous sinus, and
meninges (56). Meningitis can cause permanent neurological defects or death. Most commonly
orbital cellulitis is a result of an extension of an infection of the paranasal sinuses, but can also
occur as a result of bacterial infection from trauma or the bloodstream. Signs of orbital
cellulitis include decreased visual acuity, pain on eye movements, positive afferent pupillary
defect, fever, malaise, rhinorrhea, severe lid edema, fever, tenderness, proptosis, conjunctival
chemosis and increased intraocular pressure. A high resolution CT scan (with contrast agent) of
the orbit and sinuses can confirm the presence of paranasal sinus opacification. Coronal and
axial views are recommended. Suspected orbital cellulitis needs to be immediately referred to
emergency medicine, as it is potentially life threatening and will need to be treated with
intravenous antibiotics immediately (56).
CT scans can also be useful in helping to diagnose orbital masses when proptosis is evident
(53,54).
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Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) uses radio waves and magnetic fields to image non-calcific
body tissues. The magnetic field forces hydrogen atoms in the body to line up in a specific
manner. Radio waves are then sent toward the hydrogen atoms in the body tissues. Different
tissues bounce the radio waves back at different speeds. A computer records these bounced
signals in two dimensional cross-sections that are later compiled to create a three-dimensional
image. The different signals are recorded in different colors on the scan. For instance in the
brain, white matter will appear white, gray matter will appear gray, and cerebral spinal fluid will
appear black. Contrast agents, usually gadolinium based, are sometimes intravenously injected
to enhance the contrast of the tissues (57-59).
Contraindications to MRI are pacemakers, ferromagnetic foreign bodies (such as bullet shell
fragments) and metallic implants due to the magnetic field the MRI generates.
MRI is useful especially in the case diagnosing Multiple Sclerosis. Recall that Multiple Sclerosis
(MS) is a demyelinating autoimmune disease that attacks the central nervous system. White
matter tracks are those that are affected in the spinal cord and brain. The etiology of MS is
unknown, but it does tend to occur more often in Caucasian young adult females who live in
temperate climates. Common signs and symptoms of MS are weakness and fatigue and in the
eye, most commonly optic neuritis. Worsening of vision following exposure to heat and exercise
is called Uthoff’s sign. In addition to optic neuritis, other eye signs of multiple sclerosis can
include intraocular opthalmoplegia and diplopia. Sharp shooting pain up the back of the neck,
when the head is flexed toward the chest, is called L’hermitte’s sign. These signs and symptoms
tend to relapse and recur over time (60).
Abnormal MRI scans can be found in up to 90% of MS patients. The inflammation and
breakdown of the blood-brain barrier due to the damage from an MS lesions will cause a leak of
extravascular fluid. The MRI for suspected MS uses a special sequence called the FLAIR (Fluid
Light Attenuation Inversion Recovery) sequence. With the FLAIR sequence, free water appears
dark on the MRI, but edematous tissues remain bright. The MS lesions will glow brightly, while
cerebral spinal fluid will appear dark black (57-60).
MRI can also be used in the diagnosis of Graves Ophthalmopathy. Enlarged extraocular muscles
with sparing of the tendons, is a diagnostic sign of Graves’ disease. Contrast agents are
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especially helpful for separating normal orbital fat from infiltration. A fat contrast suppression
agent is used, allowing the normal orbital fat to appear black (57-59).
Ocular Infection Testing/Cytology
Ocular surface infections, especially those involving corneal ulcers, are most often treated
empirically using fourth generation fluroquinolones. Fourth generation fluroquinolones
include: gatifloxacin (Zymar) and moxifloxacin (Vigamox). Empirical treatment will cure the
bacterial infection in ninety percent of cases (61,62). However, ten percent of bacterial
infections will not respond to traditional therapies. In these cases, cytological testing becomes
necessary. Finding the correct infectious agent could involve any of the following techniques:
•
•
•
•
•
Smears: sample of discharge
Scrapes: sample of discharge, with some cells
Cultures: Samples are plated on nutrient media to encourage growth of micro-organisms
Sensitivity: antibiotic- soaked disks are placed onto culture plates and zones of growth are
analyzed to determine sensitivity and resistance
Stains: stains applied in organism identification
Culturing
Cultures are most effective taken before initiating treatment of the infection. Cultures can be
also be taken after treatment has begun since treating an infection before taking a culture only
slightly decreases the rate of positive cultures overall (61). It does, however, take much longer
to receive the results of the laboratory testing post treatment, because the infectious agent
needs to incubate longer to yield a positive result. In either case, pre- or post-treatment
culturing will yield good information to aid in the proper treatment of the patient.
To perform a culture, a topical anesthetic is first instilled into the eye. Proparacaine is
recommended, as it is a less bactericidal anesthetic (62). Next a sharp instrument such as a
sterile platinum spatula, scalpel blade, foreign body spud or sterile cotton swab is used to
obtain a scraping from the corneal ulcer (62). Epithelium, necrotic stroma, and infiltrate
material are the most useful, so rubbing the leading edge of the lesion is necessary (61,62,63).
Discharge alone does contain as much of the infectious agent. In the case that a fungal
infection is suspected, as in fusarium keratitis, culturing the contact lens case can also be useful
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(63). Contaminating the culture can be avoided by making sure the sample does not touch the
eyelids, lashes or other structures. Culturing should be done with care to avoid corneal
perforation (62). Culturing is not recommended if extensive corneal thinning has occurred and
there is risk of perforation (62).
The Media
The obtained scraping or smear is then swiped either directly onto a media plate or placed into
a culturette tube for transport to a laboratory (where it will be plated) (63). is important to
have the culture delivered to the lab within twenty-four hours to maximize the potential for
accurate sensitivity testing and identification of the infectious agent (62). If keeping culturing
media in the office seems too cumbersome, local laboratories will often courier media. The
following media are commonly used in infectious testing for the eye:
Stuart’s medium is used as a transport in culturettes. Stuart’s medium is composed of sodium
glycerophosphate 1.0%; sodium thioglycolate 0.1%; calcium chloride dihydrate 0.01% and
water. A common system uses a rayon-tipped swab attached to a flexible aluminum wire,
which is then used in the scraping/smear (64). The swab is then placed into a 0.5mL ampule of
Stuart’s medium and sent to the laboratory (64).
Sabouraud’s Agar is the media used when a fungal etiology is suspected. A good case history
will lead to the suspicion of a fungal etiology in instances such as contact with vegetation like as
a tree branch, or history of therapeutic contact lens wear (66). Fusarium is a fungal infection
that has gained popularity in the press lately due to suspected isolated, infected batches of
contact lens solution. The patient may be also immune-compromised or be on a ventilator (65).
A feathery corneal infiltrate is also suspicious for fungal etiology(65). Fungal infections should
not be treated empirically as these infections can often be impossible to differentiate on
appearance from bacterial infections (63). The only topical antifungal treatment, Natamycin, is
completely ineffective against bacteria and viruses. Natamycin is also very toxic and can cause
additional irritation, swelling and redness to the eye (63) Sabourd’s agar can be easily obtained
by a lab and should be refrigerated until it is needed. A positive yield normally takes seventytwo hours to grow (63). After the culture, treatment should be started with a fourth generation
fluroquinolone antibiotic in the event that the infection is actually bacterial in nature (63). Once
the results of the culture are obtained and deemed positive, treatment with natamycin can be
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initiated. Note that it is always a good idea to consult with a corneal specialist in the event that
any vision threatening corneal condition exists.
A non-nutrient agar with an Escherichia coli heat-killed overlay should be used if
Acanthameoba, a parasitic infection, is suspected. The acanthamoeba will eat through the
overlay. For the reason this test is known as the “Pac-Man” test (63).
Confocal microscopy is a different method that can also be used to detect the presence of
Acanthameoba. This method is noninvasive and may be more sensitive than any staining
method in detecting Acanthamoeba in early infections. It detects the parasite “in-vivo,”
including the double-walled cysts and trophozite forms (84). Confocal microscopy is a
miroscopic imaging technique used to increase contrast and/or to reconstruct 3-D images by
using a spatial pinhole to eliminate out-of-focus light in specimens. The image quality is much
better than that of wide-field images in traditional microscopy (85).
Ocular signs and symptoms that acanthamoeba has infected the eye are: intense pain that does
not match the presentation of the cornea, a bulls-eye lesion on the cornea with radial
infiltrates. Poor disinfection of contact lenses with tap or well water, swimming in lenses in
lakes or hot tubs can also point to a possible acanthamoeba source (65,67).
A red eye that does not respond to antibacterial or antiviral treatment should include
acanthamoeba and fungal infection as differential diagnoses. It should be noted that if either
cultures are inconclusive for acanthameoba or fungal infection, the patient should be
immediately should be referred to a corneal specialist for a corneal biopsy, which is the only
truly definitive method (although much more invasive than a culture) (65,67).
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Acantheomeoba keratitis.
Source: Kertes and Johnson (2007)
Other media that can be helpful are:
•
•
•
Chocolate Agar Media will grow most bacteria, including Neisseria and Haemophilus influenzae
(86).
Thioglycollate broth is used if an anaerobic bacteria is suspected (87).
Thayer Martin media will show Neisseria (86).
Specific Stains
In addition to culturing, staining is often used in the identification of an infectious agent. First, a
sample is smeared onto a slide and then chemically or heat fixed to that slide. Different
chemicals and dyes are then applied to sample slides. The reaction of the organisms to the
various chemicals and dyes can lead to identification of the organism.
Giemsa Staining is a mixture of methylene blue and eosin. It has various uses. One main use is
its ability to identify white and red blood cell types. Erythrocytes will stain pink, while platelets
turn pale pink. Lymphocyte cytoplasm stains sky blue and monocytes have cytoplasm that turns
light blue. And lastly, leukocyte nuclear material will stain magenta (69) (see photos under
blood testing section above.)
Giemsa Staining can also help identify bacteria, fungi (Histoplasma capsulatum) and
acanthamoeba (63,66,67,68).
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Gram Staining helps to differentiate Gram-positive and Gram-negative bacteria. A crystal violet
stain is first applied. Then iodine and decolorizer are added to clean the slide. Finally, a counter
stain, safranin is typically applied. Gram-negative bacteria take up safrinin dye and appear red.
Gram-positive take up crystal violet dye and appear purple. This type of stain can also identify
fungi (68).
Potassium hydroxide (KOH) preparation stain is used to identify fungi. When the solution is
applied to the slide, all cells other than fungi cells will dissolve. This leaves the fungi exposed for
identification (63,68)
Papanicolaou (PAP) stains cytoplasmic inclusion bodies found in Chlamydia trachomatis. The
PAP staining process includes five dyes (haematoxylin, Orange G, Eosin Y, Light Green SF and
Bismark Brown) (88).
Acid-fast staining (Ziehl-Neelsen Stain) identifies mycobacterium and Nocardia (a bacteria)
species. The reagents used in this staining process are carbol fuchsin, acid alchohol and
methylene blue. Acid fast bacteria retain the carbol fuschin and stain a red color. Non-acid-fast
bacteria with retain the methylene blue and appear blue (68,70). Mycobacterium will stain red.
A long filamentous organism with a dark red center is a typical appearance for Nocarida.
Reports of Nocardia infection have been reported following LASIK surgery. The clinical
presentation is usually: superficial patchy infiltrates, which may be arranged in a wreath
pattern. Most commonly sulfacetamide eyedrops can be tried as the initial drug. Once therapy
is initiated, the infiltrate should responds promptly and resolves, with some scarring. Good
visual recovery can be usually be expected if treated (71).
How to Choose a Lab
This article detailed the importance of medical laboratory testing for optometrists. As many
eye health and systemic conditions can be diagnosed off of laboratory tests, it is very important
that the medical laboratory tests be accurate and reliable. Some consideration should be taken
then in ordering tests from a reliable medical laboratory.
It is important to check that the medical laboratory of choice is accredited. Both the Federal
government and independent organizations accredit medical laboratories. The Clinical
Laboratory Improvements amendment passed by the Federal Government in 1988, set
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standards by which all laboratories in the United States must adhere (note that if individual
state requirements are more stringent, they will apply over the federal requirements). The
requirements a laboratory must meet include those involving education and training,
proficiency, quality control, and patient safety (72).
The Joint Commission is a private organization that “evaluates and accredits more than 15,000
health care organizations and programs in the United States. And independent not-for –profit
organization, the Joint Commission is the nation’s predominant standards-setting and
accrediting body in health care (74).” Any medical laboratory an optometrist is considering
should meet the Joint Commission Standards for safety (72). The Joint Commission has a
search engine on a website that allows the public to check on any medical laboratory to see if it
has met standards: http://www.qualitycheck.org/consumer/searchQCR.aspx.
Many times the laboratory to which the patient is sent to can depend entirely on the patient’s
insurance. The cost to the patient will vary depending on whether the patient has insurance
and what testing the insurance will cover. This being said, it is still important to know whether
or not the lab is meeting standards.
A health care provider should look for a lab that gives consistent, accurate and timely results.
As evidenced by this article, a vision or life-saving diagnosis can be entirely dependent upon the
findings.
Conclusions
The underlying cause/ systemic disease leading to an eye condition can be determined very
quickly with proper working knowledge of medical lab testing and results.
If you are unsure of which tests to run, consult a medical laboratory technologist or a Primary
Care Physician (PCP). It is always a good idea to communicate with the patient’s PCP when
referring for medical laboratory testing.
Referring a patient to the proper health care provider with properly completed laboratory
testing can increase efficiency of care of the patient and builds relationships with medicine and
osteopathic medicine and can help to emphasize the high level of training of optometry as a
profession.
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•
•
Special thank to:
Medical Laboratory Technologist
Shelley Hubka of the SouthWest Washington Medical Center
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12. Medical Waste. The U.S Environmental Protection Agency Website.
http://www.epa.gov/epaoswer/other/medical/index.htm. 10/12/07.
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