Does Contrast Testing have a Place in
YOUR CLINIC?
Device manufacturers think it will, and they're working toward more automation and efficiency.
BY DESIREE IFFT, EXECUTIVE EDITOR
Odds are that unless you've participated in a clinical trial lately, you've lost track of your contrast sensitivity tester, or you don't have one at all. But there's also a chance that you've given at least some thought recently to whether it could be of some use to you. Conversations about that crop up these days as awareness of the limits of visual acuity testing have become so clear.
Maybe you'd like to have documentation of contrast loss in your 20/25 cataract patients, start treating glaucoma suspects at the first signs of functional vision reduction, or see whether nutritional supplements are improving real-world vision for patients whose acuities may or may not be stable.
As ophthalmolgists and other eyecare professionals begin to think differently than they have in the past about how best to evaluate vision, companies that offer contrast sensitivity devices expect the market for their products to expand. Some have introduced, or plan to introduce, products that are more automated and efficient.
For example, new from Vision Sciences Research Corp., founded by Arthur Ginsburg. Ph.D., MSEE, developer of the Functional Acuity Contrast Test (FACT), is EyeView Functional Analysis Software. It makes contrast testing even simpler to administer. Responses are scored on-screen, and then converted into the contrast sensitivity curve and into pictures that illustrate what that means for the patient's vision.
Another company, M&S Technologies, Inc., is working with Jack Holladay, M.D., MSEE, FACS, on a contrast sensitivity testing system that allows patients to self-test. The patient views the targets and enters his responses, and the system prints out a report for the doctor to evaluate. Pilot studies, calibration and the normative database are being finalized, and the device should be available early next year.
Valuable Data
Glenn Pomerance, M.D., a general ophthalmologist who practices in Chattanooga, Tenn., has always used contrast sensitivity testing as an integral part of his examination. It takes him or a technician less than five minutes to test two eyes with the VectorVision CSV-1000, and the majority of his patients are tested regularly. "We never base treatment decisions on any one test, but contrast sensitivity can tell us many things," he says. "It's just like any other part of the exam that's not reimbursed separately; it gives us another piece of data to help guide proper management."
Dr. Pomerance cites several situations in which he finds contrast sensitivity testing useful:
► If a patient comes in with a small posterior subcapsular cataract and says he's blinded by bright light, it wouldn't be unusual for him to test 20/20 on the Snellen acuity chart. So, that gives the doctor no information about the difficulties he's experiencing. "But if the patient undergoes a contrast sensitivity test and there's a reduction on the 6 cycles per degree grid, that positively confirms the problem."
Also, when patients present with ill-defined functional vision complaints, the cataract screening slide indicates how their vision is working outside the office setting. For the patients, this marries the complaint to the real-life problems with daily living they're experiencing.
► In the mid-1990s, Dr. Pomerance and others described their observation that reduction in perception of the 12 cycles per degree grid indicate ongoing loss of nerve fiber layer function in glaucoma. "This tends to normalize when the patient is using the correct medication regimen," he says. "By watching the 12 cycles per degree notch, you can tell whether you have a therapeutic response satisfactory to protect the nerve fiber layer."
► Dr. Pomerance also uses contrast testing to detect subtle vision changes in patients who are taking potentially retinotoxic medications such as hydroxychloroquine or tamoxifen. "We see a lot of patients referred from rheumatologists and oncologists who are scared to death about reports of toxicity. It's best to test them meticulously."
Turning Point?
Dr. Holladay believes that more practices, those who treat retina disorders as well as general ophthalmology offices, will eventually bring contrast testing into their daily routines. "Retina and optic nerve disease are where the test is most provocative and gives the clinician the most information," he says, "but once the tests are more automated, standardized and cost-effective, they'll be utilized in comprehensive practice as well."
He suspects contrast testing will go the way of many other tests, such as the visual field exam, which only glaucoma specialists performed at first. "As treatments and diagnostic tests improve, there is less of a desire for general ophthalmologists to refer cases out," he says. "It may be gradual, but I think we'll see a resurrection of contrast sensitivity testing."
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An Integral Part of the Exam |
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Glenn Pomerance, M.D., regularly measures contrast sensitivity in most of his patients. Here he shares three cases that illustrate how it can be helpful. Case 1: Glaucoma Treatment Assessment Contrast testing reveals a 12 cycles per degree "notch" in a 61-year-old African American male with a family history of glaucoma, early visual field abnormality and topographic evidence of nerve damage. (See images below.) After treatment with a beta blocker for 4 weeks, and a reduction in IOP from 26 mmHg to 19 mmHg, there is some normalization of the notch. A prostaglandin is added; pressure decreases to 15 mmHg; and the notch is normalized, indicating likely satisfactory control of the glaucoma.
Case 2: Cataract A 70-year-old Caucasian female with nuclear cataract complains of reduced function, especially in bright light. Visual acuity tests at 20/30, but contrast sensitivity testing shows 6 cycles per degree reduction, which confirms her diminished functional acuity. (See images above.) Six months after cataract removal, re-testing shows resolution of the reduced functional vision.
Case 3: Capsular Opacity after Cataract Surgery An 82-year-old Caucasian male, who underwent cataract surgery 2 years prior, complains of hazy vision in his right eye during the day and glare while driving at night. Despite 20/20 Snellen acuity and a 20/25- BAT (medium) measurement, contrast testing shows a generalized reduction in sensitivity. One week after YAG posterior capsulotomy, the patient has reduced symptoms and contrast performance near normal for his age.
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Contrast Sensitivity Testing Devices |
Lighthouse International offers 10 contrast sensitivity testing products: SWCT Chart (Sine Wave Contrast Chart) from Stereo Vision; Pelli-Robson Contrast Chart (adult distance chart uses letters instead of sine waves) from Clement Clarke; Peek-a-Boo Patti Low Contrast Face Chart from Precision Vision (pediatric near chart); Patti-Pics Contrast Chart from Precision Vision (pediatric distance chart); ETDRS Low Contrast Letter Charts from Precision Vision (adult distance chart); Low Contrast Flip-Chart from Precision Vision (adult distance chart); Double-Sided Low Contrast Near Vision Card from Precision Vision (near double-sided chart); Continuous Text Contrast Chart from Precision Vision (near adult double-sided chart); LEA Symbols 1- Page Contrast Charts from Good-Lite (pediatric near test); Lea Numbers Low Contrast Chart from Good-Lite (pediatric near test). Lighthouse International, (800) 826-4200 M&S Technologies, Inc. offers the Smart System 2020 visual acuity and letter contrast sensitivity testing system. The system conducts visual acuity and low contrast testing from 25% pixel density down to 1%. Consistent reduction in pixel density ensures precise letter quality. Normative data is provided. Correlation and test studies were conducted by Sandra Brown M.D., of Texas Tech University. M&S Technologies, Inc. Stereo Optical Co., Inc. offers four closed vision testers with contrast sensitivity evaluation capabilities: Optec 3500, Optec 2500P, Optec 2000P and Optec 1000P. With the Optec 3500 you can use either 3-choice, 5-frequency sine wave (FACT) targets or low contrast letters (CAT). Its target illumination is day and night and continuously calibrated. Target illuminance and glare luminance can be customer defined or factory preset. These tests can also be performed: distance/near Snellen acuity (ETDRS Format), color, stereo, lateral/vertical phoria and potential acuity. Stereo Optical Co., Inc. VectorVision Inc. offers the CSV-1000 Contrast Sensitivity Test. The instrument has internal patented circuitry that constantly monitors and adjusts the testing light level to ensure standardization. In addition to contrast sensitivity, you can test ETDRS (LogMAR) acuity and low contrast acuity. Also available is the CSV-1000HGT, which is a standardized glare test. VectorVision Inc. Vision Sciences Research Corporation offers the CST 1800 Digital contrast sensitivity tester as well as the patented EyeView Functional Analysis Software. The CST 1800 Digital features standardized, adjustable lighting and a self-contained, calibrated glare source. It's equipped with the FACT sine-wave contrast sensitivity chart and ETDRS visual acuity charts. The EyeView software allows clinicians to enter patients' test responses directly into the system and receive instant FACT and ETDRS scoring. It also generates report summaries and graphs and can produce pictures that show how a street scene and newsprint appear to your patient based on his or her scores. Vision Sciences Research Corporation To order EyeView Functional Analysis Software, call the number above or e-mail eyeview@vsrc.net.
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