Contrast sensitivity test targets AMD

Take-home

A new letter contrast sensitivity test may aid in the evaluation of patients with age-related macular degeneration and other retinal diseases.

Dr. EvansNew Product Focus By Liz Meszaros; Reviewed by David W. Evans, PhD

Greenville, OH-Patients with age-related macular degeneration (AMD) and other retinal diseases may benefit from a new standardized letter contrast sensitivity test (Evans Letter Contrast Test, VectorVision).

“As baby boomers have moved into their older years, a lot of focus has been placed on AMD, diabetic retinopathy, and new treatments for these age-related diseases,” said David W. Evans, PhD, founder of VectorVision, Greenville, OH, and inventor of the CSV-1000.

Until the new letter contrast sensitivity test was developed, Dr. Evans noted, there was no standardized test to evaluate patients who have poor vision-i.e., those worse than 20/50 to 20/70.

“That was the goal in developing this diagnostic tool-an accurate, standardized way to evaluate subtle changes in vision in patients who have poor vision,” he said.

Dr. Evans has been involved in the development of this highly sensitive test for a number of years, based on requests from clinicians who dealt with age-related eye disease. He established the current design after testing a number of versions.

Letter contrast sensitivity testing determines the lowest contrast level at which a letter can be correctly identified for a given size target, Dr. Evans explained.

Letter contrast sensitivity measures the patient’s ability to see at different contrast levels, while acuity testing measures only one high level of contrast, black-on-white. Acuity is a poor measure to determine the loss of vision with disease, or more importantly, the subtle improvements in vision with treatment.

The new letter contrast sensitivity test provides for a range of contrast sensitivity levels using a letter size that was specifically chosen for evaluating the stabilization or the subtle changes in improvement in vision by patients with AMD following treatment.

The new, scientifically developed design of the test helps clinicians evaluate these patients in a standardized and comprehensive way, and it improves on current testing methods, Dr. Evans continued.

For example, the Pelli-Robson test for contrast sensitivity was developed with an arbitrary letter size and is not tested in a standardized lighting environment, he said.

“We utilize a letter size that matches the ETDRS log scale at 20/630,” Dr. Evans said. “This letter size is excellent from a testing standpoint, because it is the acuity level at which patients have their peak visual sensitivity under low contrast conditions, based on visual psychophysics.

“We wanted to ensure that it would be technically sensitive for the patient, but would also be consistent with the ETDRS standard,” he said.

Advantages of technology

One of the additional advantages of the new letter contrast sensitivity test is that it is used in a standardized lighting environment, in conjunction with an LED-based, auto-calibrated, back-lighting system (ESV3000, Good-Lite/VectorVision) that ensures uniform and consistent lighting for testing each patient.

“One of the problems with other large letter tests is that it is very difficult to test them in a standardized way,” Dr. Evans said. “There is no guarantee that when a patient is re-tested, the test lighting will be the same as the previous test.”

The new letter contrast sensitivity test is standardized, and because the LED back-lighting auto-calibrates to a specific light level, clinicians now have a large-letter type of contrast test with standardized lighting, increasing test/re-test reliability. Dr. Evans said.

Other advantages include the fact that the test is produced through a silk-screen process on translucent styrene, not printed on plastic. This manufacturing process ensures that the test will not fade over time and affect the process.

The test has been adopted for worldwide clinical trials evaluating novel treatments for retinal disease. Alcon Laboratories is currently using the test in an ongoing clinical trial.

“With the number of new drugs being introduced to treat retinal diseases, it is difficult to know which one is most effective,” Dr. Evans said “If we are waiting on a change in acuity to determine if a drug is effective, we may be missing information that could help patients’ preserve or recapture visual function.

“Acuity is not sensitive enough to detect small changes in vision,” he said. “Unfortunately, acuity also changes very slowly with treatment. [The test] is a way to determine if patients are being helped by therapy, very quickly, and in a standardized way.”

David W. Evans, PhD

E: devans@vectorvision.com

Dr. Evans has worked as a consultant and has participated in the development of study protocols and/or data analysis for clinical studies sponsored by Allergan, Autonomous Technologies, Novartis, Otsuka, Pharmacia, and VISX.

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