As a practitioner and faculty in low vision rehabilitation, as well as the Chief of Vision Rehabilitation Services, I am submitting points for consideration in regards to your vision standards.
A remaining visual field of 20 degrees or less is not, in my clinical experience and based on research, an appropriate cut off for significant functional decline. In clinical research, 40 degrees appears to be the point where significant function is compromised in terms of visual field loss. Threshold automated visual field instrumentation often lacks the capability to measure visual field beyond the central 30 degrees so use of a screening field such as a Humphrey 81 point screener should be considered.
There is a question I receive calls about often from our local social security disability offices that is a point of confusion for your employees. The question is how to determine statutory blindness based on visual field threshold results. Your employees find the field determination instructions to be confusing and complicated. As a result, I believe they are often guessing. I suggest looking at a simpler way to calculate remaining visual field based on automated testing printouts. This move would make your employees less stressed and more efficient, as well as provide more accurate results.
Clinically, the measure of contrast sensitivity has become an important part of low vision rehabilitation examinations. While visual acuity may not meet legal blindness requirements using a high contrast chart, the use of a low contrast chart to measure contrast sensitivity often reveals why function is much worse than visual acuity demonstrates. Suggestions for the use of contrast sensitivity charts include the MARS chart or the Peli-Robson Hi/Low Contrast chart. While this adds another layer of complexity to disability determination, it is perhaps one of the most important measures of visual function.