How do we gauge when visual function is impaired to the point where cataract surgery should be considered? That is the the question we left you with in Part 1. One thing we know for sure is that Snellen visual acuity is not very useful as an index of visual function. And to complicate matters, patients aren’t particularly good at gauging their own level of visual dysfunction. So let’s briefly look at some of the other parameters we have available.
The Functional Vision Analyzer (FVA) was introduced by Stereo Optical about 10 years ago to help grade and document deficits in visual function by assessing the quality of vision. It remains a phenomenal way of probing and demonstrating the patient’s contrast sensitivity as well as their susceptibility to glare.
Testing contrast sensitivity seemed as poised to go mainstream in visual assessment 20 years ago, about the same time that the metric system appeared to be going public in the U.S. for weights and measures. They both suffered similar fates, woefully underutilized but inherently valuable. We added contrast sensitivity testing to our Optec Screener from Stereo Optical 10 years ago as an upgrade from the Keystone Telebinocular. The functional vision package we customized consists of fusion, phoria, color vision, stereopsis, and contrast sensitivity testing.
Stereo Optical also uses proprietary Eye View software for its FVA to generate a comparison of what the patient’s view looks like under glare conditions compared to normal visual function.
Another clue to the quality of the image can be obtained through auto-refraction. Clearly one can infer this with retinoscopy, but the auto-refractor model that we use (Marco/Nidek) gives a rating score for the image from 5 through 9, with anything below 5 being recorded as “E” (error). I have found it useful to say to the patient that because changes in their crystalline lens is resulting in light scatter, the computer is having the same trouble from the outside in as they are having from the inside out. Any reduction from “9” is a potential problem, with an “8” indicative of light scatter, and a “7” or “6” correlating with significant pacification and reduced function. A newer model, the ARK-1s incorporates glare testing. Technology has been involving toward a better appreciation of wavefront refraction and adaptive optics.
Lastly, visual field results can be a significant index of visual function. We have found this particularly true of FDT technology, since we began using the Humphrey Matrix. A compromised field that with scattered losses, that isn’t fully attributable to classic disease patterns as in glaucomatous changes or field cuts (such as hemianopia), may often be linked to lenticular degeneration and compromised visual function. Particularly when dealing with older rehab populations in the face of cognitive decline, there is evidence that lens removal and IOL implantation can boost cognitive function through enhanced visual input and thereby improve quality of life.