Chances are you’re as likely to have heard of the term “Functional Visual Acuity” (FVA) as you are of “Funding Valuation Adjustment” – the FVA term used in the trade industry.
Which is kind of strange that here we are, experts in “functional vision”, yet the concept of FVA has evolved through research into the inadequacy of standard VA measures for unhappy patients with dry eye, cataract, or glaucoma. Stereo Optical Company produces a Functional Vision Analyzer, which is a great and underutilized tool that speaks to the heart of some of these issues, but it is still a static measure of degraded visual acuity that is a snapshot in time. So let’s roll up our sleeves and dig into the FVA concept as it has emerged over the past 10 years or so and you’ll see why it should be of interest to us.
At it’s simplest level, the concept of FVA assesses changes in visual acuity within a relatively short and finite period of time on a continuous performance task. The task employed is identifying the correct orientation of the gap in a “Landolt C” as being up, down, left, or right.
The research involving this paradigm uses an instrument with internal targets that is commercially available though Kowa in Japan, known as the AS-28 FVA pictured here. The instrument itself is less important (unless you’re doing research, of course) than the concept behind it – which is that symptomatic patients will have very good static visual acuity when looking at a chart – or even quite good dynamic visual acuity – but cannot maintain a good level of visual acuity. You might consider this the visual resolution analog of poor visual stamina with binocular vision, and is operative even on a monocular basis at all distances (having little directly to do with accommodation).
This has led to the concept of the VMR, or Visual Maintenance Ratio – an index of how well an individual can maintain their starting level of visual acuity over the course of 60 seconds, graphically represented here.