We introduced the concept of FVA in Part 1 and, by way of brief review:
a. There is a commercially made device, the AS-28 by Kowa, that presents a series of Landolt C’s continuously over the course of 60 seconds to which the patient has to respond in order to determine who well baseline VA can be maintained over that time period. At present the device is only available through Kowa in Japan, where much of the research into this function is occurring.
b. Over a 60 second period, individuals who are asymptomatic will tend to sustain a level of visual acuity very similar to their baseline BVA.
c. Symptomatic individuals will tend to deteriorate rapidly during the minute’s worth of testing. These are patients that complain they have trouble seeing, but when asked to look at an eye chart usually show high levels of snapshot VA and are therefore dismissed as being hypercritical.
The earliest article I could find on the subject was in 2002 on impaired FVA in dry eye patients. This makes sense intuitively, since we know that when patients with DED concentrate on visual tasks this blink rate reduces and they dry eye is exacerbated. FVA quantifies that effect. Subsequent studies have looked at the effect of punctual plugs on improving FVA, and this has been extended to understanding complaints that some patients have post-LASIK regarding the quality of their vision despite good unaided VA.
Another application of the FVA concept is in helping understand the complaints of patients with poor night vision. A recent study looked at FVA as a function of photopic vs. mesopic conditions. The results among healthy volunteers with 20/20 or better acuity demonstrated that there is considerably more fluctuation in FVA under mesopic conditions.
FVA has obvious utility in conjunction with assessment of degradation in visual function due to cataracts, and in judging the visual performance of IOLs. Most recently FVA has shown promise as a good, quick proxy test in the elderly for both visual and cognitive functions during driving, as it correlates well with results on the useful field of view (UFOV) test.