A. Colenbrander
California Pacific Medical Center
Smith-Kettlewell Eye Research Institute
2340 Clay Street,
San Francisco, CA 94115,
U.S.A.

To provide reasonable estimates of the ability to perform Activities of Daily Living, based on measured values of Visual Acuity and Visual Field.

In the U.S., Snell’s "Visual Efficiency" scale is often used. This scale is outdated since it was based on employability estimates in 1925. At VISION-99 new scales were presented in a "GUIDE for Evaluation of VISUAL Impairment", prepared with the help of an international work group. This year, these scales are also incorporated in the revision of the "Guides to Evaluation of Permanent Impairment" of the American Medical Association (AMA).

Results

The new ability estimates follow Weber-Fechner’s law, which states that a geometric increase in stimulus corresponds to a linear increase in perception. In doing so, they also conform to current visual acuity measurement standards (ETDRS and other protocols). More emphasis than before is placed on binocular function, which is the normal mode of visual function.

Conclusions

The ability estimates ignore individual adaptations to vision loss. They can be useful if the goal is to reduce the complexity of deficits in the visual system to a single generic number. The need for rehabilitative interventions, on the other hand, cannot ignore individual factors and should be based on an ability profile, derived from direct measurements (rather than estimates) of a person’s abilities.