The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) used the Snell Visual Efficiency Scale (1925). Following scientific progress, the Vision chapter in the fifth and sixth editions of the AMA Guides began using the Functional Vision Score (FVS) that is endorsed by the International Council of Ophthalmology and the International Society for Low Vision Research and Rehabilitation. Use of the FVS provided an opportunity to correct many inconsistencies in the VES system and also is better integrated with modern measurement methods and the ratings used for other organ systems. The FVS score is obtained by combining the Functional Acuity Score and the Functional Field Score; if any adjustments are introduced in this combination, they must be completely justified and cannot be based on subjective arguments. The disability is rated on the basis of functional considerations and is not influenced by nonfunctional factors. Combining visual acuity loss and visual field loss into a single number is attractive for administrative and legal purposes, but this step is meaningless in the context of rehabilitation because rehabilitation for visual acuity loss is entirely different from rehabilitation for visual field loss. The FVS system provides internationally endorsed statistical estimates of the effects of visual impairment on the ability to perform activities of daily living.

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