Visual acuity remains the primary surrogate marker for clinical trials In ophthalmology (and the primary outcome for most US Food and Drug Administration applications) due to its long history, ease of measurement and clear relationship to clinically meaningful characteristics of daily life. However, treatment trials are being planned for diseases that are currently untreatable where visual acuity may not be the most appropriate outcome measure. Specialized electroretinographic tests can be powerful surrogate markers In such trials. The selection of outcome measures and surrogate markers depends in part on whether the goal is to preserve remaining vision in a progressive retinal degeneration or to improve vision In an eye that has already undergone extensive degeneration. Among the electroretinographic tests available are those involving the whole retina (full-field electroretinographic), the posterior pole (pattern electroretinographic) or focal areas within the macula (multifocal electroretinographic). The advantages and disadvantages of each will be discussed along with selected applications of each test to a specific category of disease.
