Electrophysiological evaluation of the macular cone adaptation: VEP after photostress. A review.

In the present review, the methodologies and clinical applications of the visual evoked potentials (VEPs) after photostress, will be described. Photostress induces transient VEP changes consisting of an increase in response latency and a decrease in amplitude. When serial VEP recordings are obtained at discrete time intervals (i.e., every 20 s) after bleaching, the recovery of VEP waveform can be evaluated. The time needed for the VEP to recover to the pre-bleach, baseline status (recovery time after photostress) ranges in normal subjects between 68 and 78 s. Patients with different pathologies (maculopathies, ocular hypertension and glaucoma, diabetes with or without retinopathy, multiple sclerosis with optic neuritis) showed an abnormal response after photostress (higher increase in latency and decrease in amplitude and longer recovery time) with respect to age-matched controls. Our results indicate that the VEPs after photostress represent an objective, although not specific, index of the dynamic properties of macular performance after exposure to intense light stimulation.