Multifocal electroretinogram and optical coherence tomography to evaluate parafoveal fixation

Abstract

PurposeSpatial resolution of the human visual field changes depending on the distance from the fovea and fixation point. The visual field is divided in three areas: foveal, parafoveal and peripheral. The highest visual acuity (AV) is obtainded at the foveal area, covering approximately 2 °, then parafoveal area covers 2 ° to 5 °, and the peripheral vision from 5 ° to the edge of the visual field, but the AV decreases progressively in each area .MethodsWe analyzed two cases of parafoveal fixation by SD‐Spectralis OCT (Heidelberg Engineering), Triton Swept‐Source OCT (Topcon) and multifocal electroretinogram (mfERG) with RetiPort / Scan (Roland Consult). The structure and function of retinal cells have been correlated using OCT images and the three‐dimensional map of mfERG.ResultsCase 1: Patient with 100% ETDRS VA equal to 0,0 in both eyes (OU), contrast sensitivity (CS) Pelli Robson 1,35 in right eye (OD) and 1,20 in left eye (OS), presents Parafoveal fixation <1º.Case 2: Patient with previous episode of optic neuritis in OD and parafoveal fixation of 3º in OS, which presents VA ETDRS 100% of 0.7 in OD and 0.1 in OS, CS PelliRobson of 1,05 in OD and 1,20 OS.Both cases present a reduced macular peak seen at the mfERG, and a fixation point out of the foveal at the OCT.ConclusionsWe can see how VA and CS decreases as the fixation eccentricity increases, as can be clearly seen in the three‐dimensional mfERG map. CS seems to be the quickest parameter to be affected.