THE ARTIFACT OF RETINOSCOPY REVISITED - COMPARISON OF REFRACTIVE ERROR MEASURED BY RETINOSCOPY AND VISUAL-EVOKED POTENTIAL IN THE RAT

Purpose, The validity of retinoscopy in small eyes has not been clearl y established due to uncertainty regarding the source of the ocular re flections assessed during this procedure. A widely cited model which p roposes that their origin is the inner limiting membrane of the retina was evaluated in the rat by comparing refractive errors measured by r etinoscopy to those measured by visual evoked potentials (VEPs). Metho ds, Ten rats were refracted both by cycloplegic streak retinoscopy and by VEP while viewing 0.05 to 0,15 cpd square-wave gratings reversed a t 1.875 Hz. Spherical aberration of the rat eye was assessed as a pote ntially confounding variable in VEP refraction by sequential retinosco pic refractions across the rat's natural pupil through a 1.5-mm pinhol e. Results. All animals were moderately to highly hyperopic by both me thods (range = +4.5 to +18.5 D). Spherical aberration was minimal (med ian = 3.5 D of overcorrected aberration), The median difference betwee n retinoscopic refractions and those by VEP was not significant (+1.94 D more hyperopia by retinoscopy; p = 0.062, Wilcoxon signed rank) but was significantly less than the +9.64 D difference predicted by an in ner limiting membrane model (upper 95% limit = +3.76 D), Conclusion, T his suggests that the origin of the retinoscopic reflex is located rn the outer retina rather than at the inner limiting membrane. Correctio n factors for retinoscopy in small eyes may be smaller than previously assumed.