In an observer exhibiting myopic nasal super–traction of the optic nerve head, measurements were made at 22o in the nasal retina (past, but near, the optic nerve head) and also on top of the optic nerve: Stiles–Crawford Effect (SCE) measured before, just after, and after recovery from OKN stimuli.

Abstract

Abstract: : Purpose:In ca 1/3 of cases having refractions greater than –5.00 D, there is displacement of retina and choroid from the nasal edge of the optic nerve head onto the surface of the optic disc. In ARVO, paper #2776, 2003, we reported visual functions on discs of individuals exhibiting over–rides. At OSA and CVS, we reported parallel data using OCT II in the same patients, along with initial findings on cause(s) of these anomalies. Included were forces generated by eye–movements tugging on the optic nerve. Here, we examine the traction effects on photoreceptor alignment at 22^o in the temporal visual field (TVF) and at 1.5^o on top of the disc. Methods:One way to generate traction is to present in one minute 70 serial, centrally fixated, OKN stimuli. Here, we examine the effect of OKN on Stiles–Crawford–I (SCE) measurements (directional sensitivity of the retina) on a trained individual with proven myopic nasal super–traction and tilted disc. SCE was conducted before OKN stimuli, just after OKN, and after recovery from OKN. Two loci were tested, 22^o in TVF on the horizontal raphé (past the nasal disc border), and at 1.5^o on top of the disc. Different increment threshold techniques were used at the two loci examined. The subject had also been tested with Canon CPP–1 and Nidek MP–1 fundus–camera–perimeters. She experiences form vision in over–ride areas on the disc, sometimes encountering saturation–like responses on the disc. Results:The SCE is one of the most stable visual tests known. Previously, at 22^o TVF, we showed SCE responses vary in time in mid–high myopes. Responses proved to be unstable on the disc within sessions and upon repetition. Inversions of SCE functions were found and common in this observer at both test loci. SCE inversions are difficult to interpret, but they occur. Conclusions: Receptors were capable of alignment on the disc of this observer! Both relatively normal and abnormal responses were noted. Viability of the displaced retina indicates continuity of blood supply, and visual function implies connectivity. Clearly, traction is present at both test loci. The optic nerve probably contributes to traction effects. Quality of adherence of tissue to the disc also needs to be considered.

Keywords: myopia • photoreceptors: visual performance • visual fields