Abstract
Purpose :
Astigmatism is an amblyogenic factor that may be important when monitoring recovery in response to treatment. Given that little is known about orientation-specific cortical processing in children with amblyopia, it is important to first establish normative findings in children with normal visual acuity (VA) before checking for meridional effects in amblyopes. The purpose is to determine if there are meridional anisotropies relating to astigmatic status in pattern onset visual evoked potential (POVEP) amplitude, latency and grating acuity (GA) in children with normal vision.
Methods :
Monocular POVEPs was measured in response to sine wave grating stimuli of 4 cycles per degree oriented along and perpendicular (On and Against meridians, as written in sphero-minus cylinder form) to their aided astigmatic meridians. Grating acuity was assessed along the same meridians monocularly using a psychophysical staircase. In children without astigmatism, horizontal gratings were arbitrarily selected as the On meridian. Stimuli were generated on a calibrated monitor using a ViSaGe (Cambridge Research Systems, UK). Data were analysed using generalised estimating equations (GEE) for each subgroup (children with and without astigmatism): run with subject identifier as the subject variable, VEP component (C3 amplitude, C3 latency) and GA as the dependent value, and eye (right or left), meridian (On or Against), and age as predictors in a linear model.
Results :
Children with normal VA and no history of amblyopia were recruited (n=29; mean(SD) age=6.1(1.3) years); 9 had astigmatism (mostly with-the-rule) and 20 had no astigmatic refractive error. Eye was not a significant predictor of C3 amplitude, latency or GA. In non-astigmats, meridian was a significant predictor of C3 amplitude (Exp(B)=61.56, p=0.003) (vertical>horizontal), but age was not. No meridional anisotropies were found related to astigmatic axis in children with astigmatism. Non-astigmats was associated with shorter latency (Exp(B)<0.0001, p=0.029) and higher GA (Exp(B)=252.24, p=0.004) than astigmats. Age was a significant predictor for GA (Exp(B)=7.45, p<0.0001).
Conclusions :
Meridional anisotropy was only observed for C3 amplitude. Age effects were observed for GA. This suggests that C3 amplitude is better at indicating meridional anisotropy than C3 latency and GA.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.