Occipital Petalia and Albinism: A Study of Interhemispheric VEP Asymmetries in Albinism with No Nystagmus.

Alkiviades Liasis,Sian E Handley,Ken K Nischal

doi:10.3390/jcm8060802

Abstract

The purpose of this study was to assess chiasmal misrouting in a cohort of children with albinism with no nystagmus using hemifield visual evoked potentials (VEP) measures. Methods: Monocular VEPs were recorded and analyzed from three electrodes (O1, Oz, and O2 referred to Fz) from 16 children with albinism without nystagmus. Pattern reversal (full field and hemifield stimulation), full field pattern appearance and flash stimuli were used to evoke VEPs for each eye. Results: The amplitude of the pattern reversal VEPs to stimulation of the hemifield corresponding to the crossing pathways were as expected significantly larger than those to the non-crossing in each eye ((right eye p = 0.000004), (left eye p = 0.001)). Pattern reversal VEPs recorded from the left hemisphere were also larger than those from the right and most evident when comparing the crossing pathways of each eye (p = 0.004). Conclusions: This study has demonstrated electrophysiological differences in visual pathway function of the left and right hemisphere in subjects with albinism like that previously described in controls. Nasal field stimulation activated crossing and non-crossing pathways in patients with albinism and as a result, nasal hemifield VEPs in albinism are less lateralized compared to what is found in normal subjects.

Highlights

Albinism is a heterogeneous group of genetic disorders characterized by absent or reduced melanin pigment in the eye, skin, and hair [1]
The electrophysiological pattern of visual evoked potentials (VEP) trans-occipital asymmetries seen in normal subjects due to the influence of asymmetric occipital petalia is evident in our cohort of albinos without nystagmus
As evidenced by the HF VEP studies, we were able to demonstrate that stimulation of the crossing fields in albinos produces larger responses from the left hemisphere compared to the right, which is like the controls

Summary

Introduction

Albinism is a heterogeneous group of genetic disorders characterized by absent or reduced melanin pigment in the eye, skin, and hair [1]. The ophthalmological features of individuals with albinism are fundus hypopigmentation, foveal hypoplasia of varying degrees, iris transillumination, nystagmus, and an abnormal decussation pattern at the optic chiasm [2]. The abnormal pattern of decussation consists of an increased number of ganglion cell axons from the temporal hemiretina, (representing the nasal field), crossing the chiasm together with the normal crossing of fibers from the nasal hemiretina. As a result there is a net increase in the number of retinal fibers from one eye projecting to the contralateral hemisphere [3,4]. The extent of this abnormal decussation in albinism has been shown electrophysiologically to range between 2 to 15 degrees [5]. Foveal hypoplasia and optic nerve misrouting can occur independently of defects in the melanin biosynthesis pathway and has been demonstrated in recessive mutations of SLC38A8 [6,7]

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