The clinical features of albinism and their correlation with visual evoked potentials

Abstract

Aim: To investigate the relation between the clinical and electrophysiological abnormalities of patients undergoing visual evoked potential investigation for albinism.

Methods: 40 subjects with a probable or possible clinical diagnosis of albinism underwent pattern appearance and/or flash visual evoked potential (VEP) examination. The VEP findings are correlated with the clinical features of albinism determined by clinical examination and orthoptic assessment.

Results: The majority of patients with clinical evidence of albinism showed a contralateral predominance in the VEPs. There was close correlation between the clinical signs of albinism and the degree of contralateral VEP predominance. This manifested as an interhemispheric latency asymmetry to monocular pattern appearance stimulation but amplitude asymmetry to flash stimulation. The strongest correlation for pattern appearance interhemispheric latency difference was with foveal hypoplasia (rho = 0.58; p = 0.0003) followed by nystagmus (rho = 0.48; p = 0.0027) and iris transillumination (rho = 0.33; p = 0.039). The VEP abnormalities were of greater magnitude in those patients with most features of albinism. Several patients with apparently mild disorders of ocular pigmentation had small but significantly abnormal VEP latency asymmetries.

Conclusion: There is a strong association between the magnitude of the interhemispheric latency asymmetry of the pattern appearance VEP, and of amplitude asymmetry of the flash VEP, with the clinical signs of albinism. The data are consistent with a spectrum of abnormalities in albinism involving both clinical expression and electrophysiological misrouting, which is wider than previously recognised.

Figure 1

Five channel pattern appearance and flash VEPs from case 26 showing the contralateral predominance typical of albinism. All electrodes are referred to Fz. Note the markedly shorter latency of the prominent positive component in the contralateral hemisphere traces of the pattern appearance VEP and the greatly reduced amplitude of the ipsilateral response in the first 150 ms of the flash VEPs.

Figure 2

Graph showing the relation of the mean interhemispheric latency difference to the albino score.

Figure 3

Graph showing the relation of the amplitude asymmetry index to the albino score.

Figure 4

Graph showing the relation of the mean interhemispheric latency difference to the amplitude asymmetry index for all patients segregated by albino score.