Electrophysiological study of myopia

ABSTRACT

To investigate the characteristics of retinal function in myopia using full-field electroretinogram [ERG] and multifocal ERG [MF-ERG] and to determine the correlation among MF-ERG, ocular axis length, retinal thickness and degree of myopia. Twenty emmetropes [20] and sixty-eight myopes [68] underwent manifest refraction, A- and B-scan, fundus examination, fluorescein angiography [FA], optical coherence tomography [OCT], full field ERG and MF-ERG. The amplitudes and implicit times of ERG were determined. The results were further analyzed by comparing ocular axis length, refraction, retinal thickness, and macular function detected by ERG parameters. There was a significant difference in implicit times of MF-ERG of an emmetrope and a moderate and high myopia whereas implicit times of mild myopia patients and emmetropes were similar. There was a statistically significant difference in amplitude densities of first positive peak of MF-ERG P[1] wave between an emmetrope and a moderate and high myopia. In central ring and four quadrants, amplitude densities showed negative correlation to ocular axis length and diopter of myopia. There was no statistically significant difference between the average retinal thickness in emmetropic and physiological myopic eyes [low, medium, high], but there was significant difference between physiological and pathological myopia. Decreased foveal function as determined by MF-ERG is associated with high degree of myopia. Retinal function impairment is correlated with increase in the diopter of myopia, decrease of corrected visual acuity [VA], elongation of ocular axis and increased macular degeneration