Retinal Nerve Fiber Layer Thickness and Macular Thinckness in Myopia, Hyperopia and Emmetropia : An OCT Study

The world health organization (WHO) has estimated that the visual impairment caused by uncorrected refractive errors to be present in 153 million people worldwide (1) the prevalence of myopia ranges from 22.7% to 38.7% in large population study According to the WHO regions the estimated prevalence (EP) of hyperopia is 30.6% with the lowest EP in south east Asia 2.2% and the highest EP in the Americas 14.3% (2-3) During optic nerve development 2.85 million nerve fibers exist but by the third trimester we lose about 35% of these fibers (4) and the perpapillary retinal nerve fiber layer (RNFL) thickness will continue to decrease with advancing age (5). The relationship of the RNFL thickness with the refractive errors has been extensively investigated in adults and in children (6) and there was significant increase in the RNFL thickness in hypermetrope than in emmetrope and myope Understanding the derminants that affect the RNFL reserve helps us in the diagnosis and monitoring of optic nerve diseases. In macular region the thickness measured through optocal coherent tomography OCT shows high variability with value ranging from 190mm (centerpoint) to 389 mm (superior inner/nasal inner macula) (7) for both retinal and macular regions while decreasing in the retinal thickness has been reported with increasing age. Different studies have shown racial differences in RNFL thickness (8) white race (9) and myopia which has high prevelance in East Asian regions (10-12) have been associated with thinner RNFL (11) on the contrary Asian or Hispanic race has been associated with a thicker RNFL