The Relationship Between the Photopic Negative Response and Retinal Ganglion Cell Topography

Purpose: To assess the topographic relationship between the photopic negative response (PhNR) and retinal ganglion cell distribution in healthy individuals. Method: Data was recorded from 16 healthy participants. The amplitude of PhNRs obtained in response to focal long duration (250 ms) and brief flash (5 ms), red (660 nm) on blue (469 nm) stimuli of increasing size (5° - full field) were measured. The number of retinal ganglion cell receptive fields (RGCf) in each stimulus area was established from the literature and regression analysis used to determine the relationships between: PhNR amplitude and number of RGCfs stimulated, PhNR density and the RGCf density and response per RGCf as a function of eccentricity. Results: The overall amplitude of the PhNR increased with stimulus size and the response density declined from ∼0.1 μV/deg in the macular region to ∼0.003 μV/deg approximately 45° from the fovea. Contrary to expectations, the relationship between the PhNR and number of RGCf was nonlinear, the response from more eccentric neurons being about three times greater than those in the macular region. Conclusions: Although the amplitude of the PhNR broadly maps on to the topographic distribution of RGCf the increase in PhNR amplitude with increasing eccentricity is only partly explained by RGCf numbers. Increases in the PhNR amplitude may be due to topographic variations in the contributions from other non-RGC neurons, as well as eccentricity-related morphologic and physiologic differences in RGCs

Two decades of optometric education in Ghana: Update and recent developments*

Many authors have reported on the evolution and trends of optometric education in Africa. Amongst these are articles on Optometry and optometric education in Africa, West Africa, Nigeria, South Africa, Ghana, and Ethiopia. This article reports the historical perspectives of optometric education in Ghana and the developments that have been made in the last 20 years. It also attempts to relate the stride made towards legal recognition of optometry in Ghana. In presenting this historical account, it is hoped that sometime in the future, one should be able to look back at the beginning of optometry training in Ghana and be able to measure the advancement or otherwise that have been made since its inception. (S Afr Optom 2011 70(3) 136-141