Abstract
Abstract: :
Purpose:This study is the first to examine the effect of ARM on the activation of phototransduction measured by the activation of the a–wave of the rod ERG. This study evaluated whether alterations in the activation of phototransduction may contribute to previously reported rod sensitivity loss. The effect of lens density on the a–wave was assessed. Methods:The sample included 27 young adults (mean 26 yrs old), 43 old normal adults (mean 71 yrs old), 39 early ARM patients (mean 75 yrs old), and 7 late ARM patients (mean 76 yrs old). The WARMGS was used for group assignment. The rod a–wave was measured for a family of moderately bright light intensities (4.28, 3.84, 3.07, and 2.34 log scotopic Td–s). ERGs were measured using a UTAS–E 3000 ERG system and a Burian–Allen bipolar electrode. Each a–wave response family was fit with a delayed gaussian function to estimate sensitivity (S), delay before onset of the a–wave (td), and maximum amplitude (Rmp3). Results:Old normals exhibited reduced log S (p < 0.001) and log Rmp3 (p < 0.001) values compared to young normals, however old normal adults with IOLs exhibited similar parameters to young normal adults. All analyses comparing old normals and ARM patients were adjusted for age and IOL status because these variables affect the ERG. None of the parameters of a–wave activation were significantly different among the old normal group and either of the ARM groups. The only association between fundus characteristics associated with ARM and the a–wave was increased retinal pigment was associated with a decrease in log S (p < 0.05). Conclusions:The results of this study indicate that the rod phototransduction pathway is relatively unaffected by ARM at least by measurement of a–wave activation. This finding is in striking contrast to the effect ARM on the retinoid pathway, a closely related pathway that regulates visual sensitivity. One distinction between these two pathways is that the retinoid cycle is directly dependent on Bruchâ|*128*|TMs membrane and RPE health whereas phototransduction is not. Early detection or monitoring of ARM by functional measures should focus on functions that are reliant on the Bruchâ|*128*|TMs membrane/RPE health. Previous aging studies have underestimated the effect of lens density on the measurement of the ERG. These results suggest that mechanistic studies focused on the impact of aging on ERG responses should use pseudophakes to effectively control for lens density as a confounding factor.
Keywords: age–related macular degeneration • electroretinography: clinical • photoreceptors: visual performance