Effects of Pupil Diameter on Light Detection and Temporal Modulation

Purpose: This study compared the effects of pupil variation on light detection and temporal modulation across the central visual field.Methods:Light detection sensitivity (LDS) and low flickering frequency (6Hz) temporal modulation sensitivity (TMS) of 20 young subjects were measured from the central visual field of the right eyes using an automated perimeter (Medmont M600). The measurements were taken under 3 artificial pupils, I.e. 3 mm, 4.3 mm and 6 mm diameters.The sensitivities were grouped and averaged for different retinal eccentricities(3°, 6°, 10° and 15°).Results:TMS and LDS were reduced with increasing retinal eccentricities( P ＜ 0.001)and decreasing pupil diameters( P ＜ 0.001). TMS collected from all pupil diameters were significantly different from each other( P ＜ 0.001). Similarly, LDS under 3 mm pupil was statistically different from those of 4.3 mm and 6 mm(P ＜ 0.003). Comparison of the hills of vision showed that pupil variation resulted in significantly different slopes (P=0.001).The slopes were also found to be significantly different between TMS and LDS (P=0.012).Conclusions: The data showed that dilated pupil resulted in significantly higher sensitivities than those of smaller pupil for both visual functions. The difference in the slopes of hills of vision also suggested that the variation in retinal illumination affected the visual responses differently at various retinal eccentricitities for TMS and LDS.

The Saturation Characteristics of Glucose Transport in Bovine Retinal Pigment Epithelium

Purpose:To study the saturation characteristics of the glucose transport across the bovine retinal pigment epithelium(RPE).Methods:The bovine RPE preparations were munted with a modified Ussing chamber.The L-[^(3)H]-glucose and 3-0-methyl-D-[^(14)C]-glucose fluxes across the RPE from the choroid to retina were studied at different glucose concentrations.Results:The glucose transport was found to be stereospecific,with 3-0-methyl-D-glucose(MDG)being transported about three times faster than L-glucose.The glucose transport showed typical saturation characteristics in Michaelis-Menten fashion.The V_(max)and the K_(m)of corrected MDG were 2452 nmol cm^(-2)h^(-1)and 30.8 mM respectively.It was shown that the glucose transport system was saturated at 61.6 mM.Conclusions:The saturation characteristics of the corrected MDG flux suggested that the capacity of glucose transport through the bovine RPE is immense.

A Rapid Method of Preparing the Plasma Membrane Enriched Fraction of the Bovine Retinal Pigment Epithelial Cells

Purpose: To devise a rapid method of isolating the plasma membrane enriched fraction (PMEF) of the bovine retinal pigment epithelial (RPE) cells with Percoll cen-trifugation medium.Methods : The bovine RPE was homogenised with a tight fit Dounce homogeniser and centrifuged in a 16. 7% Percoll gradient for 20 minutes. The RPE particulate fractions were characterised in terms of their protein concentrations, Na/K-ATPase and bicarbonate stimulated ATPase activities.Results ; The total protein recovery was 88.7% of the RPE homogenate. The nucleus layer was identified at the first band. The mitochondrial fraction was at the second layer according to its bicarbonate stimulated ATPase activity. The 3rd and 4th bands were enriched with plasma membranes and their Na/K-ATPase activities were 31. 5 and 34.6 μmol/mg/h respectively. The Na/K-ATPase activities were about six times that of the RPE homogenate.Conclusions: A rapid method of isolating the bovine RPE PMEF has been devised which involved a single