Multifocal electroretinogram: age-related changes for different luminance levels

Abstract

Background: Age-related changes in the first-order multifocal electroretinogram (mfERG) responses were measured for two different luminance levels (200 and 700 cd.m(-2)). The relative contribution of optical and neural factors to senescent change in response was evaluated.

Methods: Data were obtained from one eye of each of 71 normal phakic subjects, age 9-80 years. The mfERG responses were recorded with the 7" stimulus-refractor unit (EDI) and VERIS 4.3 using the following protocol: bipolar contact lens, 103 hexagons, consecutive stimulation with 200 and 700 cd.m(-2), pupils > or =6 mm, amplification of 10(5), filter cut-offs at 10 and 300 Hz.

Results: Age-correlated decreases in amplitude and response density and increases in P1 implicit time were found for both luminance levels. The mean response density (nV.deg(-2)) was higher for the 700 cd.m(-2) stimulus, but the rate of change with age was not significantly different from that obtained with the 200 cd.m(-2) stimulus. Implicit time was not significantly different for the two light levels, nor was the rate of change with age. The decrease in response density and the increase in implicit time with age were significant across all retinal regions, dividing the 50 deg stimulus into six concentric rings. Age-related change in response density was greatest for the central retina and decreased with increasing retinal eccentricity.

Conclusion: Log mfERG response changes linearly as a function of age. Analyses of the effects of reduced ocular media transmission and increased stray light, along with ancillary data obtained from pseudophakes, imply that age-related changes in the mfERG are due to both optical and neural factors.

Fig. 1

Overall log response density (nV·deg⁻²) is plotted as a function of age for two light levels, 200 cd·m⁻² (open symbols) and 700 cd·m⁻² (filled symbols). Least-squares linear regression lines are shown for each data set. The regression equations are: y(200)=−0.003 age+1.43 (r=−0.60, P<0.0001) and y(700)=−0.003 age+1.59 (r=0.55, P<0.0001)

Fig. 2

Overall log implicit time (ms) is plotted as a function of age for two light levels, 200 cd·m⁻² (open symbols) and 700 cd·m⁻² (filled symbols). Least-squares linear regression lines are shown for each data set. The regression equations are: y(200)=0.00043 age+1.435 (r=0.52, P<0.0001) and y(70 0)=0.00041 age+1.426 (r=0.51, P<0.0001)

Fig. 3

Log response density (nV·deg⁻²) is plotted as a function of age for various concentric rings. Least-squares linear regression lines are shown for each data set. The regression equations are: y(ring 1)=−0.005 age+2.114 (r=−0.70, P<0.0001); y(ring 2)= −0.005 age+1.824 (r=−0.72, P<0.0001); y(rings 3 & 4)=−0.004 age+1.555 (r=−0.643, P<0.0001); and, y(rings 5 and 6)=−0.003 age+1.372 (r=−0.55, P<0.0001)

Fig. 4

Normalized log response density (nV·deg⁻²) and log implicit time (ms) are plotted as a function of log stimulus luminance (cd·m⁻²) in the left and right panels, respectively. Data points represent individual subjects. The smooth curve in the left-hand panel represents the best-fitting polynomial to the mean data: y(response density)=−0.18x²+1.125x−0.326 (r=0.99, P<0.0001). The regression line in the right-hand panel is: y(implicit time)=−0.041x+1.552 (r=0.97, P<0.0001)

Fig. 5

Normalized log response density (nV·deg⁻²) and log implicit time (ms) are plotted as a function of log stimulus contrast (%) in the left and right panels, respectively. Data points represent individual subjects. The smooth curves represent best-fitting polynomials to the mean data: y(response density)=−0.894x²+0.621x+1.497 (r=0.99, P=0.0004), and y(implicit time)=0.369x²+0.287x+1.431 (r=0.99, P=0.0015)