Early light adaptation in young, middle-aged, and older observers

The Effects of Glare on the Perception of Visual Motion as a Function of Age

Purpose

The purpose of this study was to determine the impact of glare, that simulated the effects of oncoming vehicle headlights, and age on different aspects of motion perception in central and peripheral vision.

Methods

Twenty younger (mean age = 25 years, range = 20-32 years) and 20 older (mean age = 70 years, range = 60-79 years) visually healthy adults completed four visual motion tasks. Stimuli were presented centrally and at 15 degrees horizontal eccentricity for 2 viewing conditions: glare (continuous, off-axis) versus no glare. Motion tasks included minimum Gabor contrast required to discriminate direction of motion, translational global motion coherence, minimum duration of a Gabor to determine direction of motion (2 different size Gabors to determine spatial surround suppression), and biological motion detection in noise. Intraocular straylight was also measured (C-Quant).

Results

Older adults had increased intraocular straylight compared with younger adults (P < 0.001). There was no significant effect of glare on motion thresholds in either group for motion contrast (P = 0.47), translational global motion (P = 0.13), biological motion (P = 0.18), or spatial surround suppression of motion (P = 0.29). Older adults had elevated thresholds for motion contrast (P < 0.001), biological motion (P < 0.001), and differences in surround suppression of motion (P = 0.04), relative to the younger group, for both the glare and no-glare conditions.

Conclusions

Although older adults had elevated thresholds for some motion perception tasks, glare from a continuous off-axis light source did not further elevate these thresholds either in central or peripheral vision.

Translational Relevance

A glare source that simulated the effect of oncoming headlights, did not impact motion perception measures relevant to driving.

Aging-related changes in the multifocal electroretinogram

The multifocal electroretinogram (MERG) was recorded in the central 36 degrees-diameter field in 26 young (19-30 yr) and 20 old (60-74 yr) adults in normal retinal health according to a fundus grading scale. The mean amplitude densities of the first-order and second-order responses in this retinal region were lower for old adults compared with young. The aging-related reduction of the first-order amplitude density was greatest at the fovea and decreased as a function of eccentricity. Similarly, the amplitudes of the first negative and positive peaks of the first-order MERG waveform were reduced with age, and the pattern of reduction followed a similar eccentricity dependency. The aging-related changes in the MERG waveform may be due to slowed temporal adaptation in the aged retina.

Age differences in the temporal continuity of gratings as a function of their spatial frequency

This study compared young and elderly observers on the continuity of sinusoidal grating-pairs as a function of interstimulus interval (ISI) and spatial frequency (.5, 1.0, 2.0, 4.0, 8.0, and 12.0 c/deg). Consistent with prior research, the maximum ISI over which pattern continuity was maintained increased with spatial frequency. In addition, among older observers, grating continuity occurred at significantly longer ISI's at the two lowest spatial frequencies; no age difference was observed at the higher spatial frequencies. These results could not be attributed to an age difference in retinal illumination associated with pupillary miosis. However, they do indicate an age-related decline in detecting visual offset and are consistent with the hypothesis of a decline in the effectiveness of the transient visual channels.

Temporal summation functions for detection of sine-wave gratings in young and older adults

Temporal summation functions for 0.416 and 7.5 c/deg sinusoidal gratings were measured in young and old observers in order to test the hypothesis of a shift in sensitivity from "transient" to "sustained" channels in the aging visual system. Results failed to support the transient-shift hypothesis. Additional tests showed no age-related changes in temporal summation even within a single channel. When all observers were refracted for the test distance and matched for retinal illuminance, no age-related differences in contrast sensitivity were found.

Ageing and the spatiotemporal discrimination performance of the visual system

Visual ageing is generally associated with a decline in spatial vision for stationary stimuli, especially those which are of high spatial frequency. Some, but probably not all of this loss can be attributed to apparently normal age-related changes in the ocular media that attenuate and scatter incident light. The loss in the temporal resolving capacity of the senescent visual system is even more prominent and appears to be due almost completely to neural mechanisms, including alterations in the functioning of both the 'transient' and 'sustained' types of visual channel. The losses with age in both spatial and temporal vision are highly consistent with the type and degree of visual problems elderly persons report that they experience in carrying out daily tasks. Further research will be needed to determine the mechanisms which underlie these changes as well as to determine the degree to which they can be remedied.