Chromatic and achromatic defects in patients with progressing glaucoma

Abstract

To evaluate the pattern of losses associated with glaucomatous injury in patients with progressing glaucoma, functional losses were examined in 14 patients with progressing glaucoma using tests for which detection should be selectively mediated by one of three psychophysical mechanisms. Red-on-white increments, blue-on-white increments and critical flicker frequency were used to isolate the responses of the red-green chromatic mechanism, the blue-on chromatic mechanism, and the high-frequency flicker achromatic mechanism. For our 3.1 degrees circular stimuli, chromatic defects were found in a greater number of the patients with glaucoma than were achromatic defects. We evaluated these defects in terms of two existing hypotheses: preferential loss and reduced redundancy. The greater sensitivity to glaucomatous injury of chromatic tests, compared to achromatic tests, found in this and other studies and the apparent discrepancy between anatomical and psychophysical studies can be parsimoniously explained by differences in cortical summation of ganglion cell responses for the chromatic and achromatic pathways.

Development and Evaluation of a Contrast Sensitivity Perimetry Test for Patients with Glaucoma

“…Pan et al confirmed the findings of Pearson et al 5 with chromatic stimuli and extended their approach by using Gabor patches. 6 However Pan et al were restricted to using only eight locations, to allow the use of 12-reversal staircases without fatiguing the subjects.…”

“…Another form of sinusoidal stimuli with low spatial frequencies (0.25 and 0.50 cyc/deg) is used in frequency-doubling perimetry (FDP), and the results of studies on test-retest variability with FDP are consistent with the predictions of Pearson et al 5 FDP defects are generally similar in depth to defects with conventional perimetry, when expressed as log contrast sensitivity, and test-retest variability is independent of sensitivity. 7,8 However, normal between-subject and test-retest variability are high for FDP.…”

“…Both problems can be addressed by increasing the diameter of the stimulus, but large stimuli often yield shallower defects than does the standard stimulus. [2][3][4] Pearson et al 5 showed that large chromatic stimuli can provide low test-retest variability while maintaining sensitivity to glaucomatous loss. They hypothesized that the key aspect of the stimulus was the nature of cortical pooling and that a similar result would hold for any stimulus for which detection was mediated by cortical cells tuned to low spatial frequencies.…”

A New Approach to Assess Early Progressive Loss Across Multiple Visual Channels In the Natural History of Glaucoma

“…5,[10][11][12] However, there is now histologic evidence of damage in all 3 major visual pathways 3 -magnocellular, parvocellular, and koniocellular-as well as psychophysical evidence of early damage in red-green and blue-yellow channel processing, which are related to the parvocellular and koniocellular pathways. 13,14 These findings support the reduced redundancy hypothesis. 15 This postulates that the increased sensitivity of certain tests 13,16,17 is explained by the stimulation of specific and sparse subsets of ganglion cells, without the redundancy afforded by the other cell types.…”

Aging Effects in Psychophysical Foveal Light Detection Thresholds

“…It was surprising since the perimetry is the main functional test related to the diagnosis of very frequent and important ocular disease, the glaucoma [5][6][7][33][34][35][36] but also in other retina impairment as in the diabetes [37][38][39][40][41], multiple sclerosis [10,[42][43][44], mercury intoxication [20,45], and drug intoxications with hydroxichloroquine [16,[46][47][48][49], vigabatrin [18,50] and others. A possible explanation could be since glaucoma initially shows periphery reductions in visual field the authors were much more interested and focused in study those alterations than the central ones.…”