Impairments of contrast discrimination and contrast adaptation in glaucoma.
Allison M. McKendrick 1*,
Geoff P Sampson 2,
Mark J Walland 3,
and
David Badcock 4
1 Optometry & Vision Sciences, University of Melbourne, Corner of Cardigan & Keppel Sts, Carlton, Victoria, 3053, Australia
2 Victorian College of Optometry, Carlton, Victoria, Australia
3 Department of Surgery, Royal Melbourne Hospital, The University of Melbourne, Carlton, Victoria, Australia
4 School of Psychology, University of Western Australia, Nedlands, Western Australia, Australia
* To whom correspondence should be addressed. E-mail: allisonm{at}unimelb.edu.au.
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Abstract |
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Purpose: Contrast detection is commonly measured clinically, however, discrimination between contrasts is also important for natural vision. Furthermore, optimal performance requires the visual system to adapt to ambient contrast conditions. Recent studies of primate neurophysiology demonstrate significant retinal involvement in contrast adaptation. This study investigates whether glaucoma alters contrast adaptation, and explores both detection and discrimination task performance.
Methods: Psychophysical contrast detection and discrimination thresholds were measured in central vision, for a vertically oriented D6 centred on 3 c/deg. Thresholds were measured with and without adaptation to low (15%) and high (70%) contrast vertically oriented 3 c/deg sinusoidal gratings. Fifteen people with glaucoma, and 15 age-similar controls participated. Full contrast discrimination (dipper) functions were measured for a subset (three glaucoma and three controls).
Results: On average, the glaucoma group showed elevated detection and discrimination thresholds relative to controls (detection: t(28) = 2.42; p=0.02; discrimination: F(1, 28) = 6.157, p=0.02). For the subset of additionally tested participants, normalised contrast discrimination functions were similarly shaped for all observers. Glaucoma group thresholds were less influenced by contrast adaptation than controls, for discrimination (F(1,28) = 10.89, p<0.01) but not detection (F(1,28) = 2.28; p=0.11). Differences between groups were greatest for low contrast stimuli (significant interaction between contrast and group: p<0.01).
Conclusions: Glaucoma alters the effect of contrast adaptation on discrimination performance, particularly at low contrast. The study of suprathreshold aspects of vision may reveal new insights to the pathophysiology of glaucoma and possibly relate better to real world visual performance than detection measures.
Key Words:
psychophysics, glaucoma, contrast sensitivity, visual adaptation, spatial vision
