Capturing age-related changes in functional contrast sensitivity with decreasing light levels in monocular and binocular vision.
OBJECTIVE
It is challenging to separate the effects of normal aging of the retina and visual pathways independently from optical factors, decreased retinal illuminance, and early stage disease. This study determined limits to describe the effect of light level on normal, age-related changes in monocular and binocular functional contrast sensitivity.


METHODS
We recruited 95 participants aged 20 to 85 years. Contrast thresholds for correct orientation discrimination of the gap in a Landolt C optotype were measured using a 4-alternative, forced-choice (4AFC) procedure at screen luminances from 34 to 0.12 cd/m(2) at the fovea and parafovea (0° and ±4°). Pupil size was measured continuously. The Health of the Retina index (HRindex) was computed to capture the loss of contrast sensitivity with decreasing light level. Participants were excluded if they exhibited performance outside the normal limits of interocular differences or HRindex values, or signs of ocular disease.


RESULTS
Parafoveal contrast thresholds showed a steeper decline and higher correlation with age at the parafovea than the fovea. Of participants with clinical signs of ocular disease, 83% had HRindex values outside the normal limits. Binocular summation of contrast signals declined with age, independent of interocular differences.


CONCLUSIONS
The HRindex worsens more rapidly with age at the parafovea, consistent with histologic findings of rod loss and its link to age-related degenerative disease of the retina. The HRindex and interocular differences could be used to screen for and separate the earliest stages of subclinical disease from changes caused by normal aging.
Applied Vision Research Centre, The Henry Wellcome Laboratories for Vision Sciences, School of Health Sciences, City University London, London, United Kingdom. hanna.gillespie-gallery.2@city.ac.uk
Hanna
H
Gillespie-Gallery
Evgenia
E
Konstantakopoulou
Jonathan A
JA
Harlow
John L
JL
Barbur
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D012160:Retina / Q000502:physiology*; D012684:Sensory Thresholds; D015348:Vision, Binocular / Q000502:physiology*; D015349:Vision, Monocular / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
binocular vision; contrast sensitivity; photoreceptors; retina