Perception of very small visual stimuli in the fovea: normative data for the Rarebit Foveal Test

• Published in: Clinical and experimental optometry 2006-03, Vol.89 (2), p.81-85
• Main Authors: Nilsson, M, Wanger, P, Martin, L
• Format: Article
• Language: English
• Subjects: Adult; age; Age Factors; contrast; Fovea Centralis - physiology; Humans; luminance; Medicin och hälsovetenskap; Middle Aged; Photic Stimulation; Rarebit Fovea Test; Reference Values; target detection; Vision Tests - standards; Visual Perception - physiology
• ISSN: 0816-4622; 1444-0938; 1444-0938
• DOI: 10.1111/j.1444-0938.2006.00016.x

Background:  Conventional visual tests are not sensitive enough to detect low degree neural damage, as 6/6 (1.0) visual acuity can be upheld with less than two-thirds of the normal number of optic nerve axons. The aim of the current study was to evaluate the physiologic properties of a new computerised test, the Rarebit Fovea Test (RFT), using very small stimuli, by quantifying the effect of age and binocular summation in relation to stimulus luminance. Methods:  The RFT relies on the perception of very small (less than 0.5 minutes of arc) bright stimuli. Two different experiments were performed. 1 Thirty-five subjects (age 19 to 63 years) were tested with five different stimulus luminances, 158, 64, 53, 41 and 33-cd/m 2 . 2 Nineteen subjects (age 19 to 63 years) were tested using binocular stimulation to define the binocular summation. Results:  Significantly reduced median hit rates were observed at luminances of 53-cd/m 2 or below. Age and mean hit rate correlated negatively at all luminance levels below 158-cd/m 2 . The mean hit rate from binocular stimulation, compared to the highest value from monocular stimulation in the same subject, was increased by a factor of 1.54 ± 0.45 (SD). No age effect was found regarding binocular summation. Conclusions:  The results in the current study indicate that RFT can identify some of the well-known features of the visual system, that is, the effects of age and binocular summation, provided that the stimulus luminance is adequately selected.