Depth Perception as a Function of Age

Binocular depth perception was investigated in 164 healthy Ss of the Normative Aging Study, in connection with a model of ocular aging which explains change in the dioptric media in the forties on the basis of mechanical change and later change in the retina on the basis of metabolic change. A modified Verhoeff stereopter was used. The results showed a marked diminution to make stereoptic judgments occurred in the forties decade. This is in accordance with the model. In a companion paper, retinal field shrinkage will be explored as an illustration of later metabolic age change. The Veterans Administration has been investigating eye changes in a population of initially healthy subjects (Bell et al., 1966) on an interdisciplinary, longitudinal basis. The parameters include clinical medicine, biochemistry, anthropometry, social and psychological performance, and th6special senses. In the latter category, visual function and its physiologic and morphologic correlates have been examined. We have found that substanti$ physical changes of the dioptric media (lens turbidity, glare sensitivity) begin at 40-45 years, whereas retinal (metabolic) changes begin after age 60 (Bell, 1969). The important perceptual skill of binocular depth perception was then investigated to determine its place in this model of ocular aging. Binocular depth perception has been tested by various methods: (1) The two-rod, or Howard-Dolman test (Howard, 1919) uses the least detectable difference in distance of two rods movable in relation to each other as a measure of stereoscopic discrimination. (2) In the three rod test the least dete'ktable difference between two standard rods and one moved by the examiner is determined. (3) The Ames leaf room uses spatial distortion caused by magnification as an index of stereoscopic perception (Ogle, 1962). (4) Ogle's space eikonometer measures differences in magnification of retinal images (Ogle, 1946). (5) The Verhoeff stereopter uses the number of correct responses to a set of three bars at different distances (one of them closer or farther away) to measure the furthest distance at which the relative position of the three rods is seen correctly (Verhoeff, 1942). (6) Jani (1966) has described a new device consisting of three short rods placed perpendicularly on a transilluminated diffusing screen. The testplate forming the front face of a flashlight is point@ straight toward an observer who must recognize which of the three rods is tallest. The maximum distance at which the correct answer is given represents a measure of stereopsis. 'An earlier version of this paper was presented under the title, "Stereopis and Age" at the Gerontological Society Meeting, October 1970, Toronto, Canada Aging and Iiu&an Development, Volume 3.1972 ' 77 '. 78 B. Bell, E. Wolf, and C. D. Bernholz (7) The Verhoeff stereopter has been well accepted for clinical applications because of its small size and ease of operation. The measurement consists in scoring correct responses to the discriminatory task of discerning the relative position of three rods for eight possible options at a given distance. Sloan and Gallagher (1945) compared the performance of the Howard-Dolman with the Verhoeff test. Trumbull(1951) tested the reliability of the Verhoeff test. Niven et al. (1952) have employed a modification of the standard Verhoeff test. Sloan and Altman (1954) have investigated the reliability of the Verhoeff against the Howard-Dolman test and the Armed Forces Vision Tester. The concensus was that the Verhoeff test was a reliable and convenient tool. In the present study this instrument was used to investigate the relationship between stereoscopic perception and age by determining the number of correct responses at various distances in individuals ranging in age between 20 and 70.