TNO STEREOPSIS TEST AS AN AID TO THE PREVENTION OF AMBLYOPIA

In this investigation, carried out under a Youth Health Care postgradu ate course in Nijmegen, the stereopsis of a school population of 730 c hildren, aged 4-18 years, was recorded and clinically evaluated. Stere opsis was measured using the TNO test, a random-dot stereo test especi ally designed for the early detection of amblyopia. The main aims of t his study were to establish the validity of the TNO test as a screenin g test for amblyopia, obtain information about the variability and age dependence of stereopsis, and to evaluate the efficacy of amblyopia p revention. The most important findings can be summarized as follows: 1 . All amblyopes are detected by the TNO test's recommended referral cr iterion of 240 sec arc (binocular threshold parallax in sec arc). 2. T he red-green anaglyphs used in the test do not pose problems for indiv iduals with a colour vision deficiency. 3. The ability to discriminate depth improves by a factor of two over the age interval 4-12 years. 4 . A stereoacuity of less-than-or-equal-to 120 sec arc is a good predic tor of normal or correctable normal vision, and may therefore help in evaluating the often incomplete results of eye tests of young children . 5. Where there is an increased perinatal risk, there is a greater ch ance of disturbed binocular vision. 6. It is estimated that 75% of amb lyopes remain amblyopic, possibly because of delayed detection; 60% of the amblyopes in the population examined were not identified before t he age of 5 years.