Behavioral Tests of Visual Acuity in Infants

Abstract

Two behavioral techniques--OKN and PL--have been used to test visual acuity in young infants in both laboratory and clinical settings. Clinically, OKN is used widely by ophthalmologists as an informal, subjective estimate of an infant's visual status. However, the difficulty of the judgments required and the problem of obtaining good OKN gratings that can be used at a near enough distance to maintain an infant's attention make the procedcure less than ideal. The PL procedure has been used much more widely in laboratory testing than has the OKN procedure, probably because the grating stimuli used are smaller and easier to obtain than OKN stimuli and because the judgments required of the observer necessitate only comparison of the infant's looking behavior in the presence of two stimuli, rather than judgments concerning the presence or absence of a behavior. However, it is only recently that PL procedures, in the form of the diagnostic stripes procedure, have been introduced into clinical settings for measurement of acuity. To date, the diagnostic stripes procedure has proved to be a rapid and practical test to carry out in the clinic, and it appears to be effective in diagnosing infants with ophthalmic problems that would be expected to interfere with vision tested binocularly. However, whether the procedure will be more useful than a standard pediatric or ophthalmic examination for screening infants for visual problems has yet to be determined. In addition, the treatment implications of early detection of poor visual acuity cannot yet be known. To be a truly useful test, a procedure that assesses visual acuity in infants should have prognostic or treatment value--neither of which has been clearly established for the OKN or the PL procedure. The problem is a circular one. We do not know the value of developing tests of visual acuity in infants because the treatment implications and prognostic value of early detection have not yet been established. However, knowledge of the value of early treatment is useless unless early detection is possible. Now that the cycle is beginning to be broken through development of techniques for early detection of poor acuity, research into the prognostic and treatment value of early diagnosis becomes possible for the first time. In conclusion, a number of researchers are working on the development of behavioral techniques for measurement of visual acuity in infants. Whether or not these procedures can be helpful clinically depends on what visual problems can be identified with each technique in the clinic, and whether or not it will turn out to be useful to identify these visual problems at such an early age, a question that can only be answered by further clinical and laboratory observations.