Clinical applications of preferential looking measures of visual acuity.

We have undertaken 3 lines of research aimed at the eventual transformation of the laboratory-based preferential looking (PL) acuity-testing procedures into clinically-useful techniques. (1) The first line of research involves studies of the parameters of PL testing, and the establishing of norms for various groups. The results show that acuity development is closely tied to gestational age, that infants' acuity is reduced at low luminances but does not vary significantly at levels above 1 log cd/m2, and that monocular acuity is poorer than previously-published binocular acuity norms. (2) The second line involves the development of a shortened procedure (the 'diagnostic grating' procedure) that maximizes the certainty of gaining the most critical information from an infant in a short time. In this procedure, the infant is tested with a low spatial frequency grating to screen for blindness or total lack of visual response, and another grating of a spatial frequency that is diagnostic of normal acuity for children of the patient's age. Based on the results with these two gratings and the time available, the child is then tested with other gratings to refine the acuity estimate. (3) The third line of research involves using the procedure, in a laboratory setting, with individual infants and children at risk for visual acuity deficits. Longitudinal case histories of patients with strabismus, ptosis, and suspected blindness are presented.