[A new objective visual acuity test: an automated preferential looking].

BACKGROUND The Preferential Looking test using Teller acuity cards is widely used for preverbal children but has some weaknesses, in particular because it is examiner dependent and at best half-objective. We tested a new automated method in a pilot study. PATIENTS AND METHODS In our preferential looking setting we project separate images into the left and right eye. This permits measuring each eye without having to cover the other. An infrared oculography system documents objectively and reproducibly whether or not the stimulus is seen. A square is shown which moves consecutively in a square formation on a background that has the same average brightness. Charting an XY-plot of the eye position results in a square with two diagonals, if the stimulus is seen. By using a specific baby examination unit, this test is already feasible in babies. In this study, the new setting was tested on two children. RESULTS In two healthy children we found a good correlation between visual acuities determined with the new method and Teller visual acuity charts. Fogging one eye in each of the children resulted in fixation loss of the stimulus when the required visual acuity rose above the fogging value. CONCLUSIONS This new technique permits one to perform an objective preferential looking test without the need of verbal answers. Larger studies have to validate these preliminary results.