preferential looking
Preferential looking is the most common method of measuring visual acuity in infants.1 The method rests on the observation that an infant's attention is drawn more to a patterned stimulus than to a homogeneous surface.2
The examiner shows the infant a grating of black and white stripes beside a gray patch of equal size and luminance, and watches whether the infant turns the head or eyes toward the grating.1 An infant prefers the grating as long as the stripes lie above the acuity threshold, so the finest grating that still draws the infant's gaze estimates acuity.2 If the infant shows no preference, the grating is assumed to be unresolved.1
Preferential looking measures resolution acuity rather than recognition acuity, which makes it less suited than the visual evoked potential to detecting amblyopia.3 The response also reflects extrafoveal vision.1
More detail
In the forced-choice version, an observer hidden behind a screen records the direction of the infant's head or eye movements as a striped stimulus appears at random on one side of the screen, which excludes observer bias. The method suits infants up to about 4 months of age best, because older infants are easily distracted.2 Acuity measured this way rises from about 6/240 in the newborn to 6/60 at 3 months and 6/6 at 36 months.2 Another set of norms gives 6/180 to 6/90 at 1 month, 6/90 to 6/36 at 3 months and 6/60 to 6/18 at 6 months.1
The child must be alert and able to move the head and eyes, which limits the test in developmentally delayed infants. The cards present stripes in one orientation only, so acuity may be misjudged in a child with uncorrected astigmatism. A child with nystagmus is easier to test with the cards turned 90° to the direction of the nystagmus.3
Sources (9)
- Pickwell's Binocular Vision Anomalies, ch. 3
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 11
- Yanoff and Duker, Ophthalmology (2023), ch. 11.2
- American Academy of Ophthalmology. 2019. Amblyopia Preferred Practice Pattern. San Francisco: American Academy of Ophthalmology.
- Dobson, V. and Teller, D.Y. 1978. Visual acuity in human infants: a review and comparison of behavioral and electrophysiological studies. Vision Research, 18(11), pp.1469-1483.
- Fantz, R.L. 1965. Visual perception from birth as shown by pattern selectivity. Annals of the New York Academy of Sciences, 118(21), pp.793-814.
- McDonald, M.A., Dobson, V., Sebris, S.L., Baitch, L., Varner, D. and Teller, D.Y. 1985. The acuity card procedure: a rapid test of infant acuity. Investigative Ophthalmology & Visual Science, 26(8), pp.1158-1162.
- Rutstein, R. and Daum, K. 1997. Anomalies of Binocular Vision: Diagnosis & Management. St. Louis: Mosby.
- Teller, D.Y., McDonald, M.A., Preston, K., Sebris, S.L. and Dobson, V. 1986. Assessment of visual acuity in infants and children: the acuity card procedure. Developmental Medicine & Child Neurology, 28(6), pp.779-789.
Reviewed October 2026