Vernier testing could be a substitute for the traditional Snellen eye chart test

Infant vernier acuity is not as immature as previous research has indicated according to a study published in March in the Journal of Vision, an online, free access publication of the Association for Research in Vision and Ophthalmology (ARVO).

The data from this study also suggest that vernier testing could be a substitute for the traditional Snellen eye chart test for children or others who cannot read letters. Vernier acuity is tested by viewing nearly collinear stripes with varying amounts of spatial phase displacement between them and measuring an individual's ability to gauge the displacement between the stripes.

Angela M. Brown, Veena Adusumilli, and Delwin T. Lindsey of The Ohio State University conducted the study with major funding from the National Eye Institute and the National Science Foundation. The researchers first set out to establish a "benchmark" to which vernier acuity could be compared. The benchmark they chose was the ability to see small differences in contrast. Adults (ages 20 to 48) were tested 6.096 meters (20 feet) from the contrast stimuli, and healthy three-month-old infants were tested 45.72 centimeters (1.5 feet) from the contrast stimuli, to take into account the underdeveloped vision of infants. The experiment showed that under these conditions, infants see changes contrast almost as well as adults.

The vernier acuity of the infants and adults was then tested under the same conditions as the contrast discrimination had been tested. Under these conditions, infant vernier acuity (in degrees of spatial phase displacement) was almost as good as that of adults. Furthermore, the relation between "benchmark" contrast discrimination ability and vernier acuity was the same for infants and adults.

During the testing, an adult observer held an infant in her arms using a "baby sling," standing in a position that allowed the infant to see the stimulus display, but the adult observer could not. The adult observer watched the infant's looking behavior via closed-circuit video and judged whether the test stimulus (the modulation of stimulus displacement or contrast) was contained in the right- or left-side stripes. This is an objective measure of how well infants can see a stimulus, and is in common use in the laboratory and the clinic.

Angela Brown, lead researcher of the study, says the data suggest that vernier acuity of human infants and adults is quite similar, contrary to past studies conducted in this area. The similarity of infant and adult vernier acuity suggests that vernier acuity might be a sensitive test for strabismic amblyopia and other visual disorders that normally must be diagnosed using an eye chart. "The data from this study also suggest that vernier testing could be a substitute for eye chart testing for children and others who cannot read an eye chart," says Brown.