Low-contrast visual acuity cards in pediatric ophthalmology

The usual high-contrast visual acuity chart is well known as the best indicator of central visual function. It has the limitation of only testing the high frequency, high-contrast sensitive cells in the visual system. Some conditions demonstrate a normal response on the standard visual acuity test, but abnormal results when testing visual fields or contrast-sensitivity function (CSF). A variety of diseases fall into this category (multiple sclerosis, diabetes mellitis, glaucoma, CNS tumors in the visual system, etc). The testing of CSF permits us not only to vary the size of the target (spatial frequency), but also to determine the contrast of the target first visible to the patient. Due to the time necessary to conduct the test and the important challenge of obtaining consistent subjective responses, contrast-sensitivity testing in children has been difficult. Recently, Regan has developed low-contrast visual acuity cards similar in format to those used in the Sheridan Gardiner test. Although they do not require literacy, correct responses can be immediately verified and the test can be carried out within a short period of time. These cards allow testing well within the child's limited attention span. In the future it may be possible to use this method of testing to detect CSF defects in amblyopia similar to those previously reported by Hess and others and to see how these defects are affected by standard treatment.