Visual acuity: the influence of refraction and diffraction and the use of interference fringes.

In summary, interference acuity provides an exceedingly useful technique for separating optical from retinal causes for poor vision. Opacities can cause gross disturbances of the fringe pattern, so failure in this test may or may not be caused by poor macular function. For patients who would be operated on only if indications of existing potential for vision could be obtained, this test is invaluable. We had several patients who would have been excluded from consideration for a cataract extraction but who were not because we were able to show good potential for acuity; postoperatively, they achieved acuities as predicted. The test succeeded in evaluating macular function in instances when the usual methods of testing for vision potential, such as two-point discrimination, electroretinography, and ultrasound, provided only crude estimates of retinal function. Although the apparatus required is simple-a small laser, a few optical components, and a patient chair-I am not sure how long it will take before ophthalmologists will have it available for office use. But I am optimistic about the possibilities offered by the widespread use of what I consider to be a promising new technique for evaluating macular function behind opacities of the ocular media.