Acuity Perimetry

Abstract

Measurement of peripheral visual acuity may provide useful clinical information not obtainable from classical light sense perimetry. We have designed and built a new laser interferometer which allows us to test visual acuity at various eccentricities from zero to 20° and along any meridian. The test field is round, one degree in diameter, and contains alternating red and black stripes. The orientation and separation of the stripes can be varied, as can the intensity of the background illumination. The subject is asked if he can detect the striped pattern and, if so, its orientation.

The light source is a helium neon laser. A holographic phase grating separates the light into two coherent, equal strength, spherical waves diverging from a single point. The waves are focused near the nodal point of the subject’s eye and form interference fringes on the retina. The fringes are not ‘focused’; they occur wherever the waves overlap. Thus visibility of the fringes is virtually independent of the eye’s refraction and is not impaired by minor media opacities.