The acuityscope: a resolution test target projection ophthalmoscope.

The Acuityscope projects an image of a three bar resolution test target onto the patient's retina, where it is viewed and read by an observer. The test target consists of a series of three bar targets varying in size on a logarithmic scale. Individual targets are identified in the projected image by Bailey-Lovie log visual acuity equivalents. The projected image includes only those target sizes which are useful for estimating visual acuity. The Acuityscope is used for assessing the quality of retinal image formation, and is thus able to differentiate between poor visual acuity due to image degradation, (e.g. cataract or corneal disease) and poor visual acuity due to image handling defects (e.g. retinal or optic nerve disease). The use of the instrument is relevant to both clinical situations (e.g. pre-operative assessment of opacification of optical media) and experimental situations (e.g. clinical trials).