Section New Developments, Products and Techniques The acuityscope: a resolution test target projection ophthalmoscope

Summary 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 expermental situations (e.g. clinical trials). The Acuityscope, a resolution test target projection ophthalmoscope, is introduced to provide a simple instrument for the objective estimation of visual acuity defects resultant upon optical degradation of retinal image formation by media opacification. The instrument is derived from that described by Cotlier [2], 1982. Cotlier's instrument used the USAF (United States Air Force) three bar resolution test target. (This USAF target was originally designed for testing photopraphic lenses, and is still used commercially for this purpose). The USAF three bar resolution target contains bars, the sizes of which are inappropriate to the clinical estimation of visual acuity, and for this reason a new target set has been designed at the Clinical Cataract Research Unit, Oxford, containing appropriate three bar targets. The design of the targets used data from a pilot study of patients with visual acuities between 6/4 and 6/60. Forty two eyes were included in the pilot study, eyes with retinal or optic nerve abnormal