Scanning Laser Ophthalmoscope

An instrument is described which functions as a low light level ocular fundus camera and ophthalmoscope, and which is capable of making a wide range of quantitative measurements in the eye. Light levels for ophthalmoscopy (20 ¿W/cm2 at the retina) are at least two orders of magnitude below those in current use. A focused laser bearn forms a flying spot, moved physically by scanning mirrors. This allows a 20 ¿m or smaller resolution element, with only a 0.9 mm diameter area of the patient´s pupil used for the entering beam. The remaining pupillary area forms the exit pupil¿a critical inversion of the division of pupils necessary for systems using conventional imaging. It is this inversion which allows the low light level and the unique measurement capabilities. We discuss the constraints imposed by viewing the inside of a spheroid through a small hole in its wall, and our solutions¿both optical and electronic¿to these problems. We also describe electronic problems encountered in the video system, which arise from our special detection and display systems. Some specifics of the instrument´s measurement capabilities are discussed.