Retinal densitometer with the size of a fundus camera.

This paper describes a small, user-friendly fundus reflection densitometer. All optics and part of the electronics are contained in a box with the size of a fundus camera. A personal computer is used for control and on-line display of output. A single 30 W halogen lamp provides bleaching and measuring light. A chopper wheel generates 24 light pulses in 100 msec time frames: 16 pulses of measuring light at different wavelengths covering the spectrum, four pulses of bleaching light (optionally), and four dark pulses for assessing the dark current of the photomultiplier. The fundus can be viewed when the bleaching light is on. The measuring field has four widths ranging from 1.6 to 5.4 deg; the bleaching light is fixed at 25 deg. A fixation aid may be positioned anywhere in the bleaching field. A microprocessor sorts the quanta, detected by the photomultiplier after reflection from the fundus, in 16 channels labeled with wavelength information. Real-time changes in spectral reflection can be viewed on a monitor. Due to optimal design of entrance and exit pupils foveal density differences of up to 0.5 were recorded in human subjects. This is higher than ever reported before with retinal densitometry.