Possible role of fundus circulation as an intraocular colour filter in certain fishes.

The possible role of the fundus circulation as an intraocular colour filter was studied by measuring chromatic aberration in two species of fish. One species (the goldfish) has an extensive fundus circulation while the other (the rock bass) has a minimal one. Chromatic aberration was measured retinoscopically in the living eye and by determining the spectral variation in focal length of the excised lens. In the rock bass, chromatic aberration of the excised lens is always a little less than that measured by retinoscopy. In the goldfish, the retinoscopic measurements are substantially less than measurements of the excised lens. This difference is apparently due to the limitation imposed by the goldfish fundus circulation on the possibility of performing retinoscopy with blue light. It is suggested that a fundus circulation can modify the intraocular transmission of light.