A study of Visual Perception in Fish, Especially on Resolving Power and Accommodation

Abstract

1. Three properties of the eye which are importand in visual acuity were investigated: the resolving power of the dioptric system, the resolving power of the retina, and the extent of accommodation. 2. The resolving power of the crystalline lens, the only dioptric element responsible for image formation in fishes, ranged 54-90 seconds of arc for lenses over about 5 mm in diameter. 3. Cone density varies by species and by regions of retina. The best retinal acuity was 4.2 minutes of arc, so that the retina, not the lens, limits visual acuity. 4. All eyes examined were either emmetropic or hypermetropic in untreated living fish which was fixed rigidly in a tank between two pieces of rubber sponge, but became myopic in certain directions upon injection of atropine or curare, or upon sectioning of the optic nerve. 5. The axis of greatest accommodation was lower-fore in Pagrosomus, Sparus, Evynnis, Leiognathus and Xesurus; fore in Epinephelus, Sebastiscus, Therapon, Girella and Pseudoblennius; and fore-fore-upper or upper-fore in Lateolabrax and Trachurus. These axes are usually served by the retinal region of highest cone density. 6. There is a relationship between attachment points of the suspensory ligament and retractor lentis and the axis of accommodation. From this relationship and the region of highest cone density, the visual axis was determined for some species not available in living condition. They are : fore in Cantherines, Helicolenus, and Scomber ; upper-upper-fore in Priacanthus, Malakichthys, Zenion, Chlorophthalmus and Argentina. 7. The binocular field tends to be broadest in the direction of the visual axis. © 1957, The Japanese Society of Fisheries Science. All rights reserved.