The pigeon's eye viewed through an ophthalmoscopic microscope: Orientation of retinal landmarks and significance of eye movements

The retina of live, anaesthetized pigeons was inspected with an ophthalmoscopic microscope mounted on a goniometer. Retinal landmarks (optic axis, pecten, fovea, border between the yellow and red field) and the ora terminalis were projected into the visual field of the eye and related to existing data. The resting position of the eye is determined by an orientation of the pecten 45° to the horizontal plane and the optic axis pointing to the horizon with an azimuth angle of 70° relative to the bill. The binocular overlap is maximal (≈ 30°) some 15° above the eye-bill axis. In the resting position of the eye the red field is directed to the lower frontal visual field with only marginal binocular overlap. Binocular overlap of the area donalis with the red field, however, during frontal fixation is brought about by eye movements in the range we have demonstrated. The fixation point is 10° below the eye-bill axis.