Parts I through IV1-4 of this series describe normal and pathologic retinal vascular patterns of human eyes. The technique employed allows study of the retinal vascular tree as a whole mount. Many of these mounts from diseased eyes showed capillary acellularity. While it was inferred that this acellularity was caused by ischemia, no proof could be given. The present experiment was designed to study the sequential changes following temporary and unrelieved ischemia of the eye. If the acellularity was found in such an experiment, then a more secure interpretation of changes in diseased eyes would be justified. Procedure Cats were used because the retinal vascular pattern closely resembles that of the human retina, and the fundus could be continuously visualized with the ophthalmoscope throughout the course of the experiment. Three methods of inducing retinal ischemia were employed: elevation of the intraocular pressure above the arterial pressure of the eyes;