The spectra of fiber and axon diameter, myelin sheath thickness, fiber density, and g ratio of the optic nerve were analyzed for the strain-13 guinea pig, an animal extensively utilized in the investigation of experimental disorders of demyelination. Our detailed analytical study of the normal guinea pig optic nerve provides the basis for comparison to disease states and the morphology of other species. As in the rat, mouse, and chipmunk, fiber diameters in the guinea pig were unimodal, but dissimilar to the trimodal fiber spectra of the cat and primate. The predominance of medium-sized fibers (0.80-2.00 microns), common to most species, contributed to the larger mean fiber diameter (1.45 microns) of the guinea pig optic nerve, in which small fibers (0.50 microns or less) were infrequent and fibers larger than 5.00 microns in diameter, seen in the cat and primate, were absent. While myelin sheath thickness increased with axon diameter in the guinea pig, as in other species, a g ratio of 0.81 in the guinea pig was greater than in most mammals. Since conduction velocity is dependent on axon size, as well as myelin properties, the relatively larger mean axon diameter of the guinea pig optic nerve (1.18 microns) may compensate for the decrease in its myelination.

No abstract

Electrical responses of the retinas of 4 species of microchiropteran bats stimulated by spectrally restricted light flashes were found to diverge systematically from the rhodopsin absorption spectrum. The divergence was progressively greater across the 4 species. The results appeared explainable by assuming a second photoreceptor class and photopigment which was present in progressively greater numbers in the retinas of Eptesicus fuscus, Desmodus rotundus, Artibeus jamaicensis and Carollia perspicillata.

Foveal and extrafoveal interferometric determinations of retinal resolution were made on two observers. Resolution fell with increasing decentration of fixation.For example, the two subjects exhibited retinal resolution 'equivalent' to Snellen 20/40 respectively at 6.3 ~ and 3.75 ~ from fixation. The test criterion was the ability to distinguish the vertical line (fringe) interferometric pattern formed on the retina. One must conclude that comparable interferometric determinations (resulting in equivalent resolution measurements) do not imply that a patient has central fixation. This finding means that we must use care when interpreting the results of such tests on patients. Of course, if test parameters are altered, or if media are hazy or cloudy, the result may be somewhat different.Observer JE's data follow cone separation data quite well over the range of eccentricities tested. Differences between these data and those of GREEN (1970) must be resolved (see Appendix).

During (January) 1986-(May) 1988, we examined 272 eyes in 136 rhesus monkeys in the closed Cayo Santiago colony of the Caribbean Primate Research Center of the University of Puerto Rico. Seventy-eight eyes were less than 10 years of age. One hundred and ninety-four were aged 10-28 years. The fundi were examined and photographed. Fluorescein angiography was performed in some eyes. Selected cases were evaluated for 'acuity' loss by recording of pattern-evoked retinal and cortical signals. Light and electron microscopy were used to evaluate the pigment epithelium of some animals. Thirty-eight percent of all eyes had posterior pole drusen. Incidence was highly age-related. When late-stage lesions were found, we did not see neovascularization, but late hyperfluorescence was consistent with degenerative scarring and atrophy. Electrophysiology demonstrated moderately reduced acuity in the presence of numerous macular drusen. Electrooculograms were low normal. Histopathology showed changes identical to those reported in human age-related macular degeneration. No eyes less than 10 years of age had confluent drusen or disciform-like lesions. The incidence of drusen in samples of some social groups was much higher than others.