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PURPOSE: To characterize the distribution of the foveal avascular zone circularity and its correlation with parafoveal vessel density, in subjects with and without diabetes. METHODS: Observational, descriptive, cross-sectional, and prospective study; subjects without diabetes (Group 1), with diabetes without retinopathy (Group 2), or with diabetic retinopathy (Group 3) were included. Means of foveal avascular zone circularity and parafoveal vessel density were compared between groups (Kruskal-Wallis) and their correlation was calculated with Spearman's Rho test. RESULTS: Seventy-seven eyes; central vessel density mean was higher in Group 1 than in Group 2 and higher in Group 2 than in Group 3; inner and complete vessel density means were also higher in Group 2 than in Group 3. The mean of the foveal avascular zone circularity did not differ between groups, and in Group 3 it had a positive correlation with central (0.45), inner (0.56), and complete (0.53) vessel densities. CONCLUSIONS: Circularity does not differ between subjects with diabetes, with and without retinopathy, and has only a low correlation with parafoveal vessel density in people with diabetic retinopathy, which does not allow anticipating a reduction of vessel density in this disease.

OBJETIVO: Caracterizar la distribución de la circularidad de la zona avascular foveal y su correlación con la densidad vascular perifoveal, en sujetos con y sin diabetes. MÉTODO: Estudio observacional, descriptivo, transversal y prospectivo; se incluyeron sujetos sin diabetes (Grupo 1), con diabetes sin retinopatía (Grupo 2) y con retinopatía diabética (Grupo 3). Los promedios de circularidad de la zona avascular foveal y de la densidad vascular parafoveal se compararon entre grupos (Kruskal-Wallis), y se calculó su correlación mediante la prueba Rho de Spearman. RESULTADOS: Se estudiaron 77 ojos. El promedio de la densidad vascular central fue mayor en el Grupo 1 que en el Grupo 2, y mayor en el Grupo 2 que en el Grupo 3. Los promedios de la densidad vascular interna y completa también fueron mayores en el Grupo 2 que en el Grupo 3. El promedio de la circularidad de la zona avascular foveal no difirió entre grupos, y en el Grupo 3 tuvo una correlación positiva con la densidad vascular central (0.45), interna (0.56) y completa (0.53). CONCLUSIONES: La circularidad no difiere entre sujetos con y sin diabetes, con y sin retinopatía, y solo tiene una baja correlación con la densidad vascular parafoveal en sujetos con retinopatía diabética, lo cual no permite anticipar una reducción de la densidad vascular en esta enfermedad.

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The number and topographical distribution of photoreceptors was studied in whole-mounted retinas of Cebus apella. It was estimated a total of 48 million rods and 3.8 million cones. The average peak foveal cone density and the Nyquist Limit at the foveola were estimated as 169, 127 cells/mm(2) and 46.77+/-7.98 cyc/deg, respectively. A cone-enriched rim was found near the ora serrata, more noticeable in the nasal retina. Rod distribution was asymmetrical along horizontal and vertical meridians with a higher density in the dorsal retina. The rod/cone ratio was variable and asymmetrical along both meridians.

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The foveal specializations of five New World monkeys, the marmoset, Callithrix jacchus; the golden-handed tamarin, Saguinus midas niger; the squirrel monkey, Saimiri ustius; the capuchin monkey, Cebus apella; and the howler monkey, Alouatta caraya were compared. Although retinal area varies by over a factor of two in these monkeys, the area of the fovea does not covary with retinal area and remains approximately the same absolute size, as measured by the dimensions of the high density region of cones, or the rod-free region. This constancy in foveal size also holds for rhesus monkeys and humans, bringing the variation in retinal area to a factor of five. Alouatta caraya is unusual, distinguished by a very high central cone density and a small rod-free zone. Physiological constraints that might limit foveal area over a wide range of eye sizes are considered.

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Foi investigada a existência de áster, uma estrutura radiada formada por axônios que transitam pela camada nuclear interna e presente na área central da retina de algumas espécies de aves foveadas, principalmente nas de atividade predatória. Na retina de outra aves, mamíferos e répteis estudados, a referida estrutura näo foi encontrada. O áster foi evidenciado através de técnicas histológicas variadas e de microscopia eletrônica de transmissäo

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