Structural specializations of the eye in the vizcacha (Lagostomus maximus maximus)

Abstract

Vizcachas (Lagostomus maximus maximus, Chinchillidae) are nocturnal rodents living in burrows in many regions of Argentina, Bolivia, and Chile. We have studied the eye of the vizcacha using several light and electron microscopic procedures, with the purpose of understanding the role of vision in the behavior of this species. Our observations demonstrated an avascular, rod-rich retina, with a specialized region spanning through most of the equator of the eye. In this central band, all neural retinal layers exhibited a high cell density, whereas the photoreceptor layer was characterized by the presence of very long rods. In addition, the central region was associated with a distinct pigmentation pattern, including scarce granulation of the pigment epithelium, low pigmentation of the choroid, and the selective attachment of suprachoroidal cells to the inner scleral surface. These central modifications probably form the structural basis of a reflecting tapetum. The eye of the vizcacha received both long and short ciliary vessels, and a specialized cilio-sclero-choroidal vascular network appeared at the equatorial region. Our findings suggest that the equatorial region of the eye of the vizcacha could be a highly sensitive light detector related to foraging behaviors during crepuscular or nocturnal hours.

Daily morphological variations in the viscacha (Lagostomus maximus maximus) retina. Probable local modulatory action of melatonin

“…Previous studies demonstrated that the pineal gland and its hormone, melatonin, are involved in its reproductive rhythmicity (Domínguez et al, 1987;Fuentes et al, 1991;Pelzer et al, 1999;Muñ oz et al, 1999Muñ oz et al, , 2001Mohamed et al, 2000). Lascano et al (1999) demonstrated an avascular, rod-rich retina, with a specialized region spanning through most of the equator of the eye of the viscacha, suggesting that this equatorial region could be a highly sensitive light detector related to foraging behaviors during crepuscular or nocturnal hours.…”

Microvasculature of the Retina, Ciliary Processes and Choroid in the North American Raccoon (Procyon lotor) Eye: A Scanning Electron Microscopic Study of Corrosion Casts

“…Nocturnal animals, which need to see well at night, generally have eyes with wide pupils, large lens, rod-rich retinas and tapetum [11]. The vizcacha has an avascular retina [11] while the rabbit [23] and guinea pig [19] have a partially vascularized retina.…”

“…The vizcacha has an avascular retina [11] while the rabbit [23] and guinea pig [19] have a partially vascularized retina. This optical strategy plays a significant role in improving photon capture for greater night vision capabilities.…”

“…The broad, horizontal band that lies on each side on the meridian consists of a sparsely vascularized network that may correspond to a visual streak. This horizontal band is found in many mammals and birds and functions as a hypersensitive retinal region [11]. This visual streak, which represents the field of best vision, probably serves the same purpose as the fovea in the human eye.…”

“…This action also enables them to sort out items that are not edible. Another nocturnal animal, the vizcacha (Lagostomus maximus maximus) [11], has an avascular retina, and rabbits [23], guinea pigs [19] and horses [19] are known to have poorly vascularized retinas. However, information on the vascular system of the raccoon eye has not been previously reported.…”