The fibrous tapetum of the horse eye

Abstract

The tapetum lucidum is a light-reflective tissue in the eyes of many animals. Many ungulates have a fibrous tapetum. The horse has one of the largest eyes of any living animal and also has excellent vision in low-light environments. This study aimed to clarify the macroscopic tapetal shape, relationship between the tapetal thickness and the degree of pigmentation of the retinal pigment epithelium (RPE), spatial relationship between the visual streak and the tapetum, and wavelength of the light reflected from the tapetum in the horse. Macroscopically, weak light revealed the tapetum as a horizontal band located dorsal to and away from the optic disc. The tapetum expanded dorsally as the illumination increased. The tapetal tissue consisted of lamellae of collagen fibrils running parallel to the retinal surface; these spread over almost the entire ocular fundus and were thicker in the horizontal band dorsal to the disc. Only the horizontal band of the tapetum was covered by unpigmented RPE, suggesting that this band reflects light and is responsible for mesopic and scotopic vision. The visual streak was located in the ventral part of the horizontal band, ventral to the thickest part of the tapetum. The wavelength of the light reflected from the horizontal band of the tapetum was estimated from the diameter and interfibrous distance of the collagen fibrils to be approximately 468 nm. Therefore, the light reflected from the tapetum should be more effectively absorbed by rods than by cones, and should not interfere with photopic vision.

Spatial relationships among the cellular tapetum, visual streak and rod density in dogs

“…Although the positional relationship between the tapetum and the visual streak would somewhat relieve the negative effect of the tapetum during daylight, there is concern about the possibility of the tapetum impairing visual resolution in daylight vision. A similar relationship has been reported for the horse eye [ 20 ]. They suggest that the tapetum would not have a serious influence on visual acuity in daylight vision.…”

Morphological Aspects and Microscopic Analyses of Fibrous Tunic and Uveal Components in Bovine Eye

“…While the retinal epithelium is non-pigmented in the region of the tapetum lucidum, the retinal epithelium toward the periphery of the tapetal region acquires a small amount of pigment and becomes pigmented retinal epithelium, which contains a lot of pigment, in areas other than the tapetum lucidum. The presence or absence of tapetum, thickness of tapetal tissue, degree of pigmentation in retinal epithelium, and degree of ambient light are important for the eye shine (Ollivier et al, 2004;Shinozaki et al, 2009Shinozaki et al, , 2013El-Ghazali & Mahdy, 2018).…”

Microstructure of the eye tunics, eyelids and ocular glands of the Sulawesi bear cuscus (Ailurops ursinusTemminck, 1824) (Phalangeridae: Marsupialia) based on anatomical, histological and histochemical studies

“…The second type is the choroidal tapetum lucidum, which is located immediately adjacent to the choriocapillaris and external to the retinal epithelium (Ollivier et al, 2004). On the other hand, the fibrous tapetum lucidum is present in cows, Surti buffalo, sheep, goats and horses (Donisa, Muste, Beteg, & Briciu, 2008;Malsawmkima et al, 2014;Ollivier et al, 2004;Shinozaki, Hosaka, Imagawa, & Uehara, 2010;Shinozaki, Takagi, Hosaka, & Uehara, 2013). According to Young and Braekevelt (1993) cited by Ollivier et al (2004), the red kangaroo also lacks the tapetum lucidum.…”

“…The tapetum lucidum cellulosum is present in dogs, cats, ferrets (Mustela putorius), ranch minks (Mustela vison), pacas (Cuniculus paca), rats (Long Evans rat) and grey seals (Halichoerus grypus). On the other hand, the fibrous tapetum lucidum is present in cows, Surti buffalo, sheep, goats and horses (Donisa, Muste, Beteg, & Briciu, 2008;Malsawmkima et al, 2014;Ollivier et al, 2004;Shinozaki, Hosaka, Imagawa, & Uehara, 2010;Shinozaki, Takagi, Hosaka, & Uehara, 2013). The tapetum lucidum was absent in primates, birds, squirrels, camels and pigs (Bareedy et al, 1986;Chijiiwa, Ishibashi, & Inomata, 1990;Junqueira et al, 1998;Ollivier et al, 2004;Rahi et al, 1980).…”