Macroscopic morphological aspects, ecometry and rebound tonometry of the eye bulb in sloth (Bradypus variegatus)

Abstract

The field related to the visual system of wild animals is deeply scarce. Settling anatomical and physiological parameters for these animals is still a descriptive vision for Bradypus variegatus (Schinz, 1825). Thus, our research aimed to determine patterns of normal eye for this species. For this purpose, eight eye bulbs were dissected from the carcasses obtained by natural death, and then performed an overview of ocular anatomical. Rebound tonometry (RBT) and ocular B-mode ultrasonography were also applied for eight eyes in four animals from “Parque Estadual Dois Irmãos”, situated in the city of Recife, state of Pernambuco (PE), to estimate the intraocular pressure and ocular ecobiometry. The ocular morphology of sloth is similar as described for other species, however, with some peculiarities. They present a third eyelid emerging in the nasal region of the inferior conjunctival sac and retina and also contain little differentiated blood vessels. Medium the intraocular pressure (IOP) was 4.25mmHg with no difference for both eyes. Ultrasonography of ocular anatomy is also similar regarding other species. Ecobiometric patterns were evaluated to determine the anterior chamber depth, lens width, vitreous chamber depth, and axial length (AL) of ocular globe and the averaged as shown 0.63±1.11mm, 3.73±0.24mm, 6.15±0.41mm, 3.70±0.27mm, and 8.48±0.22mm, respectively. There was no difference between the right and left eyes. The RBT and ocular B-mode ultrasonography are fast exams and easy for animal testing. This study contributed to the characterization of ocular anatomy as well as settling medium values of IOP and intraocular measures; however, further research on physiology and histology is necessary to better understand the visual function of the species.

The organ of vision morphology of the southern two‐toed sloth (Choloepus didactylus Linnaeus, 1758; Pilosa, Choloepodidae)

“…Although examined group of animals in our study were small, the obtained results of the eyeball macroscopic measurements were higher or similar to the results of the brown-throated sloth where there is a special microenvironment for their renewal and proliferation (Sanchez & Daniels, 2016). Macroscopically, the tapetum lucidum in the southern two-toed sloth was not identified, as was the case with Bradypus variegatus (Braz et al, 2020;Sena et al, 2021), while our histological studies showed the presence of choroidal tapetum lucidum cellulosum, the cells of this latter being characterized by folding of the cell membrane and irregular layering. Such structure of tapetum lucidum proves its degeneration, which was similarly demonstrated in the Asiatic black bear (Ursus thibetanus; Paszta et al, 2022) and ranch mink (Mustela vision; Braekevelt, 1989;Ollivier et al, 2004).…”

“…Bradypus variegatus;Braz et al, 2020) and the pale-throated sloth (Bradypus tridactylus;Hayssen, 2009). Histological studies revealed that the cornea in the examined southern two-toed sloth consists of only four layers (no Bowman's membrane) similar to Watillon and Goffmanni's research on Choloepus hoffmanniF I G U R E 5 Photomicrograph of the histochemistry of southern two-toed sloth upper and lower eyelids.…”

“…Macroscopic and morphometric studies in the upper and lower eyelids of the southern two-toed sloth showed thick eyelashes in the anterior palpebral margin in both fleshy eyelids, similar to the brown-throated sloth (Bradypus variegatus) (Braz et al, 2020) where they are covered outside by a short hair layer and inside by the bulbar conjunctiva. Histologically, both eyelids in our southern two-toed sloth proved the lack of tarsal glands as in the brownthroated sloth (Sena et al, 2021).…”

“…Hitherto, the study of the eyesight of the sloth was performed by a few authors (Adam, 1999; Andrade‐da‐Costa et al, 1987, 1989; Beebe, 1926; Britton, 1941; Collin, 2008; Hayssen, 2009, 2011; Krieg, 1961; Menegaux, 1908; Meritt Jr., 1985; Piggins & Muntz, 1985; Prince, 1956; Rochon‐Duvigneaud, 1943; Sena et al, 2021; Smith, 1898; Tirler, 1966; Walls, 1942; Wislocki, 1928). Additionally, the geometry and tonometry of the eyeball were described in the sloth (Braz et al, 2020). Ophthalmic examination and computed tomography were performed in other species from Pilosa order (Farha et al, 2011; Rodarte‐Almeida et al, 2021).…”

“…Additionally, the geometry and tonometry of the eyeball were described in the sloth (Braz et al, 2020). Ophthalmic examination and computed tomography were performed in other species from Pilosa order (Farha et al, 2011;Rodarte-Almeida et al, 2021).…”