Vetnews | Augustus 2025 44 « BACK TO CONTENTS Bats exist on every landmass, apart from the Polar regions and a few oceanic islands. There are more than 1230 species, which makes nearly 1 in 5 mammal species (21%) a bat, with only the order Rodentia exceeding them. As such, they are one of the most diverse groups of mammals. Bats are divided into 2 suborders. • Yinpterochiroptera, previously known as megabats (old world fruit bats or flying foxes), with seven families distributed in Africa, Asia and Oceania; • Yangochiroptera, which includes most of those previously known as microbat families. Echolocation systems are present in many species of bat, which aid in flight orientation and hunting across varied ecological niches. Some fruit bats evolved incredible olfactory senses; the Eastern tube-nosed fruit bat possesses nostrils that function independently from one another (stereo olfaction), which allows them to precisely locate and follow an odour trail three-dimensionally. Some bats possess a sensory mechanism that allows them to detect the Earth’s magnetic field, which allows them to navigate their environment. Most bat species have a very well-developed visual system, and the age-old saying “As blind as a bat” is mostly incorrect. The Yinpterochiroptera bat visual system is generally more developed, and the Yangochiroptera have visual acuity comparable to that of a mouse and can see fairly well. Some small species of bats, however, do have very small eyes (absolutely and relatively speaking), which probably will favour other sensorial skills, such as echolocation and olfaction. Visual acuity will vary according to specific needs as dictated by the ecological niche the species occupies. It has been reported that certain small insectivorous bats may have vision equivalent to that of largereyed frugivorous or nectarivorous bats. Yinpterochiroptera bats are generally crepuscular or nocturnal, and Yangochiroptera bats are nocturnal; thus, the retinas in both suborders of bats are rod-dominated. Some Yinpterochiroptera bats have the potential for trichromatic vision, with the majority possessing dichromatic vision, and some are even monochromatic. Bats possess an anangiotic retina (devoid of retinal blood vessels), which requires diffusion of oxygen from the choroid for oxygenation of the retina. Anangiotic retinas are usually very thin (<140 μm) to allow this diffusion to occur. Some Yinpterochiroptera species have surprisingly thick retinas (250–350 μm) despite being avascular, and they have a unique morphological adaptation present to ensure adequate oxygen delivery occurs to the retina. This consists of numerous choroidal spike-like projections or papilledema. This adaptation ensures that all portions of the retina are no more than 100 μm away from a blood supply. Bat globes are small and positioned well forward in the orbit with binocular overlap of 40-50˚ in the horizontal visual field. The eyeball is remarkably spherical, and the cornea is very large. The pupils are round to horizontal ovoid when constricted, depending on the species. Pupil size has a considerable range depending on ambient lighting conditions. Considering bats generally live in large colonies, ocular trauma from individual interactions and the spread of infectious organisms would be possible. In bat sanctuaries, the two most common ocular abnormalities are trauma-related (lacerations and swelling) and infectious conjunctivitis of unknown origin. Bats are considered sentinel species due to their highly specialised habitat requirements and complex interactions with the environment. They have adapted to thrive in a variety of ecosystems and on a variety of diets, including insects, small mammals, fish, blood, nectar, fruit and pollen. Many insectivorous bats are highly mobile predators and play a significant role in the control of agricultural pests. v Reference: 1. Montiani-Ferreira F, Moore BA, Ben-Shlomo G, editors. Wild and Exotic Animal Ophthalmology Volume 2: Mammals. In: Wild and Exotic Animal Ophthalmology: Volume 2: Mammals [Internet]. Cham: Springer International Publishing; 2022 [cited 2024 Feb 13]. p. 145–54. Available from: https://link. springer.com/10.1007/978-3-030-81273-7 Regulars I Ophthalmology Column Bats: not that blind after all Paul Burger (BVSc, MMedVet (Ophtho) Johannesburg and Cape Animal Eye Hospitals www.animaleyehospital.co.za
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