Some animals suffer from shortsightedness and have poor eyesight. In domestic animals, myopia, with or without

astigmatism Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at nig ...

, occurs frequently.

In cats

Evolved for low-light hunting, cats' eyes are proportionally enormous. Their eye size makes focusing between near and far so difficult that the muscles develop with an environmental bias. Outdoor cats tend to be farsighted, while most indoor cats are nearsighted but not myopic. Cats are unable to focus on anything less than a foot in front of them.

In dogs

One animal species in which myopia occurs naturally is the domestic dog. Although the prevalence of myopia in dogs is breed dependent, approximately 8% to 15% of Labrador Retrievers are reported to have myopia.

In rhinoceroses

Whereas the rhinoceros may suffer from less-than-adequate eyesight, it generally survives by concentrating with its superior hearing and sense of smell. Some reports, however state that it can see better when focusing with one eye, particularly when walking, posturing, and combatting.

Research

Myopia, with or without astigmatism, is the most common eye condition in horses. Several types of occlusion myopia have been recorded in

tree shrews The treeshrews (or tree shrews or banxrings) are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire order Scandentia, which split into two families: the Tupaiidae (19 species, "ordinary" treeshrews) ...

macaques The macaques () constitute a genus (''Macaca'') of sociality, gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit species distribution, ranges throughout Asia, North Africa, and (in barbary macaques ...

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s and

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...

s, deciphered from several animal-inducing myopia models. Preliminary laboratory investigations using

retinoscopy Retinoscopy (Ret) is a technique to obtain an objective measurement of the refractive error of a patient's eyes. The examiner uses a retinoscope to shine light into the patient's eye and observes the reflection (reflex) off the patient's retina. W ...

of 240

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

s found myopic problems with varying degrees of refraction errors depending on the breed. In cases involving

German Shepherd The German Shepherd or Alsatian is a German breed of working dog of medium to large size. The breed was developed by Max von Stephanitz using various traditional German herding dogs from 1899. It was originally bred as a herding dog, for he ...

Rottweiler The Rottweiler (, ) is a breed of domestic dog, regarded as medium-to-large or large. The dogs were known in German as , meaning Rottweil butchers' dogs, because their main use was to herd livestock and pull carts laden with butchered mea ...

s and

Miniature horse A miniature horse is a breed A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In liter ...

s, the refraction errors were indicative of myopia.

Nuclear sclerosis Nuclear sclerosis is an age-related change in the density of the crystalline lens The lens, or crystalline lens, is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. ...

of the

crystalline lens The lens, or crystalline lens, is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it can ...

was noticed in older dogs. Experiments into newborn

macaque The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and (in one instance) Gibraltar. Macaques are principally ...

monkeys have revealed that surgically fusing the eyelid for one year results in eye deterioration as the eye has not had a chance to grow and develop. Keeping monkeys in the dark for a similar period, however, does not lead to myopia. In 1996, Maurice and Mushin conducted tests on rabbits by raising their body temperatures and intraocular pressures (IOP) and noted that while younger rabbits were prone to developing myopia, older rabbits were not. Some tests have revealed that myopia in some animals can be improved with eye drops containing

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

, by increasing the activity of

superoxide dismutase Superoxide dismutase (SOD, ) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide () radical into ordinary molecular oxygen (O2) and hydrogen peroxide (). Superoxide is produced as a by-product of oxygen me ...

(SOD). The rhesus monkey's vision amplitude reduction is noticeable in its second decade of life; however the condition does not impede normal functioning. Older rhesus monkeys have more difficulty accommodating this reduction in vision amplitude, encountering difficulty in focusing on objects at close range, even objects on the ground within an arm's length.

References

{{reflist Disorders of ocular muscles, binocular movement, accommodation and refraction Vision Animal diseases