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Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats. Similar to retinitis pigmentosa in humans, [1] it is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness.
Symptoms include sudden permanent blindness, but may occur more slowly over several days, weeks or months, [3] dilated pupils.Pupillary light reflexes are usually reduced but present; the slow phase mediated by melanopsin in retinal ganglion cells is retained.
Affected cats may also display poor judgement of distance, and some cats may develop a rapid, crouching, hypermetric gait. Some affected cats may exhibit an abnormal head tilt, tremors, a vacant stare, excessive salivation, decreased grooming behaviors, polyphagia , and dilated pupils. [ 3 ]
Statements that certain species of mammals are "born blind" refer to them being born with their eyes closed and their eyelids fused together; the eyes open later. One example is the rabbit . In humans the eyelids are fused for a while before birth, but open again before the normal birth time, but very premature babies are sometimes born with ...
Mydriasis is the dilation of the pupil, usually having a non-physiological cause, [3] or sometimes a physiological pupillary response. [4] Non-physiological causes of mydriasis include disease, trauma, or the use of certain types of drugs.
The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye. [3] In the swinging flashlight test, a light is alternately shone into the left and right eyes. A normal response would be equal constriction of both pupils, regardless of which eye the light is directed at.
The extraneous pupil is c. 2.5mm away from the principal pupil. In cases of true polycoria, there is an intact sphincter muscle, which contracts and dilates the pupils. [7] In an eye without polycoria, the sphincter muscle is a part of the iris that functions to constrict and dilate the pupil.
The large ears, eyes, and many vibrissae (whiskers) of the cat adapt it for low-light predation. Cat senses are adaptations that allow cats to be highly efficient predators. Cats are good at detecting movement in low light, have an acute sense of hearing and smell, and their sense of touch is enhanced by long whiskers that protrude from their ...