Vision Problems in Cats: How Can I Tell If My Cat Has This Problem?

Abstract

Vision in cats: Cats rely on their vision to perform several tasks such as navigation, hunting, orientation, avoiding undesirable situations, interaction with other cats and watching the world go by. In order to see an image, several factors are combined including: • Detection of light and movement • Visual perspective (the angle through which the cat views the world, usually from close to the ground) • Field of view (the extent of the view which is visible) • Depth perception (the ability to judge distances) • Visual acuity (the ability to focus) • Perception of colour and shape. The brain receives this information from the eye and forms an image accordingly. The brain also receives several other pieces of information about sounds, smells, texture and taste. All of this is combined to complete the vision and perception experience. Cats have evolved to be excellent night‐time hunters. Vision in a normal cat is very good but in order to gain advantages that particularly help with night vision and hunting, some trade‐ offs mean that cats do not see in as fine detail as we do. The main reason that cats have better night (nocturnal) vision than us is because they have an extra layer in the back of their eye called a tapetum. This is a reflective layer which lies underneath the retina – the 'seeing' part of the eye. The retina contains special cells called rods and cones which absorb light converting this into information which is processed by the brain. Light which enters the eye and is not absorbed by the rods and cones contacts the tapetum and is reflected back to the rods and cones again. In other words, the cells of the feline retina get a second chance to absorb the light. The tapetum is responsible for the mirror‐like reflection which we see from cats when we catch them at night with a bright light, such as with the head‐lights of a car. It is suggested that cats' nocturnal vision is six times better than ours. Another factor which improves their nocturnal vision is the fact that they can dilate their pupils so widely, maximising the amount of light which enters the eye in dim lighting. This pupil is constricted (in this case because of bright sunlight) which means that more of the coloured iris is visible and the pupil is a narrow slit.