Tiny pupils deliver the sharpest image and perform best for stereopsis. We do this too – try walking down stairs with one eye shut.Why might being an ambush predator dictate the shape of your pupil? Because to pounce on a mouse, a cat must be superb at judging distance – and that’s where a slit-shaped pupil can help, says Banks. Their brain compares the slightly different images relayed from the left and right eye to help estimate distance – a process called stereopsis. Like most predators, a cat’s eyes face forward. Those that chase down their prey, such as cheetahs and wolves, tend to have circular pupils. Banks’ study shows the slit-shaped pupil is most often found in animals that hunt by day and night, and especially among predators that ambush their prey – including cats, snakes and crocodiles. The slit-shaped pupil, with its remarkable light control, is how a cat can hunt in near-darkness, and also in bright daylight, says Ron Douglas, an animal vision biologist at City University London. By contrast human pupils expand by a factor of 15.
Overall a cat’s pupils can expand by 135-fold and can perform like built-in night vision goggles. Like opening or closing theatre curtains, muscles on either side of the cat’s pupil open the slit wide or cause it to narrow. A cat’s pupilĭepending on the light, the shape of a domestic cat’s pupil changes from vertical slit to alluring almond to almost fully round. Their findings were published in Science Advances in August. Martin Banks from the University of California in Berkeley and colleagues examined the eyes of more than 200 land animals and found their status as predator or prey was correlated to the shape of their pupils. Any prescribed treatment will likely aim to address the underlying cause of your anisocoria.Ever wondered why cat eyes have vertical slit-shaped pupils, while sheep have horizontal bars? A recent study suggests it has to do with their place in the food chain. Depending on your symptoms and medical history, your eye doctor might conduct tests, such as eye exams and blood work, to help diagnose the underlying cause of your anisocoria. If you notice a sudden difference in size between your pupils, you should contact your eye doctor immediately. What do I do if I notice that I have unequal pupils? Certain drugs have been identified that could be potential causes of pharmacologic anisocoria, such as anti-depression medication, chemotherapy, patches used to treat motion sickness, or certain glaucoma eye drops. In this type of anisocoria, the unequal pupil sizes occur as a side effect of medication. Some examples of this condition include coloboma, which is a gap in the iris that gives the pupil a distinct cat-eye appearance, or aniridia, which is an eye condition where there is a complete or partial absence of the iris of one eye. Damage to the eye can include eye trauma, complications after or resulting from eye surgery, glaucoma or inflammation of the eye.Ĭongenital anomalies (anomalies present from birth) present in the iris are also classified under mechanical anisocoria. When unequal pupil sizes are caused by damage to the eye, it falls under the category of mechanical anisocoria. This constriction then results in anisocoria. For example, in people with Horner’s syndrome, one of the symptoms is miosis, which is the constriction of one pupil. Pathologic anisocoria is unequal pupils caused by an underlying condition or disease, such as Horner’s syndrome or Third nerve palsy. In fact, simple anisocoria can be intermittent or constant, and may sometimes even go away on its own without any medical intervention. Simple anisocoria is the most common type, and is generally not a cause for concern. Simple anisocoria, also known as essential anisocoria or physiologic anisocoria, is the term for the condition where the difference in pupil size in both the eyes is less than 1 mm, and both pupils react normally when exposed to light. There are four different types of anisocoria, and each type has different causes and manifestations: 1. 4 different types of anisocoria ( unequal pupils ) and their causes One pupil may be larger than normal, or one pupil may be smaller than normal, therefore resulting in unequal pupil sizes. In most people, they are usually the same size in both eyes.įor people with anisocoria, the pupil sizes in both eyes are different. Pupils, the black circles at the centre of our eyes, are what allows light to enter our eyes so that we can see. If you have unequal pupils, you could be suffering from anisocoria.
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