Horner's is characterised by abnormally small pupils and may be accompanied by a drooping eyelid and bloodshot eyes. The condition affects the sympathetic nervous system, which is responsible for the body's fight or flight mechanism. Horner's Syndrome is another neurological disease that can arise due to various reasons, including tumours and medical treatments. People with HAS may also suffer profuse sweating and it is more common in young women. The condition usually progresses slowly in one eye before developing in the other. It is thought to be caused by a viral infection that leads to inflammation and damage in the part of the brain that controls eye movement. Holmes-Adie Syndrome (HAS) is a neurological disorder where one pupil is significantly larger than the other and constricts slowly in bright lights. Sufferers also often complain of blurred vision. This not only causes persistent dilated pupils but headache pain will be focused around the eyes. This specific type of severe headache is thought to cause abnormal paralysis of the motor nerves of the eye. Here are some of the reasons why pupils may be different sizes or shapes.ĭilated pupils can be a symptom of certain migraines. Sometimes your pupils will return back to their normal size without need for treatment, but you should seek medical attention if the condition persists or has followed a head trauma or injury. When your pupils are different sizes, it is called anisocoria and there are several different causes. Pupils do this by contracting and dilating, thus making them appear smaller and larger respectively.

The pupil is the hole in the centre of the iris (the coloured part of the eye) and its primary function is to control the amount of light that enters the eye. However, if there is a significant difference or one of the pupils has only recently changed there could be an underlying issue. Some people have pupils that are slightly different sizes or shapes, so variations can be normal and are usually harmless.

Irregular pupil shape