Sudden change in pupil size – one pupil’s bigger than the other
Some people have slightly differently sized pupils without there being anything wrong – called physiological anisocoria if you like the proper term. In these people, the pupil size difference will be slight – barely noticeable, and when the pupil reactions are professionally checked, the reactions of both eyes are normal.
So, if someone notices that they have a pupil bigger than the other, especially of sudden onset, it’s important to get the eyes properly checked straight away. This is not so much to do with having one pupil bigger – which of itself won’t cause much bother to the vision apart from perhaps some extra glare in the eye with the larger pupil – but it’s because abnormal pupils can be a sign of more serious, even in some cases life-threatening conditions.
Don’t let reading through the rest of this slow you down from making arrangements to get your eyes checked.
Sudden changes to pupil function can be caused by some eyedrops, and medications.
It can also be because of some fault in the pathway between the eyes and the brain (on the way in), or some fault along the pathway from the brain to the eyes (on the way back out).
- The pathway in to the brain is virtually straight inward from the eyes, along the optic nerve, via the optic chiasm and optic tracts to the midbrain, where pupil function is processed.
- The pathway back out is far more circuitous, travelling down the neck and as far down as the top end of where the lungs are before looping back up and into the back of the eyes.
Injury or problems anywhere along this route can affect pupil function, and it takes careful examination to try and work our where the problem might lie.
