Pupil Size and Laser Eye Surgery

22 Oct 2013

The size of your pupil can vary from 2mm to 8mm depending on the natural accommodative power of your eyes and whether you are in bright (2-4mm) or dim (4-8mm) light conditions.


While you might think the pupil is just a big black opening in the centre of your eye that gets bigger or smaller at any given time, the truth is your pupils are responsible for controlling the amount of light allowed into the eye.


Surrounded by the iris, which gives your eyes their colour, the pupils contract and relax depending on the intensity of outside light.

Why do pupils change size?

Your pupillary reflex is controlled by the autonomic nervous system in the body, which instructs the muscles in the iris to either constrict or relax depending on how bright or dark conditions are.


Dilator muscle: Shrinks the iris when in low levels of light. This makes the pupil appear larger in order to allow as much light as possible to shine on the back of the eye.


Sphincter muscle: Expands the iris when you find yourself in bright conditions, so the pupil contracts and less light can infiltrate your eye.

Why does pupil size matters when it comes to Laser Eye Surgery?

Pupils are normally equal in size, but there is a condition called anisocoria which is when one pupil differs in size from the other.


Some people naturally have larger pupils and sometimes certain medications can cause pupils to become larger, especially in dim lighting.


Taking an accurate measurement of a prospective Laser Eye Surgery patient is extremely important as some corrective procedures aren’t suitable.


During your free consultation, pupil size will be measured in dark conditions so that the pupil is fully relaxed and at its largest.

How larger pupils can react to Laser Eye Surgery

There is a greater chance of night vision being affected in patients with large pupils, which can cause glare, halos or starbursts.


However, advances in laser technology have adapted so that those with large pupils can undergo Laser Eye Surgery safely.


The WaveFront procedure in particular is ideal for larger pupils as a 3D map of the corneal surface is taken when the pupil is fully dilated.


Corrective treatment is then programmed to correct every error on the cornea without negatively affecting night vision ability.


To find out more about WaveFront or any other corrective procedure, book your free consultation on +353 1 223 8821.

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