The pupil has a decreased or absent light reflex a slow or delayed constriction to near vision and a sluggish dilation in the dark Most of us are not even aware that our pupils dilate and constrict as light changes around us. The pupil regulates the amount of light that enters the eye so it dilates in dark environments and constricts in bright environments. In patients that have a tonic pupil the pupil has a decreased or absent light reflex a slow or delayed constriction to near vision and a sluggish dilation in the dark. This condition is usually unilateral but the second eye has a tendency to become involved – over time – in about 20 to 30 per cent of cases. Tonic pupils occur most often in women aged 20-40 years. Some people appear asymptomatic other than the slowly reacting pupil while others have a number of additional symptoms. These can include:
- facial pain
- blurry vision
- poor accommodation
Most people with a tonic pupil commonly have absent or poor reflexes particularly in the knee joint. This is because the condition involves the degeneration of a specific nerve that runs from the brain to specific receptors including both the pupil and the patella (knee) area. The cause of the nerve degeneration is not known in many cases.
Trauma is the most common cause of tonic pupil. Other causes include viral illness diabetes or inflammatory processes. Syphilis can also bring about tonic pupil and it usually affects both eyes. When the cause cannot be identified the condition is termed Adie’s Tonic Pupil
There is no definitive treatment for this condition. Each case should be treated individually in order to determine the triggering problem. If no cause is found then there are certain treatments that can be considered. If the pupil asymmetry is of a cosmetic concern your eye care practitioner can prescribe opaque contact lenses which gives the effect of equal sized pupils. If near vision is blurred glasses can be prescribed.