Intraocular pressure (IOP) or eye pressure is the most commonly identified risk factor for glaucoma. In addition, it is the only factor which can be modified, in patients of glaucoma. Decrease in IOP retards the progression of glaucoma, regardless of baseline IOPs. Moreover, eye pressure variations are known to worsen the disease over time.
How does eye pressure vary?
Eye pressure changes during the day, and over days too. Also, eye pressure peak levels and fluctuations (both short term and over longer periods), can cause glaucoma and its progression. Therefore, your doctor will check your eye pressures several times.
When does eye pressure peak?
Most commonly, the highest eye pressures are seen between 2AM and 4AM, because this is the time that the body produces the maximum cortisol. Cortisol is a hormone that influences the eye pressure. This is the normal pattern of eye pressure variation. An exaggerated difference between day and night time eye pressure is seen in patients of glaucoma.
Why is 24 hour eye pressure variation monitoring essential?
- Since eye pressure variation, or fluctuation, over time is one of the major risk factor for visual field loss, it is important to record this level.
- IOP spikes have also been related to progressive visual field loss.
- Moreover, increased eye pressure variation through the day (called diurnal variation) is an independent risk factor for glaucoma progression.
Does eye pressure variation through the day impact treatment plans?
Office hours IOP recordings can be fallacious and are not enough for the management of glaucoma. Peak IOP occur outside office hours in almost half of glaucoma patients. In fact, the treatment plan is changes in more than 35% of patients following 24 hour IOP monitoring.
What are the options for 24 hour IOP check?
- Hospitalisation for IOP: Your doctor may admit you in hospital to record your eye pressures through the night. Some hospitals ask you to visit them every two hours ( during their office hours) to record your eye pressure variations.
- Patient self-tonometry: Your doctor may give you a machine that measures your eye pressures at home. She will teach you how to measure your eye pressures with this machine. You can, then, measure your eye pressure and its variations at home.
- Sleep laboratory: Sometimes, your doctor may advise you to visit a sleep laboratory for a more elaborate study of your eye pressure variations.
- Triggerfish Contact Lens Sensor: Alternatively, you may be prescribed a contact lens monitor to check your 24 hour eye pressure variations. This contact lens continuously monitors your eye pressure, even when you are sleeping.
What is the Water Drinking Test?
Your doctor will measure your eye pressure. She will then ask you to drink a lot of water over 5-10 minutes (usually about 10ml/kg of body weight). After that, she will measure your eye pressure every 15 minutes, for an hour. This test will provide an approximate idea about your peak eye pressures (as recorded during the night), and also of eye pressure variations. This is an easy and low cost way of estimating eye pressure variations.
Points to remember
- Eye pressure variations, both short term and long term, can worsen glaucoma.
- Night time eye pressures are always higher than day time eye pressures.
- The water drinking test may estimate night time pressures.
- If your glaucoma continues to worsen despite good office hour eye pressure control, make sure to get your night time IOP checked.
