Glaucoma tests – Part 1
We conduct many tests to monitor and observe patients that we suspect may have glaucoma.
Your vision will be measured at each visit. This is important even if it is normal. You must always bring your distance glasses with you to appointments. The pinhole that is used when testing the vision corrects for any error in the glasses prescription. This gives us the best idea of the visual potential even if you have cataracts.
Eye pressure measurements
Also known as IOP or intraocular pressure, this can be measured in a variety of ways.
Opticians commonly use an air puff test known as ‘pulsair’ or non-contact tonometry. This is a reasonable screening test but often overestimates IOP. There are many cases where the air puff test measurements are above normal, but which are normal when checked in the clinic with the gold standard test. This is especially true if the cornea (the window at the front of the eye) is thicker than average.
In the clinic, the IOP may first be checked with a screening test called iCare. This is more accurate than the air puff test. If this measurement is very high you will see the doctor straight away.
The gold standard IOP measurement is called ‘Goldman applanation tonometry (GAT)’. It is very accurate and painless. An anaesthetic drop coloured with an orange dye is applied to both eyes. A blue light is used to light up the front of your eye. The pressure measurer is brought very close to the front of your eye. The doctor will hold your eyelashes out of the way to take the measurement.
It may be necessary to repeat this gold standard IOP measurement at different times of the day as the IOP rises and falls throughout the day. This is called phasing. The IOP is measured every 2 hours from 08:00 to 18:00. The IOP is usually lower in the evening and overnight. It is unusual to keep someone in the hospital to measure their IOP throughout the night. Some patients may have a very high IOP reading for 1-2 hours and thereafter the IOP is lower. Phasing is designed to find these high peaks to adjust the treatment. If a glaucoma patient has a very high IOP at 10 am yet always comes to a consultation in the afternoon, we may never record that very high IOP. Phasing is usually done in patients who appear to have glaucoma, yet their IOP has never been measured to be high. Or in patients whose glaucoma is getting worse despite having good measured IOP in the clinic.
More about Laura Crawley
Ms Laura Crawley is a Consultant Ophthalmologist at Clinica London. Her special expertise is in treating glaucoma patients as well as patients with glaucoma and cataracts. She has a lot of experience in treating glaucoma and has published extensively in scientific journals and on medical education. She still does a lot of emergency operations at the emergency department at the Charing Cross and Western Eye Hospitals for the NHS. At Clinica London, she is responsible for glaucoma patients and glaucoma patients with cataracts. She also sees patients with general eye problems.