We will measure your vision 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 vision corrects for any error in the glasses prescription. This gives us the best idea of the visual potential even if you have cataracts.
Also known as IOP (intraocular pressure) can be measured in a variety of ways.
Opticians often use an air puff test called ‘pulsair’ or non-contact tonometry. This is a reasonable screening test but often over -estimates IOP. There are many cases where the air puff test measurements are high. When checked in the clinic with the gold standard test they are normal. This is particularly the case if the cornea (the window at the front of the eye) is thicker than average. (See pachymetry)
In the clinic, we check for the IOP may first with a screening test called iCare. This testing is more accurate than the air puff test, and if this measurement is high, you will see the doctor straight away.
Another name for the gold standard IOP measurement is ‘Goldman applanation tonometry (GAT).’ It is accurate and painless. The specialist applies an anaesthetic drop coloured with an orange dye to both eyes. A blue light lights up the front of your eye. The doctor will bring the pressure measurer close to the front of your eye and 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. We call this phasing. We measure the IOP every 2 hours from 08:00 to 18;00. The IOP is usually lower in the evening and overnight. So, it is unusual to keep someone in the hospital to measure their IOP throughout the night.
Some patients may have a high IOP reading for 1-2 hours, and after that, the IOP is lower. Phasing finds these high peaks so that your doctor can adjust the treatment.
If a glaucoma patient has a high IOP at 10 am yet always comes to a consultation in the afternoon we may never record that high IOP. Phasing is done in patients who appear to have glaucoma, yet their IOP has never been measured to be high. A second group are patients whose glaucoma is getting worse despite having real measured IOP in the clinic.
Pachymetry measures the thickness of the window of the eye, the cornea. We gauge the pachymetry in all new patients at their first appointment. It does not need to be measured again unless the patient has problems with the cornea. We are all differing height and shoe size, and the cornea comes in different widths or thickness. The average cornea measures 550 microns. If your cornea is thinner or thicker than this, it does not make any difference to your vision or you. It does influence how we interpret the IOP.
A typical scenario is someone who has a cornea that is thicker than average (>600 microns). The air puff test carried out by the optician will over read the IOP suggesting there may be a problem. When in fact, none exists. The puff of air has to overcome the extra thickness of the cornea before it reads the actual pressure in the eye. Hence, the reading is falsely high.
The gold standard test (GAT) reduces this measurement error in a significant way. It may be that you come to the clinic and we find that your corneas are thicker than average. If we take this into account, plus the IOP is normal, and there are no signs of glaucoma, then we can discharge you back to the care of your optometrist. All further IOP should be GAT and not air puff. Otherwise, you will be referred each time you have an eye test.
On the contrary, if the cornea is thinner than average (
Visual field tests, also known as HVF- Humphrey Visual Field testing, are an important part of glaucoma care. They test how well you can see in the periphery of your vision. Your edge the part of your vision that is first affected by glaucoma. You will not notice a loss of the outside part of your vision. More so, if it only affects one eye as the other eye can compensate for this. As glaucoma gets worse, the more central parts of the vision are affected. So by the time you notice it glaucoma may be in an advanced stage. This vision loss is not reversible.
Visual field testing is designed to find the level of brightness of a spot that you can only just see. Patients often find the test frustrating. There are times when you are not sure whether you saw the spot or not but this is how the test is designed. Try to relax and only press the button when you see a light spot. You cannot ‘fail’ this test. It gives personalised information about your peripheral vision. Ms Crawley will show and discuss the results and what they mean for you. There is a learning curve in doing this test, and often the first few tests are not as accurate as the next tests. It is important to bear this in mind and not become anxious in doing this test.
Optical Coherence Tomography (OCT) is a test that examines the nerve at the back of the eye using light waves. It is quick and easy to do, and you usually do not have to have dilating drops to get a good scan. The picture generated does more than a colour photograph. It analyses the size and thickness of the fibres that make up the optic nerve. Then it displays these measurements in a colour coded map. This digital record of the structure of the nerve will make it easier to look for changes in the nerve over time. It means that changes can be picked up early and treatment adjusted. You will have this test each time you come for a consultation.