E y e l i g h t s Visual field defects in glaucoma The Newsletter of Glaucoma NZ Volume 8 | Issue 2 | July 2011 Inside: The Glaucoma Journey July Awareness Month Macular Degeneration vs Glaucoma How the brain fills in the blanks Glaucoma is referred to as a ‘silent thief’ as symptoms of the early stages of glaucoma are usually not readily Silver Sponsors noticeable. People with glaucoma often do not realise that there is a problem with their vision until the glaucoma has become advanced. This sometimes causes problems in people who have already been diagnosed with glaucoma. Lack of awareness that there is something wrong, or lack of symptoms, at least in the early stage, may result in less motivation to attend regular eye examinations, or put up with the inconvenience of eye drops. So why is it that people with glaucoma are not aware of a visual field defect? It is thought that their brains are filling in the blanks! Bronze Sponsor The brain appears to be filling/blending-in small visual defects as best it can by using the signals from any healthy surrounding retinal nerves. Indirect evidence for this comes from detailed accounts of people who have temporary or permanent visual field loss from other conditions such as migraine. You can try this filling-in process out for yourself with a simple test (Figure 1) which simulates the presence Supported by of a small visual field defect. A study used this test with healthy volunteers and found that it took on average 5 seconds for this defect to be filled-in. You may assume that movement, either of the eyes or of the background scene, when in a moving vehicle for example, would present more of a challenge to the brain’s ability to perform this filling-in. However, other studies suggest that movement actually printing & design ltd helps the brain to fill-in defects more easily. Continued over page... Volume 8, Issue 2 A C B Figures 3 Images and corresponding visual Above: Figure 1: This image allows you to field examinations of (a) a normal eye, and an check your own cortical adaptation. Keep eye affected by (b) an early or (c) later stage both eyes strictly fixed at the white fixation of glaucoma. The yellow symbols in Figures point. You will see the plain grey square (b) and (c) represent the patient’s fixation vanish within 10 seconds to be replaced by point. Objects located completely in the blind the pattern from the surround. areas are not seen. These areas are filled-in with the colors and patterns of the surround. So what does this mean for people with glaucoma? You may be familiar with being shown your visual field test results with glaucoma and seeing grey and black areas indicating areas of visual field loss. Many For New Readers widely available pictures (see Figure 2 a,b) Medication in eye Above: Figures 2 (a) and (b) are common try to simulate the visual field of someone To those of you who have joined drops can have side artistic representations of glaucomatous field effects on other parts with glaucoma damage by taking these grey Glaucoma NZ since the last issue and black areas we see on the visual field defects. of your body. Tell your printout and superimposing it onto a picture. of Eyelights, we welcome you! eye specialist if you However, as we have now learnt, because of notice any change in the ability of the brain to fill-in the blanks, this defects which are close to the centre of their For your information here are some your general well- is not exactly how a glaucoma patient would visual field could have symptoms at an earlier basic facts about glaucoma: being since you see the world through their eyes! stage. In particular, they may describe missing started the eye out words on a page as they are reading People of all ages can get glaucoma. drops. A more accurate representation comes from because the brain fills these defects in, but a Belgian ophthalmologist who created the There are different types of glaucoma, but If you have without producing sensible text. following scene from the viewpoint of they all involve damage to the optic nerve, glaucoma tell your someone driving along a residential street, This understanding of the nature of visual the nerve of sight, which is at the back of the relatives, especially those and attempts to show how a person with field defects in glaucoma emphasises the eye. close relatives like sisters, brothers and adult children. They have an increased risk of normal vision, early or moderate glaucoma need for regular eye examinations and Glaucoma is not curable. If you have developing glaucoma so advise them to have damage would perceive the same scene ongoing use of prescribed eye drops even if glaucoma it must be monitored for the rest of an eye examination. (Figure 3 a-c). glaucoma patients are not aware of a your life. significant problem with their vision. Glaucoma NZ is a registered charitable trust As the glaucoma damage progresses, it A family history of glaucoma means you are which receives no government funding. We reaches a point at which the brain is unable to Adapted from AM Hoste. New Insights into at much greater risk of developing glaucoma. fill-in the blanks convincingly. It is at this point Subjective Perception of Visual Field Defects rely solely on donations, sponsorship, grants that people with glaucoma first notice that they Bull. Soc. belge Ophtalmol., 287, 65-71, Current treatments for glaucoma aim to lower and fundraising. All the information available have a problem with their vision. People with 2003. eye pressure. to you from Glaucoma NZ is free. 2 3 Volume 8, Issue 2 The Glaucoma Journey – Part 2 devices relies on good technique by your eye People who are far-sighted (hypermetropic) specialist. or from Asian descent are at higher risk of angle closure glaucoma. So, you have never heard of glaucoma before The presence of small haemorrhages (bleeds) Visual field tests are designed to map a and now you have been diagnosed with it. at the optic nerve may indicate damage from person’s visual field; to document the extent Normal Pressure Glaucoma is when the You have many questions you would like glaucoma. and sensitivity of peripheral vision. This is optic nerve is damaged even though eye answers to. Concerns about your future important as glaucoma affects the side vision pressure is not particularly high. It is not yet eyesight raise the fear of blindness. first. The test requires a response every time understood why some people suffer optic Retina a flash of light appears, all the while looking nerve damage despite having intraocular This article is Part 2 of a series of three where Normal eye straight ahead. The size and brightness of pressures in the “normal” range. It is thought we will look at ‘The Glaucoma Journey’. the light flashes are varied and projected these people have optic nerves that are Part 1 explained what glaucoma is, who is at randomly to give a range of standardised vulnerable at lower pressures. risk and the importance of early detection. In measurements. Part 2 we look at how the diagnosis of occurs when Optic Nerve Pseudoexfoliation Syndrome glaucoma is made, what tests take place the trabecular meshwork, (the sponge which and the different types of glaucoma. Are there different types of glaucoma drains fluid out of the eye), becomes blocked Part 3 will look at the treatments available for by flaky, white material. It is estimated that Glaucomatous eye or is it just one disease? those with glaucoma, why one treatment may Pseudoexfoliation Syndrome accounts for Glaucoma actually refers to a range of be recommended over another and what Cupping about 25% of glaucoma worldwide. decisions may require further consideration. conditions in which the common feature is damage to the optic nerve. Pigment Dispersion Syndrome is another What is involved in diagnosing Various types of glaucoma include: condition in which the trabecular meshwork, (the sponge which drains fluid out of the eye), glaucoma? Pressure Primary Open Angle Glaucoma - the most is unable to function properly. In Pigment There are a number of tests that will be common form of glaucoma and happens Dispersion Syndrome black pigment granules undertaken when checking for glaucoma when the eye’s drainage canals resist the clog the meshwork, which prevents fluid from including: outflow of fluid. This results in the pressure in draining properly. People who are short- sighted (myopic) are at higher risk of this type - special the eye increasing because the fluid cannot Examination of the optic nerve of glaucoma. This type of glaucoma tends to instruments are used to look at the back of drain out of the eye. Every eye has a different affect men more often than women. your eye (where your optic nerve is) – a slit Eye pressure check – Pressure inside the pressure it can tolerate. Glaucoma occurs lamp or an ophthalmoscope. This enables eye is produced by the circulating fluid known when the pressure rises beyond a critical Paediatric Glaucoma - children can also get an assessment of the health of your optic as aqueous. This fluid is necessary because level for that person. Most people have no without it the eyeball would shrivel up like a symptoms and no early warning signs. glaucoma. In many cases the cause is genetic, nerve by looking at the cup, colour and but sometimes Paediatric Glaucoma can contour of the optic disc. raisin. However, sometimes the pressure is too high inside the eye.