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DIAGNOSTIC TESTS Patients who only have raised IOP do not necessarily have COAG as certain other characteristics need to be found. An ophthalmologist or a suitably trained non-medical expert will carry out a variety of tests (Box 1). This is a lengthy examination, often lasting 45 minutes or more, and may involve seeing more than one healthcare professional. The clinician uses a slit lamp (a binocular microscope) to


facilitate a systematic 3D examination of all structures within the eye. The cornea may show signs of pigment dispersion syndrome; the pupil and lens may show signs of pseudoexfoliation. Both conditions can cause partial blockage of the trabecular meshwork. A topical anaesthetic drop, Proxymetacaine Fluorescein® is


instilled, often combined with an ophthalmic dye Fluorescein, to enable the clinician to perform various tests involving touching the cornea. The GAT prism touches the corneal surface to measure IOP. CCT measurements inform the accuracy of the IOP readings, with thin CCT creating false low or normal readings, and thicker CCT causing abnormally high readings. I usually tell patients that it is the only time it’s good to be thick, which usually raises a smile during this complex examination. The drainage angle will be examined in detail to identify whether


all the layers of the angle can be seen. This involves using a mirrored contact lens (gonioscope) applied to the anaesthetised eye which creates an unusual feeling. The eyelids can feel something but the eye does not feel pain. Most patients report that this feels a little weird. The clinician examines four quadrants (inferior, superior, nasal and temporal) looking for abnormalities impeding aqueous drainage and is able to confirm an open, closed or closeable drainage angle. The patient will have dilating eyedrops instilled to facilitate


complete examination of the structures lying behind the lens. Patients are asked not to drive to their appointment as dilation drops alter vision for approximately four hours, making driving inadvisable, if not illegal. The clinician will closely examine the optic disc for size, colour, neural retinal rim, cup-disc ratio and position of vessels (Box 2).


BOX 2. OPTIC DISC ASSESSMENT


Size: optic discs may be naturally different sizes. People who are short-sighted have longer eyes therefore larger optic discs; people who are long sighted have smaller eyes therefore smaller optic discs. Size is important when judging cup-disc ratio. Colour: the normal colour of the optic disc is pinky-orange. Neural retinal rim: a specific thickness should be seen with a thicker inferior rim, minimising superiorly, then nasally, then temporally. This is because there are more retinal nerve fibres collecting at the optic disc from the inferior retina then fewer from the superior retina etc. This is called the ISNT rule. Cup-disc ratio (CDR): this is the area between the superior rim edge and the inferior rim edge. This is dependent on the size of the optic disc. A large optic disc will have a normal bigger CDR. Retinal vessels: the central retinal artery and central retinal vein enter the eye alongside the optic nerve. These should be supported as they spread out across the retina by retinal nerve fibres that create the optic nerve.


ADHERENCE: A ROLE FOR ALL The biggest challenge is supporting patient adherence. COAG and its variants cannot be cured, only controlled, and non-adherence is a big issue.8,9,10


Patients will often forget their drops - think about


short-term antibiotics and how many are left in the bottle at the end of the course - but linking drops to daily activities can trigger the memory. Patients dislike side effects and may choose not to use the


drops. They might finish one bottle and not obtain a repeat prescription. Imagine having to take something that causes you discomfort when you don’t feel anything is wrong and you can see perfectly well! Drop instillation is not always easy and can be a constant


struggle for some patients, often relying on others (family, friends, district nurses) to put in eyedrops. We would always encourage self-administration, and eye nurses can give tips and tricks to the individual. Patients should be encouraged to ask the eye nurses for help. One method is described in Box 3. You can always encour- age a patient to contact their eye unit for further advice if you feel this will help adherence.


The majority of patients manage this examination quite well


but it can be quite difficult for others. It is important to reassure the patients to enable them to be as relaxed and cooperative as possible.


THE DIAGNOSIS A patient will only be diagnosed as having COAG if there is a high IOP and optic nerve damage resulting in ocular hypotensive eyedrop treatment. If there is no optic nerve damage but a raised IOP, NICE guidance3


directs the clinician whether to start treatment


or not and a diagnosis of ocular hypertension (OHT) is made. This indicates that progression to COAG is possible if left untreated but the patient only requires to be monitored. However some patients have IOP at such a level that treatment is indicated. This can confuse the patient, as OHT does not state the word ‘glaucoma’. This is because they do not have glaucoma but are at risk of glaucoma if they do not adhere to treatment. Alternatively, if the IOP is normal but optic nerve damage is present, a patient may be prescribed treatment and a diagnosis of normal tension/normal pressure glaucoma (NTG/NPG) is made. Again this can be confusing, as they don’t have high IOP.


THE TREATMENT The first line treatment for all these conditions is ocular hypotensive (glaucoma) eyedrops; a lifelong treatment similar to those for diabetes and hypertension. There is a range of eyedrops to choose from and again NICE3


gives guidance. Most eyedrops will have


some ocular side effects such as dry eye and patients may need to use an ocular lubricant such as Hypromellose® or preservative free Optive®. These can easily be prescribed by primary care healthcare professionals and do not need specialist input in the first instance. However many glaucoma eyedrops also have systemic side


effects. Ophthalmologists avoid betablocker eyedrops in patients with known breathing problems, but prostaglandin analogues can cause shortness of breath in rare cases. Dry mouth with a tickly cough is a known side effect of Brinzolamide and Dorzolamide, so it is important to think about eyedrops as a source of systemic symptoms.


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