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Don't be surprised if your eye specialist asks you to ...


1. Put drops in one eye only

“He said I have glaucoma in both eyes and now he wants me to put drops in only one eye. Why?”
This is called a one-eye trial and is done so that the effect of an eye drop can be assessed at the next visit. Eye pressure varies throughout the day. When you are seen next time your eye pressures may be higher or lower on account of natural fluctuation. This is called diurnal variation. A one-eye trial will allow the effect of the eye drop to be assessed more accurately by comparing the IOP in each eye.

2. Lie down face towards the floor in a dark room for 15 minutes

“He asked me to lie face down in a pitch black room for 15 minutes. I hoped he would not forget me … There was a rise in IOP and he said I needed a laser iridotomy”.
This is called the dark prone test. If the eye pressure is high after this test then it is a sign that the drainage angle is overcrowded and that a laser iridotomy is warranted. The problem is that the test may be falsely negative. If the test is positive it will reassure both patient and ophthalmologist that the laser iridotomy is needed but if the test is negative and the pressure does not rise it is not helpful. Therefore many specialists do not do this test anymore.

3. Measure your eye pressure every hour for a whole day

Thirty percent of patients with glaucoma have normal eye pressures! Eye pressure fluctuates throughout the day, which is known as "diurnal variation". This is more pronounced in glaucoma patients. Someone with a normal pressure at 10am may actually have a very high pressure at 3pm. In order to gather this important information an ophthalmologist may request you have your eye pressure measured throughout the day. Other ophthalmologists get around this by scheduling return visits for different times of the day. In the old days some would admit glaucoma patients to hospital overnight so that the resident staff could do the measurements around the clock. This is still called “phasing”.

4. Suggest you have a cataract operation when you don’t have a cataract.

In eyes that are small the lens within the eye may by its size contribute to “overcrowding” and partial or complete obstruction of the drainage angle. In such cases removal of the lens and its replacement with a thin plastic lens creates more space within the front of the eye and can in some cases cure angle closure glaucoma. This is a cataract operation which ninety-nine percent of the time is done because the lens has lost its transparency and vision is reduced. But the same operation has other uses.

5. Suggest you have a head scan

Sometimes an ophthalmologists will request a head scan to rule out that there is no other sinister cause for the eye changes that have been observed, eg. a small tumour pressing on the optic nerve behind the eye. Usually the tests are negative but it is a great reassurance to both doctor and patient that the problem is purely glaucoma.

6. Suggest you have a laser operation when you do not have glaucoma

This is another situation caused by small eyes. If the drainage angle is very narrow there is a risk that the patient may develop sudden painful “acute glaucoma”. (Not at the time of the examination, or even the same day, but at some future time.) Acute glaucoma can be prevented by laser peripheral iridotomy, which is a simple office procedure with minimal complications. Such patients may have no evidence of damage to the optic nerve but have the potential for this very painful type of glaucoma.

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