Glaucoma rarely shows any early warning symptoms, and regular eye examinations every 1-2 years are the only way to accurately diagnose it. Although there is no cure for glaucoma, and any loss of vision is permanent, early diagnosis means that glaucoma can be treated and managed before too much damage occurs.
How is Glaucoma diagnosed?
If you have had an eye test, you will have experienced a number of strange eye tests which may have involved puffs of air, eye drops to dilate the pupils and being closely examined by the doctor using a pinpoint light. A specialist ophthalmologist or eye doctor has a range of diagnostic tools for testing the eyes in all sorts of different ways. Understanding glaucoma helps us to understand what the test are looking for and how the tools may help.
Glaucoma is a group of eye diseases which are caused by increased pressure inside the eye causing damage to the optic nerve. Pressure is usually caused by a failure of the aqueous fluids in the eye to drain away. The resulting damage on the optic nerve causes a gradual loss of sight. As glaucoma is pain free, and the loss of sight is so gradual, it needs an eye doctor to diagnose it by measuring the intraocular pressure in the eye and examining the optic disk for signs of damage.
What Tools are Used to Diagnose Glaucoma?
The first and most commonly used tool in any eye examination is the tonometer. This measures the pressure inside the eye. First the ophthalmologist will administer eye drops to the eye to numb it. The patient rests their chin on a support, to hold the head steady, and looks into the machine. From the opposite side, the doctor can examine the eye. The lamp inside the tonometer allows the doctor to clearly see a magnified view of the eye. A plastic prism is moved towards the eye until it just touches the cornea and the IOP (intra ocular pressure) is measured. The test is quick, easy and painless.
A pachymeter is used to measure the CCT (central corneal thickness) of the eye. Once again the doctor applies anesthetic eye drops and a small probe is placed next to the central cornea of the eye. This measurement is used before LASIK surgery to assess where the laser will cut the flap, and how deeply. It is also used to further interpret the intra-ocular pressure of the eye. This is important as those with a thin central corneal thickness will have registered higher natural pressure in the eye than those with a thicker central corneal thickness. A thin CCT is also a risk factor for predicting a high likelihood of developing glaucoma in patients with a higher than normal eye pressure.
As glaucoma typically reduces the side or peripheral vision first, the Visual Field Test is an important warning of any loss in sight. The patient rests their chin on a support and views a computerized screen. When a pinprick of light flashes on the screen, the patient must press a buzzer. A printout of the test will show the doctor the results, which can also be used to monitor any progressive loss of vision in patients over a period of time.
An ophthalmoscope, which is like a small telescope, is used by the eye doctor to look through the pupil and examine the optic nerve at the back of the eye. This is the simplest, oldest and still the most important way for doctors to diagnose or monitor glaucoma.
As the blockage of the trabecular meshwork and the drainage channel between the iris and the cornea are the cause of increased pressure in the eye (see Causes of Glaucoma) a Gonioscopy may be performed. The eye is dilated and numbed with eye drops and a contact lens with mirrors on the inside is placed on the eye. The doctor can view the trabecular meshwork to assess whether the drainage angle is open or narrowing. A narrow angle may indicate an increased risk of acute angle-closure glaucoma. This test also detects abnormal blood vessels or the presence of excessive pigment granules, another possible cause of increased pressure in the eye.
Imaging technology is the latest high-tech system for evaluating the health of the optic nerve and the retinal nerve within the eye. Scanning laser tomography, laser polarimetry and ocular coherence tomography can all give the doctor measurements of the eye, and if necessary, photographs of the optic nerve. The technology continues to be developed in this field and may eventually replace the ophthalmoscope and manual examination by the doctor.
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