A diagnosis of glaucoma no longer simply relies on the presence of pressure within the eye. Optic nerve damage or a strong suggestion of damage must also be present. This damage can be clearly seen during a dilated eye examination of the optic nerve. In general, the hallmark sign of this condition is a loss of peripheral vision. With peripheral vision loss, a person can see in front of him- or herself but has lost the vision to the side.
Because chronic glaucoma has no warning symptoms, half of patients are unaware they have the condition. Early diagnosis is the key to successful treatment of glaucoma and prevention of blindness.
There has been debate about the relative benefits and risks of routine glaucoma screening in adults. Glaucoma screening in adults can help identify signs of increased intraocular pressure (IOP) and the early stages of primary open-angle glaucoma (POAG). However, treatment of IOP and early POAG can potentially result in harmful effects, such as eye irritation and increased risk for cataracts. Because of this uncertainty, the United States Preventive Services Task Force has not found sufficient evidence to recommend for or against routine screening for glaucoma in adults.
In contrast, the American Academy of Ophthalmology strongly supports glaucoma screening, with the following specific recommendations:
Doctors determine the intraocular pressure (IOP) of the aqueous humor inside the eye using a painless procedure called tonometry, which measures the force necessary to make an indentation in the eye. A tonometer (small smooth instrument) may be used. There are several methods and the doctor may apply anesthetic eye drops to first numb the eye:
In general, normal IOP is usually maintained at measurements of 10 - 20 mmHg. Intraocular pressure over 21 mmHg indicates a potential problem. The test is not completely accurate, however. Only about 10% of people with IOP levels of 21 - 30 mmHg will actually develop glaucoma and optic nerve damage. On the other hand, many people with glaucoma have normal pressure, at least for part of the time.
Changes in posture may also affect IOP. A recent study indicated that IOP increases during sleep or when a person is lying down. As IOP tests are generally given in a doctorâ ' s office when a patient is sitting up, they may not provide a completely accurate evaluation of eye pressure.
Cornea thickness is an important indicator of disease progression in patients with elevated IOP. The doctor first applies numbing drops to the eye and then uses an ultrasonic wave instrument to measure cornea thickness.
To check for damage in the optic nerve, the doctor first uses eye drops to dilate (widens) the pupils and then examines the eyes with a magnifying lens instrument such as an ophthalmoscope, which has a light on one end.
Damaged nerve fibers may be indicated by:
The doctor will conduct tests of the visual fields (the areas that the patient can see). In most people with glaucoma, the first areas to become noticeably impaired are the peripheral visual fields (areas of sight that are not directly in front of a person but more to the sides). Perimetry tests are used to check peripheral vision. The patient looks straight ahead and is asked to indicate when a moving light appears on the side.
Using an instrument called a gonioscope, ophthalmologists can inspect the front of the eyes and assess the drainage angle between the cornea and the iris and the channels in the trabecular meshwork. This test can differentiate between closed- and open-angle glaucoma.
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