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Eye doctors-either an ophthalmologist or optometrist-diagnose glaucoma by checking for vision loss with an eye chart and with visual field testing. They also perform tonometry, a standard test to measure the fluid pressure inside the eye, and will use a special lens to examine the angle of the eye. Then, after using special eye drops to dilate (widen) your pupil, your doctor will look directly inside your eye to inspect the optic nerve for signs of damage.
Family history and regular eye exams for at-risk patients (particularly African Americans) are vital to pick up signs of glaucoma, which tends not to show early visual symptoms; instruments used by eye-care professionals are required to determine presence of the condition. Symptoms of glaucoma can include eye pain, particularly if it is severe and associated with nausea and headache, or redness.
Diagnosis of glaucoma might begin at your primary care doctor's office when he or she asks about vision or eye symptoms, but a thorough workup usually requires further tests with an ophthalmologist, or eye doctor. Tests include looking at the optic nerve disc at the back of the eye, testing visual fields with one or more types of perimetry technology, measuring the pressure within the eye, and sometimes measuring the thickness of the cornea as well. For some types of glaucoma additional exams may also include measuring the angle of closure between the chambers of the eye. Although there is evidence that early detection and management of increased ocular pressure is beneficial in preventing glaucoma, there are currently no recommendations by the U.S. Preventive Services Task Force (USPSTF) for glaucoma screening.
To diagnose glaucoma (a group of eye diseases that cause vision loss through damage to the optic nerve), the ophthalmologist evaluates pressure in the eye through tonometry. Normal pressure is 8 to 21 millimeters of mercury (mm Hg), but people with eye pressure in this range may still develop the disease. Conversely, those who have slightly elevated pressure may not be destined to get glaucoma; how much stress the optic nerve (nerve fibers that transmit visual impulses to the brain) can withstand differs for each person and each eye, largely due to genetic factors.
A thorough evaluation of the optic nerve should be part of a routine eye exam. This is best done with a dilated pupil (black hole in the center of the eye). The doctor uses both a slit lamp (instrument that magnifies internal structures of the eye with the aid of a slit beam of light) and an ophthalmoscope (instrument for examining the deep interior of the eye) to look for any deterioration of the nerve. If the optic disc, the front surface of the optic nerve, is affected by glaucoma, the doctor may observe a characteristic called cupping: the disc may appear indented, and its color -- normally pinkish yellow -- may turn pale and more yellow because the advancing disease has hindered blood flow to the optic nerve.
No single test is 100% effective in determining whether you have glaucoma. To diagnose the disease, your healthcare professional will ask you questions about your medical history. You should receive a comprehensive eye examination, which may include any of the following painless tests:
- Visual acuity. This test measures the ability of your central vision to distinguish details and shapes. You will be asked to cover an eye and read a chart to measure how well you see at various distances.
- Tonometry. This is a test to measure your intraocular pressure. It can be performed in a variety of ways. In Goldman applanation tonometry, you are given drops to numb your eye, and a pressure-sensitive tip is placed against the eye to measure its pressure. This method is the most accurate way of measuring pressure but is limited when there is an irregularity of the corneal surface.
- Gonioscopy. In this test, a special lens containing a mirror is placed lightly on the front of your eye. It allows the healthcare professional to examine the angle between the cornea and the iris inside the eye.
- Pachymetry. This test uses a measuring device to determine the thickness of your corneas. Central corneal thickness (CCT) is an important factor in diagnosing glaucoma. Thick corneas may increase eye-pressure readings in people who do not have glaucoma. However, people with thin corneas may have normal pressure readings but still have glaucoma. A thick CCT leads to an overestimation of the pressure, while a thin CCT leads to an underestimation of the pressure. The healthcare professional takes central corneal thickness into consideration when assessing risk factors.
- Perimetry. This test, also called a visual field test, measures your side or peripheral vision. Today it is often done with computerized equipment. You place your chin on a stand in front of a computerized screen. You are asked to focus on a spot on the screen and push a button or indicate when you see a tiny flash of light. This gives your healthcare professional a map of your field of vision.
- Ophthalmoscopy. In this test, your healthcare professional places drops in your eyes to widen (dilate) your pupils. Then the health professional looks through the pupil at the optic nerve using a special instrument (ophthalmoscope) or with a special lens that magnifies details at the back of the eye.
Regular eye examinations by your ophthalmologist are the best way to detect glaucoma. A glaucoma screening that checks only the pressure of the eye is not sufficient to determine if you have glaucoma. The only sure way to detect glaucoma is to have a complete eye examination.
During your glaucoma evaluation, your ophthalmologist will:
- Measure your intraocular pressure (tonometry)
- Inspect the drainage angle of your eye (gonioscopy)
- Evaluate whether or not there is any optic nerve damage (ophthalmoscopy)
- Test the peripheral vision of each eye (visual field testing, or perimetry)
Photography of the optic nerve or other computerized imaging may be recommended. Some of these tests may not be necessary for everyone. These tests may need to be repeated on a regular basis to monitor any changes in your condition.
Generally, glaucoma can be diagnosed through a comprehensive examination of the eyes. In this exam there are many different steps that test for vision, pressure, and overall health of the eyes. Before any tests begin your doctor will numb your eyes through a procedure called pachymetry. After the numbing, the preliminary test for glaucoma involves measuring the pressure inside the eye with an instrument called a tonometer. The next basic steps to the exam are a visual field test, for your peripheral vision, and a visual acuity test, for your distance vision. Your doctor can also check for optic nerve damage through a dilated eye exam.
A tonometry, the typical initial test for glaucoma, involves measuring intraocular pressure after numbing the eyes with drops. To check for optic nerve damage, an opthalmoscope is used to look directly through the pupil to the back of the eye.
Regular vision checkups help detect glaucoma in its early stages before irreversible damage occurs.
To establish a diagnosis of glaucoma, several factors must be present, including an elevated intraocular pressure (except in normal tension glaucoma), areas of vision loss, and damage to the optic nerve. In glaucoma, the optic disk shows visible signs of damage. The optic disk is the area where all of the nerve fibers come together at the back of the eye before exiting the eyeball. An optic disk that has been affected by glaucoma appears indented or excavated, as if someone scooped out part of the center of the disk. This condition is known as cupping. The normal contour and color of the disk may also be affected by the loss of nerve fibers.
Tonometry: Tonometry is the measurement of intraocular pressure (IOP, or the pressure inside the eye) and can be carried out with several different instruments. In general, Goldmann applanation tonometry (with the blue light) is used in hospitals and non-contact (air puff) tonometry is used in optometric (optician and ophthamalogical) practices. Goldmann applanation tonometry involves the administration of local anesthetic drops (with a yellow dye called fluorescein) to allow the instrument to touch the front of the eye. The drops may sting, but the procedure itself is completely painless. It is generally considered to be the most accurate method of measuring the pressure. In non-contact tonometry, a puff of air is blown at the eye from the instrument. This does not require any form of anesthetic and is generally considered to be somewhat less accurate.
Ophthalmoscopy: The appearance of the optic disc can be examined by an ophthalmologist (eye doctor) using an ophthalmoscope (a special lighted instrument) or by the use of a slit lamp. An ophthalmoscope enables the doctor to look directly through the pupil to the back of the eye. This allows the examiner to assess the degree of cupping of the optic disc, check nerve fiber damage, and the health of the retina.
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