How Can I Detect Glaucoma If There Are No Initial Symptoms?
Because glaucoma can begin to develop without noticeable symptoms, the best way to protect your sight from glaucoma is to have regular comprehensive eye examinations to assess your eye pressure, optic nerve health, thinning of the cornea, and other signs of potential problems.
An ophthalmologist or optometrist diagnoses glaucoma by doing a comprehensive medical eye examination, which should include all of the following components:
A Health and Medication History
- Your overall heath and that of your immediate family
- The medications you are taking (prescription and over-the-counter)
- Questions about high blood pressure (hypertension), diabetes, smoking, and sun exposure
A Vision History
- How well you can see at present, including any recent changes in your vision
- Eye diseases that you or your family members have had, including macular degeneration and glaucoma
- Previous eye treatments, surgeries, or injuries
- The date of your last eye examination
Visual Acuity Testing
- Distance and near vision acuity tests to determine the sharpness or clarity of your reading and distance vision
- Testing your vision with different lenses (sometimes contained in a machine called a phoropter, pictured at right) to determine if your vision can be improved or corrected with regular glasses or contact lenses. This can indirectly help your doctor determine the size of your eye to determine whether you are at risk for particular types of glaucoma.
Basic Visual Field Testing
- This test is done to determine how much side (or peripheral) vision you have and how much surrounding area you can see.
- The most common type of visual field test in a regular eye exam is called a confrontation field test. This test measures only the outer edge of the visual field and will not reveal changes in early glaucoma. See Perimetry (below) to learn about more detailed and precise visual field testing for glaucoma.
An Eye Health Evaluation
- An examination of the anterior segment of your eye (the front third of the eyeball), including the cornea, pupil, iris, lens, and aqueous drainage structures, using a special microscope called a slit lamp.
- A dilated eye (or fundus) examination that can be achieved with the use of special lenses will allow your doctor to see inside your eye and examine the retina and optic nerve. Your doctor might choose to use eye drops to see the retina and optic nerve more clearly.
- A test of the fluid (aqueous humor) pressure within your eyes, called a tonometry test. This test uses an instrument to measure the pressure inside your eyes. Your doctor might also refer to this pressure as intraocular (“within the eye”) pressure, or IOP.
Additional Tests for Glaucoma
If your eye doctor suspects that you may have glaucoma, you will need to undergo additional testing that can help your doctor make a more definitive diagnosis of glaucoma:
- This test uses a probe that emits an ultrasonic wave to measure the thickness of your cornea. Thicker than normal corneas can give IOP readings that are inaccurately high, while thinner than normal corneas can give IOP readings that are inaccurately low.
- To measure your corneal thickness, the doctor will touch the tip of the pachymeter probe to the surface of your cornea. The probe emits a painless ultrasound wave that measures your corneal thickness. The doctor will numb the surface of your eye with an anesthetic drop for this test.
- This test measures and maps your visual fields. Perimetry testing can draw a map of your visual fields and show you where you may have lost vision, especially your peripheral (or side) vision, which is the vision usually affected by early damage to the optic nerve from glaucoma.
- The most commonly used test for perimetry is the Humphrey Field Analyzer (pictured at right). The machine resembles a large bowl. One eye is covered with a patch and the other eye remains stationary and focused straight ahead. Small white lights of varying sizes and intensities will flash at different locations around the bowl. You will be instructed to press a button whenever you see a flashing light. By recording which lights you see and which ones you do not, it creates a map of your visual field.
- This test assesses the angle, or drainage canal, that is formed between your cornea and iris. Because angle-closure glaucoma requires immediate medical attention, it is important to examine the drainage canals, or angles, to ensure that they are functioning properly.
- Because the drainage angle is located around a “corner” of your cornea, the doctor can’t see whether your angle is open by looking directly into your eye.
- Gonioscopy uses a lens with a mirror to view the angle. During the exam, the doctor places this lens, called a gonioscope, on the surface of your eye like a large contact lens. The doctor will numb the surface of your eye with an anesthetic drop for this test.
For more detailed and patient-centered information about ophthalmoscopy, tonometry, pachymetry, perimetry, and gonioscopy, see Discovering the Sneak Thief: Diagnosing Glaucoma in VisionAware’s new Patient’s Guide to Living with Glaucoma and El descubrimiento del ladrón silencioso: El diagnóstico de glaucoma in Guía del Paciente: Vivir con Glaucoma.
Individuals who are over 40 should have a dilated eye examination from an ophthalmologist or optometrist at least every two years. African Americans and/or individuals with a family history of glaucoma who are over 35 should have a dilated eye examination from an ophthalmologist or optometrist every year.
From the National Eye Institute (NEI): The Difference between Screening and Comprehensive Dilated Eye Exams in Detecting Glaucoma
The U.S. Preventive Services Task Force released its final recommendation statement on screening for open-angle glaucoma. The task force found that there was not enough evidence to determine the accuracy and effectiveness of glaucoma screening in primary care settings for adults who do not have vision problems. Based on this lack of clear evidence, the task force could not make a recommendation for or against screening adults for glaucoma at this time (July 2013).
Statement from NEI
Statement by Dr. James Tsai, chair of the Glaucoma Subcommittee for the National Eye Institute’s National Eye Health Education Program: “While the task force concluded that there was insufficient evidence to prove that widespread glaucoma screening reduces blindness risk or improves quality of life, this recommendation does not mean that comprehensive dilated eye examinations are not important for preventing vision loss among Americans.”
Nearly 2 percent of Americans over age 40 (2.7 million in total) have open-angle glaucoma, a leading cause of blindness that has no early warning signs. However, early diagnosis and treatment can prevent vision loss.
Glaucoma screening is a method for assessing an entire population for glaucoma, including those without visual symptoms and those who are not at higher risk for developing glaucoma. In addition, screening usually detects only one risk factor for developing glaucoma: elevated eye pressure. However, because of individual differences in normal eye pressure and the various forms of the disease, this method by itself is not sufficient for an accurate diagnosis of glaucoma.
Dilated Eye Exams Are Important for Prevention of Vision Loss
By contrast, a comprehensive dilated exam looks at the back of the eye to detect subtle changes of the optic nerve in patients without any visual symptoms, thereby potentially leading to early detection of the disease.
They are especially recommended every one to two years for people who are at higher risk for glaucoma, including African Americans age 40 and older, everyone over age 60 (especially Mexican Americans), and those with a family history of glaucoma. The task force did find that early treatment for glaucoma is effective in keeping visual field defects from getting worse and this is very important for preserving vision.