Early Glaucoma Detection: Tests to Protect Your Vision | National Glaucoma Awareness Month

Although glaucoma is one of the leading causes of blindness, a scary fact is that many people may not know they actually have the condition.

​According to the American Academy of Ophthalmology, about half of the people with glaucoma do not know they are affected. That’s because symptoms of glaucoma typically do not occur in the early stages of the disease.
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Why Early Detection of Glaucoma Is Critical

Glaucoma is caused by an increase in eye pressure. As the pressure in the eye increases, the optic nerve may become damaged. The problem is, there are often no symptoms of increased eye pressure. Symptoms usually occur when optic nerve damage has begun.
 
Without proper treatment for glaucoma, vision impairment and loss can occur. Lost vision due to glaucoma is not reversible. By the time some people are diagnosed with glaucoma, they already have irreversible vision problems.
 
The good news is that early detection, before vision is compromised, can slow the progression of the condition and preserve vision from further loss. With early diagnosis and treatment, vision loss may be prevented.
 
It’s important to know your risk factors for developing glaucoma. Some people are at higher risk than others for developing the eye disease. People who have an increased risk of developing glaucoma are encouraged to see their ophthalmologist more frequently.
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Common Tests for Glaucoma Screening

Various eye exams may be used to diagnose glaucoma. Careful evaluation of the optic nerve is an essential part of an accurate diagnosis. Glaucoma screening tools help eye doctors determine the most appropriate course of treatment.
 
A comprehensive dilated eye exam is the best tool to make a diagnosis of glaucoma. Elements of a comprehensive exam include the following eye tests:
 
Dilated Eye Exam
During a comprehensive eye exam, your eye doctor will put a couple of drops in each eye to dilate your pupils. With your eyes dilated, your eye doctor can use a device called a slit lamp to view of the back of your eye, including the macula, optic nerve, and retina. In particular, your ophthalmologist will look for changes in the color or shape of the optic nerve, which may signal early signs of glaucoma.
 
Visual Field Test
A visual field test, also called perimetry, is often used to detect vision changes. There are different methods used to perform a visual field test, but the purpose is the same. Visual field tests are used to determine if side vision has been affected by glaucoma. 
 
A computerized visual field test is one of the most common methods used. It involves looking straight ahead at a computer screen and indicating when a moving light passes in your side vision. The test may be repeated a few times a year to determine if your vision is changing.
 
Tonometry
An eye pressure test called tonometry is also helpful in making a diagnosis of glaucoma. During the test, your ophthalmologist places numbing drops in the eyes. Light pressure is applied to the eyes using a puff of air or a small device. Your eye doctor then uses an instrument to measure the pressure in your eyes. Doctors measure eye pressure in millimeters of mercury (mm Hg). Normal eye pressure is usually between 12 and 22 mm Hg. Eye pressure greater than 22 mm Hg is considered higher than normal.
 
According to the Glaucoma Research Foundation (GRF), most people diagnosed with glaucoma have an eye pressure above 20 mm Hg. However, per GRF, “There is not specific level of elevated eye pressure that definitely leads to glaucoma; conversely, there is no lower level of IOP (intraocular eye pressure) that will absolutely eliminate a person’s risk of developing glaucoma.” When a person’s IOP is above normal, but he or she does not show signs of glaucoma upon further testing, the person is said to have ocular hypertension (high eye pressure).
 
Pachymetry
Pachymetry, a test that measures the central thickness of the cornea, may also be performed as part of a comprehensive eye exam. After numbing your eyes, your eye doctor places a small instrument called a pachymeter in front of each eye to measure the thickness. Increased thickness of the central cornea may have an impact on eye pressure. Pachymetry is completed quickly and is painless.
 
Drainage Angle Inspection
In some cases, glaucoma occurs because the fluid in the eye does not drain properly, which increases eye pressure. Part of a comprehensive screening for glaucoma may include a gonioscopy. This diagnostic exam allows your eye doctor to visualize the drainage angle in your eye to determine if it is blocked. Your eyes will be numb during the test, while your doctor places a handheld contact lens on each eye to view the area between the cornea and the iris.
 
Optic Nerve Head & Retinal Nerve Fiber Layer Analysis
For people with glaucoma, assessing the optic nerve head (ONH) and the retinal nerve fiber layer (RNFL), two important structures at the back of the eye necessary for healthy vision, is important to understanding progression of the disease. Using special scanning laser, your ophthalmologist can visualize the thickness of and any changes to the ONH and RNFL. When these images are taken over time, your ophthalmologist can use them to understand if your disease is advancing, to what degree, and how quickly. This information can help your eye doctor manage your glaucoma more effectively.
 
The number of exams used to screen for glaucoma might seem overwhelming. That’s normal. It’s important to have all of them performed anyway. Measuring eye pressure alone is not enough to diagnose glaucoma. While increased eye pressure is a significant risk factor for developing the disease, it alone does not cause glaucoma. A comprehensive eye exam helps give your eye doctor a more complete picture of your overall eye health, and in turn, the ability to determine the best course of action given your current condition.  
 
When it comes to your vision, having a thorough eye exam and an accurate diagnosis is critical. If you have glaucoma, the sooner you start treatment, the more likely you are to slow the progression of the disease and save your vision.
 
The American Academy of Ophthalmology recommends adults have a baseline comprehensive eye exam by the age of 40. Depending on your eye health and risk factors for glaucoma, your eye doctor may recommend screening earlier. Visit our related post, Understanding Symptoms, Risk Factors & Early Detection of Glaucoma, for recommendations on the frequency with which you should have comprehensive eye exams, if you are at risk for glaucoma.
 
If you have questions about early detection or diagnosis of glaucoma or you’re due for a comprehensive eye exam, please call us at 508-746-8600 to schedule an appointment with one of our eye doctors.