The optic nerve is responsible for sending signals from the eye to the brain, where visual information is interpreted. The optic nerve head, or ONH, is typically oval or round in shape, and the overall diameter is about 1.5 millimeters.
Individuals who have an abnormal optic nerve shape could have glaucoma, which results from increased intraocular pressure, or other eye conditions and may require treatment or further intervention to preserve optimal vision. Fortunately, Dr. William S. Goldstein can test for these anomalies at our Shelby Township, MI practice.
Anatomy of the Optic Nerve
The optic nerve is located at the posterior portion of the eye and is comprised of approximately one million tiny nerve fibers. The point at which these fibers enter the retina is referred to as the optic disc. At the front of the nerve head, there is a small divot. This depression came to be known as the optic nerve cup, as the disc and cup together resemble a cup on a saucer.
“Cup-to-disc ratio” is a common ophthalmological term used to describe the relationship between the optic disc and the optic nerve cup. The cup-to-disc ratio is determined by dividing the diameter of the cup by the diameter of the disc.
In a typical healthy patient, this measures approximately 0.3. Of course, there are several variations of what is considered normal. Some patients have a flattened cup, measuring approximately 0.1. Others may have a deeper cup, measuring up to 0.8.
How Abnormal Optic Nerve Shape Relates to Glaucoma
Whenever a patient has a cup-to disc ratio measuring more than 0.3, it could indicate glaucoma. Because glaucoma is largely due to an increase in intraocular pressure, it can cause additional cupping of the disc. In severe cases of glaucoma, the optic cup enlarges so much that it impedes on the majority of the disc. This pressure can decrease the blood flow to the optic nerve and cause the tiny fibers to die.
Diagnosing Glaucoma According to Optic Nerve Shape
Because a high cup-to-disc ratio may not always denote glaucoma, it is important that your ophthalmologist run a few tests to determine the culprit.
To do this, your doctor will closely assess the outer rim of the nerve through magnified clinical photographs and diagnostic testing. If the rim is sloped or abnormally thin, then glaucoma is probable.
He or she will also perform a visual field test. This assessment will help your doctor determine if the optic nerve abnormality is directly related to glaucoma, or if your previously diagnosed glaucoma is worsening.
Other Conditions Related to Abnormal Optic Nerve Shape
Glaucoma is not the only condition that can be detected by enlarged optic cups. This abnormality could also indicate brain tumors, strokes, or multiple sclerosis, among other things. However, it is important to note that these diseases typically cause the optic nerve to appear pale in color as well as enlarged.
Learn More about Glaucoma and Abnormal Optic Nerve Shape
Open-angle glaucoma, the most common type, does not generally present symptoms until the condition becomes severe. Therefore, it is important to attend routine checkups, according to your doctor’s recommendation, so you can preserve your eyesight for years to come. To find out more information, or to schedule a consultation at our practice, contact us online anytime or call us at (586) 323-2020.