Did you ever wonder while growing up what your friends with the thick glasses meant when they said they were “nearsighted”? What exactly does it mean to be nearsighted, and what issues related to vision arise from this?
Think of your eye as a camera, which has a segment to focus the light coming into it. In the eye, this focusing segment is made up of the cornea, the clear front part of the eye, the pupil, and the natural lens inside the eye behind the pupil. Like any camera, the eye has a film to make the images, and this is the retina. The retina is a thin tissue lining the entire inside of the eye like wallpaper.
Another term for nearsightedness is myopia. When someone is myopic, they see well up close but cannot see far away. A myopic eye is longer than average in length from the front of the eye to the back of the eye. In a sense, light and images from far away cannot reach the back of the eye where the camera film, the retina, resides. Therefore, glasses or contact lens are needed to help focus the light on to the retina to see clearly. Some people may elect to have refractive surgery to correct near sightedness. Because the eye is longer than average, the tissues inside it, like the retina, can become abnormally thinned due to stretching. It should be noted that people with myopia have an increased risk for retinal tear or detachment of the retina which can lead to rapid loss of vision. If sudden flashing lights, new floaters, or darkening of peripheral vision are seen, an eye care professional should be expeditiously consulted for an evaluation.
Progressive thinning of the retina resulting from elongation of the eyeball is termed myopic degeneration. Individuals with more severe nearsightedness or high myopia are at greater risk for developing myopic degeneration. When thinning and atrophy occur at the part of the retina that affects central vision (macula), vision may deteriorate gradually and may not be correctable. You can see in the Figure 2 that there are some white and black discolorations that were not present in Figure 1. These changes exemplify myopic degeneration. Glasses or contact lenses cannot correct for myopic degeneration because there is actual damage of the retina tissue when it is stretched out. There is no reversal for the actual thinning of the retina and the damage to the retina.
When the retina is stretched out and the eye is elongated, sometimes abnormal blood vessels can develop just below the retina. These blood vessels, termed choroidal neovascularization, can interfere with focusing of the light or bleed and can cause sudden decreased vision. The reddish discoloration in Figure 3 exemplifies bleeding from choroidal neovascularization in myopic degeneration. Fortunately there is a treatment in the form of medications that can be injected into the eye that can stop the growth of these abnormal bleeding vessels, if they are found early before permanent damage occurs to the eye. Therefore, early diagnosis as well as treatment of choroidal neovascularization can be helpful in limiting the degree of vision loss from these bleeding blood vessels.
Not everyone with myopia develops myopic degeneration, and there is currently no algorithm to predict its development. Self-testing one eye at a time using an Amsler grid, which looks like a graph paper, to check for any distortion of straight lines on a regular basis can be a useful tool to identify any early changes. Those with myopic degeneration should have a regular dilated eye examination with an eye care professional for early detection of any treatable changes.
Image References
1.Normal Retina. Jason Calhoun MD. ASRS Image Bank.
2.Myopic degeneration. Gerrardo Garcia Aguirre MD. ASRS Image Bank.
3.Myopic degeneration and CNVM. David Callanan MD. ASRS Image Bank.
4/6/16
Medical College of Wisconsin
NEHEP Planning Committee Member
Medical College of Wisconsin
