Nearsightedness - Myopia
Introduction
Nearsightedness, medically termed myopia, is a type of refractive error. People with nearsightedness can see close objects clearly, but have difficulty seeing objects that are far away. Distant objects appear blurry. Nearsightedness is easily corrected with glasses or contact lenses. There are several surgical procedures, including LASIK, that are used to treat nearsightedness.
Anatomy
Your eyes and brain work together with amazing efficiency. Light rays enter the front of your eye and are interpreted by your brain as images. Light rays first enter your eye through the cornea, the “window” of your eye. The cornea is a clear dome that helps your eyes focus.
The anterior chamber is located behind the cornea and in front of the iris. The anterior chamber is filled with a fluid that maintains eye pressure, nourishes the eye, and keeps it healthy. The iris is the colored part of your eye. Eye color varies from person to person and includes shades of blue, green, brown, and hazel. The iris contains two sets of muscles. The muscles work to make the pupil of your eye larger or smaller. The pupil is the black circle in the center of your iris. It changes size to allow more or less light to enter your eye.
After light comes through the pupil, it enters the lens. The lens is a clear curved disc. Muscles adjust the curve in the lens to focus clear images on the retina. The retina is located at the back of your eye.
Your inner eye or the space between the posterior chamber behind the lens and the retina is the vitreous body. It is filled with a clear gel substance that gives the eye its shape. Light rays pass through the gel on their way from the lens to the retina.
The retina is a thin tissue layer that contains millions of nerve cells. The nerve cells are sensitive to light. Cones and rods are specialized receptor cells. Cones are specialized for color vision and detailed vision, such as for reading or identifying distant objects. Cones work best with bright light. The greatest concentration of cones is found in the macula and fovea at the center of the retina. The macula is the center of visual attention. The fovea is the site of visual acuity or best visual sharpness. Rods are are located throughout the rest of the retina.
Your eyes contain more rods than cones. Rods work best in low light. Rods perceive blacks, whites, and grays, but not colors. They detect general shapes. Rods are used for night vision and peripheral vision. High concentrations of rods at the outer portions of your retina act as motion detectors in your peripheral or side vision.
The receptor cells in the retina send nerve messages about what you see to the optic nerve. The optic nerve extends from the back of each eye and joins together in the brain at the optic chiasm. From the optic chiasm, the nerve signals travel along two optic tracts in the brain and eventually to the occipital cortex in the brain, where you process and perceive vision.
Causes
Heredity appears to be a major cause of nearsightedness. If your family members have nearsightedness, you are more likely to develop the condition as well. Nearsightedness is a risk factor for retinal tears, retinal detachment, and macular disease in some individuals.
Nearsightedness results when the eye is too long, the cornea is too curved, or both. This causes visual images to be focused in front of the retina instead of directly on it. The degree of nearsightedness can vary from mild to extreme.
Symptoms
Symptoms of nearsightedness usually develop by age eight or nine and stabilize in the late teens or early twenties. Nearsightedness makes it difficult to see distant objects. Your vision may be worse in dim light, making street signs especially difficult to see while driving at night. Distant objects may appear blurred. You may squint in attempt to see well. You may develop eye strain.
Diagnosis
Your doctor can diagnose nearsightedness with a general eye exam. Your general eye examination may include visual acuity and refraction. Visual acuity testing determines your ability to see near and far distances. Refraction is used to determine the degree of the refractive error. The information is used to write a prescription for glasses.
Your eye examination may also include slit-lamp testing, in which your doctor uses a slit light and a microscope to view your inside eye structures.
Treatment
Nearsightedness is easily corrected with glasses or contact lenses. Special coatings on glasses may cut glare and make it easier to see at night. There are several types of surgery for reshaping the cornea. By doing so, images are focused accurately on the retina instead of in front of it.
Radial keratotomy was a common surgical procedure in the past. Today, it has almost entirely been replaced by LASIK, a laser procedure. Many people choose LASIK as an alternative to wearing glasses or contact lenses. The procedure is short, relatively painless, and associated with quick recovery times.
Complications
Since the eye in myopia is longer than normal, the retina is stretched thinner. This puts patients at a greater risk for retinal tears and detachment. In very nearsighted people myopic degeneration which is similar to macular degeneration may occur.
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This information is intended for educational and informational purposes only. It should not be used in place of an individual consultation or examination or replace the advice of your health care professional and should not be relied upon to determine diagnosis or course of treatment.
The iHealthSpot patient education library was written collaboratively by the iHealthSpot editorial team which includes Senior Medical Authors Dr. Mary Car-Blanchard, OTD/OTR/L and Valerie K. Clark, and the following editorial advisors: Steve Meadows, MD, Ernie F. Soto, DDS, Ronald J. Glatzer, MD, Jonathan Rosenberg, MD, Christopher M. Nolte, MD, David Applebaum, MD, Jonathan M. Tarrash, MD, and Paula Soto, RN/BSN. This content complies with the HONcode standard for trustworthy health information. The library commenced development on September 1, 2005 with the latest update/addition on February 16, 2022. For information on iHealthSpot’s other services including medical website design, visit www.iHealthSpot.com.
