Q&A About Glaucoma and Refractive Errors
Q. What are refractive errors?
A. A refractive error is an imperfection in how the eye focuses light, which typically causes noticeably blurred vision. The three main types of refractive errors are nearsightedness, farsightedness and astigmatism.
Q. Is there an association between glaucoma and refractive error?
A. According to the Mayo Clinic, nearsightedness increases your risk of developing glaucoma. Also, farsightedness can increase your risk of narrow-angle or angle-closure glaucoma, according to several sources.
Q. How are refractive errors detected and measured?
A. Typically, refractive errors are detected during a comprehensive eye exam. During the exam, your doctor or an assistant will perform an eye test called a refraction to see if you are nearsighted, farsighted or have astigmatism. The degree of refractive errors and the power of lenses to correct them are measured in units called diopters (D).
Q. What is myopia?
A. Myopia (nearsightedness), is a refractive error wherein light is focused too early in the eye, before it reaches the retina. Myopia generally caused blurred distant vision (you remain "near-sighted"). According to the National Health and Nutrition Survey (1999-2004), approximately 40 percent of Americans are nearsighted.
Q. What is hyperopia?
A. Hyperopia (farsightedness), is a refractive error wherein the eye is not powerful enough to focus light onto the retina. Farsightedness usually causes near vision to be blurred, but higher amounts of hyperopia can cause vision to be blurred at all distances. Other symptoms of farsightedness include headaches and eye strain when reading. According to the Baltimore Eye Survey (1991), approximately 45 percent of Americans over age 40 have at least 0.75 D of hyperopia.
Q. Is farsightedness the same as presbyopia?
A. No. Though both conditions cause near vision problems, hyperopia can occur at any age, whereas presbyopia is a normal age-related loss of near focusing ability that affects people over age 40. People with good vision without glasses most of their life need reading glasses to correct presbyopia when they get older. Farsighted individuals also develop presbyopia later in life and need bifocals or other multifocal lenses to restore their vision at all distances.
Q. What is astigmatism?
A. Astigmatism (sometimes wrongly called "stigmatism") is a refractive error wherein the eye's clear front surface (cornea) and/or the lens inside the eye has asymmetric curves, which prevents light from focusing properly on the retina. Astigmatism typically causes blurred or distorted vision at all distances. Approximately 30 percent of people worldwide have some degree of astigmatism, according to several studies.
Q. Do eye diseases other than glaucoma affect refractive errors?
A. In some cases, yes. Keratoconus is an eye disease that causes the cornea to become thinner and bulge forward, resulting in high amounts of irregular astigmatism that cannot be corrected with glasses. Options for keratoconus treatment include gas permeable or hybrid contact lenses, and surgical treatments such as Intacs corneal implants and corneal collagen cross-linking (CXL). In severe cases of keratoconus, a corneal transplant might be required. Cataracts also can cause changes in refractive errors.
Q. How are refractive errors corrected?
A. Refractive errors usually are corrected with prescription eyeglasses or contact lenses. LASIK and other refractive surgery also can be used to correct refractive errors.
Q. Can eye exercises prevent or correct refractive errors?
A. Most eye care professionals agree that eye exercises cannot prevent or reverse refractive errors. In some cases, certain eye exercises might even be harmful to the eye.
Eye exercises advertised online and on television that promise you can "throw away your glasses" should not be confused with legitimate vision therapy that sometimes is prescribed by eye doctors to correct binocular vision problems such as poor eye teaming or depth perception.
Consult your eye doctor before purchasing or performing any unsupervised program of eye exercises.