We must have light in order to see. Most common vision problems are caused by refractive errors – the eye’s inability to focus, or refract, light correctly on the retina (the light-sensitive layer of tissue at the back of the eye). Refractive disorders are usually the result of an eyeball that is too short or too long, a cornea (the clear front part of your eye) that is irregularly shaped, or a lens that is curved too much or too little.
Warning Signs & Symptoms
Blurry vision, either up close or at a distance, is the most common sign of a refractive disorder. Other symptoms include:
- Eye strain
- Double vision
- Glare or halos around lights
Types of Refractive Eye Conditions
Patients with myopia (nearsightedness) have clear vision up close but blurry vision at a distance. The nearsighted eye is usually too long or the cornea is too curved. When light passes through the eye, it is focused in front of the retina. Almost all cases of nearsightedness can be corrected with a concave lens or with one of several types of refractive surgery.
Hyperopia (farsightedness) is when individuals younger than 40 can see things clearly at a distance but have a problem seeing up close. The farsighted eye is shorter than average in size and the cornea may be less curved than normal. For individuals with severe hyperopia, vision can be blurry for objects at any distance, near or far. Farsightedness is treated with a convex lens or with refractive surgery.
Presbyopia is when the eye’s lens loses its ability to focus properly due to aging. The result is the loss of near vision. Most people have some degree of presbyopia by age 40, and must use reading glasses to see up close.
Astigmatism is caused when the eye’s cornea or lens is shaped irregularly. The eye cannot focus light evenly onto the retina, resulting in focus problems and images that appear blurry or “stretched”. Astigmatism can be corrected with glasses, contacts, or with refractive surgery.
Refractive disorders are usually detected through the tests administered in a routine eye exam.
Your eye doctor will determine the type and degree of refractive error you have by performing a test called refraction. This can be done with a computerized instrument (automated refraction) or with a mechanical instrument called a phoropter that allows observation of one lens at a time (manual refraction).
Eyeglasses are the simplest and safest way to correct refractive errors. Eyeglass lenses are designed with precise curves to refract light to the degree necessary to compensate for refractive errors. Your eye care professional can prescribe lenses that will provide you with optimal vision.
Contact lenses are a safe and effective option if fitted and used properly. They often provide clearer vision, a wider field of vision, and greater comfort than glasses. You may not be able to wear contact lenses if you have certain eye conditions.
Refractive surgery permanently changes the shape of the cornea. This change in eye shape restores the focusing power of the eye by allowing the light rays to focus precisely on the retina for improved vision. There are several types of refractive surgeries, but the most popular are:
- Refractive lensectomy, also called refractive lens exchange, corrects nearsightedness or farsightedness. By replacing the eye’s natural lens, which has the wrong power, with an artificial intraocular lens implant (IOL), this procedure provides the correct power for the eye. It uses the same techniques as modern cataract surgery.
- LASIK (Laser-Assisted in Situ Keratomileusis) reshapes the middle layers of the cornea so that entering light rays are focused precisely on the retina. LASIK can correct nearsightedness (myopia), farsightedness (hyperopia) and astigmatism.
- PRK (Photorefractive Keratectomy) uses a laser to reshape the surface layer of your cornea to correct the focus of light rays on your retina. PRK is effective in correcting low to moderate levels of nearsightedness, farsightedness and astigmatism. Some patients with presbyopia may benefit from PRK but could require reading glasses after surgery to obtain sharp near vision.
It’s important to schedule an annual eye exam to diagnose and correct refractive disorders. Your eye care professional will discuss your treatment options with you. Request an appointment [link to request an appointment] today!