Refractive error

Refractive error

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Refractive error

Refractive errors are a type of vision problem that makes it hard to see clearly. They happen when the shape of your eye keeps light from focusing correctly on your retina (a light-sensitive layer of tissue in the back of your eye).

Refractive error is the most common cause of reduced clarity of vision (visual acuity) and may be a readily treatable component of poor vision in patients with other diagnoses. Use of a pinhole will overcome most refractive errors and thus allows their identification as a cause of reduced visual acuity.

Symptoms

  • Double vision
  • Hazy vision
  • Seeing a glare or halo around bright lights
  • Squinting
  • Headaches
  • Eye strain (when your eyes feel tired or sore)
  • Trouble focusing when reading or looking at a computer

Some people may not notice the symptoms of refractive errors. It’s important to get eye exams regularly so your eye doctor can make sure you’re seeing as clearly as possible.

If you wear glasses or contact lenses and still have these symptoms, you might need a new prescription. Talk to your eye doctor and get an eye exam if you are having trouble with your vision.

Types of refractive errors

Myopia: (close objects are clear, and distant objects are blurry)
Also known as nearsightedness, myopia is usually inherited and often discovered in childhood. Myopia often progresses throughout the teenage years when the body is growing rapidly.

Hyperopia: (close objects are more blurry than distant objects)
Also known as farsightedness, hyperopia can also be inherited. Children often have hyperopia, which may lessen in adulthood. In mild hyperopia, distance vision is clear while near vision is blurry. In more advanced hyperopia, vision can be blurred at all distances.

Presbyopia: (aging of the lens in the eye)
After age 40, the lens of the eye becomes more rigid and does not flex as easily. As a result, the eye loses its focusing ability and it becomes more difficult to read at close range. This normal aging process of the lens can also be combined with myopia, hyperopia or astigmatism.

Astigmatism: Astigmatism usually occurs when the front surface of the eye, the cornea, has an asymmetric curvature. Normally the cornea is smooth and equally curved in all directions, and light entering the cornea is focused equally on all planes, or in all directions. In astigmatism, the front surface of the cornea is curved more in one direction than in another. This abnormality may result in vision that is much like looking into a distorted, wavy mirror. Usually, astigmatism causes blurred vision at all distances.

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Treatment

A. Contact Lenses

An estimated 40.9 million US adults wear contact lenses, mostly for correction of refractive errors, for which they provide better optical correction than glasses. Decorative contact lenses are increasingly being used.

The major risk from contact lens wear is corneal infection, potentially a blinding condition. Such infections occur more often with soft lenses, particularly extended wear, for which there is at least a five fold increase in risk of corneal infection compared with daily wear. Decorative contact lenses have a high prevalence of microbial contamination.

Contact lens wearers should be made aware of the risks they face and ways to minimize them, such as avoiding overnight wear or use of lenses past their replacement date and maintaining meticulous lens hygiene, including not using tap water or saliva for lens cleaning. Contact lenses should be removed whenever there is ocular discomfort or redness.

B. Surgery

Various surgical techniques are available to reduce refractive errors, particularly nearsightedness. Laser corneal refractive surgery reshapes the middle layer (stroma) of the cornea with an excimer laser. Other refractive surgery techniques are extraction of the clear crystalline lens with insertion of a single vision, multi-focal, or accommodative intraocular lens; insertion of an intraocular lens without removal of the crystalline lens (phakic intraocular lens); intrastromal corneal ring segments (INTACS); collagen cross-linking; laser thermal keratoplasty; and conductive keratoplasty (CK)

C. Reduction of Rate of Progression of Nearsightedness

Topical atropine and pirenzepine, a selective muscarinic antagonist; rigid contact lens wear during sleep (orthokeratology); and various types of soft contact lenses and spectacles reduce the rate of progression of nearsightedness but their long-term efficacy and safety are uncertain.

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