REFRACTIVE ERROR

​Refractive error is the most common eye disorder and common vision problems are usually caused by refractive error.

In this the eye is unable to focus light correctly on the retina (the light-sensitive layer at the back of the eye).

Refractive errors 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 less commonly by Lens that is    too curved or too flat.

 Signs & Symptoms

• Blurred vision for distance or for near, is the most common sign of a refractive disorder.
• Eye strain.
• Headache.
• Double vision.
• Glare or halos around light.

  Types of Refractive Error 

The main types of refractive errors are myopia (nearsightedness), hyperopia (farsightedness), presbyopia (loss of near vision with age), and astigmatism.

Myopia

Patients with myopia (nearsightedness) have clear vision for near but blurred vision for distance. The myopic eyes are usually too long or the cornea is too curved. When light passes through the eye, it is focused in front of the retina. Myopia can be corrected with a concave lens or with one of several types of refractive surgery.

Hyperopia

Hyperopia (farsightedness) is when individuals younger than 40 can see things clearly at a distance but have a problem seeing up near. The hyperopic eye is shorter than average in size and the cornea may be less curved than normal. When light passes through the eye, it is focussed behind the retina.  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

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 for near.

Astigmatism

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






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 Diagnosis
Refractive disorders are usually detected through the tests administered in a routine eye examination.
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 called automated refractor or by subjective refraction. Subjective  refraction is done by  using a large number of lenses of different optical powers, and  a retinoscope (a procedure entitled retinoscopy)  in which the patient views a distant spot while the clinician changes the lenses held before the patient's eye and watches the pattern of reflection of a small light shone on the eye. Cycloplegic agents are frequently used to more accurately determine the amount of refractive error, particularly in children.







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Treatment
 
Eyeglasses are the simplest and safest way to correct refractive errors. 
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.
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 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 myopia, farsightedness 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.
 
Prevention
 It’s important to schedule a yearly eye examination to diagnose and correct refractive disorders. 

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