REFRACTIVE CORRECTION

INTRODUCTION

To produce a clear image, it is necessary for the light rays from an object to focus onto the inner back layer of the eye. Just like a camera, human eye also has an opening. This opening which is at the front is called the pupils. Human eyes also consist of a focusing mechanism i.e. the cornea and the crystalline lens, and a light sensing portion. This light sensing portion which is located at the back is called as the retina.
When the light rays from an object are not focused properly on the retina, it indicates the presence of a refractive error.

TYPES OF REFRACTIVE ERRORS

There are four types of refractive errors. They are: myopia, hyperopia, astigmatism and presbyopia.

Hyperopia:
A blurry image of the near and of the distant object is created when the light rays from it are focused behind the retina. This condition is called as hyperopia. It is caused when the eye is either too short or has little focusing power. Hyperopia or farsightedness is common in childhood and correction is usually not required. Though, in severe cases it is necessary to treat the condition. In case of hyperopia refractive error, corrections can be performed with the use of converging or plus (+) power glasses. Hyperopia usually increases in early childhood and then decreases during preteen to early teenage years.

Myopia:
Myopia occurs when light rays from an object is focused in front of the retina. This generally occurs because the eye is either too long or has excessive focusing power. Myopia can occur at an age due to several reasons, such as genes or premature birth. In this condition, the objects that are distant may seem blurry, but as the get closer to the eye, they appear more clearly. This refractive error can be corrected by using a diverging or a minus (-) power glasses. Alternatively, contact lenses can be used instead of glasses. At the appropriate age, laser surgery may be an alternative if the refractive error is stable.

Astigmatism
Astigmatism is the defect in the eye, in which the cornea is curved more in one direction. This condition results in distorted images, as the light rays do not meet at a common focus point. Astigmatism is a commonly found in infants and children. To correct this defect, one can use cylindrical power glasses. Contact lenses and laser surgery are alternatives to glasses at the appropriate age.

Presbyopia
It develops with aging. Presbyopia is a condition in which the lens of the eye loses its elasticity. This makes it difficult to focus on close objects clearly.

SYMPTOMS

Symptoms of refractive errors may include the following:
  Double vision
  Haziness
  Glare or halos around bright lights
  Squinting
  Headaches
  Eye strain

TREATMENT

Refractive errors can be corrected using:
  Glasses
  Contacts lenses
  Surgeries.