Basics of Laser Refractive Surgery The basic principle of laser refractive surgery is reshaping the front transparent layer of the eye called the ‘cornea’ so as to focus the rays of light on the retina to form a clear image.

There are four types of refractive errors:

• Myopia/ Short sightedness
  The eyeball is longer than normal and hence, rays of light focus in front of the retina. Myopic patients have a minus number and can see near clearly without glasses; however, distance is a blur. With laser refractive procedures, the cornea is flattened centrally to correct the refractive error.

• Hypermetropia/Hyperopia/Long sightedenss
  The eyeball is shorter than normal and hence, rays of light focus in behind the retina. Hyperopic patients have a plus number and cannot see near clearly without glasses. With laser refractive procedures, the cornea is steepened centrally to correct the refractive error.

• Astigmatism/Cylindrical error
  This error does not relate to the length of the eyeball, but to the shape of the cornea. If the corneal shape is like an egg or baseball rather than a ball, it would result in a cylindrical error. With laser refractive procedures, the cornea is flattened on the steep axis to correct the refractive error.

• Presbyopia
  This is an age-related refractive error caused by weakening of the muscles in the eye that control the near focusing power of the eye. It leads to difficulty in reading small letters in the middle age-group, typically 40-55 yrs. This plus number may increase upto 55 yrs before stabilizing. Regular laser refractive procedures do not correct presbyopia. There are new custom treatments available for this condition that are slowly gaining acceptance.