Refractive Errors

Refractive Errors

In a normal eye, light rays pass through the cornea and lens and focus on the retina, and a sharp image is perceived by the brain. It is similar to how a camera lens focuses light onto a film. 

Refractive errors occur when light rays pass through the eye but cannot focus on the retina and blurred images are formed. This is due to factors such as shape of the cornea, lens and length of the eyeball. 

Types of Refractive Errors

• Near-sightedness (Short-sightedness)

  

  
  A near-sighted eye is longer than normal, so light rays focus in front of the retina. Close objects can be seen more clearly while distant objects look blurred.

• Far-sightedness (Long-sightedness)

  
  A far-sighted eye is shorter than normal, so light rays focus behind the retina. Distant objects can be seen better while close objects look blurred.

• Astigmatism

  
  Many people with myopia or hyperopia have some degree of astigmatism. This is caused by uneven curvature of the cornea or lens. Astigmatism distorts the light rays entering the eye and focus unevenly on the retina. Objects look distorted and blurred.

• Presbyopia

  
  In a normal eye, light rays of close objects focus behind the retina, which is similar to a far-sighted eye looking at distant objects. The lens of a normal eye can change its shape and therefore refocus light rays on the retina to form a sharp image. This process is called “accommodation”, and it is automatic. With increase in age, the lens of the eye loses its flexibility and becomes less able to change its shape to accommodate. When people reach their 40s, tasks such as reading small print become difficult.