What Causes Bad Vision? – Part One

Visual acuity is our ability to see clearly. Unfortunately, vision problems have become commonplace for a number of different reasons. It may be a problem with the way light enters the eye, the amount of light that can enter the eye or a deterioration of the light-sensitive eye tissue.

How Vision Works – In order to understand what causes bad vision, it is first important to understand how normal vision works:

  • Light rays enter the eye through the transparent cornea
  • The cornea bends (refracts) the light through the pupil
  • The partially bent light now passes through the fluid in the front chamber of the eye (aqueous humor)
  • Light then passes through the lens within the eyeball
  • The lens can alter its shape at will to change its refractive index – this ability is known as accommodation
  • The light will be refracted further by the lens
  • Upon exiting the lens, the light rays will pass through the vitreous humor in the eyeball
  • Light then reaches the retina
  • The macula on the retina is the most light sensitive area and is responsible for our sharp central vision
  • The specialized cells of the retina convert the light into nerve signals which are relayed to the brain
  • The brain decodes these signals and it is perceived as the sense of vision

Types of Eyesight Problems

There are different causes of bad vision depending on the part of eye that is malfunctioning. Sometimes the problem lies with the nerves that carry signals between the eye and brain or with the visual centers in the brain, but these are relatively uncommon. The most common problems are refractive errors of the eye. This simply means that the cornea and/or lens is not bending the light correctly. Then there are distinct lens problems where the light cannot pass through the normally clear lens.