Refractive Errors

Cornea is the clear front part of eye. It is like a window that controls and focuses the light coming into the eye. If cornea has an irregular shape, the light does not focus properly. Everything looks blurry. This is a refractive error.

 Classification

  • Myopia( nearsightedness)

Clear vision close up but blurry in the distance

  • Hyperopia( farsightedness)

Clear vision in the distance but blurry close up

  • Presbyopia

 Inability to focus close up as a result of aging

  • Astigmatism

Focus problems caused by the cornea

Hypermetropia

Presbyopia

Rays of light reflected off objects in front of the eye are focused behind the retina as shown . Such persons can see well in the distance provided they are young and the refractive error is not large. Hypermetropia actually forms a stage in normal development of the eyes. At birth practically all eyes are hypermetropic to the extent of 2.5 to 3.0 Diopters and as the growth of the body proceeds, the length of the eye increases,until adolescence is passed.So eye should theoretically be “normal” in size and refraction. Hypermetropia therefore represents an imperfectly developed eye when it persists in adult life.

CAUSES—

Hypermetropia

  1. Eyeball is shorter than it should be.
  2. Corneal may be flatter than it should be (curvature hypermetropia).
  3. Change in refractive index of the crystalline lens of the eye(cataract)
  4. Injury to the eye with dislocation of the crystalline lens of the eye.

Presbyopia

  1. After or near 40 years of age.
  2. Age related loss of accommodation due to decreased elastictiy of the crystalline lens surface .

Symptoms And Signs

Hypermetropia

  1. Eye-strain
  2. Watering
  3. Redness of the eyes
  4. Headaches in the later part of the day.
  5. Convergent squint (young children )

Presbyopia

  1. Blurring of text specially after some time.
  2. Difficulty in reading/writing and doing near work.

Myopia

The person affected is able to perform near work without correction, and has difficulty defining distance objects. Rays reflected off an object in front of the eye focus in front of the retina.

Causes–

  1. Increased length of the eyeball.
  2. Increase in the curvature of the cornea or the surfaces of the crystalline lens.
  3. Cataract
  4. Divergent squint(children)

Symptoms And Signs

  1. Can not see distant objects
  2. Child makes too many mistakes copying things from the black-board.

Astigmatism

Rays of light reflected off objects in front of the eye are focused differently on the retina of the eye, because more than one focal point exists.

Causes

  1. Distortion of the corneal surface in one or multiple planes
  2. Error of curvature(vertical curvature is greater than the horizontal )
  3. Error of centering
  4. Error of refractive index.
  5. Injuries to the eyes
  6. Surgeries to the eyes.

Symptoms And Signs

  1. Headaches
  2. Low vision
  3. Reduced vision for distance and near
  4. Watering
  5. Redness
  6. Foreign body sensation in the eyes as the day progresses
  7. Running together of text while reading
  8. Can not see well distant or near object(more so the difficulty is with distant objects)
  9. Compensatory tilt in the head posture

Treatment–

Hypermetropia

  • Convex lens in eyeglasses(+a)
  • Contact lens
  • Refractice Surgery(LASIK)

Myopia

  1. Concave lens in eyeglasses(-a)
  2. Contact lens
  3. Refractive Surgery
  4. Lens implants(special rigid contact lenses to flatten the cornea)
  5. Pin-hole glasses(low myopia)

Presbyopia

  1. Reading glasses
  2. Bifocals glasses
  3. Contact lenses
  4. Monovision LASIK
  5. Intraocular Lenses

Astigmatism

  1. Gas permeable lens (make the surface of the eye spherical)
  2. Soft toric contact lens
  3. Eyeglasses(cylindrical lens power)

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