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Errors of refraction

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					 ERRORS of
REFRACTION
Prof. Dr Zeinab El Sanabary
               Definitions
 Emmetropia        Retinoscopy

 Conjugate foci    Automated Refractors
                    Cycloplegic Refraction
 Ametropia:
   Myopia
   Hyperopia

   Astigmatism

   Presbyopia
                         Myopia
 Near-sightness means that either the eye is too long or
    the optics are too strong.
     In either case the light from a distance object focuses in
    front of the retina.
     Minus or concave lenses are used to move the image
    back on the retina when viewing distance objects.
    The vision may be corrected with glasses, contact
    lenses or refractive surgery.
    Clearly if your parents are nearsighted you have a better
    chance of becoming nearsighted.
     Identical twins have similar refractive errors.
                    Etiology
Axial
Refractive
   Curvature

   Index

   Anterior   displacement of the lens
                          Types
 Simple : no progress
  after adolescence
  (6D)
 Progressive:
  Hereditary, F, Racial
  (25D)
 Congenital: Born,
  non progressive(10D
              Progressive myopia
 Pseudoproptosis
 Apparent esotropia
 Exophoria
 Cataract
 Retina
    Temporal crescent
    Tigroid fundus
    Lacquer cracks
    Chorioretinal scars
    Fuch’s spot
    Retinal breaks & RD

 Vitreous floaters
 Posterior staphyloma
                   Myopia
 Much more common in people with a higher
 education.
 Most myopia develops during periods of
 accelerated growth (8-19).
 Previously myopia stopped by the early
 twenties. Today, we see more myopia
 progressing in the late twenties or thirties in
 those patients who spend a long time reading or
 using computer
      Correction of Myopia
 Glasses with minus concave lenses (the
  least)
 Contact lenses
 Refractive Surgery
     LASIK
     PRK
     Phakic IOL
     Clear lens extraction
LASIK
  Radial
Keratotomy
         Hypermetropia
 Definition
 Etiology:
      Axial
      Refractive:
         Curvature

         Index

         Posterior   lens displacement
         Aphakia
Components of Hypermetropia

 Total: with total cycloplegia
 Latent: corrected by the tone of the
  ciliary muscle
 Manifest: highest + lens with max VA
      Facultative: overcome by accommodation
      Absolute: lowest + lens with best VA
                Clinical Picture
 Symptoms:
      Blurring
      Asthenopia
      Early presbyopia
 Signs:
      Retinoscopy
      Small eye
      Fundus: water silk reflex, Pseudoneuritis
 Complications:
      Squint
      ACG
 Correction
          Astigmatism
 Astigmatism is very common. Some
  experts believe that almost everyone has
  a degree of astigmatism, often from
  birth, which may remain the same
  throughout life.
 The exact reason for differences in
  corneal shape remains unknown, but the
  tendency to develop astigmatism is
  inherited. For that reason, some people
  are more prone to develop astigmatism
  than others.
       Astigmatism
Types:
    Simple
    Compound
    Mixed
      Regular
            With the rule
            Against the rule
      Irregular
        What causes astigmatism?

 Astigmatism usually occurs when the cornea, has an
  irregular curvature.
 Normally the cornea is smooth and equally curved in all
  directions and light entering the cornea is focused
  equally on all planes, or in all directions.
 In astigmatism, the front surface of the cornea is
  curved more in one direction than in the other. This
  abnormality may result in vision that is much like
  looking into a distorted, wavy mirror.
 The distortion results because of inability of the eye to
  focus light rays to a point.
 If the corneal surface has a high degree of
  variation in its curvature, light refraction may be
  impaired to the degree that corrective lenses are
  needed to help focus light rays better.
 At any time, only a small proportion of the rays
  are focused and the remainder are not, so that
  the image formed is always blurred.
 Usually, astigmatism causes blurred vision at all
  distances. Some people with very high degrees
  of astigmatism may have cornea problems such
  as keratoconus.
Symptoms:
     Distortion or blurring of images at all
      distance
     Headache and fatigue
     Squinting and eye discomfort or irritation
Correction:
     Glasses
     Contact lenses
     Refractive surgery
     Keratoplasty
Anisometropia
Aphakia & Pseudophakia
Presbyopia

				
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posted:2/27/2012
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Description: A refractive error, or refraction error, is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity.