ASTIGMATISM

ASTIGMATISM


ASTIGMATISM

  • Astigmatism is a common vision condition that causes blurred vision.
  • It occurs when the cornea (the clear front cover of the eye) is irregularly shaped or sometimes because of the curvature of the lens inside the eye. 
  • An irregularly shaped cornea or lens prevents light from focusing properly on the retina, the light-sensitive surface at the back of the eye. 
  • As a result, vision becomes blurred at any distance.
  • This can lead to eye discomfort and headaches.
  • Most people have some degree of astigmatism. Slight astigmatism usually doesn’t affect vision or require treatment. 
  • Astigmatism frequently occurs with other vision conditions like myopia (nearsightedness) and hyperopia (farsightedness).
  • Together these vision conditions are referred to as refractive errors because they affect how the eyes bend or “refract” light.
  • The specific cause of astigmatism is unknown. It can be hereditary and is usually present from birth. It can decrease or increase over time.


TYPES OF ASTIGMATISM

A) Based on axis of the principal meridians

1) Regular stigmatism:
  • Principal meridians are pendicular.
  • With-the rule astigmatism-the vertical meridian is steepest.
  • Against -the- rule astigmatism- the horizontal meridian is steepest.
  • Oblique astigmatism-the steepest curve lies in b/w 120 & 150 degrees and 30 & 60 degrees.
2) Irregular astigmatism:
  • Principal meridians are not perpendicular.
B) Based on focus of the principal meridians

1) Simple astigmatism
  • Simple hyperopic astigmatism- First focal line is on retina while the second is located behind the retina.
  • Simple myopic astigmatism: First focal line is in front of the retina while the second is on the retina.
2) Compound astigmatism
  • Compound hyperopic astigmatism- both focal lines are located behind the retina.
  • Compound myopic astigmatism- both focal lines arelocated in front of the retina.
3) Mixed astigmatism
  • Focal lines are on both sides of the retina (straddling the retina).
Treatment of Astigmatism
 
1. Optical treatment:
  • Consists of cylindrical power spectacles or contact lens.
  • Types of contact lenses used are permeable contact lens, Soft toric contact lens (for high degree astigmatism), hybrid lens, i.e., soft on hard lens, hard contact lens.
2. Surgical treatment:
  • Non-laser (astigmatic keratotomy) or laser (PRK, LASIK).

Exam Important

  • Astigmatism is defined as refractory error wherein refraction varies along different meridians.
  • Astigmatism is due to irregularity of curvature of cornea.
  • Astigmatism is considered to be Spherical abberation.
  • In simple astigmatism, foci of image formed on One on retina, other behind the retina.
  • Regular stigmatism → Principal meridians are pendicular
  • Irregular astigmatism → Principal meridians are not perpendicular.
  • Lens used to treat astigmatism  Cylindrical lens.
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