It is characterized by an irregular change of refractive power in different meridia. There are multiple meridia which admit no geometrical analysis.
Etiological types
1. Curvatural irregular astigmatism is found in patients with extensive corneal scars or
keratoconus.
2. Index irregular astigmatism due to variable refractive index in different parts of the crystalline lens may
occur rarely during maturation of cataract.
Symptoms of irregular astigmatism include:
1. Placido's disc test reveales distorted circles ( discussed in other posts )
2. Photokerotoscopy and computerized corneal topography give photographic record of irregular corneal curvature.
Treatment
1. Optical treatment of irregular astigmatism consists
of contact lens which replaces the anterior surface
of the cornea for refraction.
2. Phototherapeutic keratectomy (PTK) performed
with excimer laser may be helpful in patients with
superficial corneal scar responsible for irregular
astigmatism.
Etiological types
1. Curvatural irregular astigmatism is found in patients with extensive corneal scars or
keratoconus.
2. Index irregular astigmatism due to variable refractive index in different parts of the crystalline lens may
occur rarely during maturation of cataract.
Symptoms of irregular astigmatism include:
- Defective vision,
- Distortion of objects and
- Polyopia.
1. Placido's disc test reveales distorted circles ( discussed in other posts )
2. Photokerotoscopy and computerized corneal topography give photographic record of irregular corneal curvature.
Treatment
1. Optical treatment of irregular astigmatism consists
of contact lens which replaces the anterior surface
of the cornea for refraction.
2. Phototherapeutic keratectomy (PTK) performed
with excimer laser may be helpful in patients with
superficial corneal scar responsible for irregular
astigmatism.
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