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Topography

Corneal topography provides us with a detailed description of various curvature and shape characteristics of the cornea. This information is very helpful for the illustration of corneal astigmatism, detection of corneal pathologies and perfection of contact lens fitting.

Cornea is the most powerful refractive element of the eye contributing 43D (70%) of refractive power of eye. Since the shape of corneal surface determines its refractive power, even a minor modification of its surface can lead to significant alteration of image formed on retina.

 

Normal Cornea

Prolate shape

  • Anterior surface of cornea: Elliptical

  • Horizontal diameter 11.5mm

  • Vertical diameter 10.6mm

  • Posterior surface of cornea is circular with average diameter of 11.5mm

  • Thickness of cornea: 0.52mm at centre, 0.8mm at periphery, 1mm at limbus

  • Anterior radius of curvature:7.8mm

  • Posterior radius of curvature:6.5mm

 

Clinical Uses of Corneal Topography

Screening for corneal ectasia

Corneal ectasia monitoring and treatment

Refractive surgery screening and monitoring

Pre-operative intraocular lens selection

Post-keratoplasty astigmatism evaluation and management

Ocular surface disorder evaluation

 

 

Keratometery

 Devised by Helmholtz,who originally used the term ophthalmometer. Calculations are based on the geometry of a spherical reflecting surface. Based on fact that anterior surface of cornea acts as convex mirror and size of image varies with curvature. Helps to measure the radius of curvature of anterior corneal surface from 4 reflected points within central 3mm of cornea

 
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