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Measurement of corneal topography and transparency

De Cunha, D. A. (1995). Measurement of corneal topography and transparency. (Unpublished Doctoral thesis, City, University of London)


Measurement of Corneal Topography and Transparency.

A new method is described for measuring and modelling corneal topography. The method does not make assumptions about the underlying corneal shape and calculates radius of curvature at any point on the surface. This allows derivation of apex position, apex radius of curvature and rate of flattening away from the apex. The system reconstructs the surface shape independently of alignment of the eye with the instrument and can be applied to both regularly and irregularly shaped corneas.

To measure the corneal surface without any assumption about underlying shape, a system was set up to project vertical planes of light onto the cornea. An image of the diffuse reflection of the planes on the cornea was captured by a computer frame grabber. Intersection points of the light planes with the corneal surface were calculated to give a matrix of x,y,z points lying on the corneal surface. A polynomial surface equation was fitted to these points using a u,v co-ordinate system embedded in the surface. Differential geometry theory was applied to this equation to calculate radius of curvature across the surface. The results are output in the form of a contour map showing the apex position and other numeric parameters including rate of flattening from the apex.

The system has been applied to both normal and keratoconic eyes and has been used to measure keratoconic apex radius of curvature down to 5.1mm. The contour map output gives a good visual impression of the actual shape of the cornea. Further applications would include - 1. Assessment of irregular corneal shape prior to photoablative surgery. 2. Monitoring of progression of Keratoconus. 3. Post operative assessment of corneal grafts. 4. Accurate surface description of aspheric contact lenses.

A method is also developed to give a quantitative measure of corneal scarring. The system is attached to a modified slit lamp for observation of the eye and measurement of backscatter from corneal haze. The results are output as a corneal map showing the location of the scarring and area values for different scar densities. The map and density values are in a convenient form to be kept with patient records, so that improvement or regression in scarring can be accurately monitored.

Publication Type: Thesis (Doctoral)
Subjects: R Medicine > RZ Other systems of medicine
Departments: School of Health & Psychological Sciences
School of Health & Psychological Sciences > Optometry & Visual Sciences
School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses
[thumbnail of De Cunha thesis 1995 PDF-A.pdf]
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