Combining Central and Peripheral Videokeratoscope Maps to Investigate Total Corneal Topography

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Purpose.To extend the area of standard corneal topography maps, one central map is combined with six peripheral maps after correlating them in a custom written computer program.Methods.The point corresponding to the vertex normal of the central map is found in each of the peripheral maps. Data from the peripheral maps can then be added on to the edges of the central map to create a topography map that extends from limbus to limbus horizontally and vertically.Results.The average size of the combined maps from 15 subjects was 11.3 ± 0.3 mm horizontally and 10.3 ± 0.3 mm vertically, compared to 9.2 ± 0.4 mm horizontally and 7.5 ± 0.7 mm vertically for the standard single maps. These values represent an increase in surface area of approximately 70%.Conclusions.The topography of the entire cornea can be represented by combining multiple measurements from a Placido videokeratoscope. Conic fits based on central topography data are a poor representation of the total corneal shape.

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