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ABSTRACT: Using a computer-assisted videokeratoscope, we determined the topographic findings of 14 eyes of 10 patients with keratoconus. None of these patients had worn contact lenses for at least one year prior to examination and were thus free of contact lens-induced topographical alterations. Two patterns commonly seen included inferior steepening more prominent temporally, and central steepening with a superimposed asymmetric bowtie pattern. When compared with normal eyes three quantitative parameters were significantly different (p <0.001): central corneal power, difference in corneal power between fellow eyes in the same patients, and steepening of the interior cornea compared with the superior cornea. Study of the topography in keratoconus using this technique may prove useful for documenting the pattern of involvement of the anterior corneal surface and providing new insights into the pathogenesis of this condition. [Refractive and Corneal Surgery 1989; 6:400-408].
Keratoconus is a noninflammatory corneal ecstasia that reduces vision as a result of irregular myopic astigmatism and corneal scarring. It is most commonly bilateral and its progression is variable and often asymmetrical. Early or mild forms are detectable only by examination of corneal topography.1,2
The study of topography of this disorder has fascinated individual clinicians during the early part of this century and has been useful not only in detecting early changes but also in documenting its progression. The placido disc, invented by Henry Goode in 18473 and further refined by Antonio Placido,4,5 was the first instrument used to study the corneal topography in keratoconus. It allowed qualitative appreciation of peripheral corneal topography, but has been a difficult instrument to convert to quantitative evaluation. Amsler used a modified photographic placido disc and reported the earliest change in keratoconus to be a 1 to 8 degree deviation of the horizontal axis. He termed these early changes 'keratoconus fruste', and reported his findings and their progression during a three-to-eight year follow up.6
The photokeratoscope has the advantage of providing hard copy data which can be re-examined by subsequent investigators. Rowsey and coworkers reported their photokeratoscopic findings from a study of 827 keratoconus patients seen over a period of 8 years.7 They noted the first topographic sign to be midperipheral steepening of the inferotemporal cornea producing a characteristic egg-shaped central ring. With progression, the steepening advanced to...