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K. S. Johnson, K. L. Fry, P. S. Hersh; The Location of the Corneal Apex in Refractive Surgery Candidates. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4195.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate location of corneal apex in a population of normal patients undergoing refractive surgery.
Sixty-eight eyes of 41 patients who underwent routine refractive surgery procedures were included in this study. The corneal apex was determined by the location of 3 parameters derived from the preoperative Pentacam maps: Kmax, thinnest local pachymetry, and maximum anterior elevation compared to the geographic center. Kmax and thinnest local data points were directly output by Pentacam. Maximum anterior elevation was estimated by directing the cursor over the map and recording the x and y locations.
The average Kmax was located 0.006mm (standard deviation 0.989, range -2.71 to 3.33) temporal and 0.663mm inferior (± 1.55, -3.67 to 2.23) to the geographic center. Thinnest local pachymetry was 0.377mm (± 0.284, -0.53 to 1.03) temporal and 0.197mm (± 0.249, -1.13 to 0.16) inferior to the center. Maximum anterior elevation was located 0.186mm (± 1.01, -2.92 to 2.14) temporal and 0.368mm (±0.635, -1.74 to 1.05) inferior compared to the map center.
Centration is a highly important variable in refractive surgery, as decentration can lead to postoperative visual complications. Techniques to identify the geographic location of the corneal apex may improve clinical outcomes. Measures of Kmax, thinnest pachymetry, and maximum anterior elevation by Pentacam were all inferotemporal to the center of the cornea. The average of these 3 possible proxies for the true corneal apex suggests that the average location of the apex is 0.190mm temporal and 0.409mm inferior to the geometric apex. Of the 3 individual indicators, thinnest pachymetry data were the least variable.
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