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Z. Schlegel, T. Hoang-Xuan, D. Gatinel; Comparison of the Anterior and Posterior Corneal Elevation Maps in Normal and Keratoconus-Suspect Eyes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1842. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the anterior and posterior corneal elevation maps between keratoconus-suspects (KS) and normal eyes.
We retrospectively analysed the corneal elevation of anterior and posterior corneal surface in a population of normal myopic patients (60 eyes of 30 subjects) and patients with suspicion of fruste keratoconus (40 eyes of 22 subjects). The following parameters were analysed and compared for the eyes of each group: anterior and posterior best-fit sphere (BFS) radius, central and thinnest corneal pachymetry, anterior and posterior aconic shape factors (aconic radius, aconic asphericity and aconic toricity), and anterior and posterior elevation in 1 mm of radius zone. For each eye, the correlations between elevation parameters of its anterior and posterior corneal surfaces were investigated.
The mean central and thinnest pachymetry values were thinner in the KS eyes (494 µm vs 554 µm: p<0.0001). When comparing the anterior elevation maps, the only difference between the analysed groups was anterior toricity which was greater in KS than normal eyes (0.939 D vs 1.328 D: p<0.0001). When comparing the posterior elevation maps, KS eyes showed increased posterior toricity (2.021 D vs 1.478 D: p = 0.018), more negative asphericity (Q = -0.419 vs Q’ = -0.297: p = 0.042) and higher posterior elevation (0.029 µm vs 0.022 µm: p = 0.006). There was less correlation between the anterior and posterior surfaces in KS than in normal eyes for the asphericity and elevation above the BFS and aconic radius.
Corneal elevation topography is a sensitive method to identify patients who are potentially at high risk for developing ectasia after LASIK. The posterior corneal elevation map combined with corneal thickness values appear to be an important indicator of possible mild to suspect form of keratoconus.
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