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H.-K. V. Ho, Y. Li, M. Tang, S. Iyer, W. May, D. Huang; Differential Diagnosis of Eccentric Corneal Steepening After Hyperopic LASIK by Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2810.
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© ARVO (1962-2015); The Authors (2016-present)
To differentiate between keratectasia and decentered ablation in cases of eccentric corneal steepening after hyperopic laser in situ keratomileusis (LASIK).
A series of 3 cases were selected from a prospective study of high-speed Fourier-domain optical coherence tomography (FD-OCT) in LASIK and keratoconus. Corneal scanning with the RTVue-CAM FD-OCT system (Optovue, Inc., Fremont, CA) was performed in each case, along with corneal topography by Orbscan II (Bausch & Lomb, Rochester, NY).
The first 2 cases were referred for inferior corneal steepening after hyperopic LASIK. In case 1, Orbscan showed a mean curvature peak inferotemporally in the left eye, coinciding in location with the minimum corneal thickness on OCT. In case 2, Orbscan showed mean curvature peaks inferonasally in both eyes, not coincident with the locations of minimum OCT corneal thickness in the inferotemporal quadrant. Review of pre-LASIK topography showed inferior steepening in case 1 but not case 2. A case of keratoconus is also shown to demonstrate that the location of maximum convexity on the Orbscan mean curvature map coincides with the location of minimum thickness.
Corneal ectasia after hyperopic LASIK surgery is a very rare complication that is difficult to distinguish from decentered ablation. OCT is helpful in the differential diagnosis because, in cases of ectasia, the corneal mean curvature peak coincides with the location of focal thinning. In cases of decentered ablation, the cornea should be thicker at the location of the mean curvature peak. OCT pachymetry map is of particular value because previous studies have shown that it is accurate in keratoconus and after LASIK, unlike Orbscan, which tends to underestimate corneal thickness in these situations.
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