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Hsiao-Sang Chu, I-Jong Wang, Wei-Li Chen, Fung-Rong Hu; Hidden Topographic Differences between Post-LASIK Ectasia and Keratoconus that Affect Contact Lens Fitting. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1794.
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© ARVO (1962-2015); The Authors (2016-present)
Post-LASIK ectasia has often been compared to keratoconus. Nevertheless, their contact lens fitting principles are markedly different. We conducted a matched-pair analysis, to find out the hidden topographic differences that affect the visual performance and lens fitting between these two disease groups.
This study was approved by the institutional review board of National Taiwan University Hospital (201508072RINC). The paired t test and McNemar's test were applied in a retrospective 1:1 matched-pair analysis consisting of 9 eyes with post-LASIK ectasia and 9 eyes with keratoconus. Matching criteria were age, simulated keratometry readings at the steepest (Ks)/flattest (Kf) meridians and the size/eccentricity of the ectatic cones measured by TMS-4 (Tomey, Japan). Topographic indices including surface regularity index (SRI), surface asymmetry index (SAI) were compared. Best spectacle corrected visual acuity (BSCVA) and best contact lens corrected visual acuity (BCLCVA) were converted into logMAR equivalents for analysis. Best-fit contact lens parameters were also recorded.
We paired post-LASIK ectasia and keratoconus eyes with no statistical differences of age, Ks, Kf, cone size and cone eccentricity (Table 1). We observed that the post-LASIK eyes had poorer surface regularity of SRI 1.66+/-0.33 vs.1.27+/-0.64 (p=0.035) for keratoconus eyes. In addition, the post-LASIK eyes had worse surface symmetricity of SAI 4.07+/-1.64 vs. 2.87+/-1.27 (p=0.045) for keratoconus eyes. This resulted in significantly poor logMAR BSCVA in post-LASIK ectasia eyes as compared to that in keratoconus eyes (0.8+/-0.4 vs.0.3+/-0.2, p=0.003). While corneal gas permeable (GP) lenses were tried on post-LASIK ectasia eyes, due to severe corneal asymmetry, the fitting results were poor. For all post-LASIK ectasia patients, reverse geometry mini-scleral lenses were needed for visual correction (Fig 1). On the contrary, corneal GP lenses were well-tolerated in all keratoconus eyes. The BCLCVA improved significantly in both groups with no difference in logMAR BCLCVA between post-LASIK ecstasia eyes and keratoconus eyes (0.13+/-0.14 vs. 0.08+/-0.06, p=0.40).
As compared to keratoconus eyes, post-LASIK ecstasia eyes showed worse surface symmetricity and regularity and required large diameter GP lenses to neutralize their surface asymmetries for better visual performance.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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