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Difference map or single elevation map in the evaluation of corneal forward shift after LASIK
Teruhiro Yoshida1, Kazunori Miyata, Tadatoshi Tokunaga
1Canon Sales Co. Inc., Tokyo, Japan.
Ophthalmology
|October 3, 2003
Summary
Evaluating corneal forward shift after excimer laser surgery requires comparing preoperative and postoperative elevation maps. A single postoperative map is insufficient for accurate assessment of posterior corneal surface changes.
Area of Science:
- Ophthalmology
- Refractive Surgery
- Corneal Topography
Background:
- Assessing corneal forward shift after excimer laser surgery is crucial for understanding refractive outcomes.
- Current methods rely on difference maps generated from two corneal elevation maps.
Purpose of the Study:
- To determine if corneal forward shift can be accurately evaluated using only a single postoperative color-coded elevation map.
- To compare the efficacy of single-map versus difference-map analysis for detecting posterior corneal changes.
Main Methods:
- Prospective study of 163 eyes undergoing LASIK for myopia.
- Corneal topography of the posterior surface was captured preoperatively and 1 month postoperatively.
- Analysis involved generating difference maps and evaluating single postoperative maps using color-coded criteria.
Main Results:
- Receiver operating characteristic (ROC) curve analysis showed insufficient sensitivity and specificity when using a single postoperative map.
- A weak but significant correlation was found between corneal forward shift and the posterior best-fit sphere radius.
- The study indicated that single-map analysis failed to adequately depict posterior surface protrusion.
Conclusions:
- Evaluating corneal forward shift after excimer laser surgery necessitates the use of difference maps derived from both preoperative and postoperative elevation maps.
- Single postoperative color-coded maps are not reliable for assessing these changes.