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Corneal ablation profiles for correction of hyperopia with the excimer laser
1Excimer Study Group, St Vicentius Ziekenhuis, Antwerpen, Belgium.
Journal of Refractive Surgery (Thorofare, N.J. : 1995)
|November 1, 1996
Summary
Excimer laser photorefractive keratectomy for hyperopia correction requires flattening the corneal periphery. The degree of peripheral flattening is directly related to the central steepening and the abruptness of the transition zone.
Area of Science:
- Ophthalmology
- Corneal Surgery
- Laser Vision Correction
Background:
- Hyperopia correction using excimer laser photorefractive keratectomy (PRK) aims to steepen the central cornea.
- Understanding the resulting topographical changes, particularly in the transition zone, is crucial for predictable outcomes.
Purpose of the Study:
- To calculate smooth corneal ablation profiles for hyperopic PRK.
- To quantify topographical changes in the transition zone, including axial distance and radius of curvature.
Main Methods:
- Determined conditions for smooth transitions in hyperopic PRK.
- Calculated ablation depth functions for the transition zone.
- Analyzed power variations along a semimeridian for theoretical optical zones with varying transition widths.
Main Results:
- Hyperopic PRK necessitates flattening the corneal periphery.
- A central steepening of +10 D resulted in mid-peripheral flattening of -7.00 D or -15.00 D for 2-mm and 1-mm transition zones, respectively.
- The mean rate of change in axial power within the transition zone was 15 D/mm and 45 D/mm.
Conclusions:
- Steepening the central cornea with PRK for hyperopia requires peripheral flattening.
- The extent of peripheral flattening is proportional to the central steepening and transition zone abruptness.
