Abstract
Abstract: :
Purpose: To evaluate the fitness and accuracy of Variable Spot Scanning and its algorithms in creating customized ablation plans. Methods: VSS algorithms were tested to determine the accuracy with which they could create an ablation plan for a wide variety of theoretical and actual treatments. Refractive treatments tested were: myopic, myopic with astigmatism, pure astigmatism, hyperopic, hyperopic with astigmatism, and mixed astigmatism. Non-refractive treatments tested were: specific Zernike polynomials, multi-focal shapes, and a variety of wavefront maps of highly aberrated eyes. The treatments were programmed with a variety of sizes of optical zones (4.0 mm to 9.0 mm) and transition zones (6.0 mm to 9.5 mm). The wavefronts of twelve eyes with mild to moderate hyperopia were measured and treated with VSS custom treatments. Mean preoperative MRSE was +1.98 D. Optical zones were set to 5.0 mm, transition zones were set to 9.0 mm. Results were recorded at one, three and six months. Results: The VSS algorithms consistently achieved solution accuracy of less than 0.27µm RMS of tissue ablation (.09 µm RMS of wavefront aberration). Mean RMS was 0.17 µm of tissue ablation (.06 µm RMS of wavefront aberration). In all cases the RMS ablation error was less than the ablation depth of a single laser pulse. The patients tested with hyperopic treatments achieved a one-month mean MRSE of 0.02 D ± 0.36 D, which gradually regressed to a six months mean MRSE of +0.23 ± 0.36 D. At six months 75% of the eyes achieved a UCVA of 20/20 or better; 100% of the eyes achieved a UCVA of 20/25 or better. Conclusions: The VSS algorithms produced accurate ablation patterns for the complete range of refractive and therapeutic treatments. The accuracy of the ablations, and the ability to treat irregular surfaces, as well as the flexibility of zone sizes may be of substantial clinical value. VSS for treatment of hyperopia produces safe, effective results for the range studied. Mild regression may indicate that an optical zone larger than 5 mm should be used.
Keywords: refractive surgery: LASIK • refractive surgery: PRK • computational modeling