Total and Corneal Optical Aberrations Induced by Laser in situ Keratomileusis for Hyperopia

Abstract

PURPOSE: To evaluate changes induced by standard laser in situ keratomileusis (LASIK) for hyperopia on total and corneal optical quality. METHODS: Total and corneal aberrations were measured before and after standard hyperopic LASIK in 13 eyes (preoperative spherical equivalent refractive error +3.17 ± 1.10 D). The Chiron Technolas 217C laser with PlanoScan was used. Total aberrations (measured using laser ray tracing) and corneal aberrations (estimated from a videokeratoscope) were described using Zernike terms. Root-mean-square wavefront error for both total and corneal aberrations, and through-focus Strehl ratio for the point spread function of the whole eye were used to assess optical changes induced by surgery. RESULTS: Third and higher order aberrations increased significantly after hyperopic LASIK (by a factor of 2.20 for total and 1.78 for corneal aberrations, for a 6.5-mm pupil). Spherical aberration changed to negative values (corneal average decreased by -0.85 ± 0.48 µm and total average by -0.70 ± 0.30 µm). Best Strehl ratio for the whole eye decreased by a factor of 1.84. Hyperopic LASIK induced larger changes than myopic LASIK, compared to an equivalent group of myopic eyes from a previous study. Induced corneal spherical aberration was six times larger after hyperopic LASIK, for a similar range of correction, and of opposite sign. As with myopic LASIK, changes in internal spherical aberration are of opposite sign to those induced on the corneal anterior surface. CONCLUSIONS: Hyperopic LASIK induced significant amounts of aberrations. The largest increase occurred in spherical aberration, which showed a shift (toward negative values) of opposite sign; increase was greater than for myopic LASIK. [J Refract Surg 2004;20:203-216]

Mild Decentration Measured by a Scheimpflug Camera and Its Impact on Visual Quality Following SMILE in the Early Learning Curve

“…Bueeler et al 8 reported that it was unlikely that optical quality would deteriorate if the lateral alignment error was within 0.45 mm. Llorente et al 9 reported that, in 90% of eyes, even an accuracy of 0.80 mm or better would be sufficient. However, many patients who complain of visual disturbances after refractive surgeries have visual acuities of 1.0 or better and refractions close to plano.…”

Recent advances in measurement of monochromatic aberrations of human eyes

“…Aberrations increase following hypermetropic corneal refractive surgery 173,174 (Figure 9a). Anterior corneal spherical aberration is positive before surgery and becomes negative after surgery ( Figure 9b), with the change increasing with the magnitude of correction.…”

“…This is because anterior corneas become more prolate following treatment. 173,[175][176][177] As an example of the magnitude of the changes, Llorente and colleagues 173 found that mean anterior corneal and total RMS higher-order aberrations increased following LASIK by 1.8 and 2.2 times, respectively and the mean spherical aberration co-efficient c 4 0 decreased by 0.70 ± 0.30 µm (pre-surgical mean spherical equivalent +3.2 ± 1.1 D, 6.5 mm pupil).…”

“…Two reasons for the large increases in aberrations following refractive surgery are decentration in the ablation pattern, which particularly affects third-order aberrations, 178,179 and aberrations being measured at pupil sizes exceeding the ablation zone. 180 The internal aberration contribution changes following myopic and hyperopic LASIK, 165,173 indicating some changes a. Kuroda and colleagues did not use normalisation terms so their c 4 0 co-efficients have been reduced by √5 to be consistent with ANSI Z80.28-2004. Measurement of ocular aberrations Atchison occur at the posterior corneal surface as a consequence of surgery.…”

Temporal evolution of ocular aberrations following laser in situ keratomileusis

“…7 Most problems, especially under mesopic or scotopic conditions 8 are related to a decrease in optical quality due to a significant increment of ocular aberrations after surgery. [9][10][11][12] The increase of spherical-like aberrations after LASIK is due to the ablation profile and corneal reflection losses of the laser beam, [13][14][15] while the increase of coma-like aberrations seem to be mainly related to ablation decentrations. 16 An increase of ocular aberrations may not be always related to an increase of corneal aberrations, but to a disruption of the fine balance of the aberrations of the corneal and the lens.…”