Comparison of Corneal Aberration Changes After Laser In Situ Keratomileusis Performed With Mechanical Microkeratome and IntraLase Femtosecond Laser: 1-Year Follow-up

Higher-order aberrations after wavefront-optimized photorefractive keratectomy and laser in situ keratomileusis

PURPOSE

To analyze the changes in higher-order aberrations (HOAs) that occur after wavefront-optimized photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).

SETTING

Emory Eye Center and Emory Vision, Atlanta, Georgia, USA.

METHODS

This retrospective analysis comprised eyes that had PRK or LASIK from June 2004 through October 2005. Postoperative outcome measures included 3-month uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction spherical equivalent (MRSE), changes in the root mean square (RMS) and grouped coefficient HOAs (microns) measured with a corneal analyzer, and subjective assessment of visual aberrations.

RESULTS

One hundred consecutive eyes of 54 patients had PRK, and 100 contemporaneous consecutive eyes of 71 patients had LASIK. The PRK and LASIK populations were similar in general demographics, preoperative HOAs, and postoperative UCVA and BSCVA. The mean MRSE was slightly hyperopic after PRK (mean +0.11 diopters [D]) and slightly myopic after LASIK (mean -0.19 D) (P< .0001). There were no statistically significant changes in RMS or grouped coefficient HOA values after PRK or LASIK, nor were there significant differences in postoperative RMS or grouped coefficient HOA values between PRK and LASIK. One percent of PRK and LASIK patients reported a subjective increase in postoperative visual aberrations; 5% reported a subjective improvement postoperatively.

CONCLUSIONS

Wavefront-optimized excimer laser surgery did not induce significant HOAs after PRK or LASIK. The 2 techniques were equally efficacious and had equivalent postoperative HOA profiles.

Microkeratome complications

PURPOSE OF REVIEW

Complications from laser in-situ keratomileusis surgery are extremely rare. However, most of the complications involve construction of the corneal flap, which is fashioned using various mechanical or femtosecond laser microkeratomes. Here, we review and discuss complications of microkeratome flaps.

RECENT FINDINGS

Several large studies of microkeratome laser in-situ keratomileusis cases report a similar set of complications: partial or irregular flaps, buttonholes, and free flaps. Risk factors for these complications include increased age, preoperative hyperopia, and years of contact lens wear. Numerous animal and clinical studies have shown that the femtosecond platform produces flaps with greater stability with more consistent and accurate dimensions than the mechanical microkeratome. However, there is no significant difference in final visual outcome.

SUMMARY

The aim of this review is to report complications associated with mechanical microkeratomes in the construction of laser in-situ keratomileusis flaps and to see whether there is a significant disadvantage compared with the femtosecond laser.

Importance of fixation, pupil center, and reference axis in ocular wavefront sensing, videokeratography, and retinal image quality

PURPOSE

To examine the impact of the location of the fixation target, pupil center, and reference axis of ophthalmic aberrometers and videokeratographers on the measurement of corneal aberrations relevant to vision.

SETTING

Clinical Research, Visual Optics Institute, College of Optometry, University of Houston, Houston, Texas, USA.

METHODS

The design features of a generic aberrometer and videokeratographer and their interaction with the eye were examined. The results provided a theoretical framework for experimental assessment of pupil translation errors on corneal aberrations relevant to vision and their correction in 129 eyes.

RESULTS

Two key principles emerged. First, the aberrometer's measurement axis must coincide with the eye's line-of-sight (LoS). Second, the videokeratographer's measurement axis (the vertex normal) must be parallel with the eye's LoS. When these principles are satisfied, the eye will be in the same state of angular rotation and direct comparison of measurements is justified, provided any translation of the pupil from the vertex normal is taken into account. The error incurred by ignoring pupil displacement in videokeratography varies between eyes and depends on the type of aberration and amount of displacement, with the largest residual correction root-mean-square wavefront error being 1.26 mum over a 6.0 mm pupil, which markedly decreases retinal image quality.

CONCLUSION

Translation of the pupil center with respect to the vertex normal in videokeratography should not be ignored in the calculation of the corneal first-surface, internal aberrations of the eye relevant to vision, or the design of refractive corrections based on videokeratography.

Comparative study of higher-order aberrations after conventional laser in situ keratomileusis and laser epithelial keratomileusis for myopia using the technolas 217z laser platform

PURPOSE

To examine changes in higher-order aberrations (HOAs) after PlanoScan laser in situ keratomileusis and (LASIK) and laser epithelial keratomileusis (LASEK).

DESIGN

Prospective, comparative study.

METHODS

Myopic patients undergoing LASIK (65 eyes of 36 patients) and LASEK (50 eyes of 28 patients) at a private practice were selected randomly. Surgery was performed using the Technolas 217z laser (Bausch & Lomb, Surrey, United Kingdom). Main outcome measures included uncorrected visual acuity (UCVA), manifest refractive spherical equivalent (MRSE), and aberrometry (Zywave; Bausch & Lomb, Rochester, New York, USA) and were recorded before surgery and at three and 12 months after surgery.

RESULTS

There was no statistical difference between both groups in terms of MRSE (P = .91), ablation depth (P = .47), scotopic pupil size (P = .38), or optical zone (P = .07). Before surgery, there was no statistical difference in root mean square (RMS) of total (P = .70), third- (P = .79), fourth- (P = .23), and fifth- (P = .33) order aberrations and individual terms. Three months after surgery, RMS of total HOA was raised significantly more (P = .03) after LASIK (1.46-factor increase) than LASEK (1.25-factor increase). One year after surgery, a reduction in total HOAs was observed in 13.8% of LASIK- and 48.5% of LASEK-treated eyes compared with preoperative levels.

CONCLUSIONS

Postoperative increases in total HOA and vertical coma were significantly greater in LASIK- than in LASEK-treated eyes. Postoperative reduction in total HOAs was observed in a number of eyes with high preoperative levels and occurred more frequently in LASEK-treated eyes.

[Wavefront analysis in ophthalmologic diagnostics]

Modern aberrometry measures standard and so-called higher-order refractory aberrations. Ophthalmology and optometry use Zernike polynomials to describe aberrations of the retina and lens causing refractory errors. Aberrations of a higher order sometimes follow successful laser surgery, causing reduced vision and inducing patient dissatisfaction; enhanced wavefront data can help to avoid this. Aberrometry is used also for objective measurement of refractory changes. Wavefront techniques and their clinical application enable many options for understanding the delicate balance of eye optics. The future of refractive surgery lies in increasingly individualized treatment to suppress higher degrees of aberration and thus improve clinical results. Patients will continue placing greater demand on individualized intraocular lenses that correct higher-order aberrations.