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Comparison of Corneal and Total Ocular Aberrations Before and After Myopic LASIK

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Comparison of Corneal and Total Ocular Aberrations Before and After Myopic LASIK Comparison of Corneal and Total Ocular Aberrations Before and After Myopic LASIK Damien Gatinel, MD, PhD; Pierre-Alexandre Adam, MD; Slim Chaabouni, MD; Jacques Munck, OD; Maud Thevenot, OD; Thanh Hoang-Xuan, MD; Stefan Pieger, Dipl.Ing; Masanao Fujieda, MSE; Harkaran S. Bains, BSc(Hons) he human eye is affected by aberrations that can ABSTRACT degrade retinal image quality. Recent studies have PURPOSE: To assess the compensation of total ocular T found that in pre-presbyopic patients, the magnitude and corneal wavefront aberrations after conventional of higher order aberrations for the cornea or the lens indi- myopic LASIK. vidually are larger than for the whole eye.1-4 Additionally, despite variation in size and shape, the average magnitude of METHODS: This study comprised 57 eyes of 57 patients. higher order aberrations of emmetropic eyes is similar to that Total and corneal aberrations were measured preopera- found in mild to moderate myopes and hyperopes.5 Guirao and tively and 3 months postoperatively using the OPD-Scan 2 (NIDEK Co Ltd) aberrometer. Total and corneal aberra- Artal propose a passive, simple geometric model for the ocu- tions root-mean-square (RMS) was calculated out to lar compensation of aberrations. They suggest that the compo- the 6th Zernike order for a 6.0-mm pupil diameter. The nents of the eye are similar to an auto-compensating design, percentage increase postoperatively was defi ned by the producing similar overall average optical quality for different ratio of RMS pre- and postoperatively for each corneal refractive errors, despite large structural variations.2 and total eye group. The compensation between corneal and internal aberrations for a given aberration group was The progressive lack of compensation over time may be ex- 6,7 defi ned as: (corneal aberration group RMS Ϫ total eye plained by changes in the lens shape and size throughout life. aberration group RMS)/corneal aberration group RMS. Whether a compensatory mechanism exists that operates over a period of months to account for the optical decoupling of RESULTS: Postoperatively, higher order aberrations in- corneal and lenticular higher order aberrations after corneal Ϯ Ϯ creased by a factor of 1.77 1.26 (total) and 2.47 2.25 refractive surgery remains unaddressed. The variations of the (corneal) (PϽ.05). Coma aberration increased by a fac- tor of 2.43Ϯ2.61 (total) and 2.56Ϯ2.66 (corneal). total ocular and corneal higher order aberrations and visual Spherical aberration increased by a factor of 1.46Ϯ1.83 performance before and after LASIK have been investigated (total) and 2.64Ϯ2.24 (corneal). The values of the ratio previously.8-11 One study that measured corneal and internal of compensation did not change signifi cantly before and higher order aberrations on separate instruments reports par- Ͼ after LASIK for individual aberrations (P .05). tial compensation of higher order aberrations before and after corneal refractive surgery.12 In the current study, we used CONCLUSIONS: Although myopic LASIK induced signifi - cant corneal aberrations, the level of partial compensa- a combined ocular aberrometer and corneal topographer to tion of corneal aberrations by internal structures remained compare pre- and postoperative corneal (corneal aberrations) unchanged. These results suggest that the previously described emmetropization that is effective during de- velopment may also be effective with acquired variations in corneal shape. [J Refract Surg. 2010;26:333-340.] From AP-HP Bichat Claude Bernard Hospital (Gatinel, Adam, Chaabouni, doi:10.3928/1081597X-20090617-01 Munck, Thevenot, Hoang-Xuan), Rothschild Foundation (Gatinel, Adam, Chaabouni, Munck, Thevenot), and Center for Expertise and Research in Optics for Clinicians (CEROC) (Gatinel), Paris, France; and NIDEK Co Ltd, Gamagori, Japan (Pieger, Fujieda, Bains). Messrs Pieger and Fujieda are employees of NIDEK Co Ltd. Mr Bains is a con- sultant to NIDEK Co Ltd. The remaining authors have no financial interest in the materials presented herein. Correspondence: Harkaran S. Bains, BSc(Hons), 17927-80 Ave, Edmonton, AB, Canada, T5T 0S6. Tel: 780.418.8354; Fax: 780.418.8359; E-mail: [email protected] Received: January 8, 2009; Accepted: May 5, 2009 Posted online: June 22, 2009 Journal of Refractive Surgery • Vol. 26, No. 5, 2010 333 Corneal and Total Ocular Aberrations After LASIK/Gatinel et al and total ocular aberrations (total aberrations) of eyes measures corneal topography and wavefront aberra- that underwent myopic LASIK. These measurements tions nearly simultaneously (within 0.20 seconds of were used to determine whether the sudden decoupling each other) on the same optical axis without moving of higher order aberrations due to LASIK unlocked a the patient. The corneal topography is measured using compensatory process that minimized the amount of Placido-disk technology and aberrometry is measured induced aberrations after surgery. using the principle of skiascopic phase difference.14 Wavefront measurements are performed by scanning PATIENTS AND METHODS with an infrared slit beam, and the refl ected light is captured by an array of rotating photodetectors cov- PATIENT POPULATION ering 360° within the eye in 1° increments. With this Consecutive patients undergoing conventional myo- technique, 1440 wavefront data points within a 6-mm pic LASIK by the same surgeon (D.G.) were included in pupil diameter are measured. A built-in eye tracker this study. Inclusion criteria were preoperative mani- accounts for eye movements that may occur dur- fest refraction spherical equivalent (MRSE) ϽϪ10.00 ing measurements. A quality check of the difference diopters (D) and preoperative refractive astigma- in the pupil centers between corneal and wavefront tism Ͻ0.75 D. Soft contact lens wearers had to re- measurements is included to ensure there is no shift move their lenses 1 week prior to the fi rst examination. in pupil center between measurements. This quality Patients wearing hard contact lenses prior to surgery were check alerts the operator to shifts in the pupil center not included. Eyes with topographic abnormalities such with a color-coded message. Alignment in the x-y-z as forme fruste keratoconus, keratoconus, pellucid mar- axes and automated tracking ensures all measurements ginal degeneration, contact lens warpage, marked corne- were centered without pupillary shift between corneal al irregularity, and Ͻ490 µm of central corneal thickness and wavefront measurements. Internal wavefront and preoperatively were not included in this study. Patients corneal wavefront can be computed using OPD-Station with a physiologic pupil diameter Ͻ6 mm under meso- software (NIDEK Co Ltd). The patient remained seated pic conditions were excluded from participating. in the same position for all measurements, hence the Patients with intra- or postoperative complications wavefront and corneal topography data can be directly were not included in this study. Postoperative corneal correlated. topographies were evaluated by the surgeon (D.G.) All measurements were acquired in a dark examina- to ensure a well-centered ablation and the lack of ir- tion room after 2 minutes of dark adaptation and were regular corneal astigmatism. The criteria for evaluat- repeated at least three times (with dark adaptation be- ing ablation centration using corneal topography have tween each measurement). Both the total and corneal been described previously.13 wavefronts were reconstructed using 6th order Zernike This study adhered to the tenets of the Declaration polynomial decomposition for a 6-mm pupil, centered of Helsinki. Informed consent was obtained from all on the corneal vertex. patients after an explanation of the risks and benefi ts The internal aberration calculations are proprietary. of the study. To simplify the description for the purposes of this paper, All eyes underwent a baseline ophthalmic examina- the wavefront of the internal eye was calculated using tion that included measurement of uncorrected visual the corneal wavefront derived from corneal topogra- acuity (UCVA), best spectacle-corrected visual acu- phy and whole eye wavefront measured with the OPD- ity (BSCVA) (decimal notation), manifest refraction, Scan. The wavefront was converted to Zernike poly- cycloplegic refraction, slit-lamp microscopy, dilated nomials to calculate internal aberration coeffi cients by funduscopy, ultrasound corneal pachymetry (Reichert determining the difference between corneal aberrations Ophthalmic Instruments, Depew, NY) and simulta- and whole eye aberrations. All aberrations were trans- neous corneal topography, wavefront aberrometry posed to vertex=0 (corneal vertex) prior to calculation. and pupillometry (infrared light) using the OPD-Scan The computation of corneal aberration used in the cur- (NIDEK Co Ltd, Gamagori, Japan). Postoperatively, all rent study has been described previously.15 patients underwent the same measurements as pre- operatively with the exception of dilated funduscopy SURGERY (unless clinically warranted). All patients underwent bilateral conventional (not wavefront) myopic LASIK using the NIDEK EC-5000 COMBINED ABERROMETRY AND CORNEAL MEASUREMENTS (NIDEK Co Ltd) excimer laser. All surgeries were Mean central keratometry, corneal, and total optical performed by the same surgeon (D.G.) and outcomes aberrations were measured using the OPD-Scan, which were targeted for emmetropia using a personalized 334 Copyright © SLACK Incorporated Corneal and Total Ocular Aberrations After LASIK/Gatinel et al nomogram. The
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