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PURPOSE: To investigate lenticule decentration following small incision lenticule extraction (SMILE) via the pupil center or tear film mark centration method and compare induction of corneal higher order aberrations (HOAs) between the two methods. METHODS: This study analyzed decentration values obtained from tangential topography difference maps of 100 eyes (100 patients) undergoing SMILE with the pupil center (n = 50) or tear film mark (n = 50) centration method. Total HOAs and component aberrations were measured preoperatively and 6 months postoperatively. Relationships between the magnitudes of decentration and induced corneal HOAs were assessed. RESULTS: Both vertical and total decentered displacement were significantly different ( P < .001) between the two centration groups. A significant relationship between the preoperative pupillary offset and decentration was noted in the pupil center group ( P < .001), but not in the tear film mark group ( P = .530). Significantly greater induction of total HOAs, coma, and vertical coma (all P < .001), as well as horizontal coma ( P = .001) and spherical aberration ( P = .023), were observed in the pupil center group. Association between the total decentered displacement and induced total HOAs ( P < .001), as well as all other significantly increased phenomena, was also significant in the pupil center group. Differences in decentered displacement and induced corneal HOAs were significant for preoperative pupillary offset (angle kappa) greater than 200 µm, but not for angle kappa less than 200 µm. CONCLUSIONS: SMILE with tear film mark centration can yield improved treatment centration and less induction of total HOAs, coma, and spherical aberrations. [ J Refract Surg . 2020;36(4):239–246.]

PURPOSE: To report long-term follow-up of two pediatric patients who underwent laser in situ keratomileusis (LASIK) for myopic anisometropic amblyopia. METHODS: Case series. RESULTS: Two patients who underwent unilateral LASIK in 1999 for anisometropic amblyopia were clinically assessed 16 years after their initial procedure with visual acuity testing, refraction, stereopsis, axial length, corneal topography, slit-lamp examination, and quality of life assessment. Patients had stable corrected distance visual acuity, balanced refraction, improved stereopsis, and good visual quality of life. Corneal topography showed a mildly decentered ablation bed with no evidence of ectasia. CONCLUSIONS: LASIK in the pediatric population requires special considerations, including fixation and centration issues, microkeratome selection, and refractive endpoint. The two patients were found to have stable corneal topography, visual acuity, and stereopsis 16 years after initial treatment. [ J Refract Surg. 2019;35(6):391–396.]

PURPOSE: To assess the clinically acceptable range of inlay decentration with respect to the light-constricted pupil center and the coaxially sighted corneal light reflex (CSCLR) for an inlay (Raindrop Near Vision Inlay; ReVision Optics, Inc., Lake Forest, CA) that reshapes the anterior corneal surface. METHODS: In this retrospective, observational cohort study of 115 patients with emmetropic or low hyperopic presbyopia who were implanted with a shape-changing corneal inlay, visual acuity, task performance (in good and dim light), reports of halos and glare, and satisfaction data were collected from the preoperative and 3-month postoperative examinations. Inlay centration with respect to the pupil center and CSCLR was determined from the center of the inlay effect derived from iTrace (Tracey Technologies, Houston, TX) wavefront measurements. Multivariate regression models assessed the influence of inlay position on visual outcomes. RESULTS: On average, monocular uncorrected near visual acuity (UNVA) improved 4.9 ± 1.7 lines in the treated eye, with no loss in binocular distance vision. Eighty-three percent of implants were centered radially within 0.5 mm of the pupil center. Multivariate analysis of decentration with respect to both the pupil center and CSCLR revealed no significant interaction with the above clinical outcomes, with the exception of UNVA in the treated eye (all P > .05, α = 0.05). For decentration of less than 0.75 mm, the change in UNVA was less than 1 line. CONCLUSIONS: Distance and near visual acuity, task performance, severity of halos and glare, and satisfaction were independent of radial decentration of the Raindrop Near Vision Inlay of less than 0.75 mm from the light-constricted pupil. [ J Refract Surg. 2018;34(3):164–170.]

PURPOSE: To evaluate optical zone centration of hyperopic small incision lenticule extraction (SMILE). METHODS: This prospective study of 60 consecutive hyperopic SMILE procedures used the VisuMax femtosecond laser and matched LASIK procedures with the VisuMax and MEL 80 excimer lasers (Carl Zeiss Meditec AG, Jena, Germany). Inclusion criteria were maximum attempted hyperopic meridian of between +1.00 and +7.00 diopters (D) and astigmatism up to 6.00 D. For SMILE, the optical zone was between 6.3 and 6.7 mm, with a 2-mm transition zone. Two LASIK control groups (6.5- and 7-mm optical zone) were generated matched for spherical equivalent treated. In SMILE, the corneal vertex of the coaxially fixating eye was aligned with the vertex of the curved contact glass. In LASIK, the treatment was centered on the coaxially sighted corneal light reflex (first Purkinje image) with the contralateral eye (Seiler method). A tangential (instantaneous) curvature preoperative to 3 months postoperative difference map was generated for each eye. A fixed grid and set of concentric circles were superimposed on the difference map to measure the offset between the optical zone center and corneal vertex (0,0), and vector analysis was used for comparative analysis. RESULTS: Mean attempted spherical equivalent was +5.61 ± 0.96 D (range: +3.20 to +6.50 D) and mean cylinder was −0.96 ± 0.62 D (range: 0.00 to −2.75 D) in the SMILE group. Mean age was 29 ± 7 years (range: 19 to 52 years) in the SMILE group. Mean centration offset was 0.23 ± 0.15 mm (range: 0 to 0.61 mm) for the SMILE group, 0.33 ± 0.14 mm (range: 0.14 to 0.85 mm) for the 6.5-mm LASIK group, and 0.31 ± 0.19 mm (range: 0.05 to 0.85 mm) for the 7-mm LASIK group. The mean centration offset for SMILE was less than that of both LASIK groups ( P < .05). CONCLUSIONS: Optical zone centration of hyperopic SMILE was found to be similar to eye-tracker–centered hyperopic LASIK with the MEL 80 laser. [ J Refract Surg. 2017;33(3):150–156.]

PURPOSE: To compare size, circularity, and centration outcomes of continuous curvilinear capsulorhexis (CCC) performed with or without assistance from the VERUS ophthalmic caliper (Mile High Ophthalmics, Denver, CO). METHODS: This was a multicenter retrospective consecutive case controlled series review. RESULTS: Data from 40 consecutive cases using the VERUS device for CCC were compared to 40 consecutive cases with standard manual CCC. VERUS-assisted CCC size, circularity, and centration were closer to target compared to that of manual only procedures ( P < .05). The average time from initiation to completion of the capsulotomy was shorter with manual (40 ± 11 seconds) compared to VERUS-assisted (71 ± 13 seconds) cases ( P < .0001). CONCLUSIONS: The VERUS ophthalmic caliper is effective at improving size, circularity, and centration of the CCC in a time-efficient manner when compared to manual procedures performed without VERUS guidance. [ J Refract Surg. 2016;32(10):654–658.]

PURPOSE: To report improved visual outcome after rotation of an asymmetrical multifocal intraocular lens (IOL). METHODS: Case report. RESULTS: A 58-year-old patient underwent bilateral phacoemulsification with asymmetrical multifocal IOL implantation. Postoperative uncorrected distance visual acuity (UDVA) was 0.0 logMAR (20/20 Snellen) and uncorrected near visual acuity was 0.0 logMAR (20/20 Snellen) in both eyes. Quality of vision questionnaire scores for day and night were 5 and 7, respectively. The center of the multifocal IOL in the dominant eye was initially found to be 0.2 mm superotemporally displaced, increasing the percentage area of ‘near-add’ compared to ‘distance-add’ within the physiological pupil. Rotation of this IOL 120° clockwise greatly improved the IOL centration within the pupil center and resulted in an immediate improvement in UDVA to −0.1 logMAR (20/16 Snellen) and quality of vision questionnaire scores to 8 and 9, respectively. CONCLUSIONS: Assessment of the centration of an asymmetrical multifocal IOL is important, particularly if there are dysphotoptic or other visual complaints. [ J Refract Surg . 2016;32(7):494–496.]

PURPOSE: To compare the optical zone centration accuracy between myopic eyes treated with small incision lenticule extraction (SMILE) and LASIK. METHODS: Retrospective analysis of 100 consecutive eyes treated with SMILE (the SMILE group) with the corneal fixation-based centration VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) and a matched group of 100 eyes treated with LASIK (the LASIK group) with VisuMax flap creation and eye tracker-based centration MEL 90 excimer laser (Carl Zeiss Meditec) ablation. In SMILE, the corneal vertex of the coaxially fixating eye was aligned with the vertex of the curved contact glass. In LASIK, the treatment was centered on the coaxially sighted corneal light reflex (first Purkinje image). A tangential (instantaneous) curvature preoperative to postoperative difference map was generated for each eye. A fixed grid and set of concentric circles were superimposed on the difference map to measure the offset between the optical zone center and corneal vertex (0,0), and vector analysis was used for comparative analysis at 3 months postoperatively. RESULTS: Mean centration offset was 0.20 ± 0.11 mm for the SMILE group and 0.17 ± 0.10 mm for the LASIK group, with no statistically significant difference between groups ( P >.05). In the SMILE group, the optical zone was centered within 0.1 mm of the corneal vertex in 17% of eyes, within 0.2 mm in 55% of eyes, within 0.3 mm in 81% of eyes, and within 0.4 mm in 96% of eyes. In the LASIK group, the optical zone was centered within 0.1 mm of the corneal vertex in 24% of eyes, within 0.2 mm in 62% of eyes, within 0.3 mm in 92% of eyes, and within 0.4 mm in 98% of eyes. There was no systematic directional decentration in either group. CONCLUSION: Optical zone centration accuracy was no different between SMILE and LASIK with the MEL 90 laser. [ J Refract Surg. 2015;31(9):586–592.]

PURPOSE: To review the published literature describing the use of the LenSx femtosecond laser technology (Alcon Laboratories, Inc., Fort Worth, TX) in cataract surgery. METHODS: Literature review. RESULTS: The LenSx system has been used in more than 200,000 cataract surgery procedures to date. Pre-clinical evaluations have shown that this system produces accurate and reproducible capsulorhexes, and that both the energy required for phacoemulsification and total phacoemulsification time are less than with conventional phacoemulsification. In comparative studies, femtosecond lasers have been shown to produce more precise and reproducible capsulorhexes than manual procedures, and better intraocular lens placement; capsule overlap, circularity of capsulotomy, and centration of the intraocular lens are consistently better with femtosecond lasers than with manual procedures. The improved quality of capsulorhexis and intraocular lens positioning are reflected in favorable visual and refractive outcomes. As with any new technology, there is a significant learning curve: prospective cohort studies have shown that the incidence of intraoperative complications such as suction breaks or anterior capsular tears or tags decreases with experience. In general, the incidence of such complications is within the range (< 2%) considered in recent evidence-based guidelines to be feasible and desirable. CONCLUSIONS: Although femtosecond laser cataract surgery is in its infancy, the technology is evolving rapidly and offers the potential for more consistent and predictable results after cataract surgery. [ J Refract Surg . 2014;30(11):730–740.]

PURPOSE: To evaluate the centration of the treatment zone after small incision lenticule extraction (SMILE) and compare it to femtosecond laser-assisted LASIK (FS-LASIK). METHODS: Sixty-nine myopic eyes of 36 patients who underwent SMILE were compared to 69 myopic eyes of 36 patients treated with FS-LASIK. All procedures were performed by a single surgeon using the VisuMax platform (Carl Zeiss Meditec, Jena, Germany). The Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) was used for preoperative and postoperative topography and pachymetry. The centration of the treatment zone was estimated pachymetrically by the distance of the thickest point on the corneal thickness differential map from the topographical center of the entrance pupil and the coaxial corneal light reflex. RESULTS: In SMILE cases, the mean decentration of the lenticule from the center of the entrance pupil was 0.326 ± 0.196 mm (range: 0.014 to 1.062 mm), whereas the distribution of the lenticule centers demonstrated a nasalization pattern. In FS-LASIK cases, this value was 0.452 ± 0.224 mm (range: 0.02 to 1.040 mm), whereas the ablation centers were distributed randomly. In relation to the coaxial corneal light reflex, the decentration in SMILE was 0.315 ± 0.211 mm (range: 0.0 to 1.131 mm), whereas FS-LASIK eyes demonstrated a mean decentration of 0.516 ± 0.254 mm (range: 0.103 to 1.265 mm). The decentration from the reference point of its technique (coaxial corneal light reflex in SMILE, the entrance pupil center in FS-LASIK) was significantly more extended in the FS-LASIK group ( P < .001). CONCLUSIONS: The centration of the treatment zone as measured by the Pentacam was better for patient-controlled fixation during SMILE than active eye tracker-assisted FS-LASIK. [ J Refract Surg. 2014;30(10):680–686.]

PURPOSE: To describe a method for centering ablation profiles considering pupil center and corneal vertex information simultaneously. METHODS: Novel ablation profiles were developed to cover the pupil aperture while respecting the corneal vertex as the optical axis of the ablation (asymmetric offset [AO]). The approach has been extended to combine higher order aberrations (HOA) referred to the pupil center (line-of-sight) with manifest refraction values referred to the corneal vertex (visual axis). The shapes and sizes of ablation profiles planned with AO were compared with the shapes and sizes of “classic” ablation profiles (with symmetric offset and without [no] offset, respectively). RESULTS: The introduction of asymmetric offset leads to an asymmetric ablation profile that is virtually the same depth as no offset ablation profiles (symmetric offset profiles ablate deeper), with the same diameter as no offset ablation profiles (smaller than symmetric offset ablations). The ablation volume of AO profiles lies between the ablation volumes of no offset and symmetric offset ablation profiles. When combined with HOAs, AO ablation profiles affect specific HOA terms. Asymmetric offset spherical components affect HOA coma components, and AO astigmatic components affect HOA trefoil components. CONCLUSIONS: Asymmetric offset ablation profiles provide a simple method to combine pupil and corneal vertex information for ablation procedures in refractive surgery with the optical axis of the ablation lying on the visual axis and the edges of the optical zone being concentric to the pupil boundaries. Further clinical studies must be performed to support the theoretical results.

PURPOSE Optical calculations have shown that wavefront-based ablation profiles as well as intraocular lens (IOL) implantations can cause residual aberrations or even induce significant additional aberrations due to the poor registry between the eye’s optical components. These effects can be exacerbated in eyes that require higher corrections. Individualized eye models can provide accurate ablation profiles for these cases. The aim of this report is to analyze the relevance of individualized eye models for refractive treatment planning from a theoretical point of view. METHODS A method for the customization of eye models based on various types of measurement data of a specific patient is presented and the calculation of optimal ablation profiles and IOL shapes by means of ray tracing through customized model eyes are discussed. Topography data with an original centration on the corneal apex were aligned on the pupil center for the creation of eye models. RESULTS An ideal ablation profile or a customized IOL can be calculated based on the obtained individualized eye models. Calculations have shown that in theory ray-tracing optimized ablation profiles do not leave any residual aberrations in the eye whereas wavefront- guided corrections were found to have the potential to increase specific types of aberrations by a factor of two. This is due to the negligence of the multi-lens structure of the eye. CONCLUSIONS Optical ray tracing algorithms allow the highest degree of customization. The systematic induction of higher order aberrations by means of wavefront-guided treatments or standard IOLs has to be overcome by such a method. However, these theoretical observations must be compared to the corresponding measurement accuracies and precisions and they must be supported by future clinical trials. [J Refract Surg. 2008;24:S446-S451.] ABOUT THE AUTHORS From IROC AG – Institut für Refraktive und Ophthalmo-Chirurgie, Zurich, Switzerland (Mrochen, Bueeler, Seiler); Swiss Federal Institute of Technology, Zurich, Switzerland (Mrochen); WaveLight AG, Erlangen, Germany (Donitzky); and University of Zurich, Switzerland (Seiler). Drs Mrochen, Bueeler, and Seiler are paid scientific consultants and Mr Donitzky is an employee of WaveLight AG, Erlangen, Germany. Correspondence: Michael Mrochen, PhD, IROC AG – Institut für Refraktive und Ophthalmo-Chirurgie, Stockerstrasse 37, CH-8002 Zurich, Switzerland. Tel: 41 43 488 3800; Fax: 41 43 488 3809; E-mail: michael.mrochen@iroc.ch

PURPOSE To evaluate ablation centration of flying-spot LASIK, investigate the effect of patient- and surgeon-related factors on centration, and compare flying-spot and broad-beam laser results. METHODS This retrospective study comprised 173 eyes of 94 patients who underwent LASIK with the Alcon LADARVision4000 with an active eye-tracking system. The effective tracking rate of the system is 100 Hz. The amount of decentration was analyzed by corneal topography. Patient- (low, high, and extreme myopia; effect of learning) and surgeon-related (learning curve) factors influencing centration were identified. Centration was compared to the Schwind Multiscan broad-beam laser with a 50-Hz tracker from a previous study. RESULTS Mean decentration was 0.36±0.18 mm (range: 0 to 0.9 mm). Centration did not differ in low, high, and extreme myopia or in patients’ first and second eyes. There were no significant differences in centration between the first 50 LASIK procedures and the last 50 procedures. Comparing flying-spot and broad-beam laser results, there were no differences in centration in low myopia. However, the LADARVision4000 yielded better centration results in high and extreme myopia. CONCLUSIONS The Alcon LADARVision4000 active eye tracking system provides good centration for all levels of myopic correction and better centration than the Schwind broad-beam Multiscan in eyes with high and extreme myopia. [J Refract Surg. 2008;24:371-376.] ABOUT THE AUTHORS From the Department of Ophthalmology, China Medical University Hospital, Taichung, Taiwan. The authors have no proprietary interest in the materials presented herein. Correspondence: Yi-Yu Tsai, MD, PhD, or Chun-Chi Chiang, MD, Dept of Ophthalmology, China Medical University Hospital, No 2, Yue Der Rd, Taichung, Taiwan. Tel: 886 4 22052121 ext 1141; Fax: 886 4 22052121 ext 1139; E-mail: yiyutsai@seed.net.tw Received: February 21, 2006 Accepted: March 19, 2007 Posted online: August 15, 2007

PURPOSE: To describe the use of new laser alignment and delivery software in the NIDEK Advanced Vision Excimer laser platform (NAVEX) that allows centration based on surgeon specification. METHODS: Descriptive article with a case report. RESULTS: The software allows specification via numeric entry of the exact placement of the laser tapered to the position of the visual axis or the line of sight. CONCLUSIONS: The ability to specify the exact location of the laser ablation based on pupil position is fundamental in patients undergoing custom ablation and those with eccentric fixation. A conservative treatment strategy is recommended for initial experience with this alignment software. [J Refract Surg. 2006;22:S1089-S1092.]

PURPOSE: To compare ablation centration after bilateral sequential and simultaneous myopic LASIK. METHODS: A retrospective randomized case series was performed of 670 eyes of 335 consecutive patients who had undergone either bilateral sequential (group 1) or simultaneous (group 2) myopic LASIK between July 2000 and July 2001 at the China Medical University Hospital, Taichung, Taiwan. The ablation centrations of the first and second eyes in the two groups were compared 3 months postoperatively. RESULTS: Of 670 eyes, 274 eyes (137 patients) comprised the sequential group and 396 eyes (198 patients) comprised the simultaneous group. Three months postoperatively, 220 eyes of 110 patients (80%) in the sequential group and 236 eyes of 118 patients (60%) in the simultaneous group provided topographic data for centration analysis. For the first eyes, mean decent ration was 0.39±0.26 mm in the sequential group and 0.41 ±0.19 mm in the simultaneous group (P= .30). For the second eyes, mean decentration was 0.28±0.23 mm in the sequential group and 0.30±0.21 mm in the simultaneous group (P=. 36). Decentration in the second eyes significantly improved in both groups (group 1, P =.02; group 2, P CONCLUSIONS: Simultaneous bilateral LASIK is comparable to sequential surgery in ablation centration. [J Refract Surg. 2005;21:705-708.]

PURPOSE: To evaluate the ability to accurately center and register wavefront data to provide effective custom wavefront application for vision correction.METHODS: Centration images were obtained of 40 undilated pupils at 5 different illumination levels using the Alcon LADARWave aberrometer (Alcon Laboratories Ine, Fort Worth, Tex). Pupil position relative to the limbus was determined for all eyes under all levels of illumination. Variability in centration of the pupil was based on difference in magnitude of offset between pupil center and limbal center. Human operators were compared to a computerized limbus recognition system through repeatability testing using 10 different images of one eye of a single patient.RESULTS: As determined by human operators, the pupil center in undilated pupils shifted a mean of 175 µm between the lowest level and the highest level of illumination (range 34 to 335 µm [standard deviation 84 µm]). Repeatability testing suggests human measurements can accurately position the pupil to within approximately 50 µm using current technology. Computer image processing using limbus recognition software appears equal or superior to manual pupil centration.CONCLUSION: The pupil center can have a significant change in position with changing illumination. Wavefront data must be centered on a fixed eye structure rather than the pupil center to ensure that wavefront data captured in scotopic light are appropriately matched to the pupil in the photopic light used at surgery. The goal is to avoid clinically significant decentration of the wavefront between capture and excimer laser application. [J Refract Surg 2004;20:S623-S626]

PURPOSE: Decentration of the ablation zone is an occasional complication of excimer laser refractive surgery. We describe a technique to recenter the ablation zone without changing the refractive status obtained by the first surgery. METHODS: Sixteen eyes of 14 patients had moderate or marked ablation decentration after previous excimer laser surgery for myopia, but with only minor residual refractive error. Five eyes had spectacle-corrected visual acuity loss and all these patients reported various symptoms such as halos, ghost images, or night driving difficulties. To recenter the ablation zone without changing the refraction, a combination myopic and hyperopic treatment was used. The hyperopic treatment was decentered toward the initial decentered myopic ablation. A myopia ablation of near equal dioptric value was then added, but decentered in the opposite direction. The Bausch & Lomb Technolas Keracor 217 laser was used. RESULTS: After the first retreatment, the centration of the ablation zone was improved in 15 of the 16 eyes. All eyes with initial spectacle-corrected visual acuity loss recovered lines of visual acuity. Subjective decrease of symptoms was described as follows: nil in one eye, mild in one eye, moderate in four eyes, and marked in ten eyes. A second retreatment was needed in five eyes: in two to improve centration and in three to correct residual ametropia. The only complication (one eye) was induced decentration 180° away from the initial decentration with a 1-line spectacle-corrected visual acuity loss, and additional retreatment was required. CONCLUSION: A combination of decentered myopic and hyperopic ablation of an equivalent dioptric magnitude, each decentered 180° apart, was a useful method to correct previous excimer laser treatment decentration, with minimal alteration of refractive status that was obtained by the initial surgery. [J Refract Surg 2004;20:139-148]

PURPOSE: To evaluate the efficacy of conductive keratoplasty in the treatment of pre-existing and surgically induced hyperopic astigmatism. METHODS: In this prospective, noncomparative case series, four eyes of four subjects, two female and two male (age 25 to 47 yr) were treated for hyperopia (up to +5.50 D) and hyperopic astigmatism (up to +5.75 D) with the Refractee ViewPoint conductive keratoplasty system. The follow-up period was 6 months. Uncorrected and spectaclecorrected visual acuity, manifest and cycloplegic refraction, and videokeratographs were obtained before and after surgery. We treated two patients who had already had LASDK, one of them with a decentered ablation and the other with flap striae, one patient after PRK, and one patient with keratoconus. RESULTS: No complications were observed. No eye lost lines of spectacle-corrected visual acuity. All eyes showed improvement of uncorrected visual acuity of 3 or more lines. Videokeratographs demonstrated improved centration and reduction in keratometric power readings. Each eye was analyzed separately, including a comparative analysis of the proposed nomograms and quality of vision after surgery. CONCLUSIONS: Conductive keratoplasty may be a minimally invasive solution for patients with irregular hyperopic astigmatism, offering improved quality of vision in instances of flap striae by tightening the central cornea. [J Refract Surg 2003;19:425-432]

PURPOSE: Eye tracker systems have been developed concomitantly with small scanning beams to theoretically reduce ablation zone decentration and for accurate registration of all the laser pulses on the cornea. The purpose of the study was to compare the tracker-assisted with the manual centration method. METHODS: Twenty-five patients (48 eyes) with myopia and/or astigmatism had laser in situ keratomileusis (LASIK) between August 1998 and February 1999 with the Technolas 117C laser. Twenty patients (38 eyes, 80%) were available for follow-up at 3 months after surgery. Eyes were assigned randomly to one of two ablation zone centration methods: Group 1: Tracker- assisted (20 eyes), Group 2: Manual (18 eyes). RESULTS: Mean distance between the ablation zone center and the pupillary center in the trackerassisted centration group was 0.55 ? 0.30 mm (range, 0.10 to 1.4 mm), and in the manual centration group, 0.43 ? 0.23 mm (range, 0.10 to 1.0 mm) (P=.177). There was no statistically significant difference in postoperative contrast sensitivity, glare, and Topographical Corneal Surface Regularity Index (SRI) between the two groups. CONCLUSIONS: We obtained good results with both centration methods. We did not find superiority of the tracker-assisted over manual regarding ablation zone centration, vision quality, or regularity of the ablation. [J Refract Surg 2002:18:37-42]

BACKGROUND: Adequate centration of keratorefractive surgical procedures is essential for a successful outcome. An accurate technique to mathematically describe the centration and topography of the ablation zone after photorefractive keratectomy (PRK) would be valuable in assessing the effects of these variables on subsequent visual results. METHODS: A vector center of mass formula and computerized videokeratography were used to study the postoperative treatment zone centration and topography of 17 consecutive highly myopic patients (-6.00 to 12.00 diopters [D]). Each had undergone PRK using either a single 6.0 mm (w=ll) or three-stepped ablation zone (n=6), with good visual results. RESULTS: Calculations disclosed mean ablation zone deeentration relative to the pupil center for all patients to be 0.20 ± 0.16 mm using the vector center of mass formula. Areas of uniform central corneal dioptric power (mean diameter 3.4 ± 0.8 mm) and surrounding transition zones of declining dioptric power (mean slope 1.61 ± 0.44 D/mm) were also determined. CONCLUSION: A new vector center of dioptric power distribution that analyzes centration and transition zone topography offers a rigorous but straightforward means to assess the effects of refractive corneal surgery procedures on central corneal topography. [JRefractSurg. 1996;12:483-491.]

BACKGROUND: Topography measures the centration in refractive and corneal refractive surgery, but until recently there was no effective method to measure decentration in intraocular lens (IOL) implantation. PATIENTS AND METHODS: We measured the decentration of 22 phakic eyes, in 14 high myopic patients, based upon photographs of the anterior segment using a digital analysis system (IMAGEnet Topcon Corporation 1988, Tokyo, Japan). These eyes had undergone IOL implantation for the correction of myopia with Worst-Fechner iris claw lenses. Decentration was measured with respect to the centers of both the cornea and pupil. RESULTS: Mean decentration of the IOL center from the cornea center was 0.51 ± 0.25 mm (range, 0 to 0.8374 mm). When measured with respect to the center of the pupil, the average decentration was 0.47 ± 0.29 mm (range, 0.182 to 0.9341 mm). A positive correlation between the decentration measurements of the two methods was found (p < .01 indicated statistical significance). CONCLUSIONS: This digital imaging system (IMAGEnet) accurately measured decentration of IOLs in myopic eyes. [J Refract Surg. 1995;11:26-30.]