Preoperative Refractive Error Research Articles

Comparison of high order aberration after conventional and customized ablation in myopic LASIK in different eyes of the same patient

To verify whether there exists any difference in higher order aberrations after undergoing myopic LASIK (laser in situ keratomileusis) with conventional ablation and customized ablation in different eyes of the same patient. This was a prospective randomized study of 54 myopic eyes (27 patients) that underwent LASIK using the Nidek EC-5000 excimer laser system (Nidek, Gamagori, Japan). Topography-guided customized aspheric treatment zone (CATz) was used in the first eye of the patient (study group) and the other eye of the same patient was operated on with conventional ablation (control group). Higher order aberrations [root-mean-square (RMS) in the 5-mm zone] of both groups were observed with the Nidek OPD-Scan aberrometer before and 3 months after LASIK. Preoperative mean refractive error was similar between two eyes of the same patient (t=-0.577, P>0.05). Preoperatively, higher order aberrations (RMS in the 5-mm zone) in the CATz ablation and conventional groups were (0.3600+/-0.0341) microm and (0.2680+/-0.1421) microm, respectively. This difference was not statistically significant (t=1.292, P>0.05). Three months after LASIK, higher order aberrations (RMS in 5-mm zone) in the CATz ablation and conventional groups were (0.3627+/-0.1510) microm and (0.3991+/-0.1582) microm, respectively. No statistically significant difference was noted between pre- and postoperative higher order aberrations in the CATz group (t=-0.047, P>0.05). However, a statistically significant increase in higher order aberrations was observed after conventional ablation (t=-5.261, P<0.05). A statistically significant difference was noted in the increase of higher order aberrations after LASIK between groups (t=-2.050, P=0.045). LASIK with conventional ablation and topography-guided CATz ablation resulted in the same BSCVA (best spectacle-corrected visual acuity) 3 month after LASIK. Higher order aberrations were increased, but the increase of higher order aberrations after customized ablation treatment was less than that after conventional ablation.

No Forward Shifting of Posterior Corneal Surface in Eyes Undergoing LASIK

To evaluate structural changes in the cornea and anterior chamber (AC) after LASIK for myopia. Retrospective nonrandomized study. One hundred sixty-one eyes of 83 patients (mean age, 34.5+/-8.3 years) who underwent uneventful LASIK for myopia and myopic astigmatism. The preoperative refractive error (spherical equivalent) and corneal thickness were -6.02+/-2.10 diopters (D) and 549.9+/-29.3 mum, respectively. The AC volume (ACV), AC depth (ACD), corneal thickness, central corneal true net power, and posterior corneal tangential curvature were measured using a rotating Scheimpflug camera before and 1 week and 1 month after surgery. In 84 eyes of 42 cases, anterior and posterior corneal elevations and corneal thicknesses also were measured by scanning-slit topography before and 1 month after surgery. Time course of the ACV, ACD (central, midperiphery, periphery), corneal thickness, central corneal true net power, posterior corneal tangential curvature using the Scheimpflug camera, and amount of forward shifting of the posterior corneal surface at the center of the difference map using scanning-slit topography. Preoperative and 1-month postoperative mean ACVs were 198.1 mm3 and 196.4 mm3, respectively, and preoperative and postoperative mean ACDs (center, midperiphery, periphery) were 3.24, 2.65, and 1.89 mm, and 3.21, 2.63, and 1.87 mm, respectively. The corneal thickness within the optical zone, subjective refraction, and central corneal true net power significantly changed by tissue subtraction after LASIK (P<0.0001). There were no significant differences in the ACV, ACDs (center, midperiphery, periphery), peripheral corneal thickness, and posterior corneal tangential curvature from preoperatively to 1 month after LASIK. However, using scanning-slit topography, the posterior corneal surface displayed a mean forward shift of 29.0+/-19.0 microm 1 month after surgery. The posterior corneal curvature, peripheral corneal thickness, ACDs, and ACV were consistent. These observations indicated that neither forward shifting of the central posterior corneal surface (bulging) nor backward shifting of the peripheral posterior corneal surface due to corneal swelling after ablation occurred after LASIK.

Improvement of Best Spectacle-corrected Visual Acuity After LASIK in Highly Myopic Eyes With Reduced Preoperative Best Spectacle-corrected Visual Acuity

To evaluate the visual acuity after LASIK in patients with high myopia and in patients with preoperative best spectacle-corrected visual acuity (BSCVA) <0.6. This retrospective study comprised 97 consecutive eyes in 57 patients who underwent LASlK. Preoperative spherical refractive error ranged from -1.75 to -22.00 diopters (D) (mean: -11.77+/-3.61 D) with mean astigmatism of -1.54+/-10.6 (range: 0 to -4.00 D). Pre- and postoperative BSCVA and uncorrected visual acuity (UCVA) were measured and analyzed. The mean preoperative BSCVA was 0.54+/-0.07 (range: 0.3 to 0.6). The mean postoperative BSCVA was 0.75+/-0.16 (range: 0.5 to 1.2). The mean postoperative UCVA was 0.60+/-0.25 (range: 0.5 to 1.2). A statistically significant improvement was noted in the mean postoperative BSCVA compared with the mean preoperative BSCVA (t=12.78; P<.001) and mean postoperative UCVA compared with preoperative mean BSCVA (t=2.866; P<.01). The safety index was 1.38, which was statistically significant (P<.001). The efficacy index was 1.11, which was statistically significant (P<.01). LASIK improved the mean postoperative BSCVA and UCVA compared with preoperative BSCVA in highly myopic eyes with reduced BSCVA.

Bilateral Comparison of Conventional Versus Topographic-guided Customized Ablation for Myopic LASIK With the NIDEK EC-5000

To compare visual acuity and higher order aberrations before and after myopic LASIK using conventional versus customized ablation. This prospective, randomized study included 54 myopic eyes in 27 patients who underwent bilateral LASIK using the NIDEK EC-5000 excimer laser system (NIDEK Technologies, Gamagori, Japan). Customized aspheric treatment zone (CATz) treatment was used in one eye (CATz group) and conventional ablation (conventional group) was used in the fellow eye. Uncorrected visual acuity (UCVA) and higher order aberrations (root-mean-square [RMS] in 4-mm and 6-mm zones) of both groups were observed with the NIDEK OPD-Scan aberrometer before and 3 months after LASIK. Preoperative mean refractive error was similar for both eyes of each patient (P>.05). No statistically significant differences were noted in preoperative higher order aberrations (RMS in 4-mm and 6-mm zones) between groups (P>.05). No statistically significant difference was noted between pre- and postoperative higher order aberrations in the CATz group (P>.05). However, a highly statistically significant increase in higher order aberrations was observed after conventional ablation (P<.001). There was a statistically significant higher increase of higher order aberrations after LASIK in the conventional group than the CATz group (P<.05). Postoperative UCVA with both conventional and customized ablation was not significantly different (P>.05). LASIK with conventional ablation and CATz ablation resulted in the same UCVA. The increase in higher order aberrations after CATz ablation was less than after conventional ablation.

Posterior continuous curvilinear capsulorhexis with optic capture of the posterior chamber intraocular lens in pediatric cataract

To assess the clinical effects of posterior continuous curvilinear capsulorhexis with optic capture of the posterior chamber intraocular lens in pediatric cataract. Fifty-one cases (83 eyes) received posterior continuous curvilinear capsulorhexis with optic capture of the posterior chamber intraocular lens. Preoperative and postoperative visual acuity and refractive error were recorded. Intraoperative and postoperative complications were observed. The follow-up period was from 6 to 36 months. Implantation of optic capture of the posterior chamber intraocular lens was successfully performed in 75 eyes (90.4%). The mean postoperative best corrected distant visual acuity achieved 0.5 or better in 75 eyes (48.0%). No eyes with optic capture were found optic axis opaque. The major complications of optic capture were anterior chamber fibrous exudation, iris posterior synechia and lenticular precipitates. Optic capture of the posterior chamber intraocular lens is safe and effective in the treatment of pediatric cataract to posterior continuous curvilinear capsulorhexis especially in the prevention of secondary opacification from the visual axis.

Rhegmatogenous Retinal Detachment After LASIK for Myopia

To report the characteristics and incidence of rhegmatogenous retinal detachment in myopic eyes after LASIK. The medical records of 49 patients with rhegmatogenous retinal detachment after LASIK were reviewed. The incidence of rhegmatogenous retinal detachment after LASIK was determined and potential risk factors were evaluated. LASIK was performed on 59,424 eyes with spherical equivalent refraction (SE) ranging from -0.75 to -26.50 diopters (D) (mean: -6.10 +/- 3.5 D). Forty-nine eyes developed rhegmatogenous retinal detachment between 1.5 and 76 months (mean: 27.3 +/- 21.7 months) after LASIK. The mean preoperative refractive error in these eyes was -8.6 +/- 3.9 D. Mean age of these patients was 38.2 +/- 11.2 years. Thirty-five (71.4%) patients were male. The cumulative incidence of rhegmatogenous retinal detachment was 0.082% (95% confidence interval [CI]: 0.061-0.109), and the yearly incidence was 0.032% (95% CI: 0.023-0.042) after LASIK. The most frequent location of the retinal breaks was the superior temporal quadrant (22.7%). Male sex, older age, and higher preoperative myopia were significantly related to the incidence of rhegmatogenous retinal detachment after LASIK (P<.001). Based on the results of this study, following the treatment of high-risk peripheral retinal lesions, LASIK did not appear to be an additional risk factor for the development of rhegmatogenous retinal detachment after LASIK in our patients; however, patients should be informed of the possibility of this complication as a consequence of myopia. Patients who are male, older in age, and have high myopia preoperatively may be at increased risk.

The AS biometry technique—A novel technique to aid accurate intraocular lens power calculation after corneal laser refractive surgery

Intraocular lens power (IOL) calculation for cataract surgery has been shown to be inaccurate after photorefractive keratectomy (PRK), laser-assisted subepithelial keratectomy (LASEK) and laser in situ keratomileusis (LASIK). Many techniques exist to calculate corneal power with varying results and require the clinician to be aware of the pitfalls of IOL power calculation in post-refractive eyes. The AS biometry method proposed here is a simple method which does not rely on the calculation of corneal power. This new method is compared to the current gold standard the clinical history method (CHM). Twenty-nine eyes of 15 patients had routine biometry prior to LASIK, LASEK or PRK. The range of pre-operative spherical equivalent refractive error was −5.37 to +4.00 diopters. The post-operative refraction was measured at 3–6 months. The IOL power calculation was calculated using the AS biometry method and the CHM. The two methods were compared using the Student's paired t-test and the Bland Altman technique. There was no statistical difference between the AS biometry method and the CHM. The paired Student's t-test comparing the AS biometry method and the CHM showed no statistical difference, t = 0.33 with a p-value of 0.75, at a 95% confidence interval. The authors conclude that the AS biometry technique is as accurate as the CHM. The former is a simpler method which avoids many of the pitfalls and confounding factors involved in IOL power calculation following corneal excimer laser surgery. However, like the CHM it requires measurements prior to laser surgery.

Optic Disc and Retinal Nerve Fiber Layer Analysis With Scanning Laser Tomography After LASIK

To examine whether LASIK induces changes in the optic disc and retinal nerve fiber layer using scanning laser tomography. Prospective, consecutive study of 53 myopic eyes in 38 patients (mean age: 35.7 +/- 10.4 years; range: 22 to 58 years). Preoperative average refractive error was -6.0 +/- 2.4 diopters (D) (spherical equivalent) (range: -2.0 to -10.0 D). Optic disc morphology and retinal nerve fiber layer thickness were evaluated with scanning laser tomography preoperatively and at 7 and 13 months postoperatively. No statistically significant differences were noted between the pre- and postoperative optic disc and retinal nerve fiber layer measurements. Our results suggest that transient extreme elevation of intraocular pressure during LASIK does not affect the optic disc morphology or retinal nerve fiber layer thickness in normal myopic eyes for at least 1 year after surgery.

A Predictive Model for Postoperative Intraocular Pressure Among Patients Undergoing Laser in Situ Keratomileusis (LASIK)

The aim of this study was to develop a predictive model based on preoperative variables for estimating postoperative intraocular pressure (IOP) of those eyes undergoing LASIK surgery, to predict the amount of underestimated IOP after LASIK for myopia and myopic astigmatism. Pretest-post-test longitudinal study. Both eyes of 193 eligible subjects who underwent LASIK procedures at the Department of Ophthalmology, National Taiwan University Hospital, from July 2000 to December 2002 for myopia and myopic astigmatism were identified to build up the predictive models. IOPs were measured with noncontact air-puff tonometry. Information on age, gender, preoperative central corneal thickness (CCT), preoperative central corneal curvature (CCK), preoperative spherical equivalent refractive error, and ablation depth was collected and applied for predicting postoperative IOP after LASIK based on linear mixed model. Significant predictors for postoperative IOP after myopic LASIK procedures included age, gender, preoperative IOP, ablation depth, preoperative CCT, and preoperative spherical equivalent refractive errors. The linear mixed model, taking into account these significant preoperative correlates and the correlation of IOPs between both eyes of the same patient, explained 91% of the variation of postoperative IOP. A statistical model was developed for predicting the amount of underestimated IOP after LASIK for myopia and myopic astigmatism, which is of clinical importance to uncover ocular hypertension among patients whose information on postoperative IOP immediately after LASIK is not available.

Comparison Between LASEK and LASIK for the Correction of Low Myopia

To compare the refractive results of laser epithelial keratomileusis (LASEK) and laser in situ keratomileusis (LASIK) for the correction of low myopia. A prospective, interventional, non-randomized, observer-masked study was performed of patients with myopia of < or = -2.50 diopters (D) (cylinder < or = 1.50 D) who had undergone either LASEK or LASIK. Refractive analysis was performed by a masked observer preoperatively and 1 day, 1 week, and 1 and 3 months postoperatively. Seventy-nine eyes that fulfilled the inclusion criteria in each group were included in the study. No statistically significant differences were noted in age, gender, or preoperative refractive error between groups. Postoperative uncorrected visual acuity (UCVA) was significantly lower in LASEK eyes 1 and 7 days postoperatively (P = .0001). At 1 and 3 months postoperatively, no significant differences were noted between the groups in UCVA (P = .07), but best spectacle-corrected visual acuity 3 months postoperatively was significantly better in LASEK eyes (P = .01). The refractive error was similar in both groups (P = .3). Visual improvement after LASEK for low myopia is significantly slower than after LASIK. Visual outcomes at 3 months postoperatively were similar with both techniques for the correction of low myopia.

Frequency and predicting factors of surgical complications in cataract surgery performed under topical anaesthesia

Frequency and predicting factors of surgical complications in cataract surgery performed under topical anaesthesia

Phakic IOL implantation versus clear lens extraction in highly myopic eyes

We appreciate Arne's idea of comparing phakic intraocular lens (IOL) implantation and clear lens extraction (CLE) in highly myopic eyes.1 However, we would like to comment on a few aspects of the study. The results would have been more conclusive if the inclusion criteria had been the same in both groups. There are 2 separate groups in the study. The phakic IOL group had a mean age of 35.7 years (range 32 to 43 years), whereas the CLE group had a mean age of 44.6 years (range 36 to 49 years). Also, the mean preoperative spherical equivalent refractive error was −13.6 ± 3.0 diopters (D) in the phakic IOL group and −16.7 ± 3.8 D in the CLE group. We think these are distinct groups and cannot be compared with each other. We also think that all the patients should be unilaterally or bilaterally recruited to increase the strength of the study. We would also like to clarify that the implantable contact lens from Staar is hydrophilic acrylic and not hydrophobic acrylic. In the CLE group, a retinal detachment occurred in 2 cases. Both were implanted with a poly(methyl methacrylate) IOL, and a neodymium:YAG (Nd:YAG) capsulotomy was performed to treat posterior capsule opacification. Using modern foldable IOLs with sharp edges results in a lower incidence of PCO and complications following Nd:YAG capsulotomy.1–4 We think it would have been more appropriate if the same foldable IOL had been implanted in all CLE cases. Also, the patients in the CLE group were older and more myopic. Both these preexisting factors are known to predispose to retinal detachment.3,5 Finally, although the author explained the postsurgical satisfaction, the reference on the description of the satisfaction scale is missing. A prospective randomized trial comparing these 2 methods would be more conclusive and desirable. Mayank A. Nanavaty DO Abhay R. Vasavada MS, FRCS Charlotta Zetterström MD, PhD aAhmedabad, India bStockholm, Sweden

Retinal Nerve Fiber Layer Changes After LASIK Evaluated With Optical Coherence Tomography

To determine whether the increase in intraocular pressure (IOP) during LASIK suction can induce a decrease in retinal nerve fiber layer thickness assessed by optical coherence tomography (OCT). Nineteen patients (38 eyes) were enrolled in the study. Intraocular pressure was normal at all pre- and postoperative examinations. Retinal nerve fiber layer thickness was measured using OCT-3 Stratus prior to and 1 week and 3 months after LASIK. Laser in situ keratomileusis was performed using the Bausch & Lomb Hansatome microkeratome and the NIDEK EC-5000 excimer laser. Optical coherence tomography mean retinal nerve fiber layer thickness values before and after LASIK were compared using the Student paired t test. Mean patient age was 27.8 years (range: 18 to 33 years). Mean preoperative spherical equivalent refractive error was -4.9 diopters (D) (range: -2.0 to -8.5 D). Mean time of microkeratome suction was 30 seconds (range: 20 to 50 seconds). Preoperatively, the mean retinal nerve fiber layer thickness obtained by OCT was 104.2+/-9.0 microm; at 1 week postoperatively the mean thickness was 101.9+/-6.9 microm, and 106.7+/-6.1 microm at 3 months postoperatively. Mean retinal nerve fiber layer thicknesses obtained by OCT were not significantly different between preoperative and 1 week and 3 months after LASIK (P > or = .05). Laser in situ keratomileusis performed on young myopic patients does not have a significant effect on retinal nerve fiber layer thickness determined by OCT. Further studies are required to reveal the risk of possible optic nerve or retinal nerve fiber layer damage by elevated IOP during LASIK.

Wavefront Analysis in Normal Refractive Surgery Candidates

To quantify the higher order aberrations of refractive surgery candidates and compare the wavefront-determined refractions with manifest refractions refined with a +/- 0.25 Jackson cross cylinder. Results of 226 consecutive patients (418 eyes) were analyzed with the WaveScan WavePrint system (VISX, Santa Clara, Calif). Only patients with normal eyes without previous surgery were included. The mean spherical equivalent refraction determined with wavefront analysis was -3.40 +/- 3.14 diopters (D) (range: -10.72 to +5.41 D). The largest amount of higher order aberrations was detected with : a 6-mm pupil diameter (coma 0.14 +/- 0.08 microm; trefoil 0.10 +/- 0.07 microm; spherical aberrations 0.09 +/- 0.07 microm). The mean root-mean-square of higher order aberrations and total aberrations were 0.23 +/- 0.11 microm and 4.00 +/- 2.45 microm, respectively. No statistically significant correlation was noted between higher order aberrations and gender (P = 0.7) or between higher order aberration and refractive level (P > .59). The mean differences in spherical equivalent refraction, sphere, and cylinder between WaveScan measurements and manifest refraction were 0.36 +/- 0.41 D, 0.40 +/- 0.44 D, and 0.28 +/- 0.32 D, respectively. This study provides reference values for higher order aberrations in normal refractive surgery candidates. Wavefront analysis also proved to be a valuable tool for objectively measuring preoperative refractive error.

Visual field changes after laser in situ keratomileusis

To determine whether laser in situ keratomileusis (LASIK) affects the central 30-degree visual field. University-based ophthalmology practice. This nonrandomized clinical trial comprised 14 normal patients (27 eyes) scheduled to have LASIK for myopia or myopic astigmatism. Automated static perimetry was performed before and 6 months after surgery using the Octopus 1-2-3 perimeter and the Dynamic-32 test strategy. Patient data included sex, age, preoperative and postoperative refractive errors, preoperative and postoperative best corrected visual acuity, preoperative corneal thickness, programmed optical zone, programmed total ablation diameter, and duration of microkeratome suction. All surgery was performed using the same Alcon LADARVision 4000 excimer laser. The main outcome measures were the mean sensitivity (MS) change in the central 15-degree visual field and the MS change in the 15- to 30-degree visual field. A multivariate analysis of the MS change as a function of preoperative clinical parameters was performed. There was no significant change in the MS in the central 15-degree visual field; between 15 and 30 degrees, there was a statistically significant decrease of -0.82 dB +/- 1.40 (SD) (P=.01, 2-tailed t test). The decline in MS was positively correlated with refractive error and corneal thickness; it was negatively correlated with the programmed optical zone diameter. Automatic static perimetry can detect decreased sensitivity in the midperipheral visual field after myopic LASIK. It may be a useful quantitative subjective test for measuring the effects of future improvements in surgical technique on vision quality.

Evaluación de factores pronósticos refractivos en LASIK miópico

Our objective was to evaluate myopic Lasik refractive results according to preoperative refraction findings. In 200 eyes, classified into 4 groups according to preoperative sphere and cylinder findings, different postoperative refractive parameters were compared: predictability, visual acuity (VA), security index (SI) and efficacy index (EI). Grouped by sphere: spherical correction was better than cylindrical correction. Highest negative spheres resulted in undercorrection (p<0.0171). The residual astigmatism was similar and the predictability within +/- 1.0 D was lower for the most myopic groups. Grouped according to cylinder: the higher the cylinder, the more cylinder undercorrection (p<0.05) and more sphere overcorrection was achieved (p=0.0469). Between the lowest and highest cylinder levels, the residual astigmatism difference was of -0.32 x 90 degrees and predictability +/-1.0 D was of 98 and 94% for the sphere and 96 and 88% for the cylinder respectively. Defocus Equivalent <1 D for the lowest and highest myopic groups was 74 vs. 46% for the cylinder and 82 vs. 38% for the sphere respectively. Pre and postoperative VA were lower for higher spheres or cylinders. SI >1.0 was similar to EI (+/-0.9), for preoperative sphere and cylinder groups. Best corrected visual acuity (BCVA) of 20/25 by sphere was 100% vs. 60% and of 20/30 by cylinder was 100% vs. 83%, for lower and higher myopic groups respectively. Analysis by grouping preoperative refractive errors is helpful for establishing its influence and improving LASIK prognosis and treatment. This procedure is effective and safe for all groups, and its inaccuracy is due more to astigmatism than to spherical error. As astigmatism increases, less spherical and higher cylindrical ablation should be performed.

Topographic and biomechanical differences between hyperopic and myopic laser in situ keratomileusis

To evaluate the size, shape, and uniformity of the videokeratographic functional optical zone (FOZ) after laser in situ keratomileusis (LASIK) in 2 cohorts of patients with equivalent amounts of preoperative myopic or hyperopic astigmatism. Pepose Vision Institute, St. Louis, Missouri, USA. Eyes with myopic or hyperopic astigmatism (n=27 in each group) that had LASIK with the Visx Star S3 laser were retrospectively selected to match for level of preoperative refractive error. Slit-scanning videokeratography was performed preoperatively and 6 months postoperatively and analyzed using custom software. The FOZ was calculated by analyzing refractive power maps using a region-growing algorithm. Difference maps were generated from slit images and compared for interval change in corneal elevation, tangential curvature, and refractive power. The difference maps were also averaged (mean difference maps) for each target population. A Zernike decomposition of corneal first-surface elevation was performed to compare postoperative values with baseline parameters. The mean postoperative refractive sphere at 6 months was -0.17 diopter (D) +/- 0.66 (SD) and +0.25 +/- 0.85 D in the myopia group and hyperopia group, respectively, and the mean postoperative astigmatism, -0.49 +/- 0.32 D and -0.65 +/- 0.52 D, respectively (P=.11). Based on the refractive power maps, the mean preoperative and postoperative myopic FOZ was 33.09 +/- 7.30 mm(2) and 30.94 +/- 5.43 mm(2), respectively, and the mean hyperopic FOZ, 33.19 +/- 7.96 mm(2) and 37.99 +/- 6.88 mm(2), respectively. After LASIK, there was an increase in magnitude of negative anterior corneal surface spherical-like Zernike values in the myopia group (P<.0001) and an increase in magnitude of positive spherical-like Zernike values in the hyperopia group. Postoperatively, significant induction of corneal surface horizontal coma was noted in hyperopic eyes (P<.0001). Hyperopic eyes, on average, had larger topographic FOZs after LASIK, but with less uniformity of curvature and power change than myopic eyes. Hyperopic LASIK, which involves more transition points along the ablation diameter, produced a less uniform topographic FOZ than typical myopic treatments. Less predictable biomechanical changes from the circumferential release of tension on collagen bundles after midperipheral hyperopic ablation and greater variation in beam centration and the angle of incidence may contribute to the greater variability in corneal curvature and power in hyperopic LASIK than in myopic LASIK.

A comparison of 2 methods for estimating residual stromal bed thickness before repeat LASIK

To compare 2 methods of calculating residual stromal bed (RSB) thickness after repeat LASIK, to determine which method generates more conservative RSB thickness estimates, and to determine any factors related to the discrepancy between these 2 calculation methods. Retrospective nonrandomized comparative trial. Seventy-nine patients (one eye per patient) undergoing primary LASIK and 2 repeat procedures (second and third LASIK) from 1998 to 2002. We compared calculated RSB thickness after second and third LASIK using either original corneal thickness (CT) minus flap thickness and all ablations (original CT method) or pre-enhancement CT minus flap thickness and enhancement ablation (repeat CT method). Differences in calculated RSB thickness after second and third LASIK by each method. Calculated RSB thickness averaged 329 microm by the repeat CT method compared with 305 microm by the original CT method after second LASIK (mean difference, 24 microm; P<0.0001) and 320 microm by the repeat CT method compared with 289 microm by the original CT method after third LASIK (mean difference, 31 microm; P<0.0001). After second LASIK, for 54% of eyes the repeat CT method was greater by >or=20 microm, and for 19% of eyes it was greater by >or=40 microm. After third LASIK, for 67% of eyes the repeat CT method was greater by >or=20 microm, and for 26% of eyes it was greater by >or=40 microm. The repeat CT method gave greater RSB thickness values than the original CT method in 73 of 79 eyes (92%) after second LASIK and in 72 of 79 eyes (91%) after third LASIK. The difference between the 2 methods was not associated with age, gender, initial preoperative refractive error, or refractive error before repeat LASIK. Using original preoperative CT measurements provides a more conservative and thus safer approach than using CT measurements obtained before repeat LASIK to calculate RSB thickness after repeat LASIK.

Changes in keratometric corneal power and refractive error after laser thermal keratoplasty

Purpose: To evaluate the effect of laser thermal keratoplasty (LTK) on corneal power and refractive error to develop a logical approach to calculating accurate intraocular lens (IOL) power for cataract surgery. Setting: Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. Methods: Laser thermal keratoplasty was performed in 27 eyes of 23 patients. Preoperatively and postoperatively, the refractive error was measured and the corneal power obtained by manual keratometry and topography. The changes in keratometric corneal power and refractive error after LTK were compared. Results: The mean age of the 15 women and 8 men was 45.0 years ± 4.6 (SD) (range 43 to 61 years). The mean preoperative refractive error was +1.43 ± 0.97 diopters (D) (range 0 to +3.63 D) at the spectacle plane and +1.46 ± 1.01 D (range 0 to +3.79 D) at the corneal plane. The mean postoperative refractive error was −0.44 ± 1.07 D (range −2.24 to +2.18 D) at the spectacle plane and −0.44 ± 1.08 D (range −2.18 to +2.23 D) at the corneal plane. After surgery, corneal powers measured by manual keratometry were significantly smaller than those measured by topography ( P<.001) and refractive error changes were significantly smaller than keratometric changes ( P<.001). Conclusions: After LTK, corneal power measured by manual keratometry was smaller than that measured by corneal topography and changes in corneal power measured by conventional keratometric instruments were greater than changes in refractive error. This difference should be considered in calculating IOL power in post-LTK eyes to prevent undesirable hyperopia after cataract surgery.

Contrast sensitivity after wave front–guided LASIK

Purpose To compare the effects on contrast sensitivity of wave front–guided (WFG) versus standard LASIK. Design Prospective, nonrandomized, comparative clinical study. Participants Twenty-four eyes of 13 consecutive patients (mean age, 25.2±8.4 years; spherical equivalent, −0.5 to −4.25 diopters [D]) treated with WFG LASIK (WaveLight-Allegretto scanning-spot laser and wave front analyzer) and 22 eyes of 12 consecutive patients (mean age, 28.4±9.1 years; spherical equivalent, −0.75 to −4.5 D) treated with standard LASIK (WaveLight-Allegretto scanning-spot laser). Methods Best-corrected contrast sensitivity was measured before and 1 month after surgery in both the WFG LASIK group and the standard LASIK group. A sine-wave contrast sensitivity test (functional acuity contrast test) was used to measure contrast sensitivity at 5 spatial frequencies (1.5, 3, 6, 12, and 18 cycles/degree). We compared the LASIK-induced changes in contrast sensitivity in each groups at each spatial frequency. Main outcome measure The effect on contrast sensitivity of WFG LASIK versus standard LASIK. Results Uncorrected visual acuity of 20/20 or better was achieved by 72% of eyes treated with WFG LASIK and by 70% of the eyes treated with standard LASIK. One month after LASIK, 88% of the contrast sensitivity measurements improved in the WFG LASIK group, whereas in the standard LASIK group, only 40% of the contrast sensitivity measurements improved. The contrast sensitivity improvement was significantly larger in the WFG LASIK group at all spatial frequencies ( P<0.05). The WFG LASIK patients had a negative correlation between the changes in contrast sensitivity and the preoperative refractive error. Conclusions The ability of WFG LASIK to correct optical aberrations results in significantly improved contrast sensitivity compared with standard LASIK 1 month after surgery.