Myopic Laser In Situ Keratomileusis Research Articles

Flap and stromal bed thickness in laser in situ keratomileusis enhancement

Purpose: To evaluate whether flap thickness changes after the primary laser in situ keratomileusis (LASIK) procedure and to assess the accuracy of intraoperative pachymetry and ablation depth measurements in predicting stromal bed thickness before enhancement in eyes that have had primary myopic LASIK. Setting: Bascom Palmer Eye Institute, Miami, Florida, USA. Methods: This retrospective noncomparative interventional case series comprised 57 eyes of 42 patients who had LASIK enhancement between June 2001 and September 2002. Exclusion criteria included previous ocular surgery or complications during the first LASIK procedure. Only patients who had had LASIK and enhancement by the same surgeon at our institution and had intraoperative pachymetry readings for both procedures were included. The original flap was relifted in all enhancement procedures. Corneal thickness was routinely measured intraoperatively by ultrasound pachymetry. The age, eye, refraction, date of primary LASIK, central corneal thickness (CCT) and central stromal bed thickness at primary LASIK, depth of ablation, flap thickness (subtraction pachymetry), date of enhancement, CCT and central stromal bed thickness at enhancement, and flap thickness at enhancement were recorded. Results: Thirty-one eyes of 26 patients were myopic and 26 eyes of 16 patients were hyperopic before primary LASIK. The mean time between LASIK and enhancement was 218 days ± 115 (SD) (193 ± 88 days in myopic eyes and 248 ± 136 days in hyperopic eyes [ P = .068]). The flap tended to be thicker at enhancement than in the primary LASIK procedure by 9.3 ± 25.7 μm in myopic eyes ( P = .054) and 10.5 ± 16.6 μm in hyperopic eyes ( P = .004). A strong correlation was found between flap thickness in the first and second procedures in myopic and hyperopic eyes ( r = 0.6). In myopic eyes, the mean difference between the estimated stromal bed thickness after the first procedure (central bed thickness– ablation depth) and the stromal bed thickness measured directly at enhancement was not statistically significant (3 ± 29 μm; P = .54, paired t test). A strong correlation was found between the 2 measurements ( r = 0.8, P<.001). Another strong correlation was found in myopic eyes between the estimated corneal thickness after the primary LASIK and the corneal thickness measured at enhancement ( r = 0.81, P<.001). No correlation was found between the difference in flap thickness and the time to enhancement ( r = 0.09 in myopic eyes and r = 0.01 in hyperopic eyes). Conclusions: Flap thickness tended to be thicker at enhancement than at primary LASIK. Intraoperative pachymetry and ablation depth measurements proved to be precise tools to predict stromal bed thickness before enhancement in eyes that had had primary myopic LASIK. This information may help in planning LASIK enhancements.

Effect of exogenous keratinocyte growth factor on corneal epithelial migration after photorefractive keratectomy

Purpose: To investigate the effect of topical keratinocyte growth factor (KGF) on wound healing after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Setting: Department of Ophthalmology, Rayne Institute, St. Thomas' Hospital, London, United Kingdom, St. Erick's Eye Hospital, Stockholm, Sweden, and the University of Regensberg, Regensberg, Germany. Methods: In a placebo-controlled trial, 24 New Zealand white female rabbits were divided into 3 equal groups. Group 1 (n = 8) had myopic PRK (6.0 diopters [D]) using the Technolas® 217z laser (Bausch & Lomb). Group 2 and Group 3 had myopic LASIK (6.0 D) with a flap depth of 140 μm and 180 μm, respectively. Topical KGF (20 μg/mL) was administered to half the treated eyes in each group intraoperatively and postoperatively; the other half received placebo eyedrops. Epithelial closure, corneal haze, and keratocyte activation in the rabbit eyes were analyzed and compared with those in placebo-controlled eyes for 5 weeks postoperatively. Results: In Group 1, the mean reepithelialization after PRK was 0.10 mm 2/h ± 0.02 (SD) in the KGF group and 0.33 ± 0.05 mm 2/h in the control group ( P = .001). There was no significant difference in the mean backscatter between the KGF eyes (154 ± 45.95) and the control eyes (141 ± 38.45) after PRK ( P = .42). Histology revealed reduced epithelial cell layers in the KGF group and comparable keratocyte density as in the control group. In Groups 2 and 3, there was no significant difference in backscatter, epithelial layers, and keratocyte density between KGF and control eyes after LASIK. Conclusions: Topical KGF (20 μg/mL) delayed reepithelialization after PRK. It had no effect on stromal wound healing in LASIK eyes with an intact epithelial barrier.

Wavefront-guided Ablation With Bausch and Lomb Zyoptix for Retreatments After Laser in situ Keratomileusis for Myopia

To evaluate the efficacy of wavefront-guided ablation for treatment of residual refractive error and higher order aberrations after laser in situ keratomileusis (LASIK) for myopia. Twenty-one eyes of 13 patients with residual refractive error after myopic LASIK were treated with a wavefront-guided ablation with the Zyoptix technique. In 13 eyes of 8 patients (Group A) we lifted the flap with an epitheliorhexis technique; in 8 eyes of 5 patients (Group B) we cut a new flap with a Hansatome microkeratome. Preoperative root mean square (RMS) values were 1.370 for second order aberrations, 0.382 for total higher order aberrations, 0.273 for third order, 0.243 for fourth order, and 0.052 for fifth order aberrations. Three months postoperatively, RMS values decreased significantly to 0.278 (second order), 0.189 (total higher order), 0.138 (third order), 0.107 (fourth order), and 0.038 (fifth order). Ablation depth was two times greater than needed with a standard Planoscan treatment. Patients in the microkeratome recut group showed a trend toward overcorrection, and residual astigmatism was higher (-0.75 +/- 0.58 D) than in the flap lift group (-0.25 +/- 0.29 D). Wavefront-guided ablation was an effective method to correct residual refractive error and higher order aberrations after myopic LASIK. Functional and refractive outcomes were better when we lifted the flap than when we recut the flap.

Monitoring corneal structures with slitlamp-adapted optical coherence tomography in laser in situ keratomileusis

To monitor corneal structures with slitlamp-adapted optical coherence tomography (OCT) in laser in situ keratomileusis (LASIK). Department of Ophthalmology, Vivantes Klinikum Neukölln, Berlin, Germany. In this prospective, nonrandomized, comparative clinical case series of consecutive patients who had LASIK for myopia and myopic astigmatism, the corneal structures were studied with slitlamp-adapted OCT at a wavelength of 1,310 nm. The central corneal thickness (CCT) and epithelial, flap, and residual stromal thicknesses were assessed preoperatively, immediately after surgery, on postoperative day 1, and then, on average, after 8, 35, and 160 days. Twenty-five eyes of 13 patients were included. The attempted mean spherical equivalent correction was -6.11 diopters (D) +/- 2.16 (SD) with a mean calculated stromal ablation depth of 92 +/- 24 microm. The CCT was 516 +/- 26 microm preoperatively and 453 +/- 40 microm postoperatively (P<.001). The epithelial thickness increased from 57.0 +/- 7.7 microm preoperatively to 61.0 +/- 7.5 microm postoperatively (P =.04). Imaging of the hyperreflective interface was possible in all patients for up to 15 months. The flap and residual stromal thickness was 211 +/- 28 microm and 344 +/- 48 microm, respectively, immediately after LASIK and 164 +/- 21 microm (P<.001) and 284 +/- 32 microm (P<.001), respectively, on postoperative day 1. There were no further significant changes during the follow-up. The overall mean reproducibility was +/-4.50 microm (coefficient of variation [CV] 0.94%) for CCT, +/-4.99 microm (CV 8.57%) for epithelial thickness, +/-6.25 microm (CV 3.55%) for flap thickness, and +/-7.09 microm (CV 2.42%) for residual stromal thickness. Slitlamp-adapted OCT can be used to longitudinally monitor the variable structures of the cornea, epithelium, flap, and residual stroma in LASIK.

Pupil size and night vision disturbances after LASIK for myopia.

To examine whether standardized, preoperative evaluation of pupil sizes can predict the risk of night vision visual disturbances after bilateral laser in situ keratomileusis (LASIK) for myopia. A prospective study was carried out involving 46 patients who underwent bilateral LASIK for myopia. Pupil sizes were measured before surgery using an infrared pupillometer under standardized settings. Pre- and postoperative refraction and best spectacle-corrected visual acuity (BSCVA) were registered. At the 3-month follow-up visit, the patients completed a questionnaire regarding night vision pre- and postoperatively. The mean bilateral, spherical equivalent refraction (SE) was - 8.76 D (range 6.32 to - 12.0 D) preoperatively, and - 1.69 D (range 0 to - 4.38 D) postoperatively. The mean bilateral BSCVA was not changed by the operations. We found a significant correlation between large scotopic pupil sizes and the impression of worsened night vision (p < 0.01). A significant correlation between gender (males) and subjectively reduced night vision postoperatively was also found (p < 0.05). Large pupil size measured preoperatively is correlated with an increased frequency of subjectively experienced post-LASIK visual disturbances during scotopic conditions. We recommend preoperative evaluation of pupil size in all patients prior to LASIK surgery.

Choroidal neovascularization following laser in situ keratomileusis

Two cases of choroidal neovascularization (CNV) occurring after laser in situ keratomileusis (LASIK) are reported. In the first case, an extrafoveal choroidal neovascular membrane, apparently associated with age-related macular degeneration, occurred 3 months after a LASIK procedure on a 64-year old man with hyperopia. Argon laser photocoagulation and subsequent photodynamic therapy were performed and stabilized vision. The second case occurred 3 weeks after LASIK for myopia. The CNV was apparently associated with the myopia. No treatment was recommended and vision stabilized at 20/50. Although the mechanisms are not clear, careful preoperative macular evaluation and attention to symptoms that might herald the presence of CNV are recommended for patients undergoing LASIK.—Hans E. Grossniklaus

Characteristics of corneal ectasia after LASIK for myopia.

There are numerous reports of corneal ectasia after laser in situ keratomileusis (LASIK) for myopia without a consistent definition of this condition or a definitive etiology. We conducted a retrospective analysis of published case reports to describe common characteristics of this postoperative event and compared them with findings from a group of successful LASIK patients. A MEDLINE search for "LASIK" and "ectasia" yielded 21 relevant articles published before May 2003 (n = 86 eyes, 59 patients). A comparison group (n = 103 eyes, 63 patients) was selected from a clinic-based sample of successful LASIK patients with 12 months of follow-up after treatment. Descriptive statistics are reported as median and interquartile range. Comparisons were performed using the Wilcoxon rank sum, Wilcoxon signed rank, and chi-square tests. Time to diagnosis of ectasia after LASIK was 13 months (6 to 20 months). Residual myopia in the ectasia group was -3.69 D (-6.00 to -2.13 D) and was significantly greater than the comparison group, -0.38 D (-0.75 to 0.00 D), P < 0.001. After surgery, eyes with ectasia had increased corneal toricity 2.87 D (2.00 to 4.9 D) with increased oblique astigmatism 1.3 D (0.23 to 2.89 D) relative to eyes in the comparison group 0.00 D (0.00 to 0.08 D), and a loss of 2 lines (-0.5 to -6 lines) of best spectacle-corrected visual acuity (all P < 0.001). Thirty-five percent of reported cases resulted in subsequent corneal transplantation. Preoperative characteristics of corneal ectasia include worse visual acuity, less corneal thickness, greater residual myopia, and greater corneal toricity than nonectatic eyes. Treatment factors associated with corneal ectasia after LASIK are greater stromal ablation and less residual stromal bed thickness. Postoperative characteristics of corneal ectasia are myopic refractive error with increased astigmatism, worse spectacle-corrected visual acuity, increased corneal toricity with topographic abnormality, and progressive corneal thinning.

Nomogram adjustment of laser in situ keratomileusis for myopia and myopic astigmatism with the Alcon LADARVision system.

To evaluate the visual and refractive results of conventional (non-wavefront) laser in situ keratomileusis (LASIK) for treatment of myopia and myopic astigmatism using the Alcon LADARVision 4000 excimer laser system and nomogram adjustment techniques. A retrospective analysis of 499 eyes that had LASIK for myopia and myopic astigmatism was performed. Preoperative manifest spherical equivalent refraction ranged from -0.43 to -6.00 D and preoperative astigmatism ranged from 0 to -4.75 D. Patients were evaluated during 3 months following surgery. One month after surgery, 72% of eyes examined (298/415 eyes) had uncorrected visual acuity (UCVA) of 20/20 or better. Three months after surgery, 83% of eyes examined (216/261 eyes) had UCVA of 20/20 or better. One and three months after surgery, 82% and 83% of eyes, respectively, were within +/-0.50 D of attempted correction; 97% of eyes were within +/-1.00 D at both 1 and 3 months. No eye lost more than 1 line of best spectacle-corrected visual acuity (BSCVA) at 3 months after surgery. At the 3-month examination, 83% of eyes had UCVA better than or equal to preoperative BSCVA. Conventional LASIK to correct myopia and myopic astigmatism was safe and effective using the Alcon LADARVision 4000 excimer laser system. Outcomes were substantially improved throughout development of an accurate nomogram, derived from continually updated regression analysis of previous refractive results.

Contact Lens Management of Keratectasia After Laser In Situ Keratomileusis for Myopia

To present a case in which rigid gas-permeable contact lenses were fit for a patient in whom keratectasia developed after laser in situ keratomileusis (LASIK). Case report. A 21-year-old man underwent bilateral LASIK for myopia and astigmatism. The left eye was only partially corrected because of high myopia and corneal thickness restrictions. Eight months after LASIK, visual acuity was reduced in the right eye; the central cornea had steepened; and pachymetry showed central corneal thinning. Keratectasia was diagnosed, and rigid contact lenses were fitted. Four years later, the patient achieved satisfactory visual acuity and all-day lens wear with minimal complications. The options for management of iatrogenic keratectasia include contact lenses, intracorneal ring segments, and penetrating keratoplasty. This case report shows that rigid contact lenses offer a safe, reversible option for improving visual acuity in such patients by delaying or avoiding the need for further surgical intervention.

Comparison of ablation centration in initial and retreatment active eye-tracker-assisted laser in situ keratomileusis and the effect on visual outcome

Purpose: To evaluate the relationship between initial and retreatment ablation centers in active eye-tracker-assisted myopic laser in situ keratomileusis (LASIK) and determine whether the relationship between the 2 ablation centers influences the visual outcome after retreatment. Setting: Department of Ophthalmology, China Medical University Hospital, Taichung, Taiwan. Methods: This retrospective study comprised 21 eyes of 15 patients who had retreatment at least 3 months after primary myopic LASIK by lifting the initial flap. Corneal topography and best corrected visual acuity (BCVA) were evaluated preoperatively and 3 months postoperatively. The ablation centration was analyzed by corneal topography preoperatively and at 3 months. Results: The mean decentration of the primary treatment was 0.43 mm ± 0.21 (SD) and of the retreatment, 0.34 ± 0.15 mm. There was no significant difference between them ( P = .07). The 2 ablation centers were close each other. The mean distance between the 2 ablation centers was 0.29 ± 0.18 mm and the mean angle between them, 39.7 ± 46.2 degrees. The BCVA was unchanged after retreatment regardless of the relationship between the 2 ablation centers. Conclusions: With an active eye-tracking system, the retreatment center was not only close to the pupil center but also close to the primary ablation center. Regardless of the relationship between the 2 ablation centers, the BCVA did not change if the retreatment ablation was well centered.

Corneal healing after uncomplicated LASIK and its relationship to refractive changes: a six-month prospective confocal study.

To investigate corneal healing and the factor(s) possibly responsible for refractive changes after laser in situ keratomileusis (LASIK). Twenty eyes of 10 patients who underwent LASIK for myopia were examined clinically and by real-time confocal microscopy for 6 months. Epithelial and posterior stromal thicknesses and the thickness of the keratocyte activation zone were measured, and refractive changes were compared with these values. Keratocyte morphology, flap thickness, and subbasal nerve fiber bundle morphology after LASIK were also investigated. No significant change was detected over time in epithelial thickness after LASIK treatment; however, the posterior stromal thickness was found to be significantly higher 1 month after surgery. A slight but statistically significant negative correlation was detected between the thickness of the keratocyte activation zone and the spheroequivalent refraction after LASIK. The subbasal nerve fiber bundle's morphology returned to its preoperative appearance 6 months after LASIK, but in the flap stroma the nerve fiber bundle morphology remained abnormal at 6 months after LASIK surgery. A weak but significant negative correlation between the thickness of the keratocyte activation zone and spheroequivalent refraction was found after LASIK. The different refractive properties of activated keratocytes may be responsible for the myopic shift after LASIK. Further studies are needed to clarify this hypothesis.

Effect of environmental factors on myopic LASIK enhancement rates

Purpose: To determine whether environmental factors affect laser in situ keratomileusis (LASIK) enhancement rates. Setting: Wake Forest University Eye Center, Winston-Salem, North Carolina, USA. Methods: This retrospective chart review comprised 368 consecutive eyes of 191 myopic patients who had LASIK by the same surgeon (K.A.W.). All patients had surgery in 2000 with the Visx Star S2 excimer laser. Refractive outcome, visual acuity, and enhancement rates were monitored closely for 1 year. Fifty-seven eyes (15.5%) had an enhancement procedure. Using enhancement procedure or percentage of correction as the outcome measure, factors that were suspected to affect LASIK results and the need for enhancement were examined; specifically, age, eye, sex, pachymetry, corneal curvature (K), preoperative spherical equivalent, ablation depth, and environmental factors (procedure room temperature, procedure room relative humidity, outdoor temperature, and outdoor relative humidity). Results: Using univariate and multivariate analysis, LASIK enhancement rates strongly correlated with the following variables: procedure room humidity ( P = .003; odds ratio [OR] = 1.093; 95% confidence intervals [CI], 1.030-1.160), 2-week preoperative mean outdoor humidity ( P = .011; OR = 1.054; 95% CI, 1.012-1.096), outdoor temperature ( P = .0059; OR = 1.039; 95% CI, 1.011-1.068), and age ( P = .0497; OR = 1.034; 95% CI, 1.001-1.070). The percentage of correction strongly correlated with the following variables: procedure room humidity ( P = .021), 2-week preoperative mean outdoor humidity ( P = .001), outdoor temperature ( P = .0052), and room temperature ( P = .017). Conclusions: The 2-week-preoperative mean outdoor relative humidity, procedure room relative humidity, outdoor temperature, and procedure room temperature may have to be considered during LASIK planning. The effect of these environmental variables on LASIK outcomes warrants further evaluation.

Differences between Regressive Eyes and Non-Regressive Eyes after LASIK for Myopia in the Time Course of Corneal Changes Assessed with the Orbscan

The aim of this study was to compare regressive eyes with non-regressive eyes after laser in situ keratomileusis (LASIK) for myopia with regard to the time course of biomechanical changes of the cornea and to evaluate the possible roles of these changes in refractive regression following surgery. 15 eyes of 9 patients with refractive regression and 15 eyes of 11 patients with no refractive regression after LASIK for myopia were enrolled in this study. The time courses of central corneal thickness (CCT) and anterior/posterior corneal curvature radiuses (CCR) were measured with Orbscan slit scanning before and 1 week, 1 month and 3 months after LASIK for myopia. The regressive and non-regressive eyes had similar time courses of CCT before and after LASIK, whereas the 2 groups differed in the time courses of corneal shifting movements. In the regression group, the posterior CCR after LASIK was relatively stable (all p > 0.05). By contrast, in the non-regression group, the postoperative posterior CCR at week 1 had a significantly steeper curvature than that at month 3 (p = 0.000). The anterior CCR in the regression group at week 1 had a significantly flatter curvature than that at month 3 (p = 0.002) postoperatively. In contrast, there was no significant change of anterior CCR postoperatively (all p > 0.05) in the non-regression group. Taken together, these data suggest that refractive regression after LASIK might be mainly induced by corneal protrusion rather than central corneal thickening.

Reduction of pupil size and halos with minus lenses after laser in situ keratomileusis.

To evaluate the amount of miosis induced by over-minused lenses and to assess subjective reduction of halos following laser in situ keratomileusis (LASIK) with such lenses. Part I: Infrared pupil diameter was assessed in 14 patients who had not had ocular surgery. The accommodative/miotic reflex was stimulated with concave trial lenses in -1.00-D increments up to -4.00 D while viewing the 20/40 acuity line. Part II. Subjective halos around a distant light were assessed in 14 patients following LASIK for myopia, with and without a -1.00-D lens over manifest refraction. Part I: 100%, 79%, and 64% of patients clearly saw the 20/40 line with a -1.00-D lens, -2.00-D lens, and -3.00/-4.00-D lens, respectively. Mean pupil diameter decreased by 0.2 mm with the -1.00-D lens (P = .02), 0.5 mm with the -2.00-D lens (P = .003), 0.9 mm with the -3.00-D lens (P = .008,), and 1.1 mm with the -4.00-D lens (P = .008). Part II: 11 of 14 patients (79%) noticed a decrease in the size of the halo (30% average reduction) when over-minused by -1.00 D. Pupil diameters and halos decreased with a -1.00-D overcorrection in patients following LASIK. Patients with pupil-dependent night halos after LASIK may benefit from mildly over-minused lenses.

Influence of intraoperative epithelial defects on outcomes in LASIK for myopia

PurposeInternet Advance publication at ajo.com August 28, 2003. To evaluate whether intraoperative epithelial defects have an adverse effect on achieving desired refractive outcomes following laser in situ keratomileusis (LASIK) for myopia. DesignObservational retrospective case control study. MethodsThirty eyes that had intraoperative epithelial defects on the LASIK flap were compared with 60 randomly selected control eyes, matched for age, preoperative spherical equivalent, and preoperative cylinder, that had no intraoperative epithelial defects. Preoperative and postoperative clinical data were compared between the two groups. Statistical analyses were performed using analysis of means, analysis of variance, and the Student t test. Comparison variables included preoperative spherical equivalent, 3-month postoperative best-corrected visual acuity, attempted correction, amount of undercorrection at 3 months postoperatively, and whether LASIK enhancement was performed at 3 months postoperatively. ResultsEyes with intraoperative epithelial defects showed more undercorrection at 3 months (P = .005), were more likely to have lost lines of visual acuity (P = .003), and underwent more enhancement procedures at 3 months (P = .004) compared with control eyes. ConclusionsIntraoperative epithelial defects during LASIK predispose eyes to increased wound healing, leading to myopic regression, irregular wound healing with loss of visual acuity, and increased need for enhancement procedures.

Evaluation of intraocular pressure change after laser in situ keratomileusis using the pressure phosphene tonometer

Purpose: To evaluate the applicability of pressure phosphene tonometry in measuring intraocular pressure (IOP) after laser in situ keratomileusis (LASIK). Setting: Baptist Eye Clinic, Kyoto, Japan. Methods: Thirty-six eyes of 22 consecutive patients who had had LASIK for myopia were enrolled in this prospective comparative study. The mean age of the patients was 32.6 years ± 9.0 (SD). The IOP was measured using the pressure phosphene tonometer (FPT), Goldmann applanation tonometry (GAT), and noncontact tonometry (NCT). The patients themselves took measurements with the FPT before and 1 week after surgery. One-way analysis of variance followed by a Bonferroni/Dunn multiple comparison post hoc test was administered to compare the preoperative and postoperative measurements with each tonometer. These data were represented graphically using a method described by Bland and Altman. The relationship between each tonometric change and the central corneal thickness (CCT) or keratometry (K) changes after LASIK were evaluated with by Pearson correlation coefficient. Results: Statistically significant differences were found between preoperative and postoperative measurements with GAT and NCT but not with FPT. Preoperative and postoperative FPT readings conformed to the British Standard for reproducibility of a standard test method for IOP estimation. No significant correlation between FPT changes and CCT or K changes was found. Conclusions: Pressure phosphene tonometry measures IOP through the upper eyelid, and changes in corneal shape do not appear to have an effect on the IOP. The IOP measurements with FPT were constant before and after LASIK.

Optische Online-Pachymetrie bei Laser-in-situ-Keratomileusis

Currently the microkeratome incision and the ablation depth are unpredictable in laser in situ keratomileusis (LASIK). Online optical coherence pachymetry is a high-resolution and non-contact method, which enables the corneal thickness changes to be monitored intraoperatively. METHOD. In 12 patients undergoing myopic LASIK, online optical coherence pachymetry with a wavelength of 1310 nm and a measurement frequency of 74 Hz was studied. The central corneal thickness changes were determined continuously. Online optical coherence pachymetry enabled intraoperative visualization and assessment of the central corneal thickness, the flap thickness after the microkeratome pass, the time-resolved ablation and the residual stromal thickness. Intraoperatively the mean flap thickness was 113+/-31 microm and the residual stromal thickness was 277+/-49 microm. The optically determined ablation depth was 116+/-30 micro m, which corresponded to 33 microm higher mean values than the nominal ablation depth. Online optical coherence pachymetry enabled the flap and residual stromal thickness to be measured intraoperatively. Also the individual ablation depth and possible dehydration effects of the cornea were monitored continuously. Thus, online optical coherence pachymetry could contribute to improve the safety standards during LASIK.

Binocular vision impairment after refractive surgery

Purpose: To illustrate the need for an accurate preoperative orthoptic examination to prevent postoperative changes in binocular vision. Setting: Department of Ophthalmology, University Hospital Antwerp, Edegem, Belgium. Methods: Five patients presenting major subjective complaints after refractive surgery were analyzed. Results: In 1 patient, a latent N IV palsy decompensated after laser in situ keratomileusis (LASIK) in the more myopic eye to achieve monovision. A second patient, operated on for N IV palsy 10 years earlier, presented a recurrence of the palsy after bilateral LASIK for myopia. The third patient complained of discomfort in binocular vision caused by aggravation of a preexisting intermittent esotropia that worsened after LASIK for hyperopia. The fourth patient complained of diplopia after LASIK in the highly anisometropic and exotropic eye. The fifth patient experienced a decrease in fusion and stereopsis at the time he became anisometropic after bilateral LASIK. Conclusions: Special care should be taken of patients who have a preoperative history of strabismus surgery, an overcorrection or undercorrection in 1 or both eyes, or anisometropia and of those who are unhappy with contact lenses. An orthoptic examination should be done with and without spectacle correction to detect underlying vertical phorias. Intended monovision should be examined initially using contact lenses.

Evaluation of the tear film stability after laser in situ keratomileusis using the tear film stability analysis system

Purpose To evaluate the tear film stability of patients before and after laser in situ keratomileusis (LASIK) using the tear film stability analysis system (TSAS). Design Prospective observational case series. Methods New videokeratography software for a topographic modeling system (TMS-2N) was developed that can automatically capture consecutive corneal surface images every second for 10 seconds. Thirty-four subjects (64 eyes) who underwent myopia LASIK were enrolled in this study. All subjects were examined with the new system before LASIK and at 1 week, 1 month, 3 months, and 6 months after the surgery. Corneal topographs were analyzed for tear breakup time (TMS breakup time) and breakup area (TMS breakup area). Based on pre-LASIK TSAS analysis, subjects were separated into normal and abnormal TSAS value groups. The criteria for the normal group were either TMS breakup time more than 5 seconds or TMS breakup area less than 0.2. The percentage of the occurrence of superficial punctuate keratitis was compared between the two groups with regard to subject's dry eye signs and symptoms. Results Tear film stability decreased significantly during the early period after LASIK, as indexed by decreased TMS breakup time and increased TMS breakup area. Tear film instability resolved at 6 months after surgery. Before LASIK, 22 subjects (43 eyes) had normal TSAS evaluation and 12 subjects (21 eyes) were abnormal. After LASIK, among normal TSAS value eyes, 8 of 43 (18.6%) eyes developed superficial punctuate keratitis. In sharp contrast, 14 of 21 (66.7%) eyes in the abnormal group displayed superficial punctuate keratitis, correlating well with the patients' dry eye symptoms. The difference in the presence of superficial punctuate keratitis after LASIK between normal and abnormal TSAS value groups was statistically significant ( P < .001). Subjects with abnormal TSAS evaluation also displayed resistance to dry eye treatment and had extended period of recovery. Conclusions Tear film stability analysis can be a useful means for screening LASIK candidates before surgery and for prognosticating dry eye symptoms thereafter.

Comparison of LADARVision and Visx Star S3 laser in situ keratomileusis outcomes in myopia and hyperopia

Purpose: To compare visual outcomes with 2 commonly used excimer lasers, the Autonomous LADARVision (LV) (Alcon Laboratories Inc.) and the Visx Star S3 (S3), in the performance of myopic and hyperopic astigmatic laser in situ keratomileusis (LASIK). Setting: Zale Lipshy University Hospital Laser Center for Vision, University of Texas Southwestern Medical Center, Dallas, Texas, USA. Methods: In this retrospective single-center 3-surgeon cohort comparison, 100 consecutive LV-treated myopic eyes with a mean manifest refraction spherical equivalent (MRSE) of –3.22 diopters (D) (range 0 to –6.00 D) (mean astigmatism 0.95 D [range 0 to 4.00 D]) were compared with 100 consecutive S3-treated eyes with a similar MRSE (mean MRSE –3.19 D; mean astigmatism 0.66 D [range 0 to 2.75 D]). Forty-one consecutive LV-treated hyperopic eyes with a mean MRSE of +2.59 D (range +1.00 to +6.00 D) (mean astigmatism 0.89 D [range 0 to 3.50 D]) were compared with 25 consecutive S3-treated eyes with a similar MRSE (mean MRSE +2.70 D; mean astigmatism 0.87 D [range 0 to 2.75 D]). The following outcomes were compared: uncorrected visual acuity, refractive predictability and stability, gain or loss of best spectacle-corrected visual acuity, and need for enhancement. Results: Statistically significant differences in outcomes were found between lasers in the treatment of hyperopia and hyperopic astigmatism. No outcome differences between lasers were found in the treatment of myopia and myopic astigmatism. Conclusion: The LV and S3 lasers yielded equivalent results in myopic LASIK between 0 and −6.00 D; however, the LADARVision yielded statistically significantly better results in hyperopic LASIK between +1.00 and +6.00 D.