[Clinical analysis of complications of LASIK using the WaveLight FS200 femtosecond laser].

OBJECTIVE: To explore the incidence of intraoperative and early postoperative complications associated with the WaveLight FS200 femtosecond laser-assisted flap creation in LASIK surgery. METHODS: A consecutive series of 400 patients (786 eyes) who underwent LASIK using the WaveLight FS200 femtosecond laser from March 2011 to December 2012 were included in this retrospective study. Intraoperative and early postoperative complications were described and analyzed. RESULTS: The intraoperative complications included suction loss (two eyes, 0.25%), incomplete flap creation (one eye, 0.13%), severe opaque bubble layers (three eyes, 0.38%), anterior chamber gas bubbles (eight eyes, 1.02%), skip lines (12 eyes, 1.53%), and corneal epithelial defects (eight eyes, 1.02%). The early postoperative complications included canal bleeding (eight eyes, 1.02%), diffuse lamellar keratitis (23 eyes, 2.93%), haze (six eyes, 0.76% ), and flap dislocation (one eye, 0.13% ). CONCLUSIONS: Intraoperative and early postoperative complications of LASIK using the WaveLight FS200 were relatively mild. All patients could obtain satisfactory clinical results with proper treatment.

[Intraocular pressure, ocular blood flow, and corneal biomechanics changes after LASIK surgery for myopia]. / Vliyanie operatsii LASIK pri miopii na pokazateli oftal'motonusa, ob''emnogo glaznogo krovotoka i «biomekhaniki¼ rogovitsy.

AIM: to study changes in intraocular pressure (IOP), volumetric ocular blood flow (OBF) rate, and biomechanical properties of the cornea after excimer laser ablation in patients with myopia of different degrees. MATERIAL AND METHODS: A total of 16 patients (32 eyes) with myopia ranging from 2.75 to 9.0 D were examined before and after LASIK. Ocular Blood Flow Analyzer (OBFA) was used to measure IOP and OBF as well as pulse amplitude and volume. Ocular Response Analyzer (ORA) was also employed to provide the following data: Goldmann-equivalent IOP, corneal compensated IOP, corneal hysteresis, and corneal resistance factor. The eyes were then divided into two groups: group 1 - 15 eyes with less than 70-µm deep ablation of the cornea and group 2 - 17 eyes with more than 70-µm deep ablation. RESULTS: Group 1 demonstrated a statistically reliable decrease in IOP values provided by either method and biomechanical parameters of the cornea (p<0.005), but no difference in pre- and postoperative OBF, or pulse amplitude, or pulse volume (p>0.05). In group 2, all the parameters changed reliably, except for the pulse volume (p>0.05). In particular, a decrease was recorded for IOP (with no dependence to the method of measurement; p<0.001), pulse amplitude (p<0.01), corneal hysteresis (p<0.001), and corneal resistance factor (p<0.001); an increase - for OBF (p<0.05). CONCLUSION: One should allow for possible mismeasurement of IOP and OBF as well as biomechanical parameters of the cornea in post-LASIK patients, keeping in mind that the extent of error depends on the depth of ablation. Shallow ablation (no more than 70-µm deep) has no statistically significant effect on OBF readings, while IOP seems to decrease considerably. In deep ablation (more than 70-µm deep), both parameters are reliably lower than at baseline.

Sources of medical error in refractive surgery.

PURPOSE: To evaluate the causes of laser programming errors in refractive surgery and outcomes in these cases. METHODS: In this multicenter, retrospective chart review, 22 eyes of 18 patients who had incorrect data entered into the refractive laser computer system at the time of treatment were evaluated. Cases were analyzed to uncover the etiology of these errors, patient follow-up treatments, and final outcomes. The results were used to identify potential methods to avoid similar errors in the future. RESULTS: Every patient experienced compromised uncorrected visual acuity requiring additional intervention, and 7 of 22 eyes (32%) lost corrected distance visual acuity (CDVA) of at least one line. Sixteen patients were suitable candidates for additional surgical correction to address these residual visual symptoms and six were not. Thirteen of 22 eyes (59%) received surgical follow-up treatment; nine eyes were treated with contact lenses. After follow-up treatment, six patients (27%) still had a loss of one line or more of CDVA. Three significant sources of error were identified: errors of cylinder conversion, data entry, and patient identification error. CONCLUSION: Twenty-seven percent of eyes with laser programming errors ultimately lost one or more lines of CDVA. Patients who underwent surgical revision had better outcomes than those who did not. Many of the mistakes identified were likely avoidable had preventive measures been taken, such as strict adherence to patient verification protocol or rigorous rechecking of treatment parameters.

Moving from a mechanical microkeratome to a femtosecond laser for LASIK to correct astigmatic patients: clinical outcomes of a retrospective, consecutive, comparative study.

BACKGROUND: To evaluate outcomes after optimized laser in situ keratomileusis (LASIK) for astigmatism correction with flap created by a mechanical microkeratome or a femtosecond laser. PATIENTS AND METHODS: In this retrospective study, a total of 102 eyes of 71 consecutive patients were enrolled undergoing optimized LASIK treatments using the Allegretto laser system (WaveLight Laser Technologie AG, Erlangen, Germany). A mechanical microkeratome for flap creation was used (One Use, Moria®) in 46 eyes (31 patients, spherical equivalent [SE] -4.44 D ± 2.4) and a femtosecond laser was used (LDV, Ziemer®) in 56 eyes (40 patients, spherical equivalent [SE] -3.07 D ± 3.3). The two groups were matched for inclusion criteria and were operated under similar conditions by the same surgeon. RESULTS: Overall, the preoperative spherical equivalent was -9.5 diopters (D) to +3.37 D; the preoperative manifest astigmatism was between -1.5 D and -3.5 D. At 6 months postoperatively, the mean postoperative uncorrected distance visual acuity (UDVA) was 0.93 ± 0.17 (range 0.4 to 1.2) in the Moria group and 1.0 ± 0.21 (range 0.6 to 1.6) in the Femto group, which was statistically significant (p = 0.003). Comparing the cylinder power there was a statistical difference between the two groups (p = 0.0015). CONCLUSIONS: This study shows that the method of flap creation has a significant impact on postoperative astigmatism with a significantly better postoperative UDVA in the Femto group. These findings suggest that the femtosecond laser provides a better platform for LASIK treatment of astigmatism than the commonly used microkeratome.

Does doctors' experience matter in LASIK surgeries?

In this article, we use a longitudinal census of laser in situ keratomileusis (LASIK) eye surgeries collected directly from patient charts to examine the learning-by-doing hypothesis in medicine. LASIK surgery has precise measures of presurgical condition and postsurgical outcomes. Unlike other types of surgery, the impact of unobservable underlying patient conditions on outcomes is minimal. Individual learning by doing is identified through observations of surgical outcomes over time, based on the cumulative number of surgeries performed. Collective learning is identified separately, through changes in a group adjustment rule determined jointly by all the surgeons in a structured internal review process. Our unique data set overcomes some of the measurement problems in patient outcomes encountered in other studies and improves the possibility of identifying and separating the impact of learning by doing from other effects. We cannot conclude that the outcome of LASIK surgery improves as an individual surgeon's experience increases, but we find strong evidence that experience accumulated by surgeons as a group in a clinic significantly improves outcomes.

Patient-specific modeling of corneal refractive surgery outcomes and inverse estimation of elastic property changes.

The purpose of this study is to develop a 3D patient-specific finite element model (FEM) of the cornea and sclera to compare predicted and in vivo refractive outcomes and to estimate the corneal elastic property changes associated with each procedure. Both eyes of a patient who underwent laser-assisted in situ keratomileusis (LASIK) for myopic astigmatism were modeled. Pre- and postoperative Scheimpflug anterior and posterior corneal elevation maps were imported into a 3D corneo-scleral FEM with an unrestrained limbus. Preoperative corneal hyperelastic properties were chosen to account for meridional anisotropy. Inverse FEM was used to determine the undeformed corneal state that produced <0.1% error in anterior elevation between simulated and in vivo preoperative geometries. Case-specific 3D aspheric ablation profiles were simulated, and corneal topography and spherical aberration were compared at clinical intraocular pressure. The magnitude of elastic weakening of the residual corneal bed required to maximize the agreement with clinical axial power was calculated and compared with the changes in ocular response analyzer (ORA) measurements. The models produced curvature maps and spherical aberrations equivalent to in vivo measurements. For the preoperative property values used in this study, predicted elastic weakening with LASIK was as high as 55% for a radially uniform model of residual corneal weakening and 65% at the point of maximum ablation in a spatially varying model of weakening. Reductions in ORA variables were also observed. A patient-specific FEM of corneal refractive surgery is presented, which allows the estimation of surgically induced changes in corneal elastic properties. Significant elastic weakening after LASIK was required to replicate clinical topographic outcomes in this two-eye pilot study.

[Infectious keratitis after LASIK--update and survey of the literature]. / Infektiöse Keratitis nach LASIK--aktueller Stand und Literaturübersicht.

LASIK has become the preferred surgical procedure for the correction of refractive errors. Microbial keratitis is a rare but severe complication. The incidence of post-LASIK keratitis, (uni- and bilateral) is difficult to estimate. The risk of bilateral infection could until now only be approximated by calculating it from the risk of unilateral infection. Due to the fortunately low incidence of post-LASIK keratitis, large-scale studies are necessary to obtain valid statistical data. The American Society of Cataract and Refractive surgery (ASCRS) developed a post-LASIK infectious keratitis survey in 2001. 116 post-LASIK infections were reported by the members of the society. The calculated incidence was 0.035 % or 1 infection in every 2919 procedures. Llovet et al. found 9 patients (18 eyes) with bilateral post-LASIK keratitis out of 204 586 procedures (incidence 0.0084 %). Gram-positive bacteria and atypical mycobacteria are the most common causes for microbial post-LASIK keratitis. There is an increasing literature of post-LASIK case reports caused by rare or atypical species. Severe cases of keratitis are more often correlated with a prolonged onset of infection and caused by atypical species. An overview of the current literature and our own data regarding post-LASIK keratitis (uni-, and bilateral) are presented.

Long-term assessment of visual and refractive outcomes of laser in situ keratomileusis for hyperopia using the AMARIS® 750S Excimer laser.

PURPOSE: To evaluate the long-term efficacy and safety of hyperopic laser in situ keratomileusis (LASIK) using the AMARIS® 750S (Schwind, Eye-tech-solutions, GmbH) excimer laser. METHODS: The medical records of one hundred eleven eyes of 62 patients who underwent LASIK for hyperopia using the AMARIS® 750S excimer laser were reviewed retrospectively. Patients were divided into three groups based on preoperative spherical equivalent (SE) refraction: low hyperopia (less than +2.50 diopters [D]), moderate hyperopia (+2.75D to +4.00D), and high hyperopia (over +4.00D). Uncorrected and best corrected visual acuity (BCVA), long-term stability of refraction, and complications were evaluated. RESULTS: Of the entire sample, the mean preoperative SE was +3.64D±1.22D. The mean age was 37.4±11.2 years (20-59). The mean follow-up for all eyes was 51 months. At the last visit, the mean SE was +0.85D±0.34D (SD) in the low hyperopia group, +1.09D±0.43D in the moderate hyperopia group, and +1.63D±0.47D in the high hyperopia group. (+1.15D±0.49D overall). Preoperative uncorrected visual acuity (UCVA) was 0.52±0.34 logMAR and increased to 0.18±0.15 logMAR at 4 years follow-up (P<0.01). There was no statistically significant difference between preoperative and postoperative BCVA. The UCVA was 0.30 logMAR or better in 100% of eyes in the low hyperopia group, 93.7% in the moderate hyperopia group, and 69.9% in the high hyperopia group (%89.2 overall). CONCLUSIONS: LASIK is safe and effective for correcting hyperopia in the short term; however, the efficacy of the procedure is limited in the patients with high hyperopia and longer follow-up.

Long-Term Outcomes of Refractive Surgery Performed During the Military.

INTRODUCTION: To evaluate the long-term refractive results of laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) performed by the military in a veteran population. MATERIALS AND METHODS: Three Department of Veterans Affairs (VA) hospital sites (Puget Sound, Buffalo, and Washington D.C.) obtained IRB approval for this multi-center study. Comprehensive ophthalmologic assessment including refraction and keratometry were obtained at the time of the long-term VA examination and compared to the patients' postoperative military records. RESULTS: Eighty patients (160 eyes) enrolled in this study. At the time of treatment, patients were 21-52 years of age. Long-term post-operative data was available from 4 to 17 years post-operatively. Fifteen percent of the treatment types were LASIK and 85% PRK. At the time of their military post-operative exam (range 3-14 months, mean 4 months), 82% of patients had uncorrected visual acuity (UCVA) of 20/20 or better, and their average manifest refraction was -0.08 D (SD ± 0.48 D). At the time of the long-term ophthalmological exam at the VA medical centers (range 4-11 years, mean of 8.2 years), 49% of patients had an UCVA of 20/20 or better and an average manifest refraction was -0.64 D (SD ± 0.69 D). CONCLUSION: This is the first long-term study evaluating refractive surgery outcomes up to 17 years in a military population. Our study demonstrates safety after refractive surgery in the military with less than 0.1D increase in myopia per year and strong keratometric stability. Other changes in the eye may be the likely cause for this observed mild refractive shift.

Citation analysis of the most influential authors and ophthalmology journals in the field of cataract and corneal refractive surgery 2000-2004.

PURPOSE: To identify the most published authors on the topics of 'cataract' and 'LASIK', the journals in which they publish, and the citation patterns of the most-cited articles by these authors over a 5-year publication period. METHODS: Science Citation Index Expanded (SCI) was used to identify the 30 most-published authors in 'cataract' and 'laser in situ keratomileusis' (LASIK) (2000-2004 inclusive). SCI was subsequently used to analyse the recorded articles for each author in terms of source journal, the most commonly cited articles and citation source. RESULTS: Of the 30 most-published authors in the fields of cataract and LASIK, the USA was the most well-represented source country, accounting for 33%; 20% were from Australia, and 17% from Austria. Germany and Japan each contributed 7%. Eighty per cent of the publications produced by these 30 authors (2000-2004) were in 10 journals, of which the Journal of Cataract and Refractive Surgery (JCRS) published more than one-third. Of the three most-cited articles for each author, the greatest number were published in JCRS (35.6%). The citation count of the articles had a weak correlation to the journal impact factor of the source journal; however, the self-citation rate of these articles did not. CONCLUSIONS: The USA and Australia together were the source of more than half of the most-published authors on cataract and LASIK and the majority of articles published by the 30 most prolific authors were published in only 10 journals. The impact factors of the publication journals preferred by these authors are influenced by the article citation counts, not vice versa.

The fourth New Zealand cataract and refractive surgery survey: 2007.

BACKGROUND: To examine the current practice and changing trends for cataract and refractive surgery in New Zealand (NZ) between 1997 and 2007. METHODS: A self-administered confidential postal questionnaire was sent to all consultant ophthalmologists practising in NZ in 2007, eliciting surgical volumes and technique, anaesthetic, preferred equipment and patient management. Results were compared with previous NZ surveys and international surveys of surgeons in Northern America, Europe and the UK. RESULTS: From the 113 ophthalmologists surveyed 88% responded, comprising 86 cataract surgeons and 20 refractive surgeons. Key findings for cataract surgeons were: 65% routinely used sub-Tenon's anaesthetic, 20% topical anaesthetic, 24% favoured intracameral antibiotics, 88% operated via clear corneal or anterior limbal incisions and 61% used temporal incisions. Acrylic foldable intraocular lenses (IOLs) were preferred, 27% of surgeons routinely used aspheric IOLs, 31% used presbyopia-correcting IOLs and 63% expressed high interest in toric IOLs. Of the refractive surgeons, 83% would perform bilateral LASIK at the same surgical event; phakic IOL was the treatment of choice for 30-year-old -12D myopes, and clear lens exchange for 45-year-old +5D hyperopes. CONCLUSIONS: The majority of NZ cataract surgical practice remains comparable with results from international surveys. A notable exception, as in previous comparisons, is a lower use of topical anaesthetic in NZ with a higher use of sub-Tenon's anaesthetic instead. Refractive surgery practice in NZ is generally comparable with that of American Society of Cataract and Refractive Surgery members.

An interval-censored model for predicting myopic regression after laser in situ keratomileusis.

PURPOSE: A time-varying statistical model was proposed to predict the risk of regression toward myopia after laser in situ keratomileusis (LASIK) and to identify significant predictors within a time frame. METHODS: A total of 615 eyes of 311 patients derived from a retrospective cohort who underwent LASIK in 2003 were analyzed. Refraction outcomes were recorded at 1 day, 1 week, and 1, 3, 6, 9, and 12 months or longer after LASIK. A cross-validated design was used, to split data into trained (n = 308) and validated (n = 307) data sets. These data sets were used in an interval-censored model to predict the probability of regression toward myopia and to assess the predictors including demographic features and preoperative and postoperative variables. RESULTS: Myopia regression was observed in 164 (26.7%) of 615 eyes during the follow-up period of 12 months or longer after LASIK. Significant predictors for myopia regression after LASIK included preoperative manifest spherical equivalent (P = <0.0001), mean preoperative central corneal curvature (P = 0.001), size of optic zone (P = 0.0043), undercorrection (P = 0.04), and age (P = 0.0734). The risk of regression toward myopia after LASIK increased rapidly within 1 month, slowed down between 1 and 6 months, and became steady after 6 months, regardless of risk group. The risk of myopia regression up to 6 months after LASIK was 21% in average-risk eyes (based on all eyes). CONCLUSIONS: The proposed interval-censored model was useful not only for predicting the probability of myopia regression after LASIK but also for identifying the evolution of patients within low, moderate, and high-risk groups.

[Evaluation of vision quality after laser vision correction in healthcare professionals]. / Évaluation de la qualité de vision après chirurgie réfractive au laser chez les professionnels de santé.

PURPOSE: Healthcare professionals require good quality of vision. The main objective of this study is to evaluate the satisfaction and vision quality after laser vision correction in healthcare professionals. METHODS: This is a monocentric retrospective study. An online 25-question survey was sent to ametropic physicians, surgeons and nurses who underwent corneal refractive surgery with laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) between July 2012 and February 2016. Questionnaire responses were recorded anonymously by the internet survey site. These patients' pre- and postoperative data were analyzed. RESULTS: In total, 2491 laser vision corrections were performed during this time frame. One hundred and fifty-eight patients were healthcare providers; 131 received the survey, and 111 responded. Ninety-nine were surgeons, 60 were medical physicians, and 32 were nurses. Ninety-one percent reported that they were satisfied with their postoperative vision quality, 63.9% even reported an improvement in their quality of vision compared with their corrected preoperative vision, 92.8% reported that they would have the procedure again, and 94.6% would recommend the procedure to a family member or a patient. Visual outcomes showed high levels of efficacy and predictability. CONCLUSION: While healthcare professionals require good quality of vision, those who had undergone laser vision correction reported the same satisfaction as the general population and would recommend the procedure to their family, friends and patients.

Dry Eye after Small Incision Lenticule Extraction (SMILE) versus Femtosecond Laser-Assisted in Situ Keratomileusis (FS-LASIK) for Myopia: A Meta-Analysis.

PURPOSE: To compare dry eye after small incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK (FS-LASIK) for correcting myopia. METHODS: CENTRAL, Embase and PubMed were searched in November 2016. All randomized controlled trials (RCTs) and prospective cohorts that compared dry eye after SMILE with FS-LASIK were selected. RESULTS: Five cohorts and one RCT were identified for comparing dry eye after SMILE (291 eyes) and FS-LASIK (277 eyes). The pooled results revealed that the SMILE and FS-LASIK groups did not differ significantly in terms of Schirmer's I test (SIT) and tear film osmolarity (TFO) at any postoperative visits. By contrast, tear break up time (TBUT; p = 0.04 for one month, p < 0.001 for three months, and p = 0.02 for six months) and ocular surface disease index (OSDI; p < 0.001 for one month and three months, and p = 0.006 for six months) were significantly worse in the FS-LASIK group than in the SMILE group at follow-up. At six months postoperatively, TBUT and TFO values in both the SMILE and FS-LASIK groups and OSDI scores in the SMILE group returned to preoperative levels, but SIT values in both groups (p = 0.02 for the SMILE group and p < 0.001 for the FS-LASIK group) and OSDI in the FS-LASIK group (p < 0.001) were still statistically impaired. CONCLUSION: Dry eye after both SMILE and FS-LASIK usually occurs transiently. SMILE does not show obvious superiority over FS-LASIK by exhibiting similar and acceptable objective parameters, and SMILE may have milder subjective symptoms.

Diffuse lamellar keratitis complicating laser in situ keratomileusis: post-marketing surveillance of an emerging disease in British Columbia, Canada, 2000-2002.

PURPOSE: To describe a surveillance system and summarize data between January 2000 and December 2002 regarding diffuse lamellar keratitis (DLK), a complication of laser in situ keratomileusis (LASIK) surgery. SETTING: Community-based clinics in British Columbia, Canada, in which LASIK surgery is performed. METHODS: Monthly, all clinics in which LASIK is performed reported the number of LASIK procedures and nonnominal cases of DLK (by grade and onset date) to the British Columbia Centre for Disease Control. Diffuse lamellar keratitis outbreaks were investigated, and prevention and control measures were recommended. RESULTS: From 2000 to 2002, approximately 72,000 LASIK procedures were performed, with a mean DLK incidence rate of 0.67% (95% confidence interval, 0.61-0.73). The overall proportion of DLK cases attributed to outbreaks was 64%, decreasing from 72% in 2000 to 40% in 2003. CONCLUSIONS: An effective DLK surveillance program was implemented at all laser refractive clinics in British Columbia. Reported DLK incidence was 0.67 cases per 100 procedures, with 64% occurring in outbreaks.

Refractive Surgery Survey 2004.

To determine the refractive surgery (RS) preferences of ophthalmologists worldwide, questionnaires were sent to 8897 members of the American Society of Cataract and Refractive Surgery. A total of 1053 questionnaires were returned by the deadline. The practice distribution included 29.5% cataract surgeons, 48.8% comprehensive ophthalmologists, 11.6% RS specialists, 5.1% cornea and external disease specialists, 1.9% glaucoma specialists, 1.1% retina specialists, and <1.0% oculoplastics/pediatrics/researchers/retired. Results were compared with those in the 2003 survey and demonstrate that refractive surgery continues to develop and change.

Corneal characteristics in myopic patients.

OBJECTIVES: To evaluate the characteristics of the cornea in myopic patients. MATERIAL AND METHOD: A retrospective study of 420 eyes in 210 patients who visited the Excimer Laser Surgery Clinic at Siriraj Hospital, Mahidol University from January 1999 to June 2002 was conducted. All cases that were eligible for myopic refractive surgery were included in the present study. A preoperative ocular examination was done in a fashionable method, including manifest refraction and Orbscan Topography to evaluate corneal thickness, corneal curvature and corneal diameter Statistical analysis was performed to identify the characteristics of the cornea in the patients. RESULTS: The mean age of the patients was 31.66 +/- 7.77 years. (ranging from 16-51). The mean manifest refraction (spherical equivalent) was -4.9 +/- 2.29 diopters (ranging from -0.50 to -13.75). The mean corneal diameter (white to white) was 11.60 mm +/- 0.37 mm (ranging from 10.8-12.9). The thinnest point of the cornea varied from 409 to 597 microns (mean = 522.55) and located mostly in the infero-temporal quadrant of the eye (23.69% in the right and 32.05% in the left). The mean curvature of the corneal was 44.6 +/- 13.8 diopters (ranging from 39.05-47.65). The mean corneal astigmatism was 1.34 +/- 0.71 diopters and 93.96% were with the rule astigmatism. Positive angle kappa was found in 408 eyes (97%) but all cases were within a 0.5 mm horizontal and 0.3 mm vertical radius from the pupillary axis. CONCLUSION: Characteristics of the cornea in Thai myopic patients were demonstrated in the present study. Most of the cornea showed with the rule astigmatism with positive angle kappa and the thinnest point, located at the infero-temporal quadrant.

[First Brazilian refractive surgery survey]. / Primeiro censo brasileiro em cirurgia refrativa.

PURPOSE: To perform the first Brazilian refractive surgery survey. METHODS: Between August 2001 and February 2002, a questionnaire was mailed to 7890 Brazilian ophthalmologists. The questionnaire presented questions about demographic aspects, technology, instruments, market, trends, practice patterns and cost of refractive surgery. RESULTS: Nine hundred and twenty questionnaires (11.67%) were answered. LASIK is the preferred technique for correction between +5.00 and -7.00 D. The mostly used excimer laser is Nidek EC 5000, and Hansatome is the mostly used microkeratome. Others aspects like: demographic, techniques, practice patterns, trends, market, and pre-, intra- and postoperative care, were analyzed. CONCLUSION: With this survey, the Brazilian ophthalmologists can observe and monitor these aspects of refractive surgery in Brazil, and compare them with others surveys.

Multiple regression and vector analyses of laser in situ keratomileusis for myopia and astigmatism.

PURPOSE: To construct a quantitative model relating refractive results to laser settings and other factors. METHODS: A prospective clinical trial was performed, including 14 surgeons and 523 eyes of 278 patients who desired correction of myopia from -1.00 to -16.00 D (mean, -6.20 D) and astigmatism up to 6.00 D (mean, 1.10 D). Myopia and astigmatism were corrected by laser in situ keratomileusis (LASIK) with sequential spherical and cylindrical ablations using a 5.5-mm ablation zone and a transition zone to 7.0 mm. The Nidek EC-5000 excimer laser and the Chiron Automated Corneal Shaper were used. RESULTS: Surgically induced refractive changes 3 months after surgery were measured. Spherical ablation by LASIK produced a 19% greater refractive change than that predicted by the Nidek PRK algorithm. The laser setting needed to achieve each 1.00 D of cylinder correction induced 1.30 D change in spherical equivalent refraction (0.80 D more than expected). Patient age and nonlinear effects had small but statistically significant influences on refractive outcome. Sex, left/right eye, and surgeon were not significant factors. Residual variations in spherical equivalent refraction included a 0.50-D constant plus 9% of the predicted spherical equivlanet change. Residual variations in the parallel and orthogonal components of cylinder correction were, respectively, 28% and 13% of the predicted cylinder change plus a 0.30-D constant component. The standard deviation of axis alignment error for cylinder ablation was 3.7 degrees. CONCLUSIONS: Cylindrical ablation produced a spherical change that was larger than expected. To compensate for this, spherical ablation should be reduced in eyes with astigmatism. Variability in the correction of astigmatism was proportionally larger than that for spherical correction and was primarily due to magnitude rather than axis error.