Impact of Small Incision Lenticule Extraction for High Myopia on Intraocular Pressure Measurements With Pneumotonometry.

PURPOSE: To evaluate the medium-term impact of small incision lenticule extraction (SMILE) on air-puff tonometry (APT) and how it may be corrected. METHODS: In this controlled prospective study, 69 eyes from 69 patients treated with SMILE for high myopia (mean: -7.22 diopters) were included. Central corneal thickness (CCT), spherical equivalent refraction (SEQ), corneal power, and intraocular pressure (IOP) (assessed by APT) were measured before and 3 months after surgery. RESULTS: The measured IOP decreased significantly after SMILE surgery (mean: -6.43 mm Hg), indicating a significant underestimation of the true IOP by APT. There was a significant correlation between change in SEQ, CCT, and apparent IOP. Correcting the apparent IOP measurement by applying a multiple regression correction did not provide significantly better estimates compared to adding 6.4 mm Hg to the measurement. CONCLUSIONS: This study showed that previous SMILE surgery should be considered when interpreting APT measurements, because the measurements underestimate the true IOP. Multiple regressions cannot estimate the true IOP with certainty. For screening purposes, adding 6.4 mm Hg to the apparent IOP of a patient treated for high myopia may be sufficient. [J Refract Surg. 2023;39(9):606-611.].

Patient experience and repeatability of measurements made with the Pentacam HR in patients with keratoconus.

BACKGROUND: To investigate whether the repeatability of measurements with the Pentacam HR in patients with keratoconus is improved by patients gaining more experience of the measurement situation. Such an improvement could enhance the accuracy with which progressive keratoconus can be detected. METHODS: Four replicate measurements were performed on Day 0 and on Day 3. Parameters commonly used in the diagnosis of progressive keratoconus were included in the analysis, namely the flattest central keratometry value (K1), the steepest central keratometry value (K2), the maximum keratometry value (Kmax), and the parameters A, B and C from the Belin ABCD Progression Display. In addition, quality parameters used by the Pentacam HR to assess the quality of the measurements were included, namely the analysed area (front + back), 3D (front + back), XY, Z, and eye movements. RESULTS: Neither the diagnostic parameters nor the quality parameters showed any statistically significant improvement on Day 3 compared to Day 0. The quality parameter "eye movements" deteriorated significantly with increasing Kmax. CONCLUSION: Gaining experience of the measurement situation did not increase the accuracy of the measurements. Further investigations should be performed to determine whether the increasing number of eye movements with increasing disease severity has a negative effect on the repeatability of the measurements.

The intra- and inter-day repeatability of corneal densitometry measurements in subjects with keratoconus and in healthy controls.

The healthy cornea is transparent, however, disease can affect its structure, rendering it more or less opaque. The ability to assess the clarity of the cornea objectively could thus be of considerable interest for keratoconus patients. It has previously been suggested that densitometry can be used to diagnose early keratoconus, and that the values of densitometry variables increase with increasing disease severity, indicating that densitometry could also be used to assess progressive keratoconus. Previous studies have only assessed the repeatability of corneal densitometry measurements on the same day, which does not reflect the clinical setting in which changes are evaluated over time. We have therefore evaluated the inter-day repeatability of densitometry measurements in both patients with keratoconus and healthy controls. Measurements in the middle layer of the 2-6 mm zone of the cornea showed the best repeatability. Although an objective measure of the corneal transparency could be interesting, the generally poor repeatability of densitometry measurements limits their use. The repeatability of corneal clarity measurements could be improved by using other approaches such as optical coherence tomography, but this remains to be investigated. Such improvements would allow the more widespread use of corneal densitometry in clinical practice.

Comparison of corneal shape changes and aberrations induced By FS-LASIK and SMILE for myopia.

PURPOSE: To compare corneal curvatures, corneal power calculations, and higher-order aberrations (HOAs) of femtosecond laser-assisted LASIK (FS-LASIK) with small incision lenticule extraction (SMILE) following surgery for moderate to high myopia. METHODS: A retrospective study of 736 eyes of 368 patients treated with SMILE and 148 eyes of 74 patients treated with FS-LASIK. Preoperative mean spherical equivalent was -7.3 ± 1.5 diopters in the SMILE group and -7.6 ± 1.3 diopters in the FS-LASIK group. Corneal curvatures, corneal power calculations performed by ray tracing, and HOAs measured with Scheimpflug technology before and 3 months after surgery were analyzed. RESULTS: Corneal curvatures changed significantly in the anterior corneal surface, but not in the posterior corneal surface, in both groups; after SMILE, the sagittal curvature was constant for the central 4-mm diameter, in contrast to FS-LASIK where the curvature showed a gradual steepening with increasing diameter. Corneal power calculations were different across the cornea depending on the measurement diameter between the two groups postoperatively. Measured over a 5-mm zone on the total cornea, FS-LASIK induced 0.11 µm more coma (P < .001) and 0.13 µm higher spherical aberration (P < .001) as compared to SMILE; similar results in other HOAs were seen for the anterior corneal surface. Negligible differences in HOAs were induced on the posterior corneal surface. CONCLUSIONS: SMILE and FS-LASIK produced distinct changes in anterior corneal shape evident in different postoperative corneal curvatures and power measurements between the two groups. Postoperative HOAs were much lower after SMILE as compared to FS-LASIK.

Assessing the corneal power change after refractive surgery using Scheimpflug imaging.

PURPOSE: To investigate whether the Pentacam HR could accurately predict the surgically induced refractive change in patients operated with small-incision lenticule extraction (SMILE) for myopia or femto-second laser in situ keratomileusis (FS-LASIK) for myopia or hyperopic astigmatism. METHODS: Data from three groups consisting of (1) 410 myopic eyes of 410 patients operated with SMILE, (2) 111 myopic eyes of 111 patients operated with FS-LASIK, and (3) 40 eyes of 40 patients with hyperopic astigmatism operated with FS-LASIK were retrospectively analysed. The change in manifest refraction due to surgery was compared with the objectively measured change in corneal power by the Pentacam HR in three different ways: Sagittal Power (calculated as for placido topographers), True Net Power (calculated by a Gaussian optics formula), and Total Corneal Refractive Power (calculated by ray tracing). Multiple linear regression analysis was performed to investigate which parameters influenced the Pentacam HR's prediction of the change in subjective refraction due to surgery. RESULTS: The Total Corneal Refractive Power Apex, Zone calculation in a diameter of 4.0 mm effectively predicted the surgically induced refractive change for all three patient groups. The spherical equivalent was predicted with an error of 0.08 ± 0.41 D for the SMILE eyes, 0.05 ± 0.61 D for the myopic eyes operated with FS-LASIK, and -0.15 ± 0.49 D for the hyperopic astigmatic eyes treated with FS-LASIK. Regression showed that preoperative refractive error had a significant impact on the prediction error of the Pentacam HR. CONCLUSIONS: Ray tracing calculations based on Scheimpflug imaging accurately assessed the change in manifest refraction due to corneal laser surgery.

Factors affecting the decision for refractive surgery in patients with high degrees of ametropia.

PURPOSE: To evaluate reasons referred patients do not have refractive surgery. SETTING: University Eye Clinic, Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. DESIGN: Cross-sectional study. METHODS: The case records of patients referred for refractive surgery from January 2011 to December 2012 were examined for explanatory reasons. Data measured at the clinical preexamination of those who did and those who did not have refractive surgery were compared. A logistic regression model was used to assess the measured data's influence on the decision to have or not have refractive surgery. RESULTS: Of the 2150 patients whose records were reviewed, 939 (43.7%) refrained from having refractive surgery. The most common reason was a change of mind (40.7%) followed by low central corneal thickness (CCT) (12.6%) and unstable refraction (10.8%). The 939 patients who refrained from surgery had significantly higher astigmatism and lower intraocular pressure, CCT, and corrected distance visual acuity than the patients who had surgery. The patients who changed their minds were not significantly different in any parameter from the patients who had refractive surgery. Using an outcome threshold of 0.5, the logistic regression model classified 63.04% of the patients correctly. CONCLUSIONS: Reasons for refraining from refractive surgery were numerous, with a change of mind after the preexamination being the most common. Patients who changed their minds were very similar to those who had surgery, indicating that personal factors were important determinants. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Surface quality of human corneal lenticules after SMILE assessed using environmental scanning electron microscopy.

PURPOSE: To assess the cut quality of the anterior and posterior surfaces of intrastromal refractive lenticules removed during small incision lenticule extraction (SMILE). METHODS: The VisuMax femtosecond laser (500 kHz; Carl Zeiss Meditec, Dublin, CA) was used to perform SMILE on 8 eyes of 5 individuals to correct only myopia (no cylinder). The cut energy index was 26 (equivalent to an energy of 130 nJ) with a 2.5 × 2.5 µm spot/track separation. The lenticule diameter was 6.5 mm with a minimum edge thickness of 15 µm and the cap diameter was 7.3 mm with an intended thickness of 120 µm. After laser treatment, the lenticule was loosened with a spatula and removed with forceps. The extracted lenticules were placed in 2% formalin and sent for imaging with an environmental scanning electron microscope. Images of the anterior and posterior surfaces of the lenticules were obtained at multiple magnifications (100×, 250×, and 500×). Surface quality was evaluated by an investigator who specializes in electron microscopy using three criteria: overall surface regularity, percent of surface irregularity, and position of irregular area. RESULTS: Both the anterior and posterior surfaces of the extracted lenticules were smooth and absent of surface irregularities. The cut edges also appeared uniform. Jagged edges were seen in several images, but were clearly caused by the forceps during extraction. CONCLUSIONS: Using the VisuMax laser to perform SMILE produces smooth cuts absent of surface irregularities.

Topography-guided photorefractive keratectomy for irregular astigmatism after small incision lenticule extraction.

PURPOSE: To report the outcome of topography-guided photorefractive keratectomy (PRK) after complicated small incision lenticule extraction (SMILE). METHODS: Retrospective case series of 5 eyes with irregular topography and ghost images after complicated SMILE. All eyes received transepithelial topography-guided PRK. Two eyes were treated with 0.02% mitomycin C. Patients were examined after a minimum of 3 months with evaluation of uncorrected (UDVA) and corrected (CDVA) distance visual acuity, Pentacam tomography (Oculus Optikgeräte, Wetzlar, Germany), and whole-eye aberrometry. RESULTS: In 3 eyes, subjective symptoms were diminished and UDVA, CDVA, topography, and corneal wavefront aberrations were improved. The remaining 2 eyes developed significant haze with worsened topography and wavefront aberrations. One eye experienced a two-line reduction in CDVA. Eyes with haze development had not been treated with mitomycin C. CONCLUSIONS: Transepithelial topography-guided PRK may reduce visual symptoms after complicated SMILE if postoperative haze can be controlled. To reduce the risk of haze development, application of mitomycin C may be considered.

Central corneal sublayer pachymetry and biomechanical properties after refractive femtosecond lenticule extraction.

PURPOSE: To compare central corneal sublayer pachymetry and biomechanical properties after femtosecond lenticule extraction (FLEX) and small-incision lenticule extraction (SMILE). METHODS: A prospective, randomized, single-masked clinical trial of 35 patients treated for moderate to high myopia with FLEX in one eye and SMILE in the other. Anterior segment optical coherence tomography imaging (Heidelberg Spectralis; Heidelberg Engineering GmbH, Heidelberg, Germany) was used to measure central corneal thickness (CCT) and epithelial, flap/cap, and residual stromal bed thickness centrally. The Ocular Response Analyzer (Reichert Ophthalmic Instruments, Buffalo, NY) was used to assess corneal hysteresis (CH) and corneal resistance factor (CRF). Patients were examined before and 6 months after surgery. RESULTS: Mean decrease in CCT was 105 µm in FLEX-treated eyes and 106 µm in SMILE-treated eyes (P = .70), which is equivalent to approximately 14 µm/diopters corrected. Mean central epithelial thickness increased 7 ± 6 µm in FLEX-treated eyes and 6 ± 5 µm in SMILE-treated eyes (P = .64). Achieved mean flap/cap thickness was 4 ± 6 µm from the expected thickness in FLEX-treated eyes and 4 ± 9 µm in SMILE-treated eyes (P = .37). CH was reduced 2.7 ± 1.3 mm Hg in FLEX-treated eyes and 3.3 ± 1.2 mm Hg in SMILE-treated eyes (P = .08). CRF was reduced 4.5 ± 1.2 mm Hg in FLEX-treated eyes and 4.6 ± 1.2 mm Hg in SMILE-treated eyes (P = .71). CH and CRF were highly correlated with CCT, but not patient age. CONCLUSIONS: In this paired-eye study, the flap-based FLEX and cap-based SMILE resulted in almost identical changes in central corneal sublayer pachymetry and biomechanical properties for moderate to high myopia 6 months after treatment.

Efficacy, safety, predictability, contrast sensitivity, and aberrations after femtosecond laser lenticule extraction.

PURPOSE: To compare femtosecond lenticule extraction and small-incision lenticule extraction to treat moderate to high myopia. SETTING: Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. DESIGN: Prospective clinical single-masked paired-eye study. METHODS: An intrastromal lenticule was cut by a femtosecond laser and manually extracted. In femtosecond lenticule extraction, a laser in situ keratomileusis-like flap allowed removal of the lenticule, whereas in small-incision lenticule extraction, it was removed through a small incision. Follow-up was 6 months. RESULTS: Thirty-five patients were treated with femtosecond lenticule extraction in 1 eye and small-incision lenticule extraction in the other. The mean preoperative spherical equivalent was -7.6 diopters (D) ± 1.0 (SD) (range -6.0 to -9.9 D). After both procedures, 90% of eyes had an uncorrected distance visual acuity of 20/40 or better 1 day postoperatively, increasing to 100% after 6 months. At 6 months, the mean corrected distance visual acuity (CDVA) improved significantly by approximately 1.5 letters on the logMAR chart. No eyes lost or gained 2 lines or more of CDVA after either procedure. The achieved refraction was a mean of -0.04 ± 0.38 D from the attempted refraction after femtosecond lenticule extraction and -0.09 ± 0.39 D after small-incision lenticule extraction. After both procedures, 88% of eyes were within ±0.50 D. Contrast sensitivity was unchanged. The changes in higher-order aberrations were similar. CONCLUSION: The all-femtosecond laser flap-based and cap-based techniques produced almost identical results up to 6 months postoperatively in eyes with moderate to high myopia.

Pseudophakic monovision: optimal distribution of refractions.

PURPOSE: To determine the optimal distribution of refractions in monofocal, pseudophakic monovision. METHODS: A previously reported mathematical method for describing defocus for a single eye (Acta Ophthalmol, 89, 2011, 111) is expanded to the binocular situation. The binocular distribution of refractions yielding the least defocus over the most extended fixation intervals is identified by mathematical optimization. The results are tested in a group of 22 pseudophakic patients. RESULTS: For the fixation interval 0.25-6.0 m, the optimal refractions are pure spheres of -0.27D for the distance eye and -1.15D for near eye. The mathematically derived defocus structure is confirmed in the clinical series. CONCLUSIONS: The reported mathematical method enables identification of the optimal distribution of refractions over any fixation interval. Monovision with refractions of approximately -0.25 and -1.25D may lead to spectacle independence for distance and intermediate vision. Binocular problems--such as monovision suppression, reduced stereoacuity and binocular inhibition--are likely to be minimal with the suggested anisometropia of 1.0D. This moderate monovision is fully reversible with spectacle correction, as the induced aniseikonia is minimal and it therefore represents a safe alternative to multifocal intraocular lenses (IOLs).

Subbasal nerve morphology, corneal sensation, and tear film evaluation after refractive femtosecond laser lenticule extraction.

BACKGROUND: The purpose of this study was to compare corneal subbasal nerve morphology, corneal sensation, and tear film parameters after femtosecond lenticule extraction (FLEX) and small-incision lenticule extraction (SMILE). METHODS: A prospective, randomized, single-masked, paired-eye design clinical trial of 35 patients treated for moderate to high myopia with FLEX in one eye and SMILE in the other. In both techniques, an intrastromal lenticule was cut by a femtosecond laser and manually extracted. In FLEX, a LASIK-like flap allowed removal of the lenticule, whereas in SMILE, it was removed through a small incision. In-vivo confocal microscopy was used to acquire images of the central corneal subbasal nerve plexus, from which nerve density, total nerve number, and nerve tortuosity were analyzed. Corneal sensation was measured using Cochet-Bonnet esthesiometry. A visual analog scale, tear osmolarity, non-invasive tear film break-up time (keratograph) tear meniscus height (anterior segment OCT), Schirmer's test, and fluorescein tear film break-up time were used to evaluate tear film and ocular surface symptoms. Patients were examined before and 6 months after surgery. RESULTS: There were no statistically significant differences in baseline parameters between FLEX and SMILE (p > 0.050). With regard to changes from before to 6 months after surgery, mean reduction in subbasal nerve density was 14.22 ± 6.24 mm/mm(2) in FLEX eyes, and 9.21 ± 7.80 mm/mm(2) in SMILE eyes (p < 0.05). The total number of nerves decreased more in FLEX eyes than in SMILE eyes (p < 0.05). No change was found when comparing tortuosity (p > 0.05). Corneal sensation was reduced with 0.38 ± 0.49 cm in FLEX eyes, and 0.10 ± 0.34 cm in SMILE eyes (p < 0.01). No differences were found between FLEX and SMILE in tear film evaluation tests (p > 0.05). Significantly more patients felt postoperative foreign body sensation in the FLEX eye within the first days after surgery, as compared to the SMILE eye. CONCLUSIONS: Six months after surgery, the less invasive SMILE technique seemed better at sparing the central corneal nerves as compared to FLEX. Corneal sensation was only significantly reduced in FLEX eyes. There were no differences between FLEX and SMILE when comparing tear film evaluation tests 6 months after surgery.

Long-term outcomes of photorefractive keratectomy for low to high myopia: 13 to 19 years of follow-up.

PURPOSE: To evaluate long-term outcomes after photorefractive keratectomy (PRK). METHODS: A retrospective follow-up study of patients who received PRK at 5.0- to 6.5-mm optical zones, using the Summit broad beam excimer laser (Summit Technology, Inc., Waltham, MA) at Odense University Hospital, Odense, Denmark, between 1992 and 1998. One randomly selected eye of each patient was used in the statistical analyses. Re-treated eyes were excluded. RESULTS: One hundred sixty eyes were included. Mean follow-up time was 16 years (range: 13 to 19 years). Mean preoperative spherical equivalent was -4.84 ± 2.95 diopters (D) (range: -20.25 to -1.25 D). At last follow-up examination, achieved refraction was -1.00 ± 1.56 D (range: -10.75 to +1.00 D) from attempted refraction, and the change in mean refractive error from 6 months postoperatively was less than 1.00 D. Results from a subgroup of unilateral treated patients indicated that myopic progression was the main reason for the residual refractive error. For eyes with low myopia (n = 124), the proportion of eyes within ± 1.0 D of attempted refraction was 72%, and for eyes with high myopia (-6.00 D or more, n = 36) it was 47%. Forty-five percent had uncorrected distance visual acuity of 20/20 or better at last follow-up examination. Three eyes (2%) lost two or more lines and 13 eyes (8%) gained two or more lines of corrected distance visual acuity. Fourteen percent had haze (grade 0.5 to 2). Eighty-one percent were satisfied with the surgery. CONCLUSION: PRK for low degrees of myopia seemed safe and effective up to 19 years after surgery with conventional broad beam laser ablation. Refractive predictability was significantly lower and the occurrence of haze was higher in eyes with high myopia.

Femtosecond (FS) laser vision correction procedure for moderate to high myopia: a prospective study of ReLEx(®) flex and comparison with a retrospective study of FS-laser in situ keratomileusis.

PURPOSE: To present our initial clinical experience with ReLEx(®) flex (ReLEx) for moderate to high myopia. We compare efficacy, safety and corneal higher-order aberrations after ReLEx with femtosecond laser in situ keratomileusis (FS-LASIK). METHODS: Prospective study of ReLEx compared with a retrospective study of FS-LASIK. ReLEx is a new keratorefractive procedure, where a stromal lenticule is cut by a femtosecond laser and manually extracted. Forty patients were treated with ReLEx on both eyes. A comparable group of 41 FS-LASIK patients were retrospectively identified. Visual acuity, spherical equivalent (SE) and corneal tomography were measured before and 3 months after surgery. RESULTS: Preoperative SE averaged -7.50 ± 1.16 D (ReLEx) and -7.32 ± 1.09 D (FS-LASIK). For all eyes, mean corrected distance visual acuity remained unchanged in both groups. For eyes with emmetropia as target refraction, 41% of ReLEx and 61% of FS-LASIK eyes had an uncorrected distance visual acuity of logMAR ≤ 0.10 at day 1 after surgery, increasing to, respectively, 88% and 69% at 3 months. Mean SE was -0.06 ± 0.35 D 3 months after ReLEx and -0.53 ± 0.60 D after FS-LASIK. The proportion of eyes within ±1.00 D after 3 months was 100% (ReLEx) and 85% (FS-LASIK). For a 6.0-mm pupil, corneal spherical aberrations increased significantly less in ReLEx than FS-LASIK eyes. CONCLUSIONS: ReLEx is an all-in-one femtosecond laser refractive procedure, and in this study, results were comparable to FS-LASIK. Refractive predictability and corneal aberrations at 3 months seemed better than or equal to FS-LASIK, whereas visual recovery after ReLEx was slower.

Predictors for the outcome of small-incision lenticule extraction for Myopia.

PURPOSE: To study the influence of patient- and surgery-related parameters on the predictability, efficacy, and safety of small-incision lenticule extraction (SMILE) for treatment of myopia. METHODS: This prospective, clinical quality, control study comprised 670 eyes from 335 patients with myopia up to -10.00 diopters (D) (spherical equivalent refraction) and astigmatism up to 2.00 D treated with SMILE in both eyes and followed for 3 months. RESULTS: Preoperative mean spherical equivalent refraction was -7.19±1.30 D. In eyes with emmetropia as the target refraction, 84% obtained uncorrected distance visual acuity ≤ 0.10 logMAR (20/25 or better Snellen equivalent) at 3 months. Mean corrected distance visual acuity (CDVA) improved from -0.03 to -0.05 logMAR (P<.01). Two or more lines of CDVA were lost in 2.4% (16 eyes). The achieved refraction was 0.25±0.44 D less than attempted after 3 months, and 80% (537 eyes) and 94% (631 eyes) were within ±0.50 and ±1.00 D of attempted correction, respectively. Multiple linear regression analyses revealed that spherical equivalent refraction undercorrection was predicted by increasing patient age (0.10 D per decade; P<.01) and steeper corneal curvature (0.04 D per D; P<.01). Safety and efficacy of the procedure were minimally affected by age, gender, and simultaneous cylinder correction. CONCLUSIONS: Undercorrection of 0.25 D and small effects of patient age and corneal curvature suggest that the standard nomogram for SMILE need only minor adjustments. This study suggests that safety and efficacy are not influenced to any clinically significant degree by easily discernible patient factors.

Small-incision lenticule extraction for moderate to high myopia: Predictability, safety, and patient satisfaction.

PURPOSE: To present initial clinical experience with small-incision lenticule extraction for the treatment of moderate to high myopia. SETTING: Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. DESIGN: Prospective clinical study. METHODS: For small-incision lenticule extraction, an intrastromal lenticule was cut with a femtosecond laser and manually extracted without creation of a flap. Patients were treated and followed for 3 months. Only 1 randomly chosen eye of each patient was used in the statistical analyses. RESULTS: The study enrolled 144 patients. The mean preoperative spherical equivalent was -7.18 diopters (D) ± 1.57 (SD). Of eyes with emmetropia as target refraction, 40% had an uncorrected distance visual acuity of 0.1 logMAR or less 1 day after surgery; this increased to 73% at 3 months. The mean corrected distance visual acuity (CDVA) improved significantly from -0.01 (logMAR) preoperatively to -0.03 3 months postoperatively. None of the 127 eyes lost 2 lines or more of CDVA and 6 eyes lost 1 line of CDVA after 3 months. In contrast, 1 eye gained 2 lines and 24 eyes gained 1 line of CDVA. The achieved refraction was a mean of -0.09 ± 0.45 D from the attempted refraction. Of the eyes, 77% were within ±0.50 D and 95% were within ±1.00 D. Ninety-five percent of the patients would recommend the procedure to others. CONCLUSIONS: The refractive predictability, safety, and patient satisfaction 3 months after small-incision lenticule extraction were high and comparable to results in previous studies of femtosecond laser-assisted techniques. FINANCIAL DISCLOSURE: Drs. Hjortdal and Asp received travel reimbursement from Carl Zeiss Meditec AG, Jena, Germany. No other author has a financial or proprietary interest in any material or method mentioned.

Three-year changes in epithelial and stromal thickness after PRK or LASIK for high myopia.

PURPOSE: To compare 3-year changes in corneal sublayer thickness after photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK). METHODS: Forty-six patients with spheroequivalent refraction of -6.0 to -8.0 diopters (D) were randomly assigned to PRK or LASIK. One eye from each patient was included in the study. Examinations included manifest refraction and confocal microscopy through focusing (CMTF) and were performed preoperatively and postoperatively at 1 week and at 1, 3, 6, 12, and 36 months. From CMTF scans, the thicknesses of the central cornea (CT), epithelium (ET), stroma (ST), LASIK flap (FT), and residual stromal bed (BT) were calculated. RESULTS: After LASIK, spheroequivalent refraction averaged -0.76 D by 1 week and -1.19 D by 1 month, with no subsequent significant change. ET increased 9.0 +/- 7.0 microm within 1 week and remained constant thereafter. ST increased 12.9 +/- 9.4 microm within 1 year because of increased BT. One week after PRK, refraction averaged -0.23 D and stabilized at -1.42 D by 6 months. By 1 week, ET was reduced by 7.5 +/- 5.7 microm, reached preoperative thickness by 6 months, and increased further 7.3 +/- 6.0 microm by 3 years. ST increased 25.3 +/- 17.2 microm during 1 year, correlating with the postoperative refractive regression. After both procedures, changes in CT also correlated with refractive changes. No other correlations were identified. CONCLUSIONS: PRK and LASIK induce a persistent increase in ET that stabilizes 1 week after LASIK and 1 year after PRK. Stromal regrowth is most pronounced after PRK. After LASIK, regrowth is restricted to the residual stromal bed. Postoperative refractive changes correlate with changes in ST (PRK) and CT (PRK and LASIK) but not with changes in ET.

[Efficacy and safety of laser-assisted in situ keratomileusis for myopia]. / Effekt og sikkerhed ved laser in situ-keratomileusis-operation for naersynethed.

INTRODUCTION: The aim of this study was to assess the efficacy, frequency of re-operation and type and frequency of complications after laser-assisted in situ keratomileusis (LASIK) treatment for moderate to high levels of myopia. MATERIALS AND METHODS: 357 eyes from 190 patients were reviewed. The mean of the preoperative correction was -8.38 D (-1.75; -16 D) sph. (spherical), -1.00 D (0; 4.5 D) astigmatism. 15% (55 eyes) were re-treated. The mean of the correction before re-treatment was -2.78 D (+2.25; -11.00 D) sph., -0.43 D (0; -2.00 D) astigmatism. RESULTS: The three-month follow-up rate was 96% for primarily treated eyes and 99% for re-treated eyes. Where full correction was intended, 53% of the primarily treated and 93% of the re-treated eyes achieved an uncorrected visual acuity of > or =0.5. The refractive error for myopia less than -8 D was -0.80 D +/- 0.83 D and -1.37 D +/- 1.33 D for myopia -8 D and above after one treatment and -0.47 +/- 0.66 D after re-treatment. 1.2% (4) of the primarily treated and 3.9% (2) of the retreated eyes lost more than two lines in best spectacle-corrected visual acuity (BCVA). CONCLUSION: LASIK treatment for moderate to high levels of myopia leads in all cases to a reduced degree of myopia. There is a significant degree of unreliability on the accuracy of the treatment with a tendency to under correction. Postoperatively, many patients still have to use correction for distance vision. Significant loss of visual acuity occurs infrequently.