Noncontact optical coherence tomography for measurement of corneal flap and residual stromal bed thickness after laser in situ keratomileusis

PURPOSE: Studies show significant variability in the thickness of laser in situ keratomileusis (LASIK) corneal flaps cut by various microkeratomes. Most studies of corneal flap thickness are based on contact ultrasonic pachymetry measurements taken during the surgical procedure. This study reports a technique to obtain reproducible corneal flap thickness and residual stromal bed thickness measurements using noncontact optical coherence tomography (OCT) following LASIK. METHODS: The corneal flap thicknesses of 26 eyes of 15 patients were measured following LASIK in which the flap was created using the Amadeus microkeratome: 160-microm head, 9.5-mm ring, 4.0-mm/s translation speed, 8000 oscillations/m, and full vacuum. Zeiss Humphrey OCT-2 line scans were performed on postoperative days 1 and 7. The raw data from three scans for each eye and day were exported to Microsoft Excel for processing, averaging, and analysis. RESULTS: The OCT corneal flap thickness and residual stromal bed thickness measurements correlated well with ultrasonic pachymetry measurements performed during surgery (R2 = .92). The OCT technique yielded reproducible results, as the variance for repeated scans was only 2.5% of the variance between eyes. In bilateral cases a single blade was used for both eyes. The mean flap thickness of 15 first eyes was significantly greater than that of the 10 second eyes: 181 +/- 31 microm vs. 143 +/- 41 microm (P < .01). A positive correlation was found between the preoperative pachymetry and corneal flap thickness. CONCLUSIONS: The OCT scan averaging technique is a reproducible, noncontact postoperative method for measuring corneal flap and residual stromal bed thicknesses following LASIK.     

Continuous monitoring of corneal thickness changes during LASIK with online optical coherence pachymetry

PURPOSE: To assess the continuous intraoperative monitoring of central corneal thickness (CCT) changes during laser in situ keratomileusis (LASIK) using online optical coherence pachymetry (OCP). SETTING: Department of Ophthalmology, Vivantes Klinikum Neukolln, Berlin, Germany. METHODS: In this prospective nonrandomized comparative clinical case series of consecutive patients, 32 eyes having LASIK for myopia, myopic astigmatism, or hyperopia were continuously monitored intraoperatively in real time with online OCP integrated into a clinical excimer laser. The intraoperative values were compared to the postoperative flap and residual stromal thicknesses measured with corneal optical coherence tomography (OCT) as well as the calculated myopic ablation depth. RESULTS: Continuous monitoring with online OCP enabled intraoperative visualization of the CCT changes during LASIK. The CCT, flap thickness after the microkeratome pass, time-resolved ablation, and residual stromal thickness were assessed. Intraoperatively, the mean flap thickness was 135 microm +/- 38 (SD) and the mean residual stromal thickness, 286 +/- 59 microm. The mean intraoperative flap and residual stromal thickness values were 43.7 microm and 15.4 microm lower, respectively, than the postoperative values assessed with corneal OCT (P<.001 and P=.005, respectively). The optically determined myopic ablation depth was 118 +/- 37 microm, which was 28 microm higher than the nominal ablation depth. There was a significant correlation (P<.001) between the postoperative flap (r=0.79) and residual (r=0.88) thickness measured with corneal OCT as well as the calculated myopic ablation depth (r=0.95). CONCLUSIONS: Intraoperative online OCP could be an important safety feature to monitor the flap and residual stromal thicknesses during LASIK. The individual ablation depth and possible dehydration effects were also monitored continuously.     

High-speed optical coherence tomography for management after laser in situ keratomileusis

PURPOSE: To report applications of optical coherence tomography (OCT) in the management of laser in situ keratomileusis (LASIK) related problems. SETTING: Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. METHODS: Five patients referred for LASIK-related problems were enrolled in a prospective observational study. Clinical examination, ultrasound (US) pachymetry, Placido ring slit-scanning corneal topography (Orbscan II, Bausch & Lomb), and high-speed corneal OCT were performed. RESULTS: In cases of regression and keratectasia, OCT provided thickness measurements of the cornea, flap, and posterior stromal bed. Locations of tissue loss and flap interface planes were identified in a case with a recut enhancement complication. The information was used to determine whether further laser ablation was safe, confirm keratectasia, and manage complications. Optical coherence tomography measurements of central corneal thickness agreed well with US pachymetry measurements (difference 6.4 microm +/- 11.7 [SD]) (P = .026), while Orbscan significantly underestimated corneal thickness (-67.5 +/- 72.5 microm) (P = .17). CONCLUSIONS: High-speed OCT provided noncontact imaging and measurement of LASIK anatomy. It was useful in monitoring LASIK results and evaluating complications.     

OCT visualization of corneal structural changes in traumatic dislocation of LASIK flap

A 45-year-old woman presented with a traumatic laser-assisted in situ keratomileusis (LASIK) flap dislocation in the right eye. Anterior segment optical coherence tomography (OCT) showed the presence of macrostriae, flap stromal edema, epithelial hyperplasia between the striae and epithelial ingrowth. The flap was surgically repositioned with optimal visual recovery. Anterior segment OCT can efficiently visualize corneal structural changes associated with LASIK flap dislocation.     

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

PURPOSE: To monitor corneal structures with slitlamp-adapted optical coherence tomography (OCT) in laser in situ keratomileusis (LASIK). SETTING: Department of Ophthalmology, Vivantes Klinikum Neuk?lln, Berlin, Germany. METHODS: 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. RESULTS: 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. CONCLUSION: Slitlamp-adapted OCT can be used to longitudinally monitor the variable structures of the cornea, epithelium, flap, and residual stroma in LASIK.     

Central corneal thickness measurements by ultrasound, Orbscan II, and Visante OCT after LASIK for myopia

PURPOSE: To compare central corneal thickness measurements obtained with Orbscan II scanning slit topography, Visante optical coherence tomography (OCT), and ultrasound pachymetry in myopic eyes after LASIK. METHODS: This retrospective study included 34 consecutive patients (68 eyes) who underwent LASIK for the correction of myopia. Six months after surgery, central corneal thickness measurements were obtained using ultrasound pachymetry, Orbscan scanning slit topography, and Visante OCT. Data were analyzed using paired sample t test, Bland and Altman plot, and linear regression. RESULTS: Average postoperative central corneal thickness was 436.65+/-43.82 microm for ultrasound pachymetry, 422.84+/-51.04 microm for Orbscan (0.89 acoustic equivalent correction factor), and 422.26+/-42.46 microm for Visante. Compared to the ultrasound measurement, Orbscan and Visante measurements significantly underestimated the corneal thickness by 13.81+/-17.34 microm (P<.01) and 14.38+/-10.13 microm (P<.01), respectively. CONCLUSIONS: Both Orbscan and Visante OCT underestimated central corneal thickness compared to ultrasound pachymetry 6 months after LASIK, although measurements obtained with Visante OCT had better agreement and correlation with ultrasound pachymetry than with Orbscan.     

Intraoperative optical coherence pachymetry during laser in situ keratomileusis--first clinical experience

PURPOSE: To investigate intraoperative optical coherence pachymetry during laser in situ keratomileusis (LASIK). METHODS: In an initial clinical evaluation, three patients with myopia and myopic astigmatism were studied. Corneal thickness was assessed with optical pachymetry based on low-coherence interferometry during LASIK. RESULTS: The attempted mean spherical equivalent refraction was -5.70 +/- 2.00 D with a mean calculated stromal ablation depth of 95 +/- 18 microm. Intraoperative optical coherence pachymetry was reproducible in all patients during the different stages of LASIK, demonstrating a mean flap thickness of 141 +/- 30 microm with a residual corneal stroma of 274 +/- 24 microm at the end of the laser ablation. The immediate postoperative corneal thickness revealed marked swelling. CONCLUSIONS: This initial clinical evaluation proved that intraoperative optical coherence pachymetry may be an important safety feature for monitoring flap and residual stromal thickness during LASIK. It may be particularly helpful in the effort to avoid iatrogenic corneal ectasia in patients with thin corneas, higher refractive corrections, and LASIK enhancements.     

Flap thickness reproducibility in laser in situ keratomileusis with a femtosecond laser: optical coherence tomography measurement

PURPOSE: To compare ultrasound (US) pachymetry, Orbscan, and optical coherence tomography (OCT) measurements of the central corneal thickness (CCT) before laser in situ keratomileusis (LASIK) and evaluate the reproducibility of flaps created with the IntraLase femtosecond laser (IntraLase, Inc.) using OCT. SETTING: Department of Ophthalmology, IIsan Paik Hospital, Goyang, Korea. METHODS: Central corneal thickness was measured using OCT, US pachymetry, and Orbscan in 59 eyes of 30 patients before femtosecond laser LASIK. The postoperative corneal flap thickness, measured using OCT, was compared with the preoperative intended thickness. RESULTS: Optical coherence tomography, US pachymetry, and Orbscan measurements provided similar CCT values (P>.05). Corneal thickness values obtained using US or Orbscan correlated well with those obtained by OCT, with the correlation coefficient ranging from 0.804 to 0.889 (P<.05). The OCT measurements showed no significant difference between the postoperative flap thickness and the intended flap thickness (P>.05). CONCLUSIONS: Optical coherence tomography was comparable to US pachymetry and Orbscan in cornea thickness measurement. Optical coherence tomography was easy and relatively accurate to use preoperatively and in the early postoperative period. The femtosecond laser created highly reproducible flaps that corresponded with the preoperative intended thickness.     

Undersurface ablation of the flap for laser in situ keratomileusis retreatment

OBJECTIVE: To develop a novel technique, undersurface ablation of the flap (UAF), for laser in situ keratomileusis (LASIK) retreatment in eyes with insufficient posterior stroma. DESIGN: Noncomparative, interventional case series. PARTICIPANTS: From 30 eyes examined, 25 eyes with a spherical equivalent residual refraction between -0.75 and -3.25 diopters (D) and astigmatism between 0.0 and -1.5 D were prospectively included in the study. In these eyes, calculated postenhancement flap thickness was >150 micro m using micropachymetric optical coherence tomography (OCT), whereas with further ablation of the bed, posterior stromal thickness would have been <250 micro m. Primary LASIK procedures had been performed with the Hansatome microkeratome. INTERVENTION: The flap was lifted and the eye deviated downward, so that the corneal visual axis mark aligned with the laser beam. Mirror pattern ablations with an optical zone of 5 mm were performed on the flap stroma using either the Summit Apex Plus excimer laser or the Technolas Keracor 217 spot-scanning excimer laser. New axis orientation for toric ablations was calculated with the formula: beta = 180 degrees - alpha. MAIN OUTCOME MEASURES: Refraction, visual acuity, OCT pachymetry, tangential videokeratography, and patient satisfaction. RESULTS: The average follow-up was 6.36 +/- 2.64 months (range, 3-12 months). Mean preenhancement spherical equivalent (-2.05 +/- 0.75 D) was reduced to -0.19 +/- 0.38 D at the last visit (P = 0.001). Mean cylinder decreased from -0.48 +/- 0.53 D before retreatment to -0.23 +/- 0.28 D at the last follow-up (P = 0.003). Best-corrected visual acuity worsened by 1 line in two eyes (8%), and no eye lost 2 or more lines. Satisfactory globe stabilization and stromal smoothness during ablation were more difficult to achieve than with conventional LASIK enhancements. The average central flap thickness before UAF, 187 +/- 13 micro m, decreased to 164 +/- 12 micro m after 1 month (P = 0.001). No keratectasia developed. Finally, 92% of cases were satisfied with surgery compared with 48% before UAF retreatment (P = 0.001). CONCLUSIONS: UAF retreatment for low residual refractive errors after LASIK in eyes with sufficient flap stroma seems to be effective and may prevent future keratectasia.     

Arc-scanning very high-frequency digital ultrasound for 3D pachymetric mapping of the corneal epithelium and stroma in laser in situ keratomileusis

PURPOSE: To test and demonstrate measurement precision, imaging resolution, 3D thickness mapping, and clinical utility of a new prototype 3D very high-frequency (VHF) (50 MHz) digital ultrasound scanning system for corneal epithelium, flap, and residual stromal thickness after laser in situ keratomileusis (LASIK). METHODS: VHF ultrasonic 3D data was acquired by arc-motion, meridional scanning within a 10-mm zone. Digital signal processing techniques provided high-resolution B-scan imaging, and I-scan traces for high-precision pachymetry in 4 eyes. Thickness maps of individual corneal layers were constructed. Reproducibility of epithelial, flap, and full corneal pachymetry was assessed for single-point and 3D thickness mapping by repeated measures. Thickness mapping of the epithelium, stroma, flap, and full cornea were determined before and after LASIK. Preoperative to postoperative difference maps for epithelium, flap, and stroma were produced to demonstrate anatomical changes in the thickness profile of each layer. RESULTS: Surface localization precision was 0.87 microm. Central reproducibility for single-point pachymetry of epithelium was 0.61 microm; flap, 1.14 microm; and full cornea, 0.74 microm. Reproducibility for central pachymetry on 3D thickness mapping was 0.5 microm for epithelium and 1.5-microm for full cornea. B-scans and 3D thickness maps after LASIK demonstrated resolution of epithelial, stromal component of the flap, and residual stromal layers. Large epithelial profile changes were demonstrated after LASIK. Topographic variability of flap thickness and residual stromal thickness were significant. CONCLUSIONS: VHF digital ultrasound arc-B scanning provides high-resolution imaging and high-precision three-dimensional thickness mapping of corneal layers, enabling accurate anatomical evaluation of the changes induced in the cornea by LASIK.     

Corneal and epithelial thickness in keratoconus: a comparison of ultrasonic pachymetry, Orbscan II, and optical coherence tomography

PURPOSE: To compare corneal thickness measurements in individuals with keratoconus using optical coherence tomography (OCT), Orbscan II, and ultrasonic pachymetry and to measure epithelial and stromal thickness in these individuals using OCT. METHODS: Twenty individuals with keratoconus and 20 controls (without keratoconus) were enrolled. The Orbscan II was used to locate the steepest area of the cornea, which was taken to represent the cone apex. Each instrument was used to obtain four total corneal thickness measurements-from the cone apex, corneal center, mid-nasal, and mid-temporal cornea. Optical coherence tomography scans were analyzed to provide epithelial and stromal thickness readings. RESULTS: In individuals with keratoconus, mean central corneal thickness (CCT) measured by ultrasonic pachymetry, Orbscan, and OCT was 494.2 +/- 50.0 microm, 438.6 +/- 47.7 microm, and 433.5 +/- 39.7 microm, respectively. The central keratoconic cornea was 57.7 microm thinner than the normal cornea (post-hoc P<.001). The cone apex was thinner than the central cornea (P<.001). Keratoconic epithelium was 48.2 +/- 5.5 microm centrally and 42.1 +/- 4.5 microm at the apex. Central keratoconic epithelium was 4.7 microm thinner and central keratoconic stroma was 57.8 microm thinner than the normal cornea (P<.001, respectively). Comparing instruments, Orbscan and OCT correlated in CCT measurement (r=0.890) and apical thickness (r=0.846). All instruments produced similar readings for mid-nasal and mid-temporal corneal thickness in participants with keratoconus (P>.05). CONCLUSIONS: Ultrasonic pachymetry produced the highest corneal thickness readings in the center and apex, compared to Orbscan II and OCT. Centrally, the total cornea, epithelium, and stroma were thinner in individuals with keratoconus than in normal individuals.     

Corneal optical coherence tomography before and after phototherapeutic keratectomy for recurrent epithelial erosions(2)

PURPOSE: To study the representation of corneal structures with optical coherence tomography (OCT) before and after excimer laser phototherapeutic keratectomy (PTK) for recurrent epithelial erosions. SETTING: Departments of Ophthalmology, Vivantes Klinikum Neuk?lln, Berlin, and Medizinische Universit?t, Lübeck, Germany. METHODS: This prospective study comprised 15 eyes of 14 patients with recurrent epithelial erosions. The central corneal and epithelial thickness as well as the wound-healing response in the anterior corneal stroma were assessed with slitlamp-adapted OCT before and after PTK. RESULTS: After PTK, the symptoms improved in all patients without loss of best corrected, glare, or low-contrast visual acuity. The mean central corneal OCT thickness was 540 microm +/-28 (SD) preoperatively, 492 +/- 36 microm immediately after epithelial debridement and PTK, and 519 +/- 25 microm after 7 weeks (P <.01). The mean central epithelial OCT thickness changed from 70 +/- 13 microm preoperatively to 60 +/- 7 microm after 7 weeks (P >.01). Changes in the light-scattering properties in the anterior subepithelial stroma revealed a hyperreflective area with a mean thickness of 46 +/- 13 microm after 7 weeks. CONCLUSIONS: Using noncontact corneal OCT, corneal and epithelial thickness changes and the wound-healing response in the anterior corneal stroma could be evaluated after PTK in patients with recurrent epithelial erosions.     

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

PURPOSE: 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. RESULTS: 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. CONCLUSIONS: 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.     

Epithelial ingrowth after laser in situ keratomileusis: clinical features and possible mechanisms

PURPOSE: To analyze the incidence, clinical course, and possible mechanisms of epithelial ingrowth after laser in situ keratomileusis (LASIK). DESIGN: Interventional case series. METHODS: Retrospective evaluation of 4,867 eyes of 2,502 patients who had LASIK. The type of microkeratome (LSK-One or MK-2000), corneal flap thickness, and clinical course were analyzed. We also compared the cutting characteristics of both microkeratomes in pig cadaver eyes by scanning electron microscopy. RESULTS: The frequency of epithelial ingrowth was significantly greater in the MK-2000 (34 of 1,680 eyes; 2.0%) than the LSK-One group (30 of 3,187 eyes; 0.94%; P =.001). In 24 eyes (37.5%), blood, cell infiltration, ointment under the corneal flaps, or epithelial defect were detected at the area of epithelial ingrowth postoperatively. The incidence of epithelial ingrowth was correlated with the incidence of epithelial defect during surgery (P <.001) and with incidence of diffuse lamellar keratitis after surgery (P =.003). Flap thickness was thinner in eyes with epithelial ingrowth (126.0 +/- 29.1 microm) compared with flap thickness in eyes without epithelial ingrowth (133.8 +/- 27.3 microm; P <.001). Scanning electron microscopy showed clear differences in the appearance of flap edges created by the two types of microkeratomes. Epithelial ingrowth disappeared or remained unchanged in 54 eyes (90%) and progressed in six cases (10%). CONCLUSIONS: Poor adhesion caused by excessive hydration due to epithelial defect as well as by foreign bodies between the flap stromal bed and thickness and morphologic characters of the corneal flap, depending on the type of microkeratomes, are related factors for development of epithelial ingrowth.     

Comparison of human central cornea and limbus in vivo using optical coherence tomography.

PURPOSE: The purpose of this study was to compare central corneal and limbal total and epithelial thickness using a commercially available optical coherence tomographer. METHODS: A Humphrey-Zeiss Optical Coherence Tomographer (OCT [Carl Zeiss, Meditec, Dublin, CA]) was used to obtain corneal images from 10 subjects. Central corneal and limbal total and epithelial thickness of both eyes were measured using the OCT. Each OCT image comprised 100 measurements, 10 nasal, 10 central, and 10 temporal measurements from each image were analysed. RESULTS: The central corneal and epithelial thickness of the right and the left eyes were 507.9 +/- 35.8 microm, 58.4 +/- 2.5 microm, 506.9 +/- 37.4 microm, and 58.5 +/- 2.5 microm, respectively. There were no differences between eyes (p > 0.05). The nasal and temporal limbal total and epithelial thickness of the right and left eyes were 703.8 +/- 32.1 microm, 704.9 +/- 31.0 microm, 76.8 +/- 3.5 microm, 77.9 +/- 2.9 microm, 704.4 +/- 31.8 microm, 706.3 +/- 32.5 microm, 77.5 +/- 2.8 microm, and 77.8 +/- 2.5 microm, respectively. There were no differences between the nasal and temporal total and epithelial thickness of both eyes (p > 0.05). However, there was a statistical difference between the central corneal and limbal total and epithelial thickness (both p < 0.05). CONCLUSIONS: Central cornea and limbus are measurably different using OCT. Central cornea is thinner than limbus for both total thickness and epithelial thickness. There is no difference between eyes of central corneal and limbal total and epithelial thickness. Optical Coherence Tomography is a useful instrument for in vivo human limbal morphometry.     

Noncontact measurements of central corneal epithelial and flap thickness after laser in situ keratomileusis

PURPOSE: To investigate the changes in the epithelium and flap after laser in situ keratomileusis (LASIK), when measured with optical coherence tomography (OCT). METHODS: Twenty-eight eyes of 14 patients (age: 39.9 +/- 8.6 years) underwent LASIK. The central thickness of corneal epithelium and flap were measured with a real-time 1310 nm OCT 1 day, 1 week, and 1 month after surgery. A custom software program was used to process multiple images of each eye on each visit. RESULTS: After surgery, the corneal epithelium changed significantly (ANOVA: F((3, 81)) = 12.3, P = 0.000) with not statistically significant thinning at one day (mean +/- SD: 57.8 +/- 5.9 micro m, P = 0.26, compared with baseline: 59.9 +/- 5.9 micro m) and statistically significant thickening at 1 week (60.8 +/- 5.8 micro m, P = 0.04, compared with 1 day) and 1 month (64.6 +/- 6.1 micro m, P = 0.008 compared with all others). There were statistically significant changes in the corneal flap thickness (ANOVA: F((2, 54)) = 4.59, P = 0.01) with thickening in the intervals between 1 day (143.3 +/- 20.6 micro m) and 1 week (149.7 +/- 24.6 micro m, P = 0.12), and between 1 week and 1 month (152.7 +/- 19.3 micro m, P = 0.01). There was a strong correlation (r = 0.898) between the difference of corneal thickness before and after surgery and predicted laser ablation depth. CONCLUSIONS: OCT is a useful noncontact tool for thickness measurements of the epithelium, flap, and total cornea. After LASIK, the epithelium and flap showed thickening during the study period.     

Reproducibility of corneal flap thickness in laser in situ keratomileusis using the Hansatome microkeratome

PURPOSE: To evaluate the reproducibility of flap thickness during laser in situ keratomileusis (LASIK) and to analyze the effect of preoperative central corneal thickness and corneal keratometric power on flap thickness. SETTING: Department of Ophthalmology, Cerrahpasa Medical School, Istanbul, Turkey. METHODS: One hundred forty eyes with a mean preoperative pachymetry of 554.4 microm +/- 36.3 (SD) and a mean keratometry of 43.5 +/- 1.9 diopters had LASIK using the Hansatome automated microkeratome (Bausch & Lomb Surgical) and a 193 nm argon-fluoride excimer laser (Summit SVS Apex Plus). The 180 microm microkeratome plate was used in all procedures. Corneal thickness was measured with an ultrasonic pachymeter (Advent, Mentor O&O Inc.) before and during the flap procedure, and the difference was taken as flap thickness. The data were analyzed using a 1-tailed t test and Pearson correlation coefficient. RESULTS: The mean flap thickness was 120. 8 +/- 26.3 microm. There was a low correlation between baseline central corneal thickness and corneal flap thickness (P =.6, r = 0. 046). There was no correlation between preoperative keratometry and flap thickness (P =.01, r = 0.203). CONCLUSIONS: The Hansatome microkeratome does not always produce a corneal flap of the intended thickness. Factors other than keratometry and pachymetry must affect flap thickness.     

Laser in situ keratomileusis for residual myopia after primary LASIK

PURPOSE: To analyze the results of secondary laser in situ keratomileusis (LASIK) for residual myopia after primary LASIK. SETTING: Dr. Agarwal's Eye Hospital, Chennai, India. METHODS: A retrospective study of 50 eyes of 29 patients who had a secondary LASIK procedure was carried out. After a mean follow-up of 5.84 months +/- 3.24 (SD) after the primary procedure, the mean myopic residual refraction was -4.30 +/- 1.83 diopters (D). In 10 eyes, the primary corneal flap was lifted by blunt dissection. In 40 eyes, the flap was made with a second cut. The secondary LASIK was performed using the Chiron Technolas Keracor 217 excimer laser and the Automated Corneal Shaper microkeratome (Bausch & Lomb). RESULTS: The mean follow-up was 16.58 +/- 3.06 months. At 12 months, the mean spherical equivalent was -0.45 +/- 0.68 D (P <.05). Thirty-one eyes were emmetropic, 13 eyes were within +/-1.00 D of emmetropia, and 5 eyes were within +/-2.00 D. The mean uncorrected visual acuity improved from 20/80 (range 20/60 to 20/200) to 20/40 (range 20/20 to 20/200) (P <.005). Seventeen eyes gained 1 line of best spectacle-corrected visual acuity; 1 eye lost 1 line because of a decentered ablation with an induced postoperative astigmatism of -3.50 D cylinder. No sight-threatening complications such as a free cap, flap irregularity, corneal ectasia, or retinal complication occurred postoperatively. Epithelial ingrowth developed in 5 eyes and corneal thinning, in 1 eye. Three eyes had night glare. CONCLUSION: Secondary LASIK was a safe, stable, and effective method for the treatment of residual myopia after primary LASIK.     

Optical low coherence reflectometry for noncontact measurements of flap thickness during laser in situ keratomileusis

OBJECTIVE: There is growing evidence that iatrogenic keratectasia after laser in situ keratomileusis (LASIK) for high corrections occurs more frequently than initially assumed, and that it may result from larger variation in flap thickness. DESIGN: Consecutive noncomparative case series PARTICIPANTS: Thirty-four patients who underwent LASIK for myopia and astigmatism (first treatment group) and 10 patients who received re-LASIK (retreatment group). METHODS: Central corneal thickness and thickness of the lamella during LASIK were determined by optical low coherence reflectometry (OLCR) and contact ultrasound pachymetry. MAIN OUTCOME MEASURES: Thickness of the flap and its standard deviation, as well as its correlation with age, sphere, cylinder, corneal thickness, intraocular pressure, and corneal refractive power (K-readings). RESULTS: The mean flap thickness of the first treatment group determined by OLCR was 130 +/- 29 microm; the 95 percentile was 169 microm and the 5 percentile was 86 microm. The flap thickness was not correlated with any of the investigated demographic or refractive parameters. The mean flap thickness of the retreatment group was 152 +/- 14 microm; the 95 percentile was 175 microm and the 5 percentile was 137 microm. Thus, the flap thickness of the retreatment group was significantly thicker compared with the first treatment group (P < 0.001). CONCLUSIONS: Optical low coherence reflectometry (OLCR) was shown to be an appropriate alternative to ultrasonic preoperative and intraoperative corneal pachymetry in laser assisted in situ keratomileusis. The lack of correlation between achieved flap thickness and preoperative clinical data, such as corneal thickness, corneal curvature, intraocular pressure, and refraction, emphasizes the importance of measuring flap thickness and corneal bed thickness during surgery.     

Secondary laser in situ keratomileusis 1 year after primary LASIK for high myopia

PURPOSE: To report the results of the laser in situ keratomileusis (LASIK) using a second-cut hinged corneal flap to treat regression 1 year after primary LASIK for high myopia. SETTING: Istanbul University, Eye Research Center, Istanbul, Turkey. METHODS: Six eyes of 4 patients who had a mean myopic regression of -6.20 diopters (D) +/- 1.10 (SD) 1 year after primary LASIK were retreated with secondary LASIK performed using the Automated Corneal Shaper (Chiron Vision) and a 193 nm excimer laser (Chiron Technolas, Keracor 116). Fluence was 130 mJ/cm2 and the repetition rate, 10 Hz. RESULTS: Mean follow-up was 12.16 +/- 0.75 months. At the last follow-up, the mean spherical equivalent was -0.18 +/- 0.77 D (range +0.12 to -1.25 D). Two eyes (33.3%) remained within +/- 0.50 D of emmetropia; 5 eyes (83.3%) were within +/- 1.00 D of emmetropia. No patient lost best spectacle-corrected visual acuity. No complications occurred such as detachment of the former corneal flap and rolling, irregularity, or tearing of the new corneal flap. CONCLUSION: Secondary LASIK was an effective, safe method to treat regression after primary LASIK for high myopia.