Comparison of Different Corneal Power Readings From Pentacam in Post-laser In Situ Keratomileusis Eyes.

OBJECTIVES: To compare the various Pentacam-measured K-readings with the clinical history method (CHM) in eyes that have undergone myopic laser in situ keratomileusis (LASIK). METHODS: In this prospective study, Pentacam examination was performed in 71 eyes 1 month after myopic LASIK. The true net power (TNP) 4 mm, total corneal refractive power (TCRP) 4 mm, equivalent K-reading (EKR) 4.0 mm, and EKR 4.5 mm obtained from the same scan were compared with the K derived from CHM. RESULTS: The average baseline spherical equivalence was -5.44±2.38 D. After LASIK, the mean KCHM was 37.67±2.13 D, TCRP4mm was 37.14±1.79 D, TNP4mm was 36.88±1.76 D, EKR4.0mm was 37.58±1.94 D, and EKR4.5mm was 37.51±1.94 D. TCRP4mm, TNP4mm, and EKR4.5mm showed a statistically significant deviation from the KCHM, with the mean error being 0.53 D, 0.79 D, and 0.16 D, respectively (P<0.05). Only the EKR4.0mm showed no statistically significant difference from the KCHM (mean error 0.09 D, P=0.23). The EKR4.0mm also had the narrowest 95% limits of agreement (LoA) (-1.10 to +1.28 D), whereas both TCRP4mm and TNP4mm had a wider LoA (-0.88 to +1.95 D and -0.62 to +2.20 D, respectively). All four Pentacam K-readings had a strong and statistically significant correlation with the KCHM. CONCLUSIONS: Using the CHM as reference, the EKR4.0mm demonstrated the closest agreement when compared with the EKR4.5mm, TNP4mm, and TCRP4mm obtained from the same scan.

Conventional versus accelerated corneal collagen cross-linking in the treatment of keratoconus.

BACKGROUND: This study aims to compare the effect of conventional corneal collagen cross-linking (CXL) with accelerated corneal collagen cross-linking in treatment of keratoconus. DESIGN: A comparative interventional study was employed. PARTICIPANTS: Participants were consecutive cases of progressive keratoconus receiving either conventional (3 mW/cm(2) irradiance for 30 min) or accelerated CXL (9 mW/cm(2) irradiance for 10 min). METHODS: Clinical and topographic parameters were compared between the two groups. Postoperative corneal stromal demarcation line was measured using anterior segment optical coherence tomography. MAIN OUTCOME MEASURES: Clinical and topographic parameters such as corrected distant visual acuity (CDVA), maximum keratometry (Kmax), mean keratometry (Kmean), demarcation line depth were gathered from medical records. RESULTS: There were a total of 26 eyes with an average follow up of 13.9 ± 6.3 months. Fourteen eyes received conventional CXL, and 12 eyes had accelerated CXL. In the conventional CXL group, CDVA improved significantly (P = 0.021). There was also a significant reduction in Kmax (P = 0.003) and Kmean (P = 0.002). In the accelerated CXL group, no significant changes were found in CDVA (P = 0.395), Kmax (P = 0.388) and Kmean (P = 0.952) postoperatively. A significantly greater reduction in Kmax and Kmean were seen in conventional CXL compared to its accelerated counterpart (P = 0.001 and 0.015, respectively). The demarcation line was deeper in eyes with conventional CXL (P = 0.013), and the depth correlated significantly with the change in Kmean (r = -0.432, P = 0.045). CONCLUSION: Conventional and accelerated CXL are effective in stabilizing keratoconus progression after a mean of 12 months. Patients undergoing conventional CXL showed clinical improvement with greater corneal flattening, which correlated with a deeper corneal stromal demarcation line. This current study is the first to report such correlation.

Reduced cross-linking demarcation line depth at the peripheral cornea after corneal collagen cross-linking.

PURPOSE: To compare the corneal collagen cross-linking (CXL) demarcation line depth between the central and peripheral cornea after cross-linking using anterior segment optical coherence tomography. METHODS: Retrospective interventional case series of 38 eyes with keratoconus or postoperative LASIK ectasia treated with riboflavin ultraviolet A CXL (UV-X, IROC). CXL demarcation line depth, corneal thickness, and the ratio of the CXL demarcation line depth to the corneal thickness were measured using anterior segment optical coherence tomography at the central cornea and at 2 and 4 mm from the corneal center in four regions: temporal, nasal, superior, and inferior. The CXL demarcation line depths at the center and periphery were compared using the Friedman test. RESULTS: The CXL demarcation line was deepest in the central cornea (302 µm; range: 180 to 397 µm) and was reduced progressively toward the peripheral cornea, at nasal 2 mm (289.5 µm; range: 125 to 370 µm), at nasal 4 mm (206.5 µm; range: 100 to 307 µm), at temporal 2 mm (278.5 µm; range: 128 to 375 µm), and at temporal 4 mm (194 µm; range: 80 to 325 µm) (P<.001). The penetration proportion was greatest at the central cornea (64.8%; range: 44% to 80%) and was decreased toward the periphery, at nasal 2 mm (53.8%; range: 30% to 74%), at nasal 4 mm (33.8%; range: 19% to 53%), at temporal 2 mm (54.1%; range: 29% to 77%), and at temporal 4 mm (34.1%; range: 15% to 54%) (P⩽.001). CONCLUSIONS: Both the CXL demarcation line depth and its proportion over the corneal thickness were greater at the central cornea than the peripheral cornea.

Corneal collagen cross-linking demarcation line depth assessed by Visante OCT After CXL for keratoconus and corneal ectasia.

PURPOSE: To report the demarcation line depth after corneal collagen cross-linking (CXL) for keratoconus and postoperative LASIK ectasia with Visante (Carl Zeiss Meditec) optical coherence tomography (OCT) and investigate correlations between this depth and preoperative parameters and postoperative visual and keratometry outcomes. METHODS: Retrospective interventional case series of 40 eyes with keratoconus or postoperative LASIK ectasia treated with riboflavin ultraviolet-A CXL. Ophthalmic evaluation included uncorrected distance visual acuity, corrected distance visual acuity (CDVA), corneal topography (Pentacam, Oculus Optikgeräte GmbH), and postoperative anterior segment OCT. Correlation analyses were performed. Statistical significance was indicated by P<.05. RESULTS: At 6 months postoperative, mean demarcation line depth was 281.4±53.3 µm. Thinner minimal corneal thickness (r=0.413, P=.008), older age (r=-0.490, P=.001), higher grading of ectasia (for both keratoconus and postoperative LASIK ectasia) (r=-0.332, P=.044), female sex (r=0.343, P=.030), postoperative LASIK ectasia (r=-0.420, P=.007), and longer duration of disease (r=-0.377, P=.023) were correlated with shallower demarcation line depth. Forward stepwise multiple linear regression analysis showed that among all preoperative factors, minimal corneal thickness (standardized ß=0.473, P=.003) and age (standardized ß=-0.317, P=.036) were significantly associated with demarcation line depth. The CXL demarcation line depth and change in CDVA (r=-0.16, P=.325) and change of the steepest keratometry at 6 months (r=0.084, P=.637) were not correlated. CONCLUSIONS: The Visante OCT can be used for assessing CXL demarcation line depth. The demarcation line depth may decrease with the severity of ectasia and age.

Diagnosis, Management, and Treatment of Vernal Keratoconjunctivitis in Asia: Recommendations From the Management of Vernal Keratoconjunctivitis in Asia Expert Working Group.

Vernal keratoconjunctivitis (VKC) is an underdiagnosed and underrecognized ocular surface disease with limited epidemiological data in Asia. It is more prevalent in warm, dry, and windy climates, and often has a substantial impact on a patient's quality of life. In rare cases, VKC can be associated with vision loss, either through corticosteroid overuse or inadequate treatment of persistent inflammation. As a potentially severe and complex disease, there is variability with how VKC is managed across Asia and among the various allergic eye diseases. Diagnosis and treatment of patients with VKC is a challenge for many ophthalmologists, since no precise diagnostic criteria have been established, the pathogenesis of the disease is unclear, and anti-allergic treatments are often ineffective in patients with moderate or severe disease. In addition, the choice of treatment and management strategies used for patients varies greatly from country to country and physician to physician. This may be because of a lack of well-defined, standardized guidelines. In response, the Management of Vernal Keratoconjunctivitis in Asia (MOVIA) Expert Working Group (13 experts) completed a consensus program to evaluate, review, and develop best-practice recommendations for the assessment, diagnosis, and management of VKC in Asia. The expert-led recommendations are summarized in this article and based on the currently available evidence alongside the clinical expertise of ophthalmologists from across Asia with specialism and interest in the ocular surface, VKC, and pediatric ophthalmology.

Evaluation of the apparent change in posterior corneal power in eyes with LASIK using Orbscan II with magnification compensation.

PURPOSE: To develop a mathematical model for the assessment of the apparent posterior corneal curvature changes after myopic keratorefractive surgery with Orbscan (Bausch & Lomb) and to assess its accuracy with clinical data. METHODS: Part 1: Postoperative and preoperative magnification ratio of the posterior corneal surface was calculated from a theoretical eye model. Changes of radius and power of the posterior corneal surface were estimated over a wide range of refractive corrections and preoperative anterior corneal power. Part 2: The measured radius of the posterior cornea by Orbscan II 3 months postoperatively was converted to a new value based on the mathematical model. Both the measured radius and corrected radius were compared with preoperative values using paired sample t test. RESULTS: Myopic correction is associated with apparent steepening of the posterior curvature. The higher the amount of correction, the more the apparent difference. A statistically significant difference was noted between preoperative and measured postoperative radius of the posterior cornea (0.35 +/- 0.16 mm, P<.01). However, no significant difference was seen between preoperative and corrected postoperative radius of the posterior cornea (0.008 +/- 0.11 mm, P=.44). CONCLUSIONS: The change of corneal magnification induced by refractive correction partly explains the apparent steepening of the posterior corneal curvature. The mathematical model effectively compensates for the error in Orbscan II in the assessment of posterior corneal curvature after LASIK.

Descemet stripping endothelial keratoplasty: effect of the surgical procedure on corneal optics.

PURPOSE: To determine the changes in corneal optical performance after posterior lamellar corneal transplantation. DESIGN: Retrospective case series. METHODS: The anterior segment in four eyes of four patients who underwent Descemet stripping endothelial keratoplasty (DSEK) with cataract extraction and intraocular lens (IOL) implantation were imaged with the Visante anterior segment optical coherence tomography [OCT] (Carl Zeiss Meditec, Dublin, California, USA). The curvature of the posterior surface of the donor graft was compared with that of the host cornea, and corneal thickness was measured. RESULTS: All eyes had a hyperopic refractive error after surgery. The posterior corneal curvature after surgery was more than that before surgery. Average preoperative keratometry was 43.4 diopters (D), and after surgery, it was 42.8 D using keratometry. However, when the postsurgical corneal power was calculated using the Gaussian optics method, the average value was 40.8 D. CONCLUSIONS: The addition of a donor corneal graft to the posterior surface of decompensated corneas may lessen the effective optical power of the cornea and may have implications for IOL power calculations in these eyes.

Estimation of posterior corneal power for IOL calculation after myopic LASIK.

PURPOSE: To estimate the posterior corneal power for intraocular lens (IOL) calculation after myopic LASIK. METHODS: A retrospective study of 50 patients (92 eyes) who underwent uneventful myopic LASIK was conducted. Pre- and postoperative data (12 months) were collected including refraction and Orbscan II (Bausch & Lomb) for simulated keratometry (Sim K), central corneal thickness, and posterior corneal power. Statistical analysis was performed to determine the correlation between the postoperative posterior corneal power and other variables. An empirical formula was generated to predict the postoperative posterior corneal power. The net corneal power was calculated based on the new formula and Gaussian optics formula in an additional 31 eyes that underwent myopic LASIK and compared to the Orbscan total optical power map. The net corneal power was retrospectively applied to calculate the IOL power in an additional 10 patients who underwent cataract extraction after myopic LASIK. The back-calculation for emmetropic IOL power was performed and compared to the IOL power derived from the net corneal power. RESULTS: By using multiple linear regression, a formula to predict postoperative posterior corneal power can be computed from postoperative Sim K, central corneal thickness, and the amount of myopia treated with R2 of 0.63 (standard error =0.25) (P<.05). The net corneal power was highly correlated to the total optical power (R2=0.96); no statistically significant difference (paired t test) was noted (P>.05). The error of the IOL power derived from the net corneal power was -0.30+/-0.20 diopters. CONCLUSIONS: Corneal power after myopic LASIK can be estimated using postoperative Sim K, central corneal thickness, and the amount of myopia treated, which can be used for the assessment of IOL power after myopic 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.

Comparison of techniques for corneal power assessment after myopic LASIK without the use of preoperative data.

PURPOSE: To compare the accuracy of different corneal power assessment techniques that do not require preoperative information with the clinical history method. METHODS: This retrospective study analyzed 50 eyes of 50 patients using 3-month postoperative data. Net corneal powers were obtained with each of the following methods: Maloney, Wang, Sonego-Krone, Srivannaboon, Shammas, Orbscan flat axis, and Gaussian optics formula with Orbscan. Results were compared to the clinical history method using paired sample t test, Bland-Altman plots, and linear regression. RESULTS: Both the Gaussian optics formula and Wang method were not significantly different from the clinical history method. The Sonego-Krone method significantly underestimated the corneal power, whereas the Maloney, Srivannaboon, Shammas, and Orbscan flat axis methods significantly overestimated the corneal power. CONCLUSIONS: The Gaussian optics formula and Wang method yielded comparable results with the clinical history method for assessing corneal power. The Gaussian optics formula produced the smallest standard deviation.

Measurement of LASIK flap thickness with anterior segment optical coherence tomography.

PURPOSE: To assess the interobserver variability and agreement of anterior segment optical coherence tomography (OCT) in the measurement of LASIK flap thickness, and to compare the results with intraoperative ultrasound pachymetry measurements. METHODS: Thirty-nine eyes of 20 consecutive patients undergoing LASIK with the XP microkeratome (Bausch & Lomb) and ALLEGRETTO Eye-Q laser system (WaveLight Inc) had corneal flap thickness measured with SP-100 ultrasound (Tomey Corp) intraoperatively and with OCT (Visante; Carl Zeiss Meditec Inc) postoperatively. Interobserver assessment was performed by comparing the flap thickness measurements obtained from the same scan by 2 masked, independent observers. Agreement of OCT scan was determined by assessment of 2 different scans of the same eye by the same observer. RESULTS: Mean (+/- standard deviation) flap thickness measured by ultrasound, OCT scan 1 (OCT 1-1) and scan 2 (OCT 1-2) assessed by observer 1, and OCT scan 1 (OCT 2-1) and scan 2 (OCT 2-2) assessed by observer 2 were 112.79+/-19.71, 124.69+/-17.02, 127.59+/-17.32, 130.59+/-20.34, and 133.74+/-19.70 microm, respectively. No statistically significant difference among the interobserver measurements was seen. The difference between OCT and ultrasound measurements by observers 1 and 2 was statistically significant (P<.01). Correlation among all measurements was statistically significant. Good agreement among the OCT scans was noted. CONCLUSIONS: Optical coherence tomography showed good correlation among measurements and observers for different OCT measurements in the assessment of corneal flap thickness after LASIK. However, OCT significantly overestimated flap thickness when compared to ultrasound despite a good correlation between these two modalities. Optical coherence tomography measurements should not be substituted for standad ultrasound measurements at the present time.

Posterior corneal curvature measurements with peripheral fitting zones before and after myopic LASIK using Orbscan II.

PURPOSE: To compare pre- and postoperative posterior corneal curvature measurements in peripheral fitting zones using the Orbscan II topographer in patients undergoing myopic LASIK. METHODS: Retrospective analysis of preoperative and 3-month postoperative Orbscan II data of 194 eyes that underwent myopic LASIK at a university eye center. Posterior corneal power was estimated using the peripheral 7- to 10-mm fitting zones. The pre- and postoperative values were analyzed and compared. RESULTS: The mean difference in estimated pre- and postoperative power of the posterior cornea was -0.04 +/- 0.16 diopters (P < .01). CONCLUSIONS: The difference in posterior corneal curvature measurement following myopic LASIK using the peripheral fitting zone with the Orbscan II, as compared to the preoperative values, is clinically insignificant.

Repeatability and reproducibility of pachymetric mapping with Visante anterior segment-optical coherence tomography.

PURPOSE: To determine the repeatability and reproducibility of central and peripheral corneal pachymetry mapping with anterior segment-optical coherence tomography (AS-OCT). METHODS: An observational cross-sectional study involving two groups: 27 healthy eyes and 20 eyes with keratoconus. Each subject underwent scanning sessions with AS-OCT to determine intraobserver repeatability, interobserver reproducibility, and additionally for healthy eyes, intersession reproducibility for different regions of the cornea up to a 10-mm diameter. Main outcome measures were reproducibility and repeatability coefficients, intraclass correlation coefficients, and coefficients of variation of the average central (0-2 mm), pericentral (2-5 mm), transitional (5-7 mm), and peripheral (7-10 mm) corneal thicknesses generated by the Visante AS-OCT (Carl Zeiss Meditec, Inc., Dublin, CA) pachymetric mapping protocol. RESULTS: The coefficients of repeatability were less than 2% in healthy subjects and less than 3% in patients with keratoconus. The reproducibility coefficients were less than 2% and 4% in healthy subjects and patients with keratoconus, respectively. There was no significant difference between scans obtained by different observers or during different visits. The intraclass correlation coefficients were greater than 0.99 and 0.97 in healthy subjects and patients with keratoconus, respectively. CONCLUSIONS: With the pachymetric mapping protocol of Visante AS-OCT, these results suggest that central and peripheral corneal thickness measurements in healthy subjects and in eyes with keratoconus are repeatable and reproducible.

Agreement among 3 methods to measure corneal thickness: ultrasound pachymetry, Orbscan II, and Visante anterior segment optical coherence tomography.

PURPOSE: To assess the agreement of central and paracentral corneal thickness measurements between ultrasound pachymetry (USP), Orbscan II, and Visante anterior segment optical coherence tomography (ASOCT). DESIGN: Observational cross-sectional study. PARTICIPANTS: Seventy eyes of 70 subjects. METHODS: Each subject underwent Orbscan II (using an acoustic equivalent correction factor of 0.89), ASOCT, and USP examination. Bland-Altman plots were used to evaluate agreement between instruments. MAIN OUTCOME MEASURES: Central and paracentral corneal thickness measurements by the 3 methods and agreement, as evaluated by 95% limits of agreement (LOA). RESULTS: The mean measurements of average central corneal thickness by USP, Orbscan II, and ASOCT were 553.5+/-30.26 microm, 553.22+/-25.47 microm, and 538.79+/-26.22 microm, respectively. There was high correlation between instruments: USP with ASOCT (r = 0.936, P<0.001), USP with Orbscan II (r = 0.900, P<0.001) for central corneal thickness measurements, and Orbscan II with ASOCT for average paracentral 2- to 5-mm measurements (r = 0.947, P<0.001). The mean differences (and upper/lower LOA) for central corneal thickness measurements were 0.31+/-13.34 microm (26.44/-25.83) between USP and Orbscan II, 14.74+/-10.84 microm (36.0/-6.51) between USP and ASOCT, and 14.44+/-9.14 microm (32.36/-3.48) between Orbscan II and ASOCT. The average mean difference (and upper/lower LOA) between Orbscan II and ASOCT for paracentral 2- to 5-mm corneal thickness measurements was 10.35+/-8.67 microm (27.35/-6.65). CONCLUSION: Anterior segment optical coherence tomography underestimated corneal thickness compared with that measured with USP. Anterior segment optical coherence tomography had better agreement with the gold standard USP, as compared with Orbscan II. However, important discrepancies among instruments exist. Clinicians should be aware that corneal thickness measurements are influenced by the method of measurement and that, although highly correlated, these instruments should not be used interchangeably for the assessment of corneal thickness.

Accuracy of Orbscan II in the assessment of posterior curvature in patients with myopic LASIK.

PURPOSE: To evaluate the accuracy of Orbscan II measurements in assessing posterior corneal curvature in patients undergoing myopic LASIK. METHODS: Using the Orbscan II, posterior corneal curvature was assessed pre- and postoperatively in 304 eyes that underwent myopic LASIK. The radius of curvature and corneal refractive power in diopters (D) were compared using the paired sample t test. RESULTS: The mean pre- and postoperative radius of posterior corneal curvature were 6.49 +/- 0.26 mm and 6.35 +/- 0.30 mm, respectively. Mean pre- and postoperative posterior corneal power were -6.17 +/- 0.25 D and -6.32 +/- 0.30 D, respectively, and the difference (0.14 +/- 0.14 D) was statistically significant (P < .01). CONCLUSIONS: Although the derived value for the power of the postoperative LASIK posterior corneal surface is overestimated using the Orbscan II, this small difference may not be clinically important. Orbscan II measurements can therefore be used (with caution) to measure posterior corneal curvature in patients with myopic LASIK for the assessment of intraocular lens power based on the Gaussian optics formula.

Repositioning of free cap four days after LASIK.

PURPOSE: To report management and outcome of late repositioning of flap dislodgement after LASIK. METHODS: A 27-year-old man underwent LASIK in the right eye for correction of myopia, which was complicated by free cap. The flap was repositioned, but dislodged 2 days later. The dislodged flap was stored in balanced salt solution for 48 hours and repositioned 4 days after initial surgery. RESULTS: Postoperatively, the flap remained apposed, but diffuse lamellar keratitis and epithelial ingrowth developed, which was managed with topical steroids and topical mitomycin C. Stromal haze gradually decreased by 16 months postoperatively, resulting in best spectacle-corrected visual acuity of 20/20. CONCLUSIONS: Flap dislodgement > 48 hours postoperatively can be repositioned with good visual outcome. The flap should be preserved in the event of such complication.

Comparison of corneal flap thickness between primary eyes and fellow eyes using the Zyoptix XP microkeratome.

PURPOSE: To evaluate corneal flap thickness created in myopic laser in situ keratomileusis (LASIK) using the Zyoptix XP 120 microkeratome (Bausch & Lomb). SETTING: University-based eye clinic. METHODS: Corneal thickness was measured preoperatively and intraoperatively after flap creation in 62 consecutive patients (124 eyes) who had LASIK for the correction of myopia. Corneal flap thickness was calculated by subtracting stromal bed thickness from total corneal thickness. In each patient, both corneas (right followed by left) were cut by 1 the same Zyoptix XP 120 microkeratome blade at the same session. RESULTS: The mean actual flap thickness was 115.34 microm +/- 16.34 (SD) in right eyes and 104.55 +/- 14.34 mum in left eyes. The mean actual flap thickness in right eyes was not statistically significantly different from the 120 microm proposed by the manufacturer (P = .142); however, the mean actual flap thickness in left eyes was statistically significantly different from the 120 microm (P<.001). The mean flap thickness in the second eye was also statistically significantly thinner than in the first eye (P<.001). CONCLUSIONS: The corneal flaps were thinner than expected when a Zyoptix XP 120 microkeratome was used in LASIK. Although the first cuts produced thinner flaps, this difference was not statistically significant. However, the second cuts produced significantly thinner flaps.

Central corneal thickness measurements using Orbscan II, Visante, ultrasound, and Pentacam pachymetry after laser in situ keratomileusis for myopia.

PURPOSE: To compare corneal pachymetry assessment using 4 measurement methods in eyes after laser in situ keratomileusis (LASIK) for myopia. SETTING: Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, Hong Kong SAR. METHODS: Fifty-two consecutive patients (103 eyes) who had LASIK for the correction of myopia had Orbscan II (Bausch & Lomb), Visante (Carl Zeiss Meditec), Pentacam (Oculus, Inc.), and ultrasound (US) pachymetry (Sonomed, 200P) 6 months after surgery. Data were analyzed using the paired sample t test, Bland-Altman plots, and linear regression. RESULTS: The mean postoperative pachymetry measured by US, Orbscan (0.89 acoustic factor), Pentacam, and Visante pachymetry were 438.2 microm+/-41.18 (SD), 435.17+/-49.63 microm, 430.66+/-40.23 microm, and 426.56+/-41.6 microm, respectively. Compared with the US measurement, Pentacam and Visante measurements significantly underestimated corneal thickness by a mean of 7.54+/-15.06 microm (P<.01) and 11.64+/-12.87 microm (P<.01), respectively. There was no statistically significant difference between US and Orbscan measurements. CONCLUSION: Pentacam and Visante measurements of corneal thickness 6 months after LASIK were significantly less than those obtained using Orbscan and US pachymetry, although all 4 measurement methods showed a high correlation with each other.

Topical anesthesia-induced keratopathy after laser-assisted subepithelial keratectomy.

A 42-year-old woman had uneventful bilateral laser-assisted subepithelial keratectomy (LASEK) to correct myopia. She experienced intense pain in the first postoperative week and obtained topical oxybuprocaine for pain relief. Subsequently, she developed bilateral persistent corneal epithelial defects, epithelial edema, and bullae that failed to heal with bandage contact lens and topical lubricants. Over the next 4 months, there was progressive corneal stromal thinning and descemetocele formation in 1 eye, requiring application of cyanoacrylate glue, and stromal edema and scarring in the other eye, which resulted in a visual acuity of counting fingers. Investigations did not reveal associated infection or an underlying immunological disorder; however, the patient admitted to excessive use of topical anesthetic eyedrops in the post-LASEK period. She subsequently had penetrating keratoplasty and lens extraction with IOL implantation in the right eye. The left eye healed with central corneal scarring. This case illustrates that serious sight-threatening complications may occur after LASEK due to abuse of topical anesthetic agents.

Pachymetry assessment with Orbscan II in postoperative patients with myopic LASIK.

PURPOSE: To compare central corneal thickness after LASIK for myopia, using ultrasonic pachymetry and Orbscan II measurements, and to evaluate changes in these measurements over time. METHODS: Central corneal thickness measurements obtained by ultrasonic pachymetry and Orbscan II (Bausch and Lomb, Rochester, NY) in patients who underwent myopic LASIK between July 2002 and May 2003 were analyzed. The two measurements were assessed preoperatively and postoperatively at 1 day and 1, 3, 6, and 12 months. RESULTS: In 237 eyes, using the correction factor 0.93, no significant difference was noted in the preoperative central corneal thickness measured by ultrasonic pachymetry (561.89 +/- 28.66 microm) and Orbscan pachymetry (562.28 +/- 28.18 microm) (P =.713). Postoperatively, the difference was statistically significant at day 1 and 1, 3, and 6 months (P < .001), but was not significant at 12 months (P = .130). CONCLUSIONS: Orbscan II measurements of central corneal thickness after myopic LASIK are less than those measured by ultrasonic pachymetry; however, this difference decreases with time and may not be significant after 1 year.