Sabong Srivannaboon

Avoiding serious corneal complications of laser assisted in situ keratomileusis and photorefractive keratectomy

OBJECTIVE To identify avoidable factors that can lead to serious complications of laser refractive surgery (photorefractive keratectomy [PRK] and laser assisted in situ keratomileusis [LASIK]). DESIGN Noncomparative case series. PARTICIPANTS Twenty-seven eyes of 19 patients who had undergone either LASIK or PRK with severe complications accrued retrospectively. INTERVENTION Review of clinical records. MAIN OUTCOME MEASURES Symptoms, refractive outcome, and assessment of avoidable factors contributing to the complication. RESULTS Patients were analyzed in four groups: group 1, scarring with ectasia; group 2, unrecognized keratoconus; group 3, flap related LASIK complications; and group 4, multiple retreatments. The 8 eyes with scarring and ectasia presented with the worst vision, 20/400 uncorrected visual acuity and 20/200 best spectacle-corrected visual acuity, with avoidable factors considered as high or difficult prescriptions with multiple retreatments. Four eyes in two patients with possible forme fruste keratoconus showed worsening irregular astigmatism. Laser assisted in situ keratomileusis flap complications included six eyes with partial laser treatment under an incomplete flap with subsequent severe irregular astigmatism. Six eyes in three patients who had undergone an average of three multiple retreatments showed decreased vision with irregular astigmatism. CONCLUSIONS Certain severe complications of laser refractive surgery likely can be avoided by using caution when treating high prescriptions, particularly with retreatments, recognizing early keratoconus and avoiding laser treatment under a partial flap in LASIK.

NORMAL HUMAN CORNEAL CELL POPULATIONS EVALUATED BY IN VIVO SCANNING SLIT CONFOCAL MICROSCOPY

Purpose To analyze cellular populations in healthy human corneas. Methods The study group consisted of 58 eyes of 45 patients with normal corneas. The age distribution was 45 ± 17 years (mean ± SD; range, 20–84). Scanning slit confocal microscopy of the central corneas was performed. The images were analyzed visually for cell morphology, and the densities and areas of cells were measured. Results No statistically significant differences were measured in cell densities or cell areas of any corneal layer between female and male patients (p = 0.22–0.50) nor between right and left eyes (p = 0.16–0.45). The area of superficial epithelial cells was 913 ± 326 μm2 (mean ± SD; range, 518–2,112), and the superficial epithelial cell density was 1,213 ± 370 cells/mm2 (mean ± SD; range, 473–1,929). The area of basal epithelial cells was 177 ± 19 μm2 (mean ± SD; range, 138–242), and the basal epithelial cell density was 5,699 ± 604 cells/mm2 (mean ± SD; range, 4,135–7,267). The average apparent keratocyte density was 1,058 ± 217 cells/mm2 (mean ± SD; range, 604–1,599) in the anterior stroma, and 771 ± 135 cells/mm2 (mean ± SD; range, 493–1,145) in the posterior stroma. The difference in apparent keratocyte densities between the anterior and posterior stroma was statistically significant (p < 0.001). The average endothelial cell area was 334 ± 51 μm2 (range, 273–553), and the cell density was 3,055 ± 386 cells/mm2 (mean ± SD; range, 1,809–3,668). The endothelial cell density had a negative, statistically significant correlation with age (r = −0.68, p < 0.001). The densities of the other corneal cell layers did not have a statistically significant correlation with age. Conclusion In vivo scanning slit confocal microscopy is a useful tool for studying corneal cell populations. Central corneal cell densities were found to decrease significantly with age only in the endothelium. For the first time in human corneas using in vivo confocal microscopy, this study statistically confirms a higher apparent number of keratocytes in the anterior stroma than in the posterior stroma.

Accuracy of Orbscan total optical power maps in detecting refractive change after myopic laser in situ keratomileusis

PURPOSE To determine whether the refractive change obtained using the Orbscan-derived total optical power (TOP) map is in concordance with the manifest refractive change produced by laser in situ keratomileusis (LASIK). SETTING LASIK Vision Canada, Vancouver, BC, Canada (an ambulatory surgical center for refractive surgery). METHODS Twenty eyes of 10 consecutive bilateral LASIK patients were included in the study. Orbscan topographical analysis and manifest refraction were performed preoperatively and at least 1 month postoperatively. The change in manifest refraction (corrected to the corneal plane) before and after LASIK was correlated with the corneal power change averaged within the 2.0, 3.0, 4.0, and 5.0 mm diameter zones of TOP and axial power maps. RESULTS The central 4.0 mm zone TOP map gave the best correlation between manifest refractive change and Orbscan-measured corneal power change (r2 = 0.835, P < .004). The correlation was higher with TOP maps than with anterior axial power maps. CONCLUSION The corneal power change measured by the Orbscan TOP maps correlated highly with the changes in manifest refraction after LASIK.

Epithelial Thickness Profile Changes Induced by Myopic LASIK as Measured by Artemis Very High-frequency Digital Ultrasound

PURPOSE To characterize changes in the corneal epithelial thickness profile induced by myopic LASIK. METHODS This was a prospective study of 37 eyes of 19 myopic LASIK patients. Eyes were divided into three groups according to sphere in the maximum myopic meridian: low (-1.00 to -4.00 diopters [D]), moderate (-4.25 to -6.00 D), and high myopia (-6.25 to -13.50 D). The epithelial thickness profile was measured by prototype Artemis very high-frequency (VHF) digital ultrasound scanner (ArcScan Inc) across the central 10-mm corneal diameter preoperatively and between 3 and 6 months postoperatively. The epithelial thickness profile was determined by averaging the epithelial thickness within annular bands centered on the corneal vertex. The change in epithelial thickness profile was calculated as the difference between the preoperative and postoperative epithelial thickness profiles. RESULTS The corneal epithelium thickened after myopic LASIK across the central 6 mm with maximum thickening centrally and progressively less thickening centrifugally in low myopia, and a more homogenous thickening in moderate and high myopia within the 5-mm diameter. The mean epithelial thickening at the corneal vertex was 7.41 +/- 1.09 microm, 9.29 +/- 1.22 microm, and 12.33 +/- 1.05 microm for low, moderate, and high myopia, respectively. The rate of epithelial thickening at the corneal vertex per diopter of myopia treated decreased with increasing myopia. CONCLUSIONS Although the magnitude of epithelial thickening increased with increasing ablation depth, in accordance with Barraquers Law of Thicknesses, the myopic refractive shift due to epithelial thickness profile changes was paradoxically more significant in low myopia than in high myopia.

Topical 0.002% Mitomycin C for the Treatment of Conjunctival-corneal Intraepithelial Neoplasia and Squamous Cell Carcinoma

PURPOSE To demonstrate the efficacy of topical 0.002% mitomycin C (MMC) as an adjunctive and alternative treatment in primary and recurrent conjunctival-corneal intraepithelial neoplasia (CCIN) and squamous cell carcinoma (SCC). METHODS The medical records of 7 patients with histopathologically confirmed CCIN and conjunctival SCC were retrospectively reviewed. All cases were treated with topical 0.002% MMC 4 times daily. The tumor size pre- and post-treatment, clinical response, and ocular complications were evaluated. RESULTS The mean age of the patients was 56 +/- 13.4 years. The most common presenting symptom was foreign body sensation (57.1%) with a mean duration of 2.3 +/- 3.8 months. Six patients had pathologically proven CCIN (85.7%) and 1 had SCC (14.3%). Before MMC treatment, 6 eyes (85.7%) had recurrences after surgical excision. The tumor-free period ranged from 2 to 19 months. Two patients had multiple recurrences. MMC 0.002% 4 times daily was applied for a period of 5.4 +/- 4.4 weeks (range, 2-14). All had complete tumor regression as observed clinically and confirmed by impression cytology. Side effects of MMC therapy included ocular irritation, mild conjunctival hyperemia, and punctate keratopathy. There were no serious complications detected. The mean follow-up time was 30.7 +/- 15 months (range, 2-52) with no evidence of clinical recurrence in any case. CONCLUSIONS Topical 0.002% MMC showed a favorable outcome as an adjunctive and alternative treatment of CCIN and SCC with regression of primary and recurrent tumors.

Clinical comparison of a new swept-source optical coherence tomography–based optical biometer and a time-domain optical coherence tomography–based optical biometer

Purpose To evaluate the repeatability and reproducibility of a newer swept‐source optical biometer and to compare it with a standard partial coherence interferometry (PCI) biometer. Setting Siriraj Hospital, Mahidol University, Bangkok, Thailand. Design Prospective comparative study. Methods One hundred eyes from 100 cataract patients were enrolled in this study. Each patient was measured with 2 optical biometers, a newer swept‐source optical biometer (IOLMaster 700) and a standard partial coherence interferometry biometer (IOLMaster 500) by 2 independent operators. The keratometry, axial length (AL), anterior chamber depth, white‐to‐white corneal diameter, and intraocular lens (IOL) power, calculated by the SRK/T and the Haigis formulas for each device, were recorded. Intraoperator repeatability and interoperator reproducibility of both devices were analyzed using intraclass correlation coefficients (ICCs). Agreement of ocular biometry and IOL power between the 2 devices was evaluated using the Bland‐Altman method. Results The repeatability and reproducibility of the swept‐source and standard biometers were high for all ocular biometry parameters (ICC, 0.93‐1.00). The agreement between the 2 biometers was also high (ICC, 0.92‐1.00). The IOL powers obtained from both devices were not distinct. Because of the density of the cataracts, the AL in 5 eyes could be measured only by the swept‐source biometer. Conclusions Repeatability and reproducibility of a swept‐source optical biometer was excellent and agreement with a standard biometer was very high. Better lens penetration ability and AL measurements were obtained with the swept‐source biometer than with the standard biometer. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Epithelial and stromal changes induced by intacs examined by three-dimensional very high-frequency digital ultrasound.

PURPOSE To examine epithelial and stromal layers by three-dimensional very high-frequency (VHF) digital ultrasound scanning before and after implantation of Intacs (intracorneal ring segments [ICRS]). METHODS Three-dimensional scanning was performed in five eyes before and 3 months after Intacs insertion. Digital signal processing techniques provided high-resolution B-scan imaging and I-scan traces for high-precision (1-microm) three-dimensional pachymetry. Thickness maps of individual corneal layers were constructed of the epithelium, stroma, and full cornea before and after surgery. Difference maps for epithelium and stroma were produced to examine anatomical changes in the thickness profile induced in each layer and correlate these to refractive changes. RESULTS B-scan examination revealed stromal and epithelial anatomy anterior and adjacent to the Intac. Ring depth could be measured topographically. There was stromal lamellar displacement by the ring segments that produced a concave anterior stromal groove within an annulus central to the ring. Epithelial filling of this concavity was shown in three dimensions in such a way as to produce orthogonally asymmetrical flattening of the corneal surface, thus potentially accounting for induced astigmatism. Mapping of the central stroma demonstrated thickening, potentially also accounting for astigmatic changes ascribable to orthogonal asymmetry. CONCLUSIONS VHF digital ultrasound scanning provided imaging and three-dimensional thickness mapping of corneal layers, enabling anatomical evaluation of the changes induced in the cornea by Intacs.

Evaluating microkeratome efficacy by 3D corneal lamellar flap thickness accuracy and reproducibility using artemis VHF digital ultrasound arc-scanning

PURPOSE To present a method that determines the efficacy of flap creation using a microkeratome. METHODS Thirty-six eyes of 18 patients were included in the study, operated by two experienced surgeons using the Moria LSK-One microkeratome. Very high-frequency (VHF) digital ultrasound arc-scanning using Artemis technology was used to measure the Reinstein Flap Thickness Profile created by addition of the preoperative epithelial thickness profile to the postoperative stromal component of the flap. Descriptive statistics revealed central flap thickness accuracy and reproducibility. Univariate and multivariate regression analysis was used to determine correlations between central flap thickness and preoperative clinical parameters. Three-dimensional flap thickness maps demonstrated the mean, median, standard deviation, and range of thickness. RESULTS Intended flap thickness was 160 microm. Mean central flap thickness was 161 microm in the right eye and 166 microm in the left eye. Central reproducibility (standard deviation of the mean) was 30.3 microm, with a range of 106 to 228 microm. Central flap thickness correlated to preoperative corneal thickness measured by VHF digital ultrasound but not by Orbscan. On qualitative analysis, no consistency among eyes was observed in the three-dimensional flap thickness map. Flaps were on average thinner in the center, but not in all cases. CONCLUSIONS A systematic qualitative and quantitative statistical evaluation of microkeratome accuracy and reproducibility can be performed by measuring corneal flap thickness with arc-scanning VHF digital ultrasound.

Comparison of ocular biometry and intraocular lens power using a new biometer and a standard biometer

Purpose To compare the repeatability and reproducibility of ocular biometry and intraocular lens (IOL) power obtained with a new optical biometer (AL‐Scan) and a standard optical biometer (IOLMaster 500). Setting Siriraj Hospital, Mahidol University, Bangkok, Thailand. Design Prospective comparative study. Methods Two independent operators measured eyes with cataract using both biometers. The keratometry values, axial length, anterior chamber depth, white‐to‐white (WTW) corneal diameter, and IOL power calculated using the Holladay 1 formula obtained with each device were recorded. Intraoperator repeatability and interoperator reproducibility of both devices were analyzed using the intraclass correlation coefficient (ICC). The agreement in ocular biometry and IOL power between the 2 devices was evaluated by the Bland‐Altman method. Results The study recruited 137 eyes of 81 patients. The repeatability and reproducibility of both devices were high for all ocular biometry measurements (ICC, 0.87‐1.00). Except for the WTW corneal diameter (ICC, 0.44), the agreement between the biometers was also high (ICC, 0.98‐0.99). The IOL powers calculated by the Holladay 1 formula were similar between the 2 biometers. Conclusion The new optical biometer provided excellent repeatability and reproducibility for all ocular biometry. Agreement with the standard optical biometer was good except for the WTW corneal diameter. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Comparison of corneal astigmatism and axis location in cataract patients measured by total corneal power, automated keratometry, and simulated keratometry

PURPOSE: To compare the corneal astigmatism (magnitude and axis location) derived by total corneal power (TCP), automated keratometry, and simulated keratometry. SETTING: Siriraj Hospital, Mahidol University, Bangkok, Thailand. DESIGN: Prospective comparative study. METHODS: Eyes with previous ocular surgery or abnormalities were excluded. All patients were examined with the ARK 730A autokeratometer and the Galilei analyzer. The steepest and flattest corneal power along with the steepest axis of the TCP, automated keratometry, and simulated keratometry were recorded. Vector analysis (J0 and J45) was calculated. Analysis of variance with Bonferroni correction was performed for multiple comparisons. Outcome measures were the magnitude and axis location of astigmatism. RESULTS: One hundred eyes of 100 cataract patients were randomly selected. There was no statistically significant difference in the mean steepest axis between TCP (93.31 ± 68.75 [SD]), automated keratometry (94.24 ± 64.78), and simulated keratometry (92.42 ± 64.30). However, the mean magnitude of astigmatism measured by TCP (1.23 ± 0.75) was significantly higher than that measured by automated keratometry (0.93 ± 0.68) (P=.01) but not than that measured by simulated keratometry (1.08 ± 0.68) (P=.43); there was no statistically significant difference in J0 or J45. Twenty two (40%) of 54 eyes with more than 1.00 diopter of TCP astigmatism had more than 10 degrees of axis difference from automated keratometry. CONCLUSIONS: The magnitude of TCP astigmatism was higher than that of automated keratometry. The axis location was similar. However, there was more than 10 degrees of axis difference between automated keratometry and TCP in patients with high astigmatism. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.