Publications (31)97 Total impact
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Article: The Effect of Amniotic Membrane De-epithelialization Method on its Biological Properties and Ability to Promote Limbal Epithelial Cell Culture.
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ABSTRACT: PURPOSE: To characterize the de-epithelialized human amniotic membrane (HAM) and compare cell attachment and proliferation efficiencies. METHODS: HAM was de-epithelialized by 20% ethanol (AHAM), 1.2 U/ml Dispase (DHAM), 0.02% EDTA (EHAM), 0.25% trypsin-EDTA (THAM) and 5M urea (UHAM), respectively, followed by gentle scrapping with #15 blade. Surface topology, extracellular matrix (ECM) and growth factor content were characterized and compared to intact HAM by electron microscopies (EM), atomic force microscopy (AFM), immunohistochemistry and western blotting. Primary human limbal epithelial cells (LEC) attachment and proliferation efficiencies were assayed. Statistical significance was calculated by SPSS and Fisher's Least Significant Difference test. RESULTS: EHAM, THAM and UHAM had intact basal lamina and smooth basement membrane surface shown under transmission and scanning EM and AFM. Cell remnants stayed on AHAM. Disrupted basement membrane and stroma was found in DHAM. Immunostaining intensity quantification and hierarchical clustering revealed that ECM composition of EHAM and UHAM resembled to intact HAM. In contrast, DHAM and THAM had drastic loss of ECM and growth factor content. LEC attachment efficiency at 24 hours post-seeding was the highest in EHAM (51% as on conventional culture surface), followed by UHAM and AHAM. However, cell proliferation indices at day 10 of culture were similar among different HAM substrates, suggesting repair of ECM and basement membrane by growing epithelial cells. CONCLUSION: Urea denudation preserved the basement membrane integrity, ECM and growth factor composition, and had higher cell attachment and proliferation efficiencies. With its short processing time, urea treatment offers a novel alternative for HAM de-epithelialization.Investigative ophthalmology & visual science 04/2013; · 3.43 Impact Factor -
Article: Comparison of Four Different VisuMax Circle Patterns for Flap Creation After Small Incision Lenticule Extraction.
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ABSTRACT: To compare four different Circle patterns for flap creation after small incision lenticule extraction (SMILE). SMILE was performed on six rabbits. Twenty-eight days after the initial procedure, corneal flaps were created using Circle patterns. Rabbits were divided into four groups (patterns A, B, C, and D). Pattern A creates a circular side cut to meet the cap cut within the clearance zone (outside of the optical zone). Patterns B, C, and D create a lamellar ring posterior, anterior, and at the same depth, respectively, to the cap to meet the cap cut in the clearance zone with the help of a junction cut. Difficulty of flap lift was graded from 1 (easiest) to 5 (most difficult). The bed quality was assessed by scanning electron microscopy. Flaps created by patterns A and D were the easiest to lift (grade 2). The resulting flap bed was smooth and undisrupted. However, pattern A resulted in a reduced re-treatment area. Flaps created by pattern B were the most difficult to lift (grade 4). The stromal dissection was difficult in an attempt to ascertain the original optical zone from the lamellar ring, placed posterior. Flaps produced by pattern C were easy to lift, with minor intrastromal resistance experienced during the lifting process (grade 3). The transition between the lamellar ring and cap cut was hardly discernible in pattern C-treated corneas. Pattern D, a lamellar ring adjacent to the cap cut, was the most optimal to be used for flap creation in cases of SMILE re-treatment.[J Refract Surg. 2013;29(4):236-244.].Journal of refractive surgery (Thorofare, N.J.: 1995) 04/2013; 29(4):236-44. · 2.54 Impact Factor -
Article: Cost-Effectiveness of Descemet's Stripping Endothelial Keratoplasty versus Penetrating Keratoplasty.
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ABSTRACT: PURPOSE: Selective endothelial transplantation in the form of Descemet's stripping endothelial keratoplasty (DSEK) is rapidly replacing traditional full-thickness penetrating keratoplasty (PK) for endothelial disease. An incremental cost-effectiveness analysis was performed to determine whether the benefits of DSEK are worth the additional costs. DESIGN: Retrospective cohort study. PARTICIPANTS: Patients at the Singapore National Eye Center, a tertiary eye center in Singapore, with Fuchs' dystrophy or bullous keratopathy who underwent either PK or DSEK. INTERVENTION: Patients underwent either PK (n = 171) or DSEK (n = 93) from January 2001 through December 2007. Data were collected from inpatient and outpatient notes corresponding to the time immediately before the procedure to up to 3 years after. MAIN OUTCOME MEASURES: Improvements in best spectacle-corrected visual acuity were used to calculate the increase in quality-adjusted life years (QALYs) 3 years after the procedure. This was combined with hospital charges (a proxy for costs) to determine incremental cost-effectiveness ratios (ICERs) comparing PK with no intervention and DSEK with PK. RESULTS: Three-year charges for DSEK and PK were $7476 and $7236, respectively. The regression-adjusted improvement in visual acuity for PK relative to no intervention was -0.613 logarithm of the minimum angle of resolution (logMAR) units (P<0.001), and for DSEK relative to PK, it was -0.199 logMAR units (P = 0.045). The regression-adjusted marginal gain in utility for PK relative to no intervention was 0.128 QALYs (P<0.001) and for DSEK relative to PK was 0.046 QALYs (P = 0.031). This resulted in ICERs of $56 409 per QALY for PK relative to no intervention and $5209 per QALY for the more expensive DSEK relative to PK. CONCLUSIONS: If the goal is to maximize societal health gains given fixed resources, DSEK should be the preferred strategy. For a fixed budget, it is possible to achieve greater QALY gains by providing DSEK to as many patients as possible (and nothing to others), rather than providing PK. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.Ophthalmology 11/2012; · 5.45 Impact Factor -
Article: Refractive lenticule extraction flap and stromal bed morphology assessment with anterior segment optical coherence tomography.
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ABSTRACT: To evaluate the flap and stromal bed after refractive lenticule extraction using optical coherence tomography (OCT). Singapore National Eye Centre, Singapore. Longitudinal case series. Horizontal scans (RTVue) were taken preoperatively and after refractive lenticule extraction. Two procedures were performed: femtosecond lenticule extraction and small-incision femtosecond lenticule extraction. Flap and bed thicknesses were measured at the center (0.0 mm) and 1.5 mm and 3.0 mm to either side. At 1 week, the mean flap at 0.0 mm was borderline thicker (P=.056) and at +3.0 mm significantly thicker after femtosecond lenticule extraction than after small-incision femtosecond lenticule extraction (P=.003). The mean bed at 0.0 mm was thinner after femtosecond lenticule extraction (P=.03). The flap at -3.0 mm showed thinning between 1 week and 3 months after small-incision femtosecond lenticule extraction (P=.018). The flap at +3.0 mm thinned between 1 week and 1 month after femtosecond lenticule extraction (P=.009). After femtosecond lenticule extraction, there were increases in bed (P=.027) and total corneal (P=.013) thicknesses at 0.0 mm between 1 week and 3 months, remaining stable thereafter (3 months: P=.842 and P=.508, respectively). The mean spherical equivalent decreased and the uncorrected acuity improved after both procedures (P<.001), with stabilization of both variables at 3 months. A significant difference in stromal bed thickness between femtosecond lenticule extraction and small-incision femtosecond lenticule extraction was detectable by AS-OCT 1 week postoperatively.Journal of cataract and refractive surgery 09/2012; 38(9):1544-51. · 2.75 Impact Factor -
Article: Effect of different femtosecond laser-firing patterns on collagen disruption during refractive lenticule extraction.
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ABSTRACT: To evaluate the changes in corneal collagen architecture subjected to different laser-firing patterns during refractive lenticule extraction. Singapore Eye Research Institute, Singapore. Experimental study. Refractive lenticule extraction was performed in rabbits without lenticule removal. Rabbits were divided into 4 groups that had incisions in the following firing patterns: (A) from periphery in (lenticule's posterior surface) and from center out (lenticule's anterior surface); (B) from center out and from center out; (C) from periphery in and from periphery in; and (D) from center out and from periphery in. The corneas were collected 18 hours postoperatively and were subjected to immunofluorescent staining of fibronectin, CD11b, and collagen type I. Ultrastructural analysis was performed using transmission electron microscopy (TEM). Refractive lenticule extraction-treated corneas showed no significant difference in fibronectin and CD11b expression. Similar expression patterns of collagen type I were observed in corneas that had femtosecond firing patterns A, B, and C; however, a discontinuous and relatively more intense staining pattern along the anterior plane of the lenticule was detected in corneas treated with pattern D. The TEM also showed a more disrupted collagen arrangement along the anterior incision site in pattern D-treated corneas. Differential laser firing patterns during refractive lenticule extraction resulted in different levels of collagen derangement along the anterior plane of the lenticule, with pattern D showing the most disrupted surface. Such disruption in the collagen architecture might affect postoperative visual recovery and refractive outcomes. No author has a financial or proprietary interest in any material or method mentioned.Journal of cataract and refractive surgery 08/2012; 38(8):1467-75. · 2.75 Impact Factor -
Article: Reproducibility of Corneal Graft Thickness measurements with COLGATE in patients who have undergone DSAEK (Descemet Stripping Automated Endothelial Keratoplasty).
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ABSTRACT: The CorneaL GrAft Thickness Evaluation (COLGATE) system was recently developed to facilitate the evaluation of corneal graft thickness from OCT images. Graft thickness measurement can be a surrogate indicator for detecting graft failure or success. The purpose of this study was to determine the reproducibility of the COLGATE system in measuring DSAEK graft area between two observers. This was a prospective case series in which 50 anterior segment OCT images of patients who had undergone DSAEK in either eye were analysed. Two observers (MW, AC) independently obtained the image analysis for the graft area using both semi automated and automated method. One week later, each observer repeated the analysis for the same set of images. Bland-Altman analysis was performed to analyze inter and intra observer agreement. There was strong intraobserver correlation between the 2 semi automated readings obtained by both observers. (r = 0.936 and r = 0.962). Intraobserver ICC for observer 1 was 0.936 (95% CI 0.890 to 0.963) and 0.967 (95% CI 0.942 to 0.981) for observer 2. Likewise, there was also strong interobserver correlation (r = 0.913 and r = 0.969). The interobserver ICC for the first measurements was 0.911 (95% CI 0.849 to 0.949) and 0.968 (95% CI 0.945 to 0.982) for the second. There was statistical difference between the automatic and the semi automated readings for both observers (p = 0.006, p = 0.003). The automatic readings gave consistently higher values than the semi automated readings especially in thin grafts. The analysis from the COLGATE programme can be reproducible between different observers. Care must be taken when interpreting the automated analysis as they tend to over estimate measurements.BMC Medical Imaging 08/2012; 12:25. · 1.09 Impact Factor -
Article: Correlation of anterior segment optical coherence tomography measurements with graft trephine diameter following descemet stripping automated endothelial keratoplasty.
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ABSTRACT: To assess repeatability of the Zhongshan Assessment Program (ZAP) software measurement of Anterior Segment Optical Coherence Tomography (ASOCT) images and correlate with graft trephine diameter following Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) METHODS: Retrospectively evaluated interventional case series. 121 consecutive eyes undergoing DSAEK over a 26 month period underwent ASOCT imaging 1 month after their surgery. ASOCT images were processed using ZAP software which measured the graft and cornea parameters including anterior and posterior graft arc length and cord length, posterior cornea arc length (PCAL) and anterior chamber width. The graft measurements showed good repeatability on ASOCT using ZAP with high intra class coefficient and small variation in the coefficient of variation. On ASOCT, the mean recipient PCAL was 12.99+/-0.69 mm and the anterior chamber width was 11.16+/-0.57 mm. The mean Graft anterior arc length was 9.69+/-0.66 mm and the mean Graft anterior cord length was 8.92+/-2.94 mm. The mean graft posterior arc length was 9.24+/-0.75 mm and the mean graft posterior cord length was 8.15+/-0.57 mm. Graft posterior arc length (rho=0.788, p< 0.001) correlated best with intra-operative graft trephine diameter. The mean ratio of posterior graft arc length to PCAL was 0.712 +/- 0.056. We have validated the repeatability of the ZAP software for DSAEK graft measurements from ASOCT images and shown that the graft arc length parameters calculated from the ASOCT images correlate well with the intra-operative graft trephine diameter. This software may help surgeons determine the optimal DSAEK graft size based on pre-operative ASOCT measurements of the recipient eye.BMC Medical Imaging 07/2012; 12:19. · 1.09 Impact Factor -
Article: Effect of fibrin glue on the biomechanical properties of human Descemet's membrane.
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ABSTRACT: Corneal transplantation has rapidly evolved from full-thickness penetrating keratoplasty (PK) to selective tissue corneal transplantation, where only the diseased portions of the patient's corneal tissue are replaced with healthy donor tissue. Descemet's membrane endothelial keratoplasty (DMEK) performed in patients with corneal endothelial dysfunction is one such example where only a single layer of endothelial cells with its basement membrane (10-15 µm in thickness), Descemet's membrane (DM) is replaced. It is challenging to replace this membrane due to its intrinsic property to roll in an aqueous environment. The main objective of this study was to determine the effects of fibrin glue (FG) on the biomechanical properties of DM using atomic force microscopy (AFM) and relates these properties to membrane folding propensity. Fibrin glue was sprayed using the EasySpray applicator system, and the biomechanical properties of human DM were determined by AFM. We studied the changes in the "rolling up" tendency of DM by examining the changes in the elasticity and flexural rigidity after the application of FG. Surface topography was assessed using scanning electron microscopy (SEM) and AFM imaging. Treatment with FG not only stabilized and stiffened DM but also led to a significant increase in hysteresis of the glue-treated membrane. In addition, flexural or bending rigidity values also increased in FG-treated membranes. Our results suggest that fibrin glue provides rigidity to the DM/endothelial cell complex that may aid in subsequent manipulation by maintaining tissue integrity.PLoS ONE 01/2012; 7(5):e37456. · 4.09 Impact Factor -
Article: Osteo-odonto keratoprosthesis: systematic review of surgical outcomes and complication rates.
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ABSTRACT: Case series on osteo-odonto keratoprosthesis (OOKP) published in English from 1950-June 2010 were identified in Medline/PubMed. Indications for surgery, visual acuity, anatomical survival, complication and repeat surgery rates were compared among the different studies. Our own case series is a retrospective review of all OOKP surgeries performed in our center from February 2004-July 2011. Eight case series including our own were systematically reviewed. Sample sizes ranged from 4-181 eyes. The most common indications for surgery were severe cases of Stevens-Johnson syndrome and thermal and chemical burns that were unamenable to other forms of surgery or had had previous surgical failure. Anatomical survival rate in all the studies was 87.8% (range 67-100%) at 5 years, and three studies showed survival rates of 81.0% (range 65-98%) at 20 years. Visual acuity was more than 6/18 in 52% (range 46-72%) of the eyes with OOKP surgery. The most common intraoperative complication was vitreous hemorrhage (0-52%) and the most common long-term blinding complication was glaucoma (7-47%). Endophthalmitis rates ranged from 2-8%. The most common repeat surgical procedure was mucosal trimming due to mucosal overgrowth at the optical cylinder and mucosal grafting for extrusion of the OOKP or mucosal ulceration. Of the available biological and synthetic keratoprosthesis, OOKP appears to be an excellent option for the treatment of end-stage corneal diseases.The ocular surface 01/2012; 10(1):15-25. · 3.93 Impact Factor -
Article: Intraoperative use of spectral-domain optical coherence tomography during Descemet's stripping automated endothelial keratoplasty.
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ABSTRACT: To evaluate the intraoperative changes in the donor lenticule, recipient cornea, and the reduction of interface fluid thickness during Descemet's stripping and automated endothelial keratoplasty with EndoGlide™ (Angiotech Pharmaceuticals Inc, Vancouver, Canada) donor insertion, using intraoperative spectral-domain optical coherence tomography. Prospective observational case series of patients underwent Descemet's stripping and automated endothelial keratoplasty using the EndoGlide inserter. Spectral-domain optical coherence tomography (iVue; Optovue Inc, Fremont, CA) with a handheld probe was used to image the cornea and anterior chamber. Standardized software was used to measure interface fluid gap, host cornea, and donor lenticule thicknesses during the following surgical stages of Descemet's stripping and automated endothelial keratoplasty: (1) after donor insertion and immediately before full air tamponade; (2) after air tamponade and expression of fluid from venting incisions; (3) at 6 minutes of air tamponade; and (4) at 10 minutes of air tamponade. Ten patients with a mean age of 74.9 ± 11.8 years were recruited. Spectral-domain optical coherence tomography measurements of the interface fluid gap after fluid was expressed through the venting incisions (P < 0.001), at 6 minutes of air tamponade (P < 0.001) and at 10 minutes of air tamponade (P < 0.001 and P = 0.001, respectively), were significantly decreased compared to the measurements immediately before air tamponade. Donor thickness increased significantly at 6 minutes of air tamponade (P = 0.004) but reduced by 10 minutes compared to immediately before air tamponade. Significant intraoperative changes in the donor, recipient cornea, and interface fluid thickness occurred following endothelial keratoplasty donor insertion.Clinical Ophthalmology 01/2012; 6:479-86. -
Article: Hemi-automated lamellar keratoplasty (HALK).
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ABSTRACT: To describe a hybrid technique for anterior lamellar keratoplasty in corneas with topographical irregularities that circumvents the limitations of the microkeratome, namely reproduction of surface irregularities in the lamellar cut when creating the recipient flap. Hemi-automated lamellar keratoplasty, a procedure that combines manual recipient bed lamellar dissection with automated donor preparation using a microkeratome, was performed on 14 eyes of 14 patients with heterogeneous causes of anterior stromal scarring. There was an overall improvement in uncorrected visual acuity (UCVA) in 78.6% (11/14) eyes and in best-corrected visual acuity (BCVA) in 78.6% (11/14) eyes at a mean of 9 months postoperatively. Mean preoperative and postoperative logMAR UCVAs were 1.31 ± 0.74 and 0.83 ± 0.46 (p=0.04), respectively. Mean preoperative and postoperative logMAR BCVAs were 0.72 ± 0.58 and 0.38 ± 0.23 (p=0.05). Mean preoperative and postoperative manifest refractive spherical equivalents were -0.76 ± 3.61 D and -0.52 ± 3.44 D (p=0.872). There was no difference in preoperative and postoperative sphere and cylinder (p=0.871 and 0.965, respectively). In a subset of six eyes with longer follow-up >12 months, the UCVA and BCVA show continuing improvement. All grafts remained clear at the final appointment. Hemi-automated lamellar keratoplasty is an effective and safe surgical procedure in the treatment of corneas with irregular topographic profiles with varying depths of anterior stromal scarring. It combines the benefits of smooth microkeratome lamellar dissection of the donor with customised lenticule thickness and diameter together with a manual lamellar dissection technique for the recipient providing encouraging visual outcomes that show continuing improvement with time.The British journal of ophthalmology 09/2011; 95(11):1513-8. · 2.92 Impact Factor -
Article: Reproducibility of cornea measurements in anterior segment OCT images of normal eyes and eyes with bullous keratopathy analyzed with the Zhongshan Assessment Program.
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ABSTRACT: To determine the interobserver and intraobserver measurement reproducibility of cornea parameters of both normal eyes and eyes with bullous keratopathy (BK) obtained with the Zhongshan Assessment Program (ZAP) on anterior segment optical coherence tomography (AS-OCT) images. A comparative study was carried out on 24 healthy volunteers and 25 subjects with BK. AS-OCT images were independently analyzed by two examiners. Parameters examined: anterior chamber depth (ACD), central corneal thickness (CCT), posterior corneal curvature (PCC), and posterior corneal arc length (PCAL). Interobserver and intraobserver reproducibility of these parameters was calculated in terms of limits of agreement (mean of differences ± 1.96SD of differences). In the normal group, both horizontal and vertical ACD were successfully measured in 23 of 24 (96%) images. The mean bias for two measurements by two different observers ranged from 0.003 to 0.117 mm for ACD, PCC, and PCAL measurements and from 0.013 to 2.25 μm for CCT measurements, and there were no differences between the two observers (P > 0.05). Mean bias for two measurements by the same grader ranged from 0.005 to 0.327 mm for ACD, PCC, and PCAL measurements and 1.46 to 2.53 μm for CCT measurements. There was no difference between the two observations (P > 0.05). Similar results were found in the BK group. There was high inter- and intraobserver reproducibility for normal and pathologic corneas using the ZAP software. The ZAP software may serve as a new investigatory tool for accurately evaluating the anterior segment and corneal parameters for corneal procedures.Investigative ophthalmology & visual science 08/2011; 52(12):8884-90. · 3.43 Impact Factor -
Article: Early corneal wound healing and inflammatory responses after refractive lenticule extraction (ReLEx).
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ABSTRACT: To compare the early corneal wound repair and inflammatory responses after refractive lenticule extraction (ReLEx) and LASIK. Eighteen rabbits underwent ReLEx and another 18 underwent LASIK. Each group was divided into three subgroups of six rabbits each and these were subjected to refractive corrections of -3.00 diopters (D), -6.00 D, and -9.00 D. Slit lamp photography, anterior segment optical coherence tomography (AS-OCT), corneal topography, and in vivo confocal microscopy were performed 1 day after surgery. After euthanatization, the corneas were subjected to immunofluorescent staining for fibronectin, CD11b, Ki-67, and TUNEL assay. On slit lamp microscopy, all corneas appeared clear pre- and postoperatively in both ReLEx and LASIK eyes. Corneal topography showed a more significant corneal flattening after LASIK than after ReLEx as the degree of correction was increased (P = 0.916 after -3.00 D correction to P = 0.097 after -9.00 D correction). In vivo confocal microscopy showed less light-scattering particles at the flap interface after ReLEx compared with LASIK. Immunostaining of fibronectin showed a less abundant expression in corneas that underwent ReLEx than LASIK. The differences became more marked as the power of correction was increased. Similar trend was seen in the number of CD11b-positive cells (P = 0.476 after -3.00 D correction to P < 0.001 after -9.00D correction). There was no marked disparity observed in cell death and proliferation between post-ReLEx and -LASIK eyes. This study has shown that the ReLEx procedure may result in less topographic changes, inflammation, and early extracellular matrix deposition than LASIK, especially at high refractive correction.Investigative ophthalmology & visual science 06/2011; 52(9):6213-21. · 3.43 Impact Factor -
Article: Evolution of deep anterior lamellar keratoplasty (DALK).
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ABSTRACT: The concept of selective tissue transplantation was theorized over two centuries ago. However, deep anterior lamellar keratoplasty (DALK) was difficult to perform with the instruments available at that time, and visual acuity results were poor compared to those achieved by full-thickness transplantation. Recently, many technical improvements in surgical instrumentation and advances in eye bank technology have led to the re-emergence of DALK. Now, patients with stromal pathologies not affecting the corneal endothelium can benefit from this surgery, which allows total stromal replacement of the recipient's cornea, leaving an intact recipient Descemet membrane and endothelium. Along with the advances in surgical instrumentation, improvements in surgical techniques and imaging technology have contributed to improved visual outcomes obtained with DALK. DALK is now seen as a viable alternative to penetrating keratoplasty with equivalent visual results and better long-term graft survival.The ocular surface 04/2011; 9(2):98-110. · 3.93 Impact Factor -
Article: Laser in situ keratomileusis flap measurements: Comparison between observers and between spectral-domain and time-domain anterior segment optical coherence tomography.
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ABSTRACT: To evaluate the between-observer (interobserver) and between-instrument (intraobserver) variability in flap thickness measurements after laser in situ keratomileusis (LASIK) using spectral-domain and time-domain anterior segment optical coherence tomography (AS-OCT). Singapore National Eye Centre. Evaluation of diagnostic test or technology. Two independent masked observers measured flap thickness 1 month after LASIK using spectral-domain (RTVue) or time-domain (Visante) AS-OCT. The measurements were taken at central (0.0 mm), -1.5 mm, and +1.5 mm locations. Measurements were repeated to assess between-instrument variability. There was no statistically significant difference in mean flap thickness between the 2 observers at -1.5 mm, 0.0 mm, and +1.5 mm on spectral-domain AS-OCT and at -1.5 mm and +1.5 mm on time-domain AS-OCT (P < .01). There was a statistically significant difference between the 2 observers in the central (0.0 mm) values on time-domain AS-OCT (P=.0008). There was stronger interobserver correlation for spectral-domain AS-OCT at -1.5 mm (r = 0.82), 0.0 mm (r = 0.88), and +1.5 mm (r = 0.88) than for time-domain AS-OCT (r = 0.73, r = 0.62, and r = 0.79, respectively). There was no statistically significant difference in between-instrument measurements. There was stronger between-instrument correlation with spectral-domain AS-OCT than with time-domain AS-OCT at all locations. The mean standard deviation (measure of instrument repeatability) for spectral-domain AS-OCT was 4.19 μm. Spectral-domain AS-OCT had closer agreement in between-observer and between-instrument measurements than time-domain AS-OCT and provided more consistent measurements of post-LASIK flap thickness.Journal of cataract and refractive surgery 03/2011; 37(3):544-51. · 2.75 Impact Factor -
Article: Human corneal endothelial cell expansion for corneal endothelium transplantation: an overview.
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ABSTRACT: The monolayer of cells forming the human corneal endothelium is critical to the maintenance of corneal transparency and is not known to regenerate in vivo. Thus, dysfunction of these cells constitutes the most often cited reasons for the 150,000 or so corneal transplants performed yearly. Although current corneal transplantation is more than 90% successful at 1 year, longer term results are not as encouraging with approximately 70% success at 5 years. Nonimmunologic graft failure and allograft endothelial rejection are the main problems. Furthermore, the global shortage of donor corneas greatly restricts several corneal transplantations performed. With advances in understanding corneal endothelial cell biology, it is now possible to cultivate human corneal endothelial cells (HCECs) in vitro, thus providing new opportunities to develop novel tissue-engineered human corneal endothelium. This review will provide an overview of (a) the characteristics of human corneal endothelium; (b) past and present HCECs isolation and culture protocols; (c) various potential carriers for the generation of tissue-engineered corneal endothelium, together with some of the functional studies reported in various animal models; and (d) the current rapid advancements in surgical techniques for keratoplasty. A successful combination of tissue-engineered human corneal endothelium coupled with innovative and groundbreaking surgical procedures will bridge basic research involving cultured HCECs, bringing it from bench to bedside.Transplantation 02/2011; 91(8):811-9. · 4.00 Impact Factor -
Article: Cultivation of human corneal endothelial cells isolated from paired donor corneas.
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ABSTRACT: Consistent expansion of human corneal endothelial cells (hCECs) is critical in the development of tissue engineered endothelial constructs. However, a wide range of complex culture media, developed from different basal media have been reported in the propagation of hCECs, some with more success than others. These results are further confounded by donor-to-donor variability. The aim of this study is to evaluate four culture media in the isolation and propagation of hCECs isolated from a series of paired donor corneas in order to negate donor variability. Isolated primary hCECs were cultured in four previously published medium coded in this study as: M1-DMEM; M2-OptiMEM-I; M3-DMEM/F12, & M4-Ham's F12/M199. Primary hCECs established in these conditions were expanded for two passages and analyzed for (1) their propensity to adhere and proliferate; (2) their expression of characteristic corneal endothelium markers: Na+K+/ATPase and ZO-1; and (3) their cellular morphology throughout the study. We found that hCECs isolated in all four media showed rapid attachment when cultured on FNC-coated dishes. However, hCECs established in the four media exhibited different proliferation profiles with striking morphological differences. Corneal endothelial cells cultured in M1 and M3 could not be propagated beyond the first and second passage respectively. The hCECs cultured in M2 and M4 were significantly more proliferative and expressed markers characteristics of human corneal endothelium: Na+K+/ATPase and ZO-1. However, the unique morphological characteristics of cultivated hCECs were not maintained in either M2 or M4 beyond the third passage.The proliferative capacity and morphology of hCECs are vastly affected by the four culture media. For the development of tissue engineered graft materials using cultured hCECs derived from the isolation methodology described in this study, we propose the use of proliferative media M2 or M4 up to the third passage, or before the cultured hCECs lose their unique cellular morphology.PLoS ONE 01/2011; 6(12):e28310. · 4.09 Impact Factor -
Article: Cornea lenticule viability and structural integrity after refractive lenticule extraction (ReLEx) and cryopreservation.
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ABSTRACT: To assess and compare keratocyte viability and collagen structure in cornea stroma lenticules collected immediately after refractive lenticule extraction (ReLEx) and one month after cryopreservation. The fresh and cryopreserved human stroma lenticules procured after ReLEx were processed for ultrastructural analysis of keratocytes and collagen fibrils with transmission electron microscopy (TEM), apoptotic cell detection with deoxynucleotidyl transferase-mediated nick end labeling assay (TUNEL) assay, and cultured for keratocyte-specific gene expression analysis using reverse transcriptase polymerase chain reaction (RT-PCR). The periphery of the lenticule had greater TUNEL-positive cells compared to the center of the lenticule in both fresh and cryopreserved groups. There was an increase in TUNEL-positive cells after cryopreservation, which was significantly higher in the center of the lenticule, but not in the periphery. TEM showed apoptotic, necrotic and viable quiescent keratocytes in fresh and cryopreserved lenticules. Collagen analysis with TEM showed a well preserved and well aligned structure in fresh and cryopreserved lenticules; without significant change in the total number of collagen fibrils but with an increased collagen fibril density (CFD) after cryopreservation. In vitro, isolated keratocytes derived from fresh and cryopreserved lenticules exhibited a typical fibroblastic phenotype. RT-PCR showed a positive gene expression for keratocan (KERA) and aldehyde dehydrogenase 3A1 (ALDH3A1) in cells isolated from fresh and cryopreserved lenticules. The stromal lenticules extracted from ReLEx surgery remain viable after cryopreservation. Although they showed a decrease in CFD, the collagen architecture was preserved and there was good cellular viability.Molecular vision 01/2011; 17:3437-49. · 2.20 Impact Factor -
Article: In vivo real-time intraocular pressure variations during LASIK flap creation.
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ABSTRACT: To monitor and compare in vivo real-time intraocular pressure (IOP) in rabbit eyes undergoing LASIK flap creation using microkeratome and femtosecond laser. Thirteen rabbit eyes in each group underwent LASIK flap creation using a microkeratome and a femtosecond laser. In vivo real-time IOP profile was measured using a 30-gauge needle with an IOP catheter sensor inserted into the anterior chamber from the limbus during surgery. In vivo real-time IOP monitoring was achieved in all cases, showing IOP variations during different phases of LASIK flap creation from docking of the instrument, start of surgery to the end of procedure, and monitoring the post-LASIK stabilization. IOP fluctuations were significantly lower in corneal flaps made with the femtosecond laser than with the microkeratome during globe suction (81.78+/-10.55 vs. 122.51+/-16.95 mm Hg), cutting (62.25+/-3.28 vs. 141.02+/-20.46 mm Hg), and suction (41.40+/-2.99 vs. 89.30+/-12.15). In contrast, femtosecond laser requires double the time (19+/-2 vs. 10+/-2 seconds for globe suction and 19+/-2 vs. 9+/-2 seconds for cutting) for completion of the procedure. The authors describe an accurate and reliable setup to measure and record in vivo real-time changes in IOP measurement from the anterior chamber during laser surgery. Femtosecond laser flap creation exerts less extreme IOP fluctuations with improved chamber stability but requires more procedure time than does microkeratome.Investigative ophthalmology & visual science 09/2010; 51(9):4641-5. · 3.43 Impact Factor -
Article: Biometry of the cornea and anterior chamber in chinese eyes: an anterior segment optical coherence tomography study.
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ABSTRACT: PURPOSE. To investigate the normative data of corneal and anterior segment biometric parameters and their associations in Chinese adults, for use in preoperative assessment for corneal and anterior segment surgery. METHODS. This cross-sectional, population-based study included 750 subjects aged > or =50 years. The subjects underwent an ophthalmic examination including imaging with anterior segment optical coherence tomography (AS-OCT). Dimensions were subsequently measured with the Zhongshan Assessment Program (ZAP). Also measured was posterior corneal arc length (PCAL), a novel parameter defined as the arc distance between scleral spurs on the posterior border of the cornea. Correlations with age, sex, height, weight, body mass index (BMI), refractive sphere and cylinder, and intraocular pressure were also measured. RESULTS. The subjects' mean age was 63.3 +/- 7.9 years and 349 (46.5%) were men. Corneal parameters (mean +/- SD) included PCAL (12.924 +/- 0.544 mm), anterior chamber depth (ACD; 2.684 +/- 0.309 mm), central corneal thickness (562.39 +/- 31.85 microm), anterior chamber curvature (7.35 +/- 0.37 mm), and posterior corneal curvature (6.65 +/- 0.34 mm). A moderate correlation was observed between PCAL and ACD (R = 0.55, P < 0.001) and a poor correlation between PCAL and age, height, weight, and BMI. Multivariate analysis showed a significant association between PCAL and ACD, ACC, PCC, and cylinder (P < 0.05). CONCLUSIONS. In this Chinese population, PCAL was found to correlate moderately with ACD. The data may be useful for corneal and anterior segment procedures such as Descemet's stripping automated endothelial keratoplasty (DSAEK).Investigative ophthalmology & visual science 07/2010; 51(7):3433-40. · 3.43 Impact Factor
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Institutions
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2013
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Duke-NUS Graduate Medical School Singapore
Singapore, Singapore
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2012
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National University of Singapore
- Singapore Eye Research Institute
Singapore, Singapore
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2009–2012
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Singapore Eye Research Institute
Singapore, Singapore
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2007–2012
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Singapore National Eye Center
Singapore, Singapore
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