Donald T H Tan

Singapore National Eye Centre, Tumasik, Singapore

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Publications (278)1004.14 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: To describe outcomes and complications following Descemet's stripping automated endothelial keratoplasty (DSAEK) in eyes with pseudophakic bullous keratopathy (BK) while retaining the anterior chamber intraocular lenses (ACIOL). We included consecutive patients who underwent DSAEK for BK at a single tertiary centre from 1 January 2008 to 1 April 2010, from our prospective cohort (Singapore Corneal Transplant Study). We compared eyes with BK, which underwent DSAEK while retaining ACIOL (n=18), to those with DSAEK alone with the posterior chamber intraocular lenses left in place as a comparison group (n=114). Main outcome measures were endothelial cell (EC) loss and graft survival. The percentage EC loss at 1 year was 31.9±21.3% in the DSAEK with ACIOL group compared to 24.5±21.2% in the DSAEK group (p=0.516); however, this figure was significantly greater in the DSAEK with ACIOL group at 3 years compared to the DSAEK group (55.3±29.2% vs 33.3±20.8%; p=0.01 respectively). Graft survival was also significantly poorer in the DSAEK ACIOL group compared to the DSAEK group over 3 years (log rank p=0.002). We found that although eyes with BK and ACIOL that underwent DSAEK while retaining the ACIOL suffered EC loss which was not significantly greater at 1 year, EC loss and graft survival were significantly poorer compared to DSAEK controls at 3 years postoperatively.
    The British journal of ophthalmology 03/2014; · 2.92 Impact Factor
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    ABSTRACT: Anterior chamber depth (ACD) is a key anatomical risk factor for primary angle closure glaucoma (PACG). We conducted a genome-wide association study (GWAS) on ACD to discover novel genes for PACG on a total of 5,308 population-based individuals of Asian descent. Genome-wide significant association was observed at a sequence variant within ABCC5 (rs1401999; per-allele effect size = -0.045 mm, P = 8.17×10-9). This locus was associated with an increase in risk of PACG in a separate case-control study of 4,276 PACG cases and 18,801 controls (per-allele OR = 1.13 [95% CI: 1.06-1.22], P = 0.00046). The association was strengthened when a sub-group of controls with open angles were included in the analysis (per-allele OR = 1.30, P = 7.45×10-9; 3,458 cases vs. 3,831 controls). Our findings suggest that the increase in PACG risk could in part be mediated by genetic sequence variants influencing anterior chamber dimensions.
    PLoS Genetics 03/2014; 10(3):e1004089. · 8.52 Impact Factor
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    ABSTRACT: To compare 3-year endothelial cell loss and graft survival following Descemet stripping automated endothelial keratoplasty (DSAEK) using the EndoGlide (AngioTech, Reading, Pennsylvania, USA/Network Medical Products, North Yorkshire, UK) donor insertion device compared to donor insertion using the sheets glide technique. Retrospective comparative case series METHODS: Consecutive patients who underwent DSAEK with Fuchs endothelial dystrophy or pseudophakic bullous keratopathy at a single tertiary center. Clinical data with outcomes, donor and recipient characteristics were obtained from our ongoing prospective cohort from the Singapore Corneal Transplant Study. Main outcome measures were percent endothelial cell loss and graft survival up to 3 years. Overall percent endothelial cell loss was significantly lower in the EndoGlide group (100 eyes) compared to Sheets glide group (119 eyes) at 1 year (16.3±16.6% vs. 29.5±22.2%, P<0.001), 2 years (23.8±17.8% vs. 35.7±22.9%, P=0.001); and at 3 years (29.7±20.9% vs. 38.5±24.1%, P=0.015) post-operatively. Overall graft survival was greater in the EndoGlide compared to Sheets glide group up to 3 years (97.9% vs. 86.5%, log-rank P value=0.005). In eyes with Fuchs endothelial dystrophy, endothelial cell loss was significantly lower in the EndoGlide group (3-year: 28.2±17.9% vs. 43.4±27.1%, P=0.032). In eyes with pseudophakic bullous keratopathy, the EndoGlide group had a superior graft survival compared to Sheets glide (log-rank P=0.031). Endothelial cell loss was lower using a donor insertion device during DSAEK, compared to using the sheets glide technique for DSAEK in Asian eyes with Fuchs endothelial dystrophy, and resulted in better graft survival in eyes with pseudophakic bullous keratopathy.
    American journal of ophthalmology 02/2014; · 3.83 Impact Factor
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    ABSTRACT: Purpose: To compare early corneal nerve changes after SMILE (small incision lenticule extraction) and LASIK (laser in situ keratomileusis). Methods: Twelve rabbits underwent LASIK in one eye and SMILE in fellow eye. Baseline and follow-up evaluations at 1, 2 and 4 weeks post-operatively were performed with in vivo confocal microscopy to evaluate 5 different areas within the treated zone: center, superior, inferior, nasal and temporal. Cryosections of the corneas and whole mount of the extracted SMILE lenticules were analyzed with immunostaining of βIII-tubulin. Results: One week post-SMILE and -LASIK, a decrease in nerve length and density was observed in all evaluated areas. A trend towards greater sub-basal nerve length and density (SLD), more eyes with sub-basal nerves (ESN), more eyes with sub-basal nerves longer than 200µm (SNL), and higher mean number of sub-basal nerves by frame (NSN) in SMILE than in LASIK groups was observed at subsequent follow-up time points. Only the SMILE group showed a recovery of SLD, ESN and NSN by week 4 (P>0.05). A trend towards more eyes with sprouting sub-basal nerves and greater mean number of sprouting nerves was observed in LASIK than in SMILE, indicating that more sub-basal nerves were disrupted and undergoing regeneration after LASIK. Immunostaining at post-operative week 4 revealed a faster stromal nerve recovery in post-SMILE eyes compared to post-LASIK eyes. Conclusions: Our findings suggest that SMILE results in less nerve damage and faster nerve recovery than LASIK.
    Investigative ophthalmology & visual science 02/2014; · 3.43 Impact Factor
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    ABSTRACT: To describe the subjective experience of patients and surgeons during laser in situ keratomileusis (LASIK) using the Intralase 60 kHz or the Visumax 500 kHz femtosecond laser. Singapore National Eye Centre, Singapore. Prospective randomized clinical study. In myopic patients, LASIK was performed with the corneal flap created using the 60 kHz laser in 1 eye and the 500 kHz laser in the contralateral eye. Postoperatively, patients completed a standardized validated questionnaire about their subjective intraoperative experiences (eg, light perception, pain, fear). Surgeons reported their intraoperative experiences and preferences. Loss of light perception occurred in 50.0% of 60 kHz laser cases and 0% of 500 kHz laser cases during docking and in 63.0% and 0% of cases, respectively, during laser flap creation (P < .0001). The mean pain score with the 60 kHz laser was significantly higher during docking (P < .0001) but not during laser flap cutting (P = .006). Subconjunctival hemorrhage occurred in 67.4% of eyes with the 60 kHz laser and in 2.2% of eyes with the 500 kHz laser (P < .0001). The 500 kHz laser was preferred by 78.3% of patients, while 21.7% preferred the 60 kHz laser (P < .0001). The surgeons preferred the 60 kHz laser in 50.0% of cases and the 500 kHz laser in 8.7% (P < .0001); 41.3% had no preference. Patients preferred surgery with the 500 kHz laser with no loss of light perception, less pain, less fear, and less subconjunctival hemorrhage. Surgeons preferred the 60 kHz laser. No author has a financial or proprietary interest in any material or method mentioned.
    Journal of Cataract and Refractive Surgery 01/2014; · 2.75 Impact Factor
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    ABSTRACT: To study the change in spherical equivalent and other ocular parameters 1 year after stopping the administration of atropine. Prospective randomized double-masked clinical trial. We assigned 400 myopic children, 6 to 12 years of age, to receive atropine 0.5%, 0.1% or 0.01% for 24 months, after which medication was stopped. Parents and children gave informed consent to participate in the research. Children were reviewed at 26, 32 and 36 months, and changes in cycloplegic spherical equivalent (SE), axial length (AL), visual acuity, pupil size, and accommodation were assessed. Of the children, 356 (89%) entered into the washout phase. At entry, there was no significant difference in age, gender, SE, or AL among the children in the various atropine groups. Over the following 12 months, myopic progression was greater in the 0.5% eyes (-0.87 ± 0.52 D), compared to the 0.1% (-0.68 ± 0.45 D) and 0.01% eyes (-0.28 ± 0.33 D, P < 0.001). AL growth was also greater in the 0.5% (0.35 ± 0.20 mm) and 0.1% (0.33 ± 0.18 mm) eyes, compared to the 0.01% eyes (0.19 ± 0.13 mm, P < 0.001). Pupil size and near visual acuity returned to pre-atropine levels in all groups, but accommodation at 36 months was less in the 0.5% eyes (13.24 ± 2.72 D) compared to the 0.1% (14.45 ± 2.61 D) and 0.01% eyes (14.04 ± 2.90 D, P < 0.001). The overall increase in SE over the entire 36 months in the 0.5%, 0.1% and 0.01% groups was -1.15 ± 0.81 D, -1.04 ± 0.83 D and -0.72 ± 0.72 D, respectively (P < 0.001). There was a myopic rebound after atropine was stopped, and it was greater in eyes that had received 0.5% and 0.1% atropine. The 0.01% atropine effect, however, was more modulated and sustained.
    American journal of ophthalmology 12/2013; · 3.83 Impact Factor
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    ABSTRACT: Corneal endothelium?associated corneal blindness is the most common indication for corneal transplantation. Restorative corneal transplant surgery is the only option to reverse the blindness, but global shortage of donor material remains an issue. There are immense clinical interests in the development of alternative treatment strategies to alleviate current reliance on donor materials. For such endeavors, ex vivo propagation of human corneal endothelial cells (CECs) is required but current methodology lacks consistency with expanded CECs losing cellular morphology to a mesenchymal?like transformation. In this study, we describe a novel dual media culture approach for the in vitro expansion of primary human CECs. Initial characterization included analysis of growth dynamics of CECs grown in either proliferative (M4) or maintenance (M5) medium. Subsequent comparisons were performed on isolated CECs cultured in M4?alone against cells expanded using the dual media approach. Further characterizations were performed using immunocytochemistry, quantitative real?time PCR and gene expression microarray. At the third passage, results showed that human CECs propagated using the dual media approach were homogeneous in appearance, retained their unique polygonal cellular morphology, and expressed higher levels of corneal endothelium?associated markers in comparison to CECs cultured in M4?alone, which were heterogeneous and fibroblastic in appearance. Finally, for CECs cultured using the dual media approach, global gene expression and pathway analysis between confluent CECs before and after seven days exposure to M5 exhibited differential gene expression associated predominately with cell proliferation and wound healing. These findings showed that the propagation of primary human CECs using the novel dual media approach presented in this study is a consistent method to obtain bona fide human CECs. This in turn will elicit greater confidence in facilitating downstream development of alternative corneal endothelium replacement using tissue?engineered graft materials or cell injection therapy.
    Cell Transplantation 11/2013; · 4.42 Impact Factor
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    ABSTRACT: To describe the indications for and approaches to vitreoretinal surgery in patients with osteo-odonto-keratoprosthesis (OOKP). Retrospective case series. This was a retrospective review of all patients who had undergone OOKP surgery between 2003 and 2012 at our center. OOKP procedures were performed for severe ocular surface disease according to the indications and techniques described in the patient demographics of the Rome-Vienna Protocol. Indications for retinal surgery, surgical outcomes, and intraoperative and postoperative complications were documented. Operative techniques were reviewed from the surgical records, and any subsequent surgeries were also recorded. Thirty-six patients underwent OOKP, and retinal surgery was indicated in 13 (36%). The indications for and approaches to surgery were retinal detachment repair using an Eckardt temporary keratoprosthesis; assessment of retina and optic nerve health prior to OOKP surgery, using either a temporary keratoprosthesis or an endoscope; endoscopic cyclophotocoagulation for intractable glaucoma; endoscopic trimming of a retroprosthetic membrane; or vitrectomy for endophthalmitis with visualization through the OOKP optic using the binocular indirect viewing system. In all cases, retinal surgical aims were achieved with a single procedure. Postoperative vitreous hemorrhage occurred in 16 patients (44%), but all resolved spontaneously. OOKPs represent the last hope for restoration of vision in severe ocular surface disease, and the retinal surgeon is frequently called upon in the assessment and management of these patients. Temporary keratoprostheses and endoscopic vitrectomies are valuable surgical tools in these challenging cases, improving functional outcomes without compromising OOKP success.
    American journal of ophthalmology 10/2013; · 3.83 Impact Factor
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    ABSTRACT: To describe the use of high-resolution anterior segment optical coherence tomography (AS-OCT) during deep anterior lamellar keratoplasty (DALK). Prospective case series. At the Singapore National Eye Centre we performed sequential intraoperative AS-OCT scans using iVue 100-2 (Optovue, Fremont, CA, USA) during various DALK techniques. In case 1 (corneal scarring) the OCT images helped to guide manual dissection, showed the depth of the needle track before air injection, and identified the location of a small bubble when the big bubble failed. In cases 2 (macular dystrophy) and 3 (lattice), viscodissection was undertaken, but in case 2 the OCT showed the viscoelastic trapped intrastromally, compared to case 3, in which the viscobubble dissection was successful. In case 4 (irregular corneal thinning and scarring), AS-OCT enabled accurate decision on initial trephination and guided dissection. In case 5 (keratoconus), the OCT showed the achieved big-bubble and detached Descemet membrane. Case 6 was a repeat DALK; the OCT guided the manual dissection of the residual stroma underlying the failed graft. In case 7, the OCT showed an intrastromal retention of fluid that was not detectable by the operating microscope due to diffuse scarring following alkaline injury. The OCT helped to assess the location of the Descemet membrane and guided the manual dissection. Intraoperative high-definition AS-OCT obtained good-quality images of the cornea during DALK and proved useful in various cases of DALK to help the surgeon decide on a number of surgical steps.
    American journal of ophthalmology 10/2013; · 3.83 Impact Factor
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    ABSTRACT: To determine the long-term cost-effectiveness of osteo-odonto keratoprosthesis (OOKP) relative to no treatment among patients with end-stage corneal and ocular surface diseases in Singapore. Cost-effectiveness analysis based on data from a retrospective cohort study. From a health system perspective, we calculated the incremental cost-effectiveness ratio of OOKP treatment relative to no treatment over a 30-year horizon, based on data from a cohort of 23 patients who underwent OOKP surgery between 2004 and 2009 at Singapore National Eye Centre. Preoperative and postoperative vision-related quality-of-life values were estimated from patients' visual outcomes and were used to calculate the gain in quality-adjusted life years (QALYs) resulting from OOKP treatment. Unsubsidized costs for surgery, consultations, examinations, medications, follow-up visits, and treatments for complications were retrieved from patients' bills to estimate the total costs associated with OOKP treatment. Sensitivity analyses were conducted to test the robustness of the model. Over a 30-year period, OOKP treatment, compared with no treatment, improved QALYs by 3.991 among patients with end-stage corneal and ocular surface diseases at an additional cost of S$67 840 (US$55 150), resulting in an incremental cost-effectiveness ratio of S$17 000/QALY (US$13 820/QALY). Based on commonly cited cost-effectiveness benchmarks, the OOKP is a cost-effective treatment for patients with end-stage corneal and ocular surface diseases.
    American journal of ophthalmology 09/2013; · 3.83 Impact Factor
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    ABSTRACT: To compare the efficacy, predictability, and safety outcomes of 2 femtosecond laser platforms for flap creation during laser in situ keratomileusis (LASIK) for myopia and myopic astigmatism. Singapore National Eye Centre, Singapore. Retrospective case review. In this single-center multisurgeon study, patients had LASIK with flaps created using a Visumax 500 kHz or Intralase 60 kHz femtosecond laser system. Ablation was performed with the Wavelight Allegretto Eye-Q 400 Hz excimer laser in all patients. Preoperative and 3-month postoperative manifest refraction, attempted treatment spherical equivalent (SE), visual acuity, and complications were compared. The 500 kHz femtosecond laser group comprised 381 patients (381 eyes) and the 60 kHz femtosecond laser group, 362 patients (362 eyes). Three months postoperatively, the uncorrected distance visual acuity was 20/40 or better in 99.1% of eyes in the 60 kHz laser group and 99.4% of eyes in the 500 kHz laser group (P=.678). Regarding predictability, 98.6% of eyes and 97.4% of eyes, respectively, were within ±1.0 diopter of the attempted SE correction postoperatively (P=.228). The safety index was similar in the 60 kHz laser group and the 500 kHz laser group (mean 1.06 ± 0.16 [SD] versus 1.05 ± 0.14) (P=.321). The safety, predictability, and efficacy profiles of the 500 kHz femtosecond platform for LASIK were excellent and comparable to those of the 60 kHz platform. No author has a financial or proprietary interest in any material or method mentioned.
    Journal of Cataract and Refractive Surgery 09/2013; · 2.75 Impact Factor
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    ABSTRACT: We investigated an outbreak of 47 probable and 6 confirmed cases of microsporidial keratoconjunctivitis involving participants of an international rugby tournament in Singapore in April 2012.The mode of transmission was eye contact with soil. Vittaforma corneae was identified in 4 of 6 corneal scrapings and in 1 of 12 soil water samples.
    Emerging Infectious Diseases 09/2013; 19(9):1484-6. · 6.79 Impact Factor
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    ABSTRACT: Purpose. To establish an animal model of congenital hereditary endothelial dystrophy (CHED) using Slc4a11 Knock-out (KO) and evaluate the abnormalities in the cornea and kidney. Methods. Slc4a11 knock-out (KO) mouse model was generated by gene deletion. Corneal abnormalities were evaluated using slit-lamp photography, anterior segment optical coherence tomography (AS-OCT), immunohistochemistry, reverse transcription polymerase chain reaction (RT-PCR), corneal endothelial cell staining and electron microscopy. The temporal corneal changes were also monitored. Histological and functional changes of kidney were also evaluated. Results. Successful knock-out of the Slc4a11 gene was confirmed by immunohistochemistry and RT-PCR. Slit lamp photography and AS-OCT showed progressive corneal edema. Increased corneal endothelial cell size with decreased corneal endothelial cell density was observed with increased age. Scanning electron microscopy also revealed progressive cell swelling and distortion of the hexagonal cell morphology with time. Transmission electron microscopy showed characteristic ultrastructural findings of CHED including endothelial vacuolization, thickening of Descemet membrane, disorganization of collagen fibril, deposition of amorphous material, and progression of these changes with age. Decreased urine osmolarity and electrolyte concentrations suggesting abnormality in water resorption were also detected. Conclusions. Our Slc4a11 KO mouse model successfully represents clinical manifestations of human CHED. We were able to show chronological corneal progression for the first time in a knock out mouse model as well as renal abnormalities.
    Investigative ophthalmology & visual science 08/2013; · 3.43 Impact Factor
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    ABSTRACT: To study the clinical outcomes of Descemet stripping automated endothelial keratoplasty (DSAEK) with the EndoGlide donor insertion device. Retrospective interventional case series. We included 100 eyes that underwent DSAEK for Fuchs endothelial dystrophy or pseudophakic bullous keratopathy (PBK) at a single institution. Eyes with anterior segment pathology or previous intraocular surgery (except for uncomplicated cataract surgery) were excluded. Preoperative data included visual acuity and donor endothelial cell density by specular microscopy. The main outcome measures were postoperative best spectacle-corrected visual acuity (BSCVA) and endothelial cell loss at 3, 6, and 12 months. There were 59 eyes with Fuchs dystrophy and 41 eyes with PBK. In eyes without vision-limiting pathology, the median postoperative BSCVA was consistently 20/40 (range 20/20-20/400) at 3 months (n = 61 eyes), 6 months (n = 55 eyes), and 12 months (n = 48 eyes). Endothelial cell loss was 13.7% at 3 months (n = 57), 13.5% at 6 months (n = 61), and 14.9% at 12 months (n = 53). Primary graft failure occurred in 1 eye, attributable to incorrect use of the insertion device. Two eyes with complete donor dislocation were rebubbled successfully. The most common complication was glaucoma/ocular hypertension in 29 eyes (34.1%) without prior glaucoma and treatment escalation in 6 eyes (40.0%) with prior glaucoma. Of the 78 eyes with 12 months follow-up, 2 (2.6%) developed endothelial rejection, and 1 (1.3%) subsequently failed. The use of this donor insertion device during DSAEK demonstrates good outcomes and potentially low endothelial cell loss at up to 12 months after surgery.
    American journal of ophthalmology 07/2013; · 3.83 Impact Factor
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    ABSTRACT: PURPOSE: To compare the efficacy, predictability, and refractive outcomes of laser in situ keratomileusis (LASIK) using 2 femtosecond platforms for flap creation. SETTING: Multisurgeon single center. DESIGN: Clinical trial. METHODS: Bilateral femtosecond LASIK was performed using the Wavelight Allegretto Eye-Q 400 Hz excimer laser system. The Visumax femtosecond platform (Group 1) was used to create the LASIK flap in 1 eye, while the Intralase femtosecond platform (Group 2) was used to create the LASIK flap in the contralateral eye. The preoperative, 1-month, and 3-month postoperative visual acuities, refraction, and contrast sensitivity in the 2 groups were compared. RESULTS: The study enrolled 45 patients. Three months after femtosecond LASIK, 79.5% of eyes in Group 1 and 82.1% in Group 2 achieved an uncorrected distance visual acuity of 20/20 (P=.808). The mean efficacy index was 0.97 in Group 1 and 0.98 in Group 2 at 3 months (P=.735); 89.7% of eyes in Group 1 and 84.6% of eyes in Group 2 were within ±0.50 diopter of emmetropia at 3 months (P=.498). No eye in either group lost more than 2 lines of corrected distance visual acuity. The mean safety index at 3 months was 1.11 in Group 1 and 1.10 in Group 2 (P=.570). CONCLUSION: The results of LASIK with both femtosecond lasers were similar, and both platforms produced efficacious and predictable LASIK outcomes. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.
    Journal of Cataract and Refractive Surgery 05/2013; · 2.75 Impact Factor
  • Journal of Medicinal Chemistry 04/2013; · 5.61 Impact Factor
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    ABSTRACT: PURPOSE: To describe outcomes of corneal transplantation for irreversible corneal decompensation from corneal endotheliitis in Asian eyes. DESIGN: Retrospective, observational case series. METHODS: We reviewed consecutive patients with corneal endotheliitis (32 eyes of 31 subjects) who underwent keratoplasty (January 1, 2008-December 1, 2009). All eyes had preoperative aqueous polymerase chain reaction (PCR) analysis for viruses, including cytomegalovirus (CMV). CMV-positive patients were treated preoperatively with topical corticosteroids and anti-CMV treatment (oral valganciclovir 900 mg twice daily, topical ganciclovir 0.15% 5 applications per day, for 6 weeks) with complete resolution of ocular inflammation, and quiescence for at least 6 months before corneal transplantation. Our main outcome measure was recurrence of endotheliitis within 1 year after corneal transplantation. RESULTS: Five eyes were CMV positive; the remaining 27 eyes were negative for all viruses on PCR analysis. CMV-positive patients had a higher rate of recurrence of endotheliitis within 1 year after corneal transplantation, compared with CMV-negative eyes (60% vs 7.4%, P = .01). The CMV-positive eyes had recurrent endotheliitis at a median of 10 months (range 3-11 months) after corneal transplantation. After successful anti-CMV treatment, all 5 CMV-positive eyes then continued to have clear grafts for a median duration of 21 months (range 13-44 months). CONCLUSION: Our study suggests that Asian patients with corneal endotheliitis may benefit from preoperative aqueous PCR analysis before corneal transplantation. Such patients were more likely to have a recurrence of endothelial inflammation if they were CMV positive preoperatively, despite successful anti-CMV treatment before surgery.
    American journal of ophthalmology 04/2013; · 3.83 Impact Factor
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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
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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. · 2.47 Impact Factor
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    ABSTRACT: Purpose: To evaluate longitudinal changes in corneal sensitivity, tear function, and corneal staining in patients who underwent laser in situ keratomileusis (LASIK) using two different femtosecond lasers. Methods: In a prospective, randomized clinical trial, contralateral eyes of 45 patients underwent flap creation by either VisuMax or IntraLase™ femtosecond laser. Corneal sensitivity, tear break up time (TBUT), Schirmer’s test, and corneal fluorescein staining were assessed preoperatively and at 1 week, 1 month, and 3 months postoperatively. Results: There were no statistical differences in any clinical outcome measure between the two femtosecond lasers (P . 0.05), although there was a trend towards slightly lower reductions for corneal sensitivity and TBUT in VisuMax-operated eyes. Overall, corneal sensitivity was significantly reduced at 1 week (P , 0.05), 1 month (P , 0 .001), and 3 months (P , 0.001) postoperatively. A significantly greater reduction of corneal sensitivity was noted in eyes with a myopic spherical equivalent of −6.00 diopters (D) to −11.25 D as compared with eyes that had a relatively lower level of myopia of less than −6.00 D (P , 0.001). TBUT and Schirmer’s test values were significantly diminished at 1 week postoperatively (P , 0.04). Overall, corneal staining was significantly increased at 1 week postoperatively (P , 0.001). The level of myopia did not significantly affect postoperative changes in TBUT, Schirmer’s test values, or corneal staining (P . 0.05). Conclusion: This study showed that changes in corneal sensitivity, tear function, and corneal staining were statistically similar in LASIK using VisuMax and IntraLase femtosecond lasers for flap creation. However, the trend towards faster recovery of corneal sensitivity and TBUT observed in VisuMax-operated eyes may be attributable to improved technical specifications.
    Clinical Ophthalmology 03/2013; 7:591-598.

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  • 2003–2014
    • Singapore National Eye Centre
      Tumasik, Singapore
  • 2013
    • National University Health System
    • Seoul National University Bundang Hospital
      Sŏul, Seoul, South Korea
  • 2011–2013
    • Duke-NUS Graduate Medical School Singapore
      Tumasik, Singapore
    • Duke University Medical Center
      Durham, North Carolina, United States
    • Shanghai Jiao Tong University
      • Department of Ophthalmology
      Shanghai, Shanghai Shi, China
  • 2002–2012
    • National University of Singapore
      • • Singapore Eye Research Institute
      • • Department of Ophthalmology
      • • Saw Swee Hock School of Public Health
      Singapore, Singapore
    • Singapore Eye Research Institute
      Tumasik, Singapore
  • 2006–2011
    • Tianjin Eye Hospital
      T’ien-ching-shih, Tianjin Shi, China
  • 2009
    • Singapore Institute for Clinical Sciences
      Tumasik, Singapore
  • 2008
    • University of Melbourne
      • Department of Ophthalmology
      Melbourne, Victoria, Australia
  • 2004
    • Queensland University of Technology
      • School of Optometry and Vision Science
      Brisbane, Queensland, Australia