Paul T K Chew

• National University of Singapore

We present a case series, describing the utility of micropulse cyclophototherapy in the treatment of uveitic glaucoma.

We aim to describe different imaging modalities to localize cyclodialysis clefts and direct cyclopexy repair of cyclodialysis clefts. We reviewed the record of a patient with traumatic cyclodialysis cleft who underwent direct cyclopexy retrospectively. Preoperative and postoperative visual acuity and intraocular pressure (IOP) were recorded. Gonios...

Prcis: In primary angle open glaucoma, micropulse trans-scleral cyclophototherapy is effective in lowering intraocular pressure but its effects are not permanent. Hence, it can serve as a temporizing measure prior to definitive glaucoma surgery. Purpose: There is limited data on micropulse trans-scleral cyclophototherapy(MPTCP) in POAG. This is...

Purpose To investigate efficacy one year after implantation of a novel glaucoma tube shunt, the PAUL® Glaucoma Implant (PGI) in the treatment of eyes with refractory glaucoma Design Clinical trial Participants Glaucoma patients who are recalcitrant to maximum tolerated medical therapy and require tube shunt surgery Methods Interventional cohort...

Results: The cumulative failure rates were 9.5%, 20.0%, 32.5%, and 46.0% at six months, one year, two years, and three years of follow-up. At final follow-up, complete success and qualified success rates were 23.8% and 33.3%, respectively; mean IOP and number of medications decreased by 5.6 mmHg (23.9%) and 1.7 mmHg (54.8%), respectively, from pre...

Purpose: There is a lack of long-term Asian studies on the efficacy and safety of Ahmed glaucoma valve (AGV) implantation. This study seeks to determine the outcomes and complications of AGV implantation in Asians. Methods: Retrospective review of AGV surgeries performed at a single centre in Singapore was conducted. 76 patients with primary and...

Fortschritte in der Bildgebung des vorderen Segments haben neue Erkenntnisse für ein besseres Verständnis der verschiedenen Mechanismen des Engwinkelglaukoms (EWG) geliefert. Diese Entwicklung ist von großer Bedeutung für eine gute Entscheidungsfindung bei Patienten mit EWG, die eine adäquate Therapie benötigen. Das chirurgische Management des EWG...

Background To evaluate the outcome and complications of transscleral suture-fixated posterior chamber intraocular lens (PCIOL) implantation combined with Ahmed glaucoma valve (AGV) surgery in Asian eyes. Design This was a retrospective study that included 22 eyes from 22 participants. The surgeries were performed at Singapore's National University...

Purpose: To determine the long-term outcomes of 2-site phacoemulsification combined with fornix-based trabeculectomy using mitomycin C (MMC) for primary angle-closure glaucoma (PACG) and primary open-angle glaucoma (POAG) in an Asian population. Methods: We reviewed the records of all patients with POAG or PACG who underwent phacoemulsification...

Background To investigate the determinants of pupil diameter (PD), amplitude of pupil diameter change (PD-change) and speed of pupil constriction (SPC) using video anterior segment optical coherence tomography (AS-OCT) in a population-based sample of Chinese adults. Methods Chinese adults aged 40 to 80 years who were free from glaucoma were consecu...

Primary angle closure glaucoma (PACG) is a major cause of blindness worldwide. We conducted a genome-wide association study (GWAS) followed by replication in a combined total of 10,503 PACG cases and 29,567 controls drawn from 24 countries across Asia, Australia, Europe, North America, and South America. We observed significant evidence of disease...

Purpose To investigate the efficacy and safety of a punctum plug-based sustained drug release system for a prostaglandin analog, travoprost (OTX-TP), for intraocular pressure (IOP) reduction in an Asian population. Methods This is an initial feasibility, prospective, single-arm study involving 26 eyes and a bioresorbable punctum plug containing OT...

Purpose: To identify the factors which significantly contribute to the thickness variabilities in macular retinal layers measured by optical coherence tomography with or without magnification correction of analytical areas in normal subjects. Methods: The thickness of retinal layers {retinal nerve fiber layer (RNFL), ganglion cell layer plus inn...

Semipartial correlation of various factors with the thickness of the retinal nerve fiber layer in each analytical area. (DOCX)

Semipartial correlation of various factors with the thickness of the ganglion cell layer plus inner plexiform layer in each analytical area. (DOCX)

Semipartial correlation of various factors with the thickness of the ganglion cell complex in each analytical area. (DOCX)

Semipartial correlation of various factors with the thickness of the total retina in each analytical area. (DOCX)

Semipartial correlation of various factors with the thickness of the outer retina in each analytical area (DOCX)

Between-gender differences in the thickness of retinal layers in each analytical area. (DOCX)

AS-OCT videography showing pupillary constriction in response to illumination

Classification of different mechanisms of angle closure glaucoma (ACG) is important for medical diagnosis. Error-correcting output code (ECOC) is an effective approach for multiclass classification. In this study, we propose a new ensemble learning method based on ECOC with application to classification of four ACG mechanisms. The dichotomizers in...

Purpose: To determine the effectiveness of argon laser peripheral iridoplasty (ALPI) in primary angle closure (PAC) and primary angle-closure glaucoma (PACG). Design: Randomized controlled trial. Participants: Eighty PAC or PACG subjects who underwent laser iridotomy (LI) and had at least 180° of persistent appositional angle closure and intra...

To compare the effect of argon laser peripheral iridoplasty (ALPI) and conventional medical therapy in the immediate treatment of acute primary angle closure (APAC) using anterior segment optical coherence tomography (ASOCT). In this single tertiary centre, prospective comparative study, we randomised 30 consecutive patients with unilateral APAC in...

To determine the occurrence of intraoperative and postoperative complications up to three years after primary phacotrabeculectomy with intraoperative use of Mitomycin C (MMC) in primary open angle (POAG) and primary angle closure glaucoma (PACG) patients, and the effect of postoperative complications on surgical outcome. Retrospective review of 160...

Glaucoma is an eye disease where a loss of vision occurs as a result of progressive optic nerve damage usually associates with high intraocular pressure. A subtype of glaucoma called primary angle-closure glaucoma (PACG) has been observed to be the result of one or more mechanisms such as Pupil block, Plateau iris, Peripheral iris roll, and Lens in...

Systems, devices, and methods for treating a glaucomatous eye are provided. An amount of pulsed laser energy is delivered to the pars plana of the eye by a hand-holdable device which comprises a hand-holdable elongate member and a contact member disposed on an end of the elongate member. A contact surface of the contact member is placed in direct c...

Effective feature selection plays a vital role in anterior segment imaging for determining the mechanism involved in angle-closure glaucoma (ACG) diagnosis. This research focuses on the use of redundant features for complex disease diagnosis such as ACG using anterior segment optical coherence tomography (AS-OCT) images. Both supervised (Minimum Re...

Objective: To systematically review the efficacy and tolerability of 4 prostaglandin analogues (PGAs) as first-line monotherapies for intraocular pressure (IOP) lowering in adult patients with primary open-angle glaucoma or ocular hypertension. Data sources: A literature search was performed in PubMed (1965-June 2013) and the Cochrane Library (1...

Background: With the use of ultrasound biomicroscopy, we aim to look at differences in anterior segment parameters of eyes with primary open angle glaucoma (POAG) and primary angle closure glaucoma (PACG) in dark and light conditions. Methods: Ultrasound biomicroscopy was performed for 30 subjects with PACG and 30 subjects with POAG at initial pres...

Background The aim of this study was to compare the efficacy and safety of micropulse and continuous-wave diode trans-scleral cyclophotocoagulation in refractory glaucoma.DesignRandomised, comparative, exploratory study in a tertiary hospital settingParticipantsPatients with refractory, end-stage glaucomaMethods48 patients were randomised to either...

Author Summary The anterior chamber is the space within the eye which is bound by the cornea, and the anterior surfaces of the iris and lens. Anterior chamber depth (ACD) is the distance measured along the eye's optical axis, from the cornea to the lens surface. ACD is an important risk factor for primary angle closure glaucoma (PACG), a major caus...

To describe anterior segment optical coherence tomography (ASOCT) parameters during acute primary angle closure (APAC) before therapeutic interventions and comparative analyses of biometric parameters of APAC eyes with fellow eyes. Prospective, comparative case series. Thirty-one consecutive patients with APAC. All patients underwent ASOCT imaging...

We hypothesize that patients with primary angle closure (PAC) have common significant facial characteristics that set them apart from an age-matched, sex-matched, and race-matched control population. The primary objective of this study was to test whether a 3-dimensional (3D) camera could pick up these differences in order to differentiate PAC pati...

To review the management regimes of acute primary angle closure (APAC) in two hospitals in Singapore, and to identify the incidence of and risk factors for progression to glaucomatous optic neuropathy. We conducted a retrospective review of 40 patients from National University Hospital (NUH) and 52 patients from Singapore National Eye Centre (SNEC)...

Background/aims: To investigate longitudinal changes in anterior chamber depth (ACD) and axial length (AXL) over 5 years after trabeculectomy surgery in Asian patients with primary glaucoma, and to identify factors associated with these changes. Methods: In this prospective cohort study, phakic subjects with primary glaucoma who underwent trabec...

Introduction: To describe the optic disc, visual field and ocular characteristics of a consecutive cohort of Asian patients with chronic primary angle-closure glaucoma (CPACG), and compare them with those having primary open-angle glaucoma (POAG). Methods: In a prospective comparative case series of new patients with POAG or CPACG in Singapore,...

Introduction: This prospective observational case series aimed to determine whether the lateral decubitus position, which is commonly adopted during sleep, has an effect on intraocular pressure (IOP) in normal controls. Methods: Patients without glaucoma were recruited from those visiting outpatient clinics for non-glaucomatous conditions. The l...

Objective: To evaluate changes in the speed of pupil constriction and in anterior segment parameters after laser peripheral iridotomy (LPI) in patients with angle closure using anterior segment optical coherence tomography. Methods: In this prospective observational study, videos of pupil and anterior segment changes in response to illumination...

Selection of relevant features is of fundamental importance in building robust classifiers for computer-aided detection (CAD) of angle closure glaucoma mechanism. Typically one is interested in determining which, of a large number of potentially redundant or noisy features, are most discriminative for classification. The objective of the paper is t...

Objective: To assess the effect of prophylactic laser peripheral iridotomy (LPI) on corneal endothelial cell density (ECD) and morphology in primary angle closure suspects (PACS) over 3 years. Methods: In this prospective cohort study, subjects underwent LPI in one eye, while the fellow eye was untreated. Specular microscopy was performed at bas...

Optic nerve head swelling after acute primary angle-closure (APAC) has been associated with significant visual loss. We provide the first description of a good visual outcome following transient isolated optic nerve swelling associated with APAC. A 64 year-old man presented with right eye pain and poor vision for a day. Examination revealed right e...

Purpose: To evaluate the acceleration of pupil constriction (APC) in response to illumination using video anterior segment optical coherence tomography (AS-OCT) in angle closure and normal eyes. Methods: This was an observational study of 342 Chinese subjects. Iris and angle changes in response to illumination were captured with real-time video...

Primary angle closure glaucoma (PACG) is a major cause of blindness worldwide. We conducted a genome-wide association study including 1,854 PACG cases and 9,608 controls across 5 sample collections in Asia. Replication experiments were conducted in 1,917 PACG cases and 8,943 controls collected from a further 6 sample collections. We report signific...

Background: To evaluate different mechanisms of primary angle closure and to quantify anterior chamber parameters in these mechanisms using anterior segment optical coherence tomography in an Asian population. Design: Hospital-based cross-sectional observational study. Participants: Forty-eight consecutive patients with primary angle closure glauco...

In this editions’ ‘Experts Opinion’, the management of hy-potony and choroidal effusion following glaucoma filtration surgery is discussed. We are delighted to welcome Clinical Associate Professor Ivan Goldberg and Professor Franz Grehn and Paul Chew to the panel to provide opinion on this very challenging clinical situation.

The main objective of surgical treatment in angle closure is to quickly decrease the intraocular pressure and therefore reduce the risk of further glaucomatous optic nerve damage. Surgical treatment of angle-closure glaucoma also helps to ensure that progressive angle closure does not occur, and that the risk of acute angle closure is abolished. Th...

Novel anterior segment optical coherence tomography (ASOCT) parameters associated with angle closure include anterior chamber area (ACA), anterior chamber volume (ACV), anterior chamber width (ACW), lens vault (LV), iris thickness (IT), iris area (I-area), and iris curvature (I-curv). We aimed to investigate changes in these parameters after laser...

To determine whether the timing of cataract surgery after trabeculectomy has an effect on trabeculectomy function in terms of intraocular pressure control. This was a cohort study nested within a randomized clinical trial. There were 235 participants with glaucoma who had a single previous trabeculectomy augmented with either intraoperative 5-fluor...

To evaluate the speed of pupil constriction (SPC) in response to a standardized change in illumination from dark to light using anterior segment optical coherence tomography (AS-OCT) in eyes with closed angles, compared to those with open angles. This was a prospective, comparative, observational study. Study subjects with primary angle-closure gla...

Primary angle closure glaucoma (PACG) is equally prevalent in Indian in Asian population as the primary open angle glaucoma. Eighty-six percent of people with PACG are in Asia, with approximately 48.0% in China, 23.9% in India and 14.1% in southeast Asia. To understand PACG, it is mandatory to understand its classification and type of presentation...

To evaluate the risk of primary acute angle closure (AAC), changes in intraocular pressure (IOP), and associated risk factors after pupil dilation in Asian subjects with narrow angles (primary angle-closure suspects [PACS]). Prospective clinical study. A total of 471 subjects aged more than 50 years with narrow angles in Singapore. This study was p...

To examine the association between central corneal thickness (CCT) and glaucoma. This was a nested case-control study using 1090 subjects from an eye disease population survey in Singapore and 243 participants from a hospital glaucoma surgery clinical trial in Singapore. Mean CCT in 938 community subjects was 539 μm ± 32 μm, and in 12 community sub...

Background: Glaucoma is the leading cause of irreversible blindness. Although primary open-angle glaucoma is more common, primary angle-closure glaucoma (PACG) is more likely to result in irreversible blindness. By 2020, 5·3 million people worldwide will be blind because of PACG. The current standard care for PACG is a stepped approach of a combin...

To quantify changes in bleb morphology after laser suture lysis (LSL) using anterior segment optical coherence tomography (AS-OCT). This was a prospective observational case series of patients who underwent trabeculectomy surgery with mitomycin-C and required subsequent LSL. Subjects were assessed before and immediately after LSL, and at 3 months a...

AIMS/PURPOSE: To determine and correlate the long-term changes in retinal nerve fibre layer (RNFL) thickness, optic nerve head (ONH) morphology, and visual fields after a single episode of acute primary angle closure (APAC). This was a cross-sectional comparative study of patients at National University Hospital (Singapore) from 2000 to 2006 after...

Transscleral diode laser cyclophotocoagulation (TSCPC) is an established method of treatment for refractory glaucoma, but is associated with significant complications. This study evaluates the efficacy and safety of a new form of TSCPC using micropulse diode laser and trans-pars plana treatment with a novel contact probe. Prospective interventional...

To determine if imaging of blebs with anterior segment optical coherence tomography (ASOCT) affects clinical decision-making with regard to laser suture lysis (LSL) after trabeculectomy. In this prospective observational case series, we included patients with poorly controlled intraocular pressure (IOP) after standardized trabeculectomy from May to...

Data regarding development of primary angle closure glaucoma (PACG) following acute primary angle closure (APAC) is conflicting. This study looks at outcomes after an APAC episode with a secondary aim to identify any risk factors that could predict progression to PACG. This is a retrospective review of the charts of consecutive patients who were di...

The aim of this work was to image trabeculectomy blebs using spectral domain optical coherence tomography (SDOCT). In this prospective cross-sectional study, patients who had undergone trabeculectomy with at least 3 months of follow up were included. Blebs were imaged using an adapted SDOCT system (Cirrus HD-OCT, Carl Zeiss Meditec Inc., Dublin, CA...

This study compared the intraocular pressure (IOP)-lowering efficacy of 2 fixed combination products, brinzolamide 1%/timolol 0.5% suspension (Azarga, Brinz/Tim) and dorzolamide 2%/timolol 0.5% solution (Dorz/Tim), in patients with open-angle glaucoma or ocular hypertension who required a change in therapy due to elevated IOP while receiving IOP-lo...

To report 3-year results of a randomized, controlled trial comparing the use of a single application of 5-fluorouracil (5-FU) with placebo in trabeculectomy surgery. Prospective, randomized, double-blinded treatment trial. Two hundred forty-three Asian patients with primary open-angle or primary angle-closure glaucoma undergoing primary trabeculect...

The purpose of this study was to describe a novel method of repair for exposed glaucoma drainage implants (GDIs) using corneal patch grafts. This is a retrospective review of patients who underwent corneal patch graft repair of exposed GDIs at 2 tertiary ophthalmic centers in Singapore from November 1, 2000, to January 31, 2006. Surgical outcome wa...

To measure changes in angle width after phacoemulsification and intraocular lens (IOL) implantation using anterior segment optical coherence tomography (AS-OCT). Twenty-one patients undergoing cataract surgery were recruited from the National University Hospital, Singapore. AS-OCT images were obtained of nasal and temporal angle quadrants before an...

Aim: To investigate the effectiveness of 8-shot argon laser peripheral iridoplasty for treating Asian eyes with primary angle closure. Methods: Eight laser shots, placed 2 shots per quadrant, were applied using the following parameters: power, 0.4 W to 0.7 W; duration, 150 ms to 200 ms; and spot size, 100 μ to 200 μ. Before treatment, all eyes had...

The genetic basis of primary angle closure glaucoma (PACG) has yet to be elucidated. Ocular characteristics related to PACG such as short hyperopic eyes with shallow anterior chambers suggest the involvement of genes that regulate ocular size. CHX10, a retinal homeobox gene associated with microphthalmia, and MFRP, the membrane-type frizzled-relate...

A recent study identified the single nucleotide polymorphism (SNP) rs2664538 within the MMP-9 gene with risk for acute primary angle closure glaucoma (PACG). The aim of this study was to confirm this association in Singaporean Chinese subjects with both acute and chronic PACG. This was an observational cross-sectional study. Genomic DNA was extract...

To determine the prevalence of plateau iris in a cohort of primary angle closure suspects (PACSs) using ultrasound biomicroscopy (UBM). Cross-sectional observational study. Subjects over the age of 50 years diagnosed as PACSs. Subjects were randomized to undergo laser peripheral iridotomy (LPI) in one eye. Ultrasound biomicroscopy was performed bef...

To evaluate the relationship between angle width as determined by anterior segment optical coherence tomography (AS-OCT) and the presence of peripheral anterior synechiae (PAS). This was a prospective observational case series in which 203 subjects with primary angle closure or open angles were recruited. Images of the nasal, temporal and inferior...

Approximately 10% of Chinese people older than 50 years in Singapore have asymptomatic narrow angles [also termed primary angle closure suspects (PACS)]. The aim of this study was to determine the attitudes and practices of ophthalmologists in Singapore regarding the management of these patients. A nation wide questionnaire-based survey was conduct...

The glaucoma drainage devices (GDD) are increasingly popular as the primary procedure over trabeculectomy and cyclo-destructive in the management of refractory glaucoma. Interest in this field is warranted because studies have found significant rates of desirable intraocular pressure (IOP) control as well as maintenance of visual acuity in these di...

Using the anterior segment optical coherence tomography (AS-OCT) to quantify changes in anterior segment morphology going from light to dark and following laser iridotomy (LI). Prospective observational study. 17 consecutive subjects without peripheral anterior synechiae undergoing LI were evaluated using gonioscopy and AS-OCT. Angle configuration...

To evaluate the reproducibility of anterior chamber (AC) angle measurements obtained using anterior segment optical coherence tomography (AS-OCT). Patients with suspected glaucoma and those with glaucoma, ocular hypertension, or anatomically narrow angles were recruited from the glaucoma service at the National University Hospital, Singapore. All s...

A deformable-model based approach is presented in this paper for robust detection of optic disk and cup boundaries. Earlier work on disk boundary detection up to now could not effectively solve the problem of vessel occlusion. The method proposed here improves and extends the original snake, which is essentially a deforming-only technique, in two a...

To image trabeculectomy blebs before and after laser suture lysis (LSL) using anterior segment optical coherence tomography (AS-OCT). Prospective observational study. Blebs were imaged with a prototype of the AS-OCT (Carl Zeiss Meditec, Inc, Dublin, California, USA) before and after LSL. Blebs were assessed for bleb height, bleb wall thickness, app...

Case report: A 51-year-old woman present with bilateral acute primary angle-closure glaucoma. Glaukomflecken were prominent. Anterior lens growth in front of the glaukomflecken was measured 12 years later. Comments: Lens thickness is important in the pathogenesis of acute primary angle closure, and lens growth can become significant with time in...

This paper presents a novel deformable-model-based algorithm for fully automated detection of optic disk boundary in fundus images. The proposed method improves and extends the original snake (deforming-only technique) in two aspects: clustering and smoothing update. The contour points are first self-separated into edge-point group or uncertain-poi...

To image trabeculectomy blebs using anterior segment optical coherence tomography (AS-OCT). Prospective cross-sectional study. Fifty-five patients who had previously undergone trabeculectomy surgery. All blebs were imaged with a prototype of the AS-OCT. Standardized color monophotographs of blebs were also obtained. Blebs were assessed for the foll...

To evaluate noncontact anterior segment optical coherence technology (AS-OCT) as a qualitative method of imaging the anterior chamber angle and to determine its ability to detect primary angle closure when compared with gonioscopy in Asian subjects. Prospective observational case series. Two hundred three subjects were recruited from glaucoma clini...

To investigate the effect of lens opacity on the performance of the multi-focal visual evoked potential (mfVEP) test in patients with glaucoma and its relationship with the Humphrey's automated static perimetry. This is a prospective, non-randomized study. Twenty-two patients were enrolled with moderate cataract and primary glaucoma scheduled for c...

To determine the long-term outcome of the contralateral eye in Asian persons with a unilateral attack of acute primary angle closure (APAC). Cross-sectional observational case series. Seventy-nine individuals who were examined from 4 to 10 years after a unilateral episode of APAC at 2 Singapore hospitals. All subjects underwent a complete eye exami...

To examine the progression of lens opacity in Asian people after trabeculectomy and determine associated risk factors. This was an observational case series of 243 people aged 36 to 82 years. Trabeculectomy was performed on 1 eye of each subject. Lens opacity was measured yearly using the Lens Opacification Classification System III. The main outco...

The three dimensional (3-D) visualisation of the optic disc in true colour will give essential meaning in clinical application. It is not only useful for clinicians in the evaluation of the condition of the optic disc, but it also simplifies the pathological diagnosis and disease progression monitoring. This paper describes a complete 3-D optic dis...

Aim: To compare the intraocular pressure-lowering efficacy and safety of travoprost 0.004% with latanoprost 0.005% for patients with chronic angle closure glaucoma. Patients and methods: 320 patients with chronic angle closure glaucoma, who had previously undergone laser peripheral iridotomy, were randomised to receive travoprost 0.004% once daily...

Optic disk is one of the main components on retina. It is an indicator of various ophthalmic pathologies. This paper presents a novel algorithm to segment the optic disk, based on snake model. The proposed method improves and extends original snake technique in two aspects: clustering and smoothing update. The contour first deforms to the location...

To evaluate the clinical efficiency, safety and subjective visual outcomes of multifocal intraocular lenses (IOL) in the Singapore population. This is a retrospective case series of 45 phacoemulsification with multifocal lens implantation performed in 27 patients for cataracts, over a two-year period. The efficacy, stability and safety of the lens...

We studied the reliability of different measures of the visual contribution to postural steadiness by recording the postural sway during standing with eyes open (EO) or eyes closed (EC). The COP trajectory was recorded in 21 subjects aged 42-61 standing on a firm or foam support. The improvement of postural steadiness due to vision was measured wit...

Background: Ischaemic changes in the iris occur frequently after an episode of acute primary angle closure (APAC). The aim of this study was to investigate the significance of such changes with regards to visual outcome. Methods: Acute primary angle closure cases were treated with medical therapy followed by laser peripheral iridotomy after resolut...

This study evaluated the visual contribution to postural steadiness in primary open angle glaucoma (POAG), in correlation with the mean deviation (MD) measured through conventional perimetry, and with the Advanced Glaucoma Intervention Study (AGIS) score, which quantifies the extent of losses in the visual field. In 35 POAG patients and 21 age-matc...