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Biomedical subjects

D T Tan

Publications and source records attributed to D T Tan.

At least 19 recordsLinked to original sources
PubMed2003

Corneal replacement using a synthetic hydrogel cornea, AlphaCor: device, preliminary outcomes and complications.

PURPOSE: Clinical assessment of outcome of corneal replacement with a synthetic cornea, AlphaCor, in patients considered at too high risk for conventional penetrating keratoplasty with donor tissue to be successful, but excluding indications such as end-stage dry eye that might be suited to traditional prosthokeratoplasty. METHODS: All patients in the multicentre clinical trial were managed according to an approved protocol, with Ethics Committee approval in each centre. Preoperative visual acuity ranged from perception of light (PL) to 6/60 (20/200). Implantation was by means of an intralamellar technique, with a conjunctival flap in most cases. Tissues anterior to the optic were removed as a secondary procedure. RESULTS: Up to 30 November 2001, 40 AlphaCor devices had been implanted in 38 patients, of mean age 60 years. Follow-up ranged from 0.5 months to 3 years. There had been one extrusion (2.5%) and four cases (10%) where a device had been removed due to melt-related complications. All five of these cases received a donor corneal graft after the device was removed, with these grafts remaining anatomically satisfactory and epithelialised to date. Corneal melts in AlphaCor recipients were found to be strongly associated with a history of ocular herpes simplex infection. Two further devices (5%) were removed owing to reduced optic clarity after presumed drug-related deposition, and have been successfully replaced with second devices. Mean preoperative best-corrected visual acuity was hand movements. Visual acuities after surgery ranged from PL to 6/6(-2) (20/20(-2)). CONCLUSIONS: Early results suggest that the AlphaCor, previously known as the Chirila keratoprosthesis (Chirila KPro), has a low incidence of the complications traditionally associated with keratoprostheses and can be effective in restoring vision in patients considered untreatable by conventional corneal transplantation. Importantly, the device can be replaced with a donor graft in the event of development of a significant complication. A history of ocular herpes simplex is a contraindication to AlphaCor implantation. Ongoing monitoring of clinical outcomes in all patients will allow the indications for AlphaCor, as opposed to donor grafts, to be determined.

Adult↗
PubMed2001

Environmental lead exposure and progressive renal insufficiency.

BACKGROUND: Several recent studies show that serum creatinine level or creatinine clearance is inversely associated with blood lead levels. However, the studies did not allow direct inferences about causality. OBJECTIVE: To evaluate the relation between body lead burden (BLB) and progressive renal insufficiency in patients without previous heavy lead exposure. DESIGN: A prospective, longitudinal study with a controlled clinical trial. PATIENTS: One hundred ten patients with chronic renal insufficiency (serum creatinine level, 133-354 micromol/L [1.5-4.0 mg/dL]) and normal BLB (EDTA mobilization tests, <600 microg per 72-hour urine collection) and without a history of previous heavy lead exposure were divided into 2 groups according to BLB: the high-normal BLB group (BLB > or =80 microg and <600 microg) and the low BLB group (BLB <80 microg). Patients were prospectively followed up for 2 years. MAIN OUTCOME MEASURES: The primary outcome was a 1.5 times increase in the initial creatinine level. The secondary outcome was a change over time in the value of creatinine clearance. At the end of follow-up, a 3-month clinical trial with chelation therapy for patients with high-normal BLB was performed to clarify the role of environmental lead exposure in progressive renal insufficiency. RESULTS: Fifteen patients (14 in the high-normal BLB group and 1 in the low BLB group) reached the primary outcome within 24 months. Renal outcome was significantly better in the low BLB group (P<.001). From month 12 to month 24, renal function of high-normal BLB patients had a greater rate of progressive renal insufficiency than that of low BLB patients. In the Cox multivariate regression analysis, BLB was the most important risk factor for determining the progression of renal insufficiency. After chelation therapy, significant improvement in renal function was noted. In addition, the effect of improving renal function lasted for more than 12 months in these patients. CONCLUSIONS: Long-term low-level environmental lead exposure may subtly affect progressive renal insufficiency in the general population. Progressive renal insufficiency may be improved for at least 1 year after lead chelating therapy. Further investigations are needed to clarify this observation.

Adolescent↗
PubMed2001

The prevalence and risk factors for pterygium in an adult Chinese population in Singapore: the Tanjong Pagar survey.

PURPOSE: To determine the prevalence and risk factors for pterygium in the Chinese population of Singapore. METHODS: A population-based survey was conducted in Singapore, an island located 1 degree north of the equator with a stable tropical climate. A disproportionate, stratified, clustered, random sampling procedure was used to select the names of 2000 Chinese people aged 40 to 79 years from the 1996 electoral register in the Tanjong Pagar district of Singapore. Selected subjects underwent a comprehensive interview and ocular examination. Pterygium was diagnosed and graded clinically as grade 1 (transparent), 2 (intermediate), and 3 (opaque). Risks factors associated with pterygium and grade 3 pterygium were evaluated with logistic regression models. RESULTS: From a total of 1717 eligible subjects, 1232 (71.8%) were examined. There were 120 people with either unilateral (n = 70) or bilateral (n = 50) pterygium, equivalent to an overall prevalence of 6.9% (95% confidence interval [CI], 5.2, 8.8) in the Chinese population aged 40 and older. The prevalence increased linearly with age (chi-square test of trend P <.001) and was higher among men than women (age-adjusted odds ratio [OR], 4.2; 95% CI, 2.5, 6.9). Men aged 70 and above had the highest overall prevalence of 25.4% (95% CI, 18.2, 19.4), but pterygium was not seen in women aged 40 to -49 years. In multivariate analysis, ptergyium was independently associated with increasing age (OR, 7.8; 95% CI, 3.2, 18.8 for persons 70 to 81 years, compared with 40 to 49 years), male sex (OR, 5.1; 95% CI, 2.9, 9.3) and certain occupations; factory workers, production workers and machine operators (OR, 3.1; 95% CI, 1.5, 6.3), as well as laborers and agricultural workers (OR, 3.3; 95% CI, 1.6, 7.0) had higher risks, compared with professionals and office workers. Grade 3 pterygium (n = 36) was also independently associated with male sex (OR, 11.6; 95% CI, 3.5, 38.6) and similar occupations but was not related to age. CONCLUSIONS: The prevalence of pterygium in Singapore is 7% among Chinese aged 40 years and older. Independent associations with increasing age, male sex, and occupations linked to outdoor work and other exposures suggest a multifactorial cause of this condition.

Adult↗
PubMed2001

Therapeutic lamellar keratoplasty for limbal dermoids.

PURPOSE: To assess the surgical outcomes of appearance, vision, refraction, and graft survival and integrity in patients with histologically proven limbal dermoid choristomata who underwent lamellar keratoplasty. DESIGN: Retrospective noncomparative analysis of a consecutive case series with patient recall and examination. PARTICIPANTS: Eleven patients (six female, five male, median age, 9.6 years; range, 1-29 years) with 12 limbal dermoids in 11 eyes operated on between 1995 and 1998 were identified from the eye bank database at the Singapore National Eye Centre. METHODS: Case records, photographs, and eye bank data were examined. Patients not already seen by the authors within the previous 3 months were recalled and examined. OUTCOME MEASURES: Descriptive data: size and location of the dermoid, presence of lipid keratopathy; visual acuity; refraction and astigmatism, vector analysis, surgically induced refractive change; corneoscleral and limbal match, haze, vascularity; graft integrity, clarity, vascularization, and rejection episodes. RESULTS: Most (7 of 11) patients had single inferotemporal limbal dermoids, although one patient had two dermoids in one eye. Median follow-up time was 21.6 months (range, 9.0-46.4 months). Most (8 of 11) patients had good or excellent cosmetic results with minimal interface haze and no vascularization. Two cases with previously excised lesions had postoperative vascularization develop. One of these cases had graft infection develop, underwent subsequent debridement, and has an opaque graft. Best-corrected visual acuity was maintained or slightly improved in 9 of 11 patients. For the group and most individual patients, mean astigmatism, spherical equivalent, and refraction, as assessed by surgically induced refractive change and h-vector analysis, were not significantly changed. CONCLUSION: Lamellar keratoplasty as primary surgery for limbal dermoids gave good cosmetic results. However, improvement in refractive, astigmatic, and visual status is not guaranteed, and these procedures should be viewed more cautiously, although established good vision was maintained in our series.

Adolescent↗
PubMed2001

Randomized clinical trial of Surodex steroid drug delivery system for cataract surgery: anterior versus posterior placement of two Surodex in the eye.

OBJECTIVE: To evaluate safety and antiinflammatory efficacy of placing two Surodex (Oculex Pharmaceuticals, Inc., Sunnyvale, CA) in the eye after cataract surgery in comparison with steroid eyedrops and to compare anterior versus posterior chamber placement. DESIGN: Randomized, masked, controlled trial. PARTICIPANTS: One hundred four eyes of 104 Asian patients undergoing extracapsular cataract extraction with intraocular lens implantation were examined. Of these, 33 eyes of 33 patients served as control eyes (group A). INTERVENTION: Two Surodex pellets were inserted in the anterior chamber (AC) of 35 eyes (group B), and two Surodex pellets were inserted in the ciliary sulcus of 36 eyes (group C) at the conclusion of surgery. Control eyes received neither Surodex nor a placebo implant, but were prescribed conventional 0.1% dexamethasone eyedrops four times daily for 4 weeks. MAIN OUTCOME MEASURES: Anterior chamber flare and cells were graded clinically at the slit lamp. Anterior chamber flare was assessed objectively with the Kowa FC500 Laser Flare Meter (Kowa Co. Ltd, Tokyo, Japan). Intraocular pressure and corneal endothelial specular microscopy with morphometric cell analysis were performed for up to 1 year after surgery. RESULTS: Lower flare meter readings occurred in both Surodex groups at all postoperative visits, as compared with the dexamethasone eyedrop group, with statistical significance at days 4 (P = 0.001), 8 (P = 0.001), and 15 (P = 0.02). No difference in flare occurred between AC and ciliary sulcus placement. Clinical slit-lamp assessment of anterior chamber flare and cells showed no difference between Surodex-treated eyes and dexamethasone-treated eyes. Nine of 33 eyes (27.3%) in group A required steroid augmentation, as opposed to 4 of 71 eyes (5.6%) in groups B and C. Inflammatory symptoms were reduced in the Surodex-treated eyes, with statistical significance for ocular discomfort (P = 0.001), photophobia (P = 0.04), and lacrimation (P = 0.01). No complications occurred with Surodex-treated eyes, and no significant difference in endothelial cell loss was noted between Surodex-treated eyes and dexamethasone-treated eyes up to 1 year after surgery. CONCLUSIONS: Intraocular placement of two Surodex is a safe and effective treatment method to reduce intraocular inflammation after cataract surgery and clearly is superior to eyedrops in reducing inflammatory symptoms and aqueous flare as measured with the laser flare meter. No difference in efficacy between AC placement and ciliary sulcus placement of Surodex was detected in this study.

Aged↗
PubMed2001

Recurrent corneal erosion after laser in situ keratomileusis.

PURPOSE: To describe how laser-assisted in situ keratomileusis (LASIK) may induce recurrent corneal erosion (RCE) syndrome and the preventive measures for avoiding this complication. METHODS. A case series was used. RESULTS: We report the development of RCE syndrome in eight eyes of six patients after LASIK. In five cases, the RCE was triggered by epithelial trauma at the time of the LASIK procedure, as evidenced by the observation of RCE occurring at the same site as the initial epithelial disturbance. In case 6, RCE occurred with undiagnosed basement membrane dystrophy. The patients responded to treatment with ocular lubricants with one patient undergoing penetrating keratoplasty for RCE after LASIK. CONCLUSION: LASIK can induce or precipitate RCE, and RCE should perhaps be included as a potential complication in the informed consent process. It is important to minimize epithelial damage to prevent RCE after LASIK, and measures to reduce this include adequate irrigation of the corneal surface immediately before the microkeratome pass and careful attention to flap epithelium during flap replacement. Cases in which loose epithelium is noted after LASIK should be identified as potential RCE cases, and extra care should be taken for subsequent enhancement procedures or LASIK of the second eye.

Adult↗
PubMed2001

Corneal and refractive error astigmatism in Singaporean schoolchildren: a vector-based Javal's rule.

BACKGROUND: Traditional approaches to Javal's rule do not use data from subjects with oblique astigmatism and have not been used to make predictions about subjects with oblique astigmatism. Vector approaches to analyzing refractive error can circumvent these problems. METHODS: Subjects were 993 Singaporean schoolchildren. We performed linear regression of refractive error astigmatism on corneal astigmatism, using J0 vectors to describe with-the-rule and against-the-rule astigmatism and J45 vectors to describe oblique astigmatism. RESULTS: We obtained the following statistically significant regression relationships: RJ0 = 0.931 x CJ0 - 0.276 and RJ45 = 0.638 x CJ45 + 0.010, where R and C denote refractive error astigmatism and corneal astigmatism, respectively. CONCLUSION: Our vector-based Javal's rule gives closer predictions of refractive astigmatism than the original Javal's rule and the simplified Javal's rule and can be applied in cases of corneal oblique astigmatism.

Adolescent↗
PubMed2001

Vascular patterns in pterygium and conjunctival autografting: a pilot study using indocyanine green anterior segment angiography.

AIMS: To characterise the vasculature of pterygium using indocyanine green (ICG) anterior segment angiography and to demonstrate the pattern of revascularisation following conjunctival autografting. METHODS: ICG anterior segment angiography was performed on nine patients with pterygium. Angiography was repeated at 1-2 weeks and 2 months following conjunctival autografting in these patients. RESULTS: Angiography showed a single feeder vessel originating from the anterior conjunctival circulation in six cases (66.7%). This vessel branched to form the radial vessels of the pterygium. Following conjunctival autografting, reperfusion of the vessels in the conjunctival autograft was demonstrable as early as 1 week postoperatively from the episcleral bed. At 2 months postoperatively, the graft appeared well perfused with mild leakage demonstrable at the edges of the graft. CONCLUSIONS: A single feeder vessel from the anterior conjunctival circulation branches to form the radial vessels in pterygium. Reperfusion of conjunctival autografts occurs as early as 1 week postoperatively from the episcleral bed.

Anterior Eye Segment↗
PubMed2001

Patient reliability in the administration of topical ocular medication.

PURPOSE: To evaluate patient's reliability in the administration of eyedrops. METHOD: The study is based on a randomised, controlled clinical trial in which a steroid-containing drug delivery system (DDS) was directly compared to conventional steroid eyedrops after cataract surgery. 32 eyes undergoing extracapsular cataract extraction with intra-ocular lens insertion received a DDS, while 31 eyes received 0.1% dexamethasone eyedrops q.d.s for 30 days. Patients with DDS were given a placebo eyedrop in the form of 0.9% sodium chloride, while all 63 eyes received topical chloramphenicol eyedrops q.d.s for 30 days. At the conclusion of the 30 day visit, the eyedrop containers were collected and the residual volume of medication remaining in each bottle was then measured to the nearest 10 microlitre using a pipette. RESULTS: 31 patients returned the complete set of eyedrop containers. There was no statistical significant difference in the volume used between the types of eyedrops, sex and diabetic status. All the patients used more than the prescribed amount. Older patients tended to use less medication. CONCLUSION: The amount of medication that patients actually administered in this trial varied widely according to the individual, and patient age may be a factor affecting compliance in using eyedrops.

Age Factors↗
PubMed2001

Therapeutic use of Bausch & Lomb PureVision contact lenses.

PURPOSE: To evaluate the Bausch & Lomb PureVision contact lens as a continuous wear contact lens for therapeutic indications in a prospective open-ended non-randomized clinical trial. METHODS: Patients with a variety of corneal and ocular surface disease conditions presenting at the Singapore National Eye Centre who required therapeutic continuous contact lens wear were enrolled. Therapeutic indications included pain relief, corneal protection, and enhancement of corneal wound healing. Success or failure of specific treatment indications was assessed in all cases, with evaluation of lens performance and fit characteristics, and the presence of ocular complications or lens-related complications was noted. RESULTS: There were 54 patients (54 eyes), and the mean duration of continuous contact lens wear was 1.1 months. Conditions treated included post-surgical indications (n = 36) (post-keratoplasty or ocular surface transplantation, post-LASIK or PRK surgery) bullous keratopathy (n = 7), chemical burns (n = 3), epithelial abrasions or recurrent corneal erosion syndromes (n = 3), corneal perforations (n = 3), neurotrophic ulcer (n = 1), and corneal laceration (n = 1). For the indication of corneal healing (40 eyes), improved healing was noted in 38 eyes (96%), with full healing occurring in 33 eyes (83%). For pain relief (28 eyes), 27 patients (96%) had considerable or complete pain relief, and the remaining patient reported partial pain relief. For corneal protection (21 eyes), lens wear was fully protective in all cases. The lens performance and fitting characteristics surpassed any previous therapeutic lenses used by the investigators. Complications related to contact lens wear were limited to one case of a culture-negative corneal infiltrate requiring cessation of therapeutic lens wear and one case of a loosely fit lens. CONCLUSIONS: Our results show that the PureVision contact lens exhibits good safety and efficacy when utilized as a continuous wear therapeutic lens. With the theoretical advantage of increased oxygen transmissibility reducing the risk of hypoxia-related complications, this new lens may be one step closer to the ideal therapeutic contact lens. The PureVision contact lens is now our primary bandage lens of choice in our corneal, external disease, and refractive surgery services.

Adolescent↗
PubMed2000

Reverse geometry contact lens wear after photorefractive keratectomy, radial keratotomy, or penetrating keratoplasty.

PURPOSE: To determine if a super diffusion coefficient of lens/lens thickness (Dk/L) reverse geometry gas permeable (steep peripheral and flatter central curve) contact lenses can be successfully worn after excimer photorefractive keratectomy (PRK), radial keratotomy (RK), or penetrating keratoplasty (PK). METHODS: Patients with residual ametropia after PRK, RK, or PK were fitted with reverse geometry lenses (Plateau lens in SF-P material; Menicon USA, Inc, Clovis, CA, U.S.A.). Contact lens fit characteristics and comfort were assessed. Lens centration, visual quality, and ocular surface status were graded and visual acuity charted. RESULTS: Thirteen eyes of 11 patients were fitted; eight eyes with PRK, one eye with RK, and four eyes with PK previously performed. The mean follow up of the patients was six months. The visual acuity prior to lenses ranged from 6/12 to counting fingers, and the acuity with lenses ranged from 6/6 to 6/30. Eight of the 11 patients wore the lenses the whole day without problems; 3 patients discontinued lens wear due to discomfort or unsatisfactory vision. CONCLUSIONS: The combination of super Dk/L and reverse geometry lenses facilitate lens wear and is associated with good visual acuity.

Adult↗
PubMed2000

Apoptosis and apoptosis related gene expression in normal conjunctiva and pterygium.

BACKGROUND: Pterygium is a relatively common eye disease in the tropics whose aetiology and pathogenesis remain uncertain. As such, interest has focused on understanding the underlying mechanism of pterygia development. METHODS: 15 specimens of pterygia from 15 eyes were examined, together with normal conjunctival tissue from the same eyes for the pattern of gene expression of genes associated with the induction or repression of apoptosis (p53, bcl-2, and bax). In addition, the samples directly for apoptotic cells were examined by the terminal deoxynucleotide transferase (TdT) mediated nick end labelling (TUNEL) methodology. RESULTS: In pterygia specimens apoptotic cells were found mainly confined to the basal layer of cells of the epithelial layer, situated immediately adjacent to the fibrovascular support layer. These cells were shown to express significant levels of p53 and bax, as well as the apoptosis inhibiting protein bcl-2. In contrast, normal conjunctival specimens displayed no bcl-2 expression and apoptotic cells were seen throughout the entire width of the epithelial layer, coupled with high levels of bax expression. CONCLUSION: These results support a model whereby pterygia development is a result of disruption of the normal process of apoptosis occurring in the conjunctiva.

Apoptosis↗
PubMed2000

Analysis of variation in success rates in conjunctival autografting for primary and recurrent pterygium.

AIMS: To evaluate the success rates of conjunctival autografting for primary and recurrent pterygium performed in a tertiary ophthalmic centre. METHODS: The outcome of 139 cases with primary pterygia and 64 cases with recurrent pterygia who underwent excision with conjunctival autografting was retrospectively reviewed. Outcome was evaluated in terms of recurrence of pterygia onto the cornea. The recurrence rates were determined using Weibull survival functions, in a mixture model that included a component allowing for cure. The suitability of this model was verified using Turnbull's non-parametric method for interval censored data (1974). Estimated recurrence free probabilities were based on the fitted Weibull survival curves. RESULTS: Mean follow up was 8.4 months in the primary group, and 9.5 months for the recurrent group. 29 out of 139 cases of primary pterygia recurred (20.8%) while 20 out of 64 cases in the recurrent group (31.2%) recurred. Recurrence rates varied widely among surgeons, ranging from 5% to 82%. Recurrence rates were inversely related to previous experience in performing conjunctival grafting. The recurrence free probability was 84% at 3 months, 73% at 1 year for primary pterygia, and 80% at 3 months, 67% at 1 year for recurrent pterygia. There was no statistical difference in recurrence rates between primary and recurrent groups (p= 0.80). CONCLUSION: The success of conjunctival autografting for pterygium in this series varies widely, and may be related to a significant learning curve or differing surgical techniques for this procedure. This may account for the wide variation in reported success of this procedure in the ophthalmic literature.

Adult↗
PubMed2000

Necrotising scleritis after bare sclera excision of pterygium.

AIM: To report cases of scleral necrosis after simple pterygium excision in which adjunctive treatment was not used. METHODS: We reviewed four patients who presented with scleral melt after pterygium excision without the use of adjunctive treatment in the form of beta irradiation, mitomycin C, or thiotepa. Each patient was thoroughly investigated to exclude underlying disease. RESULTS: Certain similarities were found between our patients with pterygium melt and cases of surgically induced necrotising scleritis including the location of melt, associated inflammation, and its response to steroid treatment in the latent period before they presented. CONCLUSION: Bare sclera pterygium excision can cause surgically induced necrotising scleritis years after the surgery.

Aged↗
PubMed2000

Effect of splanchnectomy on jejunal motility and fos expression in brain stem after intestinal anaphylaxis in rat.

This study was to determine whether alterations in jejunal motility observed after antigen challenge of sensitized rats occurred after extirpation of the celiac-superior mesenteric ganglia. Hooded-Lister rats were prepared with an intact or extirpated celiac-superior mesenteric ganglion, an isolated Thiry-Vella loop of ileum for instillation of antigen, and jejunal electrodes for myoelectric recording. Animals were sensitized by injection of 10 microg egg albumin (EA, ip), and specific anti-EA IgE titers were determined to be >1:64. In both control and splanchnectomized rats, normal fasting migrating myoelectric complexes (MMC) were observed before challenge with EA. MMCs were disrupted, and diarrhea was observed immediately after EA challenge of control but not splanchnectomized animals. Brain stems were removed and processed for Fos immunoreactivity. The absence of perivascular neuropeptide Y immunoreactivity in the submucosa was used to confirm the success of splanchnectomy. The number of Fos-immunoreactive neuronal nuclei was significantly reduced in the brain stem after splanchnectomy. Thus the mesenteric sympathetic ganglia are an integral part of the extramural neuronal pathways required for altered motility in this model of intestinal anaphylaxis.

Anaphylaxis↗