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Biomedical subjects

D S Lam

Publications and source records attributed to D S Lam.

At least 19 recordsLinked to original sources
PubMed2001

The miracle of microarray data analysis.

A report on the tenth Annual Bioinformatics and Genome Research meeting of the Cambridge Healthtech Institute's Beyond Genome 2001 series, San Francisco, USA, 17-19 June 2001.

Humans↗
PubMed2001

RP1 in Chinese: Eight novel variants and evidence that truncation of the extreme C-terminal does not cause retinitis pigmentosa.

Heterozygous truncating mutations in the RP1 gene cause approximately 7% of autosomal dominant retinitis pigmentosa (RP) cases. To examine the role of RP1 mutations in RP, we screened 101 unrelated Chinese RP patients (unselected for mode of inheritance) and 190 elderly normal control subjects for sequence changes in the coding exons for the 2156 amino acid RP1 protein. One patient had a mutation, thus RP1 mutations cause about 0.0% to 5.4% (95% confidence interval) of all RP among Chinese. The mutation was R677X, the most common found in Americans. Five other known sequence changes were found. In addition, nine novel sequence alterations were identified: 746G>A (R249H), 1437G>T (M479I), 2116G>C (G706R), 3024G>A (Q1008Q), 3188G>A (Q1063R), 5797C>T (R1933X), 6423A>G (I2141M), and the variants 6542C>T and 6676T>A, both in the 3' untranslated region. One control subject and three members of a non-RP family were heterozygous for R1933X, which is therefore likely to be a non-disease-causing variant. The most C-terminal truncation previously reported was due to Tyr1053 (1-bp del) and occurred in RP patients. Thus the presence of a normal level of at least part of RP1 between amino acids 1052 and 1933 appears necessary to prevent RP. Hum Mutat 17:436, 2001.

3' Untranslated Regions↗
PubMed2001

Surgical technique for transcleral-fixation of a dislocated posterior chamber intraocular lens.

PURPOSE: To report a cornea-pars plana through-and-through technique for the repositioning and transcleral suture fixation of a dislocated posterior chamber intraocular lens. DESIGN: Interventional case series. METHODS: For transscleral suture fixation of a dislocated posterior chamber intraocular lens, one needle of a double-arm 10-0 Prolene needle is passed through the paracentesis site then underneath the intraocular lens haptic, and through the intended scleral outlet on the opposite side. The other needle of the Prolene suture is also passed through the same paracentesis, above the same haptic, and through the intended scleral outlet on the opposite side. The haptic is now well supported, and the knot is tied. A similar procedure is performed for the second haptic if necessary. RESULTS: Three eyes (three patients) were operated on using this technique with good visual and anatomic outcome. CONCLUSION: The described technique is simple, safe, allows early visual rehabilitation, and can be accomplished without an assistant.

Female↗
PubMed2001

Ultrasound biomicroscopy of conventional and sutureless pars plana sclerotomies: a comparative and longitudinal study.

PURPOSE: To report the rate of ultrasonically visible vitreous incarceration and longitudinal changes of incarcerated vitreous in pars plana sclerotomies after conventional suturing or sutureless technique using ultrasound biomicroscopy. METHODS: Twenty-five consecutive eyes (25 patients) undergoing primary three-port pars plana vitrectomy participated. The first 16 pars plana vitrectomies were performed with standard conventional sutured sclerotomies, and the following nine pars plana vitrectomies were performed with modified sutureless sclerotomies. Patient demographics, diagnoses, procedures, and complications were recorded. Each patient had ultrasound biomicroscopy performed 1 week before surgery, and also after surgery at 1 week, 2 weeks, 3 weeks, 4 weeks, 2 months, 3 months, and 6 months. Visible vitreous incarceration was graded as 0 to 3. RESULTS: Vitreous incarceration was seen in 41 of 48 sclerotomies (85.4%) in the conventionally sutured group, and in 23 of 27 sclerotomies (85.2%) in the sutureless group, with no significant difference in severity among sclerotomies within each group and between the two groups. There was a significant difference in the rate of vitreous incarceration between diabetic patients with proliferative retinopathy and others (P =.002). No progressive change of visible vitreous incarceration was noted in any eye during the 6-month postoperative period. No sclerotomy-related complications occurred during the study period. CONCLUSIONS: Ultrasound biomicroscopy showed no difference in the amount of visible vitreous incarceration in conventionally sutured or sutureless sclerotomies. There was no visible longitudinal change in the incarcerated vitreous during the 6 months of follow-up in uncomplicated cases.

Adult↗
PubMed2001

Indocyanine green staining and removal of internal limiting membrane in macular hole surgery: histology and outcome.

PURPOSE: To report the surgical technique, outcome, and histologic findings involving indocyanine green staining and removal of internal limiting membrane in primary macular hole surgery. METHODS: Prospectively, consecutive patients with idiopathic macular hole or myopic macular hole with retinal detachment were recruited. After pars plana vitrectomy and epiretinal membrane removal, the internal limiting membrane was stained and removed. The specimens were stained using hematoxylin and eosin and periodic acid-Schiff. Immunohistochemical staining was also performed for glial fibrillary acidic protein, vimentin, type I and type IV collagen, and actin. RESULTS: Among 10 patients (10 eyes) in the study, nine eyes had stage 3 or 4 macular hole. Four of them had chronic macular hole. The tenth patient had retinal detachment resulting from a myopic macular hole. Postoperatively, all cases had closure of macular hole without an elevated edge and the retina was attached. Seven patients had improvement of 2 or more Snellen lines, whereas visual acuity remained the same for the other three patients. In six eyes in which complete histologic examinations were feasible, internal limiting membrane was confirmed and two eyes also had a small amount of epiretinal membrane. Myofibrocytes in internal limiting membrane, either scattered or as a single layer, were found in three cases. CONCLUSIONS: Removal of indocyanine green--stained internal limiting membrane around idiopathic macular hole or myopic macular hole with retinal detachment is confirmed with histology and may contribute to macular hole closure and retinal reattachment.

Actins↗
PubMed2001

Molecular diagnostics for retinitis pigmentosa.

BACKGROUND: At least 1 million people worldwide have retinitis pigmentosa (RP), making it relatively common among the inherited forms of blindness. Mutations in many genes may cause RP. The most common known mutation, Pro347Leu in rhodopsin, is found in no more than about 1% of unrelated patients, implying the impracticality of a diagnostic test which would screen only for a few, common mutation sites. CONCLUSIONS: Ongoing discovery and study of RP genes makes it feasible to consider a molecular diagnostic test which would screen coding regions of all known RP genes by a mutation detection method such as conformation-sensitive gel electrophoresis followed by sequencing. The parallel development of RP genetic knowledge and treatments such as gene therapy will make such tests both possible and necessary.

China↗
PubMed2001

A prospective study on ocular hypertensive and antiinflammatory response to different dosages of fluorometholone in children.

OBJECTIVE: To investigate the ocular hypertensive and antiinflammatory response to different dosages of fluorometholone (FML). DESIGN: Prospective clinical trial with randomization of fellow eyes to different postoperative treatment. PARTICIPANTS: Thirty-one consecutive children undergoing bilateral symmetrical strabismus operation. INTERVENTION: Among 31 children who received bilateral squint operations, one eye was randomized to receive topical FML six times daily (group 1), whereas the other eye received topical FML three times daily (group 2), both for 4 weeks. Intraocular pressure (IOP) and antiinflammatory response were measured serially in the postoperative period for 8 weeks. MAIN OUTCOME MEASURES: Intraocular pressure was measured on the day before surgery and on postoperative days 1, 3, 6, 13, 20, 27, 41, and 55. The antiinflammatory response was also assessed subjectively and objectively at days 6, 13, 20, and 27 after the operations. Peak IOP, net increase in IOP, and antiinflammatory responses in the two study groups were analyzed. RESULTS: Thirty-one children, age 3 to 9 years, (mean +/- standard deviation [SD], 5.52 +/- 1.81) participated in the study. Intraocular pressure increased significantly in both groups compared with the preoperative values (P < 0.001). The peak IOP ranged from 12.00 to 31.00 mmHg and 12.30 to 25.00 mmHg in groups 1 and 2, respectively. The mean peak IOP (19.00 +/- 5.06 mmHg vs. 17.13 +/- 3.32 mmHg) was significantly higher in group 1 (P < 0.001). The net increase in IOP was similar (mean +/- SD, 4.37 +/- 4.79 vs. 2.57 +/- 3.32 mmHg; P = 0.005). Ranges of the net IOP increase were -1.00 to 16.00 mmHg and -2.50 to 10.30 mmHg in groups 1 and 2, respectively. Children in group 1 reached the peak IOP earlier than those in group 2 (median, 6 vs. 13 days; P = 0.033). However, there was no significant difference in antiinflammatory response between the two groups. CONCLUSIONS: Ocular hypertension occurs in a dose-dependent manner in children treated with FML. Children in group 1 had a quicker onset and more severe ocular hypertensive response than those in group 2. It would be desirable to monitor the IOP regularly when FML is used with a high frequency and for a long duration in children.

Administration, Topical↗
PubMed2001

Cystoid macular edema after pediatric intraocular lens implantation: fluorescein angioscopy results and literature review.

PURPOSE: To evaluate the occurrence of cystoid macular edema (CME) after lens extraction, anterior vitrectomy, and intraocular lens implantation (IOL) in children using angioscopy after administration of oral fluorescein. SETTING: Centers in Tamil Nadu, India, and Hong Kong, China. METHODS: This study comprised 18 children (28 eyes) who had cataract extraction, posterior capsulorhexis, anterior vitrectomy, and in-the-bag IOL implantation. The presence of CME was evaluated 1 week and 4 to 6 weeks after surgery using fluorescein angioscopy. RESULTS: Anterior chamber fibrin occurred in 4 eyes (14.3%). Fluorescein angioscopy was performed 1 week after surgery in all eyes and after 1 month in 25 eyes (89.3%). No eye demonstrated the presence of CME on fluorescein angioscopy. CONCLUSIONS: Cystoid macular edema did not occur in the early period after pediatric cataract surgery using current surgical techniques. Longer follow-up is required to ascertain the incidence of CME in the late postoperative period.

Capsulorhexis↗
PubMed2001

Effect of intracameral acetylcholine on latanoprost in preventing ocular hypertension after phacoemulsification and intraocular lens implantation.

PURPOSE: To evaluate the effect of intracameral acetylcholine on latanoprost in preventing ocular hypertension in the early period after phacoemulsification with posterior chamber intraocular lens (PC IOL) implantation. SETTING: Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, Shatin, Hong Kong, China. METHODS: Patients with uncomplicated cataract having phacoemulsification with PC IOL implantation were included in this prospective randomized double-masked clinical trial. The eyes were randomly assigned to 1 of 4 groups based on postoperative application of latanoprost 0.005% alone (Group 1), latanoprost 0.005% with intracameral acetylcholine (Group 2), intracameral acetylcholine alone (Group 3), and no medication (controls (Group 4). Intraocular pressure (IOP) was measured 3 and 24 hours postoperatively. The anterior chamber was examined for the level of cells and flare using slitlamp biomicroscopy. RESULTS: Three and 24 hours after surgery, the decrease in mean IOP in eyes receiving latanoprost alone was not statistically significantly different from that in control eyes (P >.05). Eyes receiving intracameral acetylcholine alone had a significant decrease in the mean IOP at 3 hours (P <.05) but not at 24 hours compared to control eyes (P >.05). There were no significant differences in the mean postoperative IOP decrease between eyes receiving latanoprost with intracameral acetylcholine and those receiving intracameral acetylcholine alone (P >.05). CONCLUSIONS: A single application of latanoprost did not significantly lower IOP in the first 24 hours after phacoemulsification with PC IOL implantation. Eyes receiving intracameral acetylcholine alone had a significantly greater decrease in IOP than control eyes at 3 hours but not at 24 hours. The addition of intracameral acetylcholine to latanoprost did not enhance or reduce latanoprost's IOP-lowering effect.

Acetylcholine↗
PubMed2001

Effect of preoperative keratometry on refractive outcomes after laser in situ keratomileusis.

PURPOSE: To evaluate the effect of preoperative keratometry on the refractive outcome after laser in situ keratomileusis (LASIK) for myopia. SETTING: University Eye Clinic, Prince of Wales Hospital, Hong Kong, China. METHODS: In this retrospective study, the records of patients who had LASIK for myopia greater than -6.0 diopters (D) using the Chiron Automated Corneal Shaper and the Schwind Keratome-F excimer laser were reviewed. RESULTS: Laser in situ keratomileusis was performed in 167 eyes of 103 patients (mean age 34.7 years +/- 7.5 [SD]). Preoperative myopic spherical equivalent (SE) refraction was -9.0 +/- 2.0 D (range -6.0 to -13.9 D). Three months after surgery, SE refraction was -0.04 +/- 1.1 D (range +2.3 to -3.3 D); uncorrected visual acuity > or = 20/40 was present in 91.8% of 110 eyes in which emmetropia was the postoperative goal. Mean preoperative keratometry was 43.9 +/- 1.5 D (range 40.3 to 48.1 D). When eyes were stratified by the degree of preoperative myopia in 1.0 D steps, a trend toward greater undercorrection was noted in eyes with preoperative keratometry < 43.5 D than in those with steeper keratometry (> 44.5 D) in all myopia groups except the -7.0 to -7.9 D group. This difference was statistically significant in eyes with a preoperative SE of -10.0 to -10.9 D and -11.0 to -11.9 D. CONCLUSIONS: Preoperative keratometry appeared to influence the refractive outcome after myopic LASIK. Eyes with flatter corneas tended to have greater undercorrection than eyes with similar myopia and steeper corneas. Validation of these findings in larger data sets using the methodology described may improve the predictability of current LASIK nomograms, particularly in eyes with high myopia.

Adolescent↗
PubMed2001

Direct measurement of microkeratome gap width by electron microscopy.

PURPOSE: To perform an accurate direct measurement of the microkeratome gap width using scanning electron microscopy (SEM). SETTING: Electron Microscope Unit, University of Hong Kong, Hong Kong, China. METHODS: The Cambridge Stereoscan S440 scanning electron microscope was used to measure the gap width of 4 SCMD microkeratomes with high accuracy (+/-1.5 microm). RESULTS: The manufacturer's gap specification for the 4 microkeratomes was 150.0 microm. The gap width measurements using SEM were 164.7 microm, 190.0 microm, 200.6 microm, and 145.9 microm and the respective errors, 9.8%, 26.7%, 33.7%, and 2.7%. Two of the 4 microkeratomes had more than a 25% error in gap width from the specification. CONCLUSIONS: The great variation in gap width from the manufacturer's specification for the 4 SCMD microkeratomes was beyond the standard of tolerance normally accepted in laser in situ keratomileusis (LASIK). Many unexpected LASIK-related keratectasia and corneal perforations may be related to substandard microkeratome manufacturing and calibration. All new microkeratomes and blades should be validated before use to avoid keratectasia and other flap problems in LASIK.

Calibration↗
PubMed2001

Preoperative latanoprost to prevent ocular hypertension after phacoemulsification and intraocular lens implantation.

PURPOSE: To evaluate the efficacy of latanoprost given 2 hours preoperatively to prevent ocular hypertension in the early period after phacoemulsification and posterior chamber intraocular lens (PC IOL) implantation. SETTING: Departments of Ophthalmology, United Christian Hospital and Prince of Wales Hospital, Hong Kong, China. METHODS: Sixty-four eyes of 64 patients with uncomplicated cataract having phacoemulsification with PC IOL implantation were included in this prospective randomized double-masked clinical trial. The eyes were randomly assigned to 1 of 2 groups: application of latanoprost 0.005% 2 hours before surgery or no latanoprost (control). Intraocular pressure (IOP) was measured 3 and 24 hours postoperatively. The anterior chamber was examined for the level of cells and flare using a slitlamp biomicroscope. The level of significance was 5%. RESULTS: The decrease in the mean IOP was not statistically significantly different between eyes receiving latanoprost 2 hours preoperatively and control eyes 3 hours (P =.843) and 24 hours (P =.721) postoperatively. CONCLUSION: A single application of latanoprost given 2 hours before phacoemulsification and PC IOL implantation did not produce a statistically significant IOP-lowering effect when compared with a control group in the first 24 hours after surgery.

Aged↗