Steve K. L. Seah

A prospective ultrasound biomicroscopy evaluation of changes in anterior segment morphology after laser iridotomy in asian eyes

PURPOSE To prospectively quantify changes in anterior segment morphology after laser iridotomy using gonioscopy and ultrasound biomicroscopy (UBM). DESIGN Prospective comparative observational case series. PARTICIPANTS Fifty-five fellow eyes of patients presenting with acute primary angle closure (APAC). METHODS The fellow eyes of patients presenting with APAC were examined with UBM, A-scan ultrasonography, and optical pachymetry at presentation and 2 weeks after sequential argon/neodymium yttrium-aluminum-garnet laser peripheral iridotomy (LPI). UBM images were analyzed using UBM Pro 2000 software. Baseline measurements were made both under standard lighting conditions and in darkness to look for changes in anterior segment findings. MAIN OUTCOME MEASURES The degree of angle opening was measured using the angle-opening distance (AOD) at 250 and 500 microm from the scleral spur (AOD250 and AOD500, respectively) and angle recess area (ARA). RESULTS Fifty-five Asian patients were examined; AOD250, AOD500, and ARA all significantly increased after sequential laser iridotomy (P < 0.002). Gonioscopic grading of the angle opening significantly increased in all 4 quadrants (P < 0.001). The Van Herick grade of limbal anterior chamber depth increased (P < 0.001), whereas the number of eyes classified as occludable decreased (73%-33%, P < 0.001). Anterior chamber depth did not change significantly (2.41 mm +/- 0.28 mm vs. 2.42 mm +/- 0.30 mm, P = 0.43) as measured with optical pachymetry. Increased illumination increased the angle-opening measures, but induced a different alteration in peripheral iris morphology. Illumination-induced changes were greater after iridotomy than before laser treatment. CONCLUSIONS In Asian eyes at high risk of developing APAC, sequential LPI produced a significant widening of the anterior chamber angle without deepening the anterior chamber centrally. LPI produces changes in iris morphology that are different from those caused by an increase in illumination, indicating that different mechanisms account for angle opening under these 2 conditions.

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.

Rates of hospital admissions for primary angle closure glaucoma among Chinese, Malays, and Indians in Singapore

AIM To estimate the rates of hospital admissions for primary angle closure glaucoma (PACG) in Chinese, Malays, and Indians in Singapore METHODS A population-wide hospital discharge database in Singapore was used to identify all hospital admissions with a primary discharge diagnosis of PACG (International Classification of Disease—CM code: 365.2). The Singapore census was used for denominator data. RESULTS Between 1993 and 1997 there were 894 hospital admissions for PACG. The mean annual rate of PACG admissions was 11.1 per 100 000 (95% confidence interval (CI), 10.4, 11.8) among people aged 30 years and over. The annual rate was highest for Chinese (age and sex adjusted rate: 12.2 per 100 000), which was twice that of Malays (6.0 per 100 000) and Indians (6.3 per 100 000). Females had two times higher rates than males in all three races (age adjusted relative risk: 2.0, 95% CI: 1.7, 2.3). CONCLUSION Malay and Indian people had identical rates of hospital admissions for PACG, which were only half the rates compared with Chinese.

Trabeculectomy for acute primary angle closure.

OBJECTIVE To analyze the results of trabeculectomy performed for all cases of acute primary angle closure (APAC). DESIGN Retrospective, noncomparative case series PARTICIPANTS Fifty-six consecutive patients who underwent trabeculectomy for APAC at two Singapore centers from 1993 through 1995. METHODS The conventional treatment for APAC is to lower intraocular pressure (IOP) medically, after which laser peripheral iridotomy (PI) is performed. However, in Asian eyes, the acute attack is often refractory to standard treatment. Trabeculectomy is occasionally performed on eyes that do not respond to medical therapy, as well as eyes with APAC that respond to medical therapy but are assessed as having underlying chronic angle-closure glaucoma. In such cases, laser PI is not performed before trabeculectomy. MAIN OUTCOME MEASURES The surgical outcome was assessed in terms of final IOP and the incidence of complications. Success was defined as final IOP less than 21 mmHg without medication, and qualified success was defined as final IOP less than 21 mmHg with medication. Patients whose IOP was more than 21 mmHg, required further glaucoma surgery, lost light perception, or whose eye became phthisical were classified as failures. RESULTS The mean follow up was 22 months (range, 6-42 months). In group A, the medical failure group (n = 32), success in IOP control was obtained in 18 patients (56.2%), qualified success was achieved in 3 patients (9.4%), and failure resulted in 11 patients (34.4%). Ten patients (31.3%) encountered early postoperative complications such as shallow anterior chamber. In group B, the medical success group (n = 24), success in IOP control was achieved in 21 patients (87.5%), qualified success was achieved in 3 patients (12.5%), and there were no cases of failure. The incidence of postoperative complications was low (4 eyes [16.7%]). In terms of IOP outcome, trabeculectomy outcome was significantly worse in group A (P<0.001, Fishers exact test). CONCLUSIONS Because there is a high risk of surgical failure and complications, trabeculectomy may not be the procedure of choice in medically unresponsive cases of APAC.

Prevalence of lens opacity in Chinese residents of Singapore: the tanjong pagar survey

OBJECTIVE To determine the prevalence of lens opacity among Chinese residents of Singapore. DESIGN Population-based, cross-sectional survey. PARTICIPANTS Chinese men and women aged 40 years or more in Singapore. METHODS A stratified, clustered, random sampling method, with more weights given to the older age groups, was used to initially select 2000 Chinese persons aged 40 to 79 years from the 1996 electoral register in the Tanjong Pagar district in Singapore. Eligible subjects (n = 1717) were invited for a comprehensive ocular examination at a centralized clinic, after which nonrespondents were examined in their homes with portable instruments. MAIN OUTCOME MEASURES Lens opacity, as determined clinically at the slit lamp using a modification of the Lens Opacity Classification System III. Prevalence rates were age adjusted to the 1997 Singapore census population. RESULTS Of the 1232 persons examined (71.8%), 1206 (70.2%) provided lens data for this analysis. The age-adjusted prevalence of any cataract surgery was 5.1% (95% confidence interval [CI], 3.6, 6.5), with similar rates between men and women. The age-adjusted prevalence of specific types of lens opacity was 22.6% (95% CI, 19.8, 25.4) for any nuclear opacity, 23.9% (95% CI, 21.0, 26.8) for any cortical opacity, and 7.0% (95% CI, 5.3, 8.8) for any posterior subcapsular opacity. The overall age-adjusted prevalence of any cataract or cataract surgery was 34.7% (95% CI, 31.5, 38.0), increasing from 7.0% in those 40 to 49 years and to 94.3% in those 70 years and older (P < 0.001, test for trend for age). When the prevalence of distinct types of lens opacity in an eye was considered, the most common was mixed (age-adjusted prevalence, 11.5%, based on right eye data), followed by nuclear only (9.7%), cortical only (8.3%), and posterior subcapsular only (0.6%). For all cataract types, the prevalence was similar in men and women and was higher in persons examined at their homes than in those examined at the study clinic. CONCLUSIONS These population-based data suggest that cataract is common among adult Chinese residents in Singapore, despite ready access to cataract surgical services. Persons accepting the offer of free eye examinations were less likely to have cataract than those who did not take up this offer.

Population Prevalence of Tilted and Torted Optic Discs Among an Adult Chinese Population in Singapore: The Tanjong Pagar Study

OBJECTIVE To determine the prevalence of tilted and torted optic discs and associated risk factors among Chinese adults in Singapore. METHODS As part of a population-based survey, optic disc stereophotographs of both eyes were obtained, and left eyes were analyzed using imaging software. A tilted optic disc was defined as an index of tilt (ratio of minimum to maximum optic disc diameter) less than 0.75. The angle of tilt was defined as the angle between the maximum and vertical optic disc diameter, and optic discs were graded as torted if the angle of tilt exceeded 15 degrees . RESULTS Twenty-six of 739 subjects (3.5%) had tilted optic discs, and 478 (64.7%) had torted optic discs. Myopia was present in 23 of 26 eyes (88.5% [95% confidence interval, 69.9%-97.6%]) with tilted optic discs and in 211 of 661 eyes (31.9% [28.4%-35.6%]) without tilted optic discs (P < .001). On multivariate analysis, myopia (spherical equivalent) was a significant risk factor for tilted optic discs (P < .001). Index of tilt was not associated with corneal astigmatism or with cylindrical refractive error. Seventeen eyes (65.4%) with tilted optic discs had an optic disc morphologic abnormality, but none were glaucomatous. CONCLUSIONS The prevalence of tilted optic discs among this Chinese population was 3.5%. Tilted optic discs were associated with myopia but not with glaucoma.

Automated static perimetry : the influence of myopia and its method of correction

OBJECTIVE To determine how the magnitude of myopia and its method of correction influence visual field testing. DESIGN Prospective observational case series, including comparison of spectacles and contact lenses. PARTICIPANTS One hundred forty-six ophthalmologically normal males 19 to 24 years of age with myopia (spherical equivalent from -0.50 to -14.0 diopters). METHODS Participants performed automated static threshold perimetry. Refractive errors were corrected using trial lenses and soft contact lenses. Subjects were tested with both methods of correction, the order of which was randomized. MAIN OUTCOME MEASURES Threshold sensitivity and global indexes. RESULTS Only one subject (0.7%) had a significant reproducible visual field defect on both methods of correction. Six subjects (4.1%) had a focal visual field defect on one method of correction but not the other. For myopia greater than -4.0 diopters, the mean defect decreased significantly as axial length and degree of myopia increased (P: < 0.01). Similar results were obtained with either method of correction. CONCLUSIONS Threshold sensitivity is reduced in moderate and high myopia, regardless of the method of correction. The surprisingly low prevalence of visual field defects in this myopic population disputes the widely held view that myopia is associated commonly with visual field abnormalities. If field defects are found in myopes on automated perimetry, it is advisable to repeat the test with another method of optical correction to check that such defects are genuine and not related to the method of refractive correction.

Mitomycin-C concentration in human aqueous humour following trabeculectomy.

The aim of the study was to determine mitomycin-C (MMC) concentrations in human aqueous humour during trabeculectomy and to correlate anterior chamber concentrations with method of application. MMC was applied intra-operatively by saturating sponges, ranging in size from 2 × 2 × 5 mm to 2 × 4 × 10 mm on dry cut, with 0.5 mg/ml MMC during trabeculectomy for 3–5 minutes. Applications to episclera were made in 18 cases and to the scleral bed after scleral flap dissection in 9 cases. Aqueous samples were collected by paracentesis with a 30 gauge needle 2–7 minutes after removal of sponge and external irrigation. Aqueous MMC concentrations were determined by high-performance liquid chromatography. Aqueous MMC concentration in 27 samples ranged from below minimum detectable concentration (less than 5 ng/ml) to 120.8 ng/ml. Mean aqueous drug levels obtained when the applications were to the scleral bed were 35.65 ± 39.17 ng/ml (range 5–120.8 ng/ ml). Applications on episclera gave mean aqueous concentrations of 4.98 ± 9.11 ng/ml (range 0–33.3 ng/ml). The difference was statistically significant (p = 0.004). There were no correlations between sponge size, time of MMC exposure and aqueous MMC level. In conclusion, MMC is detectable in aqueous humour within minutes of external application and the aqueous concentration level is higher if the application is in the scleral bed than on the episclera. Toxicity of the drug at this concentration range for corneal endothelial cells needs further investigation via in vitro and clinical studies.

Cataract Surgery After Trabeculectomy

BACKGROUND AND OBJECTIVE To determine the effect of cataract surgery on glaucomatous eyes with good intraocular pressure (IOP) control after trabeculectomy. PATIENTS AND METHODS Twenty-two eyes with functional blebs that underwent cataract extraction were retrospectively analyzed. RESULTS The mean (+/- SD) preoperative IOP was 11.0 +/- 4.3 mm Hg. The mean (+/- SD) postoperative IOPs at 1, 2, 6, and 9 months were 15.5 +/- 4.9, 12.6 +/- 4.7, 14.6 +/- 5.6, and 19.0 +/- 7.9 mm Hg, respectively. At each interval except for the second month, the mean IOP was statistically significantly higher than the preoperative value (P = .0003, .24, .02, and .0009, respectively). The total number of medications was also higher (3 preoperatively versus 27 postoperatively). The interval between the two surgeries had no influence on IOP control. Intraoperative complications during cataract surgery, particularly vitreous loss, were associated with poor IOP control. Phacoemulsification had less of an effect on the postoperative IOP control than did extracapsular cataract extraction. CONCLUSIONS Eyes with previous successful trabeculectomies had higher IOPs and required more medications after subsequent cataract surgeries.

Original articleInitial Management of Acute Primary Angle Closure: A Randomized Trial Comparing Phacoemulsification with Laser Peripheral Iridotomy

PURPOSE To compare the 2-year efficacy of phacoemulsification and intraocular lens implant (phaco/IOL) with laser peripheral iridotomy (LPI) in the early management of acute primary angle closure (APAC) and coexisting cataract. DESIGN Randomized, controlled trial. PARTICIPANTS We included 37 subjects presenting with APAC who had responded to medical treatment such that intraocular pressure (IOP) was ≤30 mmHg within 24 hours, and had cataract with visual acuity of ≤6/15. MAIN OUTCOME MEASURES The primary outcome measure was failure of IOP control defined as IOP between 22 to 24 mmHg on 2 occasions (readings taken within 1 month of each other) or IOP ≥25 mmHg on 1 occasion, either occurring after week 3. Secondary outcome measures were complications, degree of angle opening, amount of peripheral anterior synechiae, visual acuity, and corneal endothelial cell count (CECC). METHODS Subjects were randomized to receive either LPI or phaco/IOL in the affected eye within 1 week of presentation and were examined at fixed intervals over 24 months. Patients underwent a standardized examination that included Goldmann applanation tonometry, gonioscopy, and CECC measurements. Logistic regression was used to estimate the effect of treatment on failure of IOP control. Time to failure was evaluated using the Kaplan-Meier technique and Cox regression was used to estimate the relative risk of failure. RESULTS There were 18 patients randomized to LPI and 19 to phaco/IOL. The average age of subjects was 66.0±9.0 years and mean IOP after medical treatment was 14.5±6.9 mmHg. The 2-year cumulative survival was 61.1% and 89.5% for the LPI and phaco/IOL groups, respectively (P = 0.034). There was no change in CECC for either group from baseline to month 6. There was 1 postoperative complication in the phaco/IOL group compared with 4 in the LPI group (P = 0.180). CONCLUSIONS Performed within 1 week in patients with APAC and coexisting cataract, phaco/IOL resulted in lower rate of IOP failure at 2 years compared with LPI.