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Biomedical subjects

S J Chew

Publications and source records attributed to S J Chew.

At least 19 recordsLinked to original sources
PubMed2001

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.

Adult↗
PubMed2001

Familial clustering and myopia progression in Singapore school children.

BACKGROUND: Familial factors may be related to the progression of myopia in children. A cohort study was conducted to determine the relationship between familial factors and myopia progression in children. METHODS: From a larger clinical trial (n = 311), 153 Singapore children aged 6--12 years were recruited to participate in a cohort study of the risk factors for myopia progression. An in-person interview was conducted whereby information on the history of myopia in first-degree relatives was obtained. Other information collected included housing type, parental education and income. Cycloplegic refractive error as measured by subjective refraction and autorefraction were ascertained every six months. The average length of follow-up was 28 months. RESULTS: The adjusted mean rate of progression of myopia was -0.60 (95% confidence interval -0.66, -0.55) diopters per year. The average rate of progression of myopia for children with a parental history of myopia was -0.63 (95% confidence interval -0.69, -0.56) diopters per year compared to -0.42 (95% confidence interval -0.57, -0.27) diopters per year for children whose parents were not myopic. The different measures of family history of myopia were related to rate of change in refractive error and refractive error in the final visit. There was no association between close work and myopia progression. CONCLUSIONS: A positive family history is related to the progression of myopia and final refractive error in Singapore children, thus supporting evidence that hereditary factors may play an important role in myopia progression.

Child↗
PubMed2001

Characteristics of cataracts in the Chinese Singaporean.

PURPOSE: To conduct an epidemiological survey of cataracts and examine the characteristics of lens opacities in Chinese Singaporeans. The results are then compared with those from two similar surveys previously done in Japan in Noto Area, Honshu, and Amami, Kyushu, respectively. SUBJECTS AND METHODS: 468 subjects of > or = 50 years of age, who responded to the invitation to participate, were examined. Examination principally included photo-documentation of the anterior and posterior segments of both eyes. Evaluation and grading of lens opacities were done using graphical analysis of Scheimpflug and retro-illumination images. Inter-group comparisons were based on statistical analysis of cataract prevalence and distribution. RESULTS: The prevalence of clear lenses decreased with aging with no significant difference between males and females--a finding common to Singapore and the two Japanese study groups. The prevalence of cataracts (or lens opacities of Grade II and above) in 60-79 year-old Singapore subjects was significantly higher than Noto and Amami subjects in the same age group. Further, cortical opacity was the main type in Singapore subjects in their 50s and which was significantly higher than Noto subjects of the same age group. In all age groups, the distribution and prevalence of both nuclear and subcapsular types in the Singapore group were higher than the two Japanese study groups. CONCLUSIONS: Cataracts in Chinese Singaporeans are characterized by a high prevalence of nuclear opacities which was generally seen in tropics and sub-tropics. Our study also suggested the involvement of solar-UV in cortical cataracts as well as that of additional risk factors, such as environmental temperature and race, in nuclear and subcapsular cataract formation.

Aged↗
PubMed2001

Myopia in Singapore kindergarten children.

PURPOSE: The purpose of this study was to examine whether close-up work was related to myopia in Singapore kindergarten children. METHODS: One hundred twenty-eight children, ages 3 to 7 years, from a kindergarten in Singapore were examined by cycloplegic autorefraction. The parents also completed a questionnaire on the different types of close-up work activities each child was engaged in, socioeconomic status, and parental history of myopia. RESULTS: Myopic children spent 3.0 hours per day (median) on close-up work activity, while nonmyopic children spent 2.0 hours per day (median) on close-up work activity. The prevalence of myopia in the sample was 8.6%. CONCLUSION: Close-up work activity was not related to myopia in pre-school children.

Child↗
PubMed2000

Refractive errors in Singapore and Xiamen, China--a comparative study in school children aged 6 to 7 years.

PURPOSE: To compare and contrast the prevalence of myopia and other refractive errors in Xiamen city, Xiamen countryside (Southern China), and Singapore. METHODS: One hundred thirty-two schoolchildren aged 6 to 7 years from Xiamen city, 104 from Xiamen countryside, and 146 from Singapore city were recruited to join the study. Cycloplegic autorefraction, keratometry, and biometry measurements were performed on all children. RESULTS: The prevalence of myopia was 12.3% in Singapore city, 9.1% in Xiamen city, and 3.9% in Xiamen countryside. The prevalence of astigmatism was higher in Singapore compared with Xiamen. The rates of hyperopia and anisometropia were similar in all three locations. CONCLUSIONS: The myopia rate in Singapore city was higher than in Xiamen city; the lowest rates were found in Xiamen countryside. As the Chinese population from all three sites is of similar genetic stock (predominantly from Southern China), it is postulated that the differences in myopia rates in these three localities may be related to environmental factors.

Anisometropia↗
PubMed2000

Temporal variations in myopia progression in Singaporean children within an academic year.

PURPOSE: Excessive nearwork is believed to be associated with myopia development and progression. To investigate this further, we studied refractive error changes and their correlation with nearwork in a cohort of grade school children in Singapore. METHODS: Cycloplegic autorefraction was performed 5 times over 10 months on 168 children aged 7, 9, and 12 years who were further divided into myopic and nonmyopic subgroups based in their initial refractive errors. Information about nearwork was obtained through diaries filled out over 24 h at the commencement of the study. RESULTS: Myopia progression was high (overall mean: -0.87 D per year) and largely linear throughout the year, but significantly higher rates were seen after the final school examinations in 7-year-old myopes and nonmyopes. Overall, myopic groups exhibited higher progression rates than nonmyopic groups, although 33.6% of subjects from the latter groups had become myopic by the end of the study. Nearwork scores derived from the diaries were generally not well correlated with overall myopia progression. CONCLUSIONS: The tendency for myopia progression rates to increase after the final school examinations in 7-year-olds is interpreted as a delayed effect of the intense nearwork associated with preparing for them. The timing of nearwork-diary data collection at the beginning of the study could be responsible for the poor correlation between these data and overall myopia progression rates.

Child↗
PubMed2000

Factors related to the progression of myopia in Singaporean children.

PURPOSE: To examine the possible factors related to the progression of myopia in Singapore children. METHODS: One hundred fifty-three Singapore children aged 6 to 12 years were recruited to participate in a concurrent cohort study of the risk factors for the progression of myopia. Socioeconomic status, outdoor activity, and near-work activity were documented in a face-to-face clinic interview. The changes in cycloplegic subjective refraction and autorefraction were ascertained with the use of a Nidek ARK 900 over a 2-year period. RESULTS: The average rate of progression of myopia as measured by subjective refraction was -0.59 D per year (95% confidence interval -0.52, -0.66). Younger children and children who were more myopic at the beginning (refractive error worse than -2.0 D) of the study had higher myopia progression rates. CONCLUSIONS: Myopia progression was faster for younger children and for children who had more severe myopia at baseline. Socioeconomic status and near-work activity were not related to myopia progression.

Child↗
PubMed2000

Prevalence and risk factors for refractive errors in adult Chinese in Singapore.

PURPOSE: To determine the epidemiology of refractive errors in an adult Chinese population in Singapore. METHODS: A disproportionate, stratified, clustered, random-sampling procedure was used to select names of 2000 Chinese people aged 40 to 79 years from the 1996 Singapore electoral register in the Tanjong Pagar district in Singapore. These people were invited to a centralized clinic for a comprehensive eye examination, including refraction. Refraction was also performed on nonrespondents in their homes. Myopia, high myopia, and hyperopia were defined as a spherical equivalent (SE) in the right eye of less than -0.5 D, less than -5.0 D, and more than +0.5 D, respectively. Astigmatism was defined as less than -0.5 D of cylinder. Anisometropia was defined as a difference in SE of more than 1.0 D between the two eyes. Only phakic eyes were analyzed. RESULTS: From 1717 eligible people, 1232 (71.8%) were examined. Adjusted to the 1997 Singapore population, the overall prevalence of myopia, hyperopia, astigmatism, and anisometropia was 38.7% (95% confidence interval [CI]: 35.5, 42.1), 28.4% (95% CI: 25.3, 31.3), 37.8% (95% CI: 34.6, 41.1), and 15.9% (95% CI: 13.5, 18.4), respectively. The prevalence of high myopia was 9.1% (95% CI: 7.2, 11.2), with women having significantly higher rates than men. The age pattern of myopia was bimodal, with higher prevalence in the 40 to 49 and 70 to 81 age groups and lower prevalence between those age ranges. Prevalence was reversed in hyperopia, with a higher prevalence in subjects aged 50 to 69. There was a monotonic increase in prevalence with age for both astigmatism and anisometropia. Increasing educational levels, higher individual income, professional or office-related occupations, better housing, and greater severity of nuclear opacity were all significantly associated with higher rates of myopia, after adjustment for age and sex. CONCLUSIONS: The results indicate that whereas myopia is 1.5 to 2.5 times more prevalent in adult Chinese residing in Singapore than in similarly aged European-derived populations in the United States and Australia, the sociodemographic associations are similar.

Adult↗
PubMed1999

Estimating the magnitude of close-up work in school-age children: a comparison of questionnaire and diary instruments.

BACKGROUND: Numerous scientists have noted a relationship between close-up work and myopia. METHODS: A questionnaire and four 24-hour diaries were developed to estimate close-up work activity in a cohort study of close-up work and myopia progression in Singapore children. The number of hours per day that children engaged in each type of close-up work activity over a weekday and weekend during the school term, during the examination period, and in the vacation were estimated. RESULTS: The children spent an average of 6.6 hours per day on total weighted average close-up work, of which 4.3 hours were spent on reading and writing. The intra-class correlation coefficient for the reproducibility of the questionnaire was 0.87 (95% CI 0.85-0.91). The intra-class correlation coefficient for total weighted close-up work was 0.50 (95% CI 0.34-0.66) when the questionnaire was compared with the four 24-hour diaries. The amount of close-up work activity increased with age. CONCLUSIONS: A questionnaire for close-up work was developed and proven to be reproducible and comparable to four 24-hour diaries.

Activities of Daily Living↗
PubMed1999

Distance, lighting, and parental beliefs: understanding near work in epidemiologic studies of myopia.

PURPOSE: To develop measures and indices of factors (distance of eye from object, posture, and lighting) that may modify a possible effect of near work activity on myopia. METHODS: The duration of near work, the distance of an object from eye, lighting conditions, and other sociodemographic characteristics were asked in an interview. Both distance and lighting information from the questionnaire were compared with more precise measurements. RESULTS: Diopter hours were quantified as the duration of near work multiplied by the reciprocal of the distance which the activity was performed. The intraclass correlation coefficient of the reliability of distance information for each type of near work activity ranged from 0.43 to 0.91. Home light meter readings were significantly higher for children who were reading under both room and reading light, and the distances from the questionnaire were comparable to the measured distances. CONCLUSIONS: Measures of posture, distance, and lighting factors have been developed to study the possible effect modifiers of the effects of near work on myopia.

Accommodation, Ocular↗
PubMed1999

Relation between work and myopia in Singapore women.

BACKGROUND: Work and related activities may be connected to myopia development and progression. We investigated the relationship between working activities and the onset as well as worsening of myopia. METHODS: Information on the working status of the mothers of 374 children, the number of hours of close-up work activity, and whether the mother was short-sighted, was obtained by a face-to-face interview. In addition, a subsample of 84 mothers was interviewed over the telephone and asked whether the myopia occurred in adulthood and, if so, the age of cessation of myopia. RESULTS: The adjusted odds ratio for myopia in working women was 1.9 [95% confidence interval (CI) 1.2 to 3.2] and the adjusted odds ratio for high myopia (> -6.0 D) was 1.6 (95% CI 0.8 to 3.0). Women who were working also had higher rates of adult-onset myopia, odds ratio 4.4 (95% CI 0.9 to 21.2), and a later age of cessation of myopia than nonworking women. CONCLUSIONS: In our study, work was related to myopia in Singapore women. Work may be a surrogate for another risk factor, close-up work activities such as reading, writing, and computer use.

Adolescent↗
PubMed1999

Eye care when using video display terminals.

OBJECTIVE: To examine the scientific data in the literature regarding eye problems and possible damage during the use of computer video display terminals. DATA SOURCES: Medline and non-Medline literature search and personal experience. STUDY SELECTION: Studies that provided evidence-based information about eye damage and eye care during the use of video display terminals were selected. DATA EXTRACTION: Data were extracted independently by multiple observers. DATA SYNTHESIS: Most studies have shown that the levels of ionizing and non-ionizing radiation that are emitted by video display terminals are not harmful to the human eye. Eye complaints associated with the use of video display terminals include the McCollough effect, accommodative spasm, 'dry eyes', and eye strain. Ergonomic considerations and good visual hygiene can help alleviate symptoms. CONCLUSION: There is currently no convincing evidence that shows that using video display terminals is harmful to the eye.

Journal Article↗
PubMed1998

OphthWeb---cost-effective telemedicine for ophthalmology.

'OphthWeb' is an ophthalmic electronic medical record that can be accessed locally and globally via the Internet. OphthWeb can provide secure multimedia patient data to doctors, patients, and health care providers at any time and in any place. Patients have secured access to their own records in the convenience of their homes or during any emergency at any time or place around the world. OphthWeb provides interactive educational information and answers frequently asked questions by way of multimedia images on the Worldwide Web. A data transmission trial was conducted between the Xiamen Eye Centre in the Fujian province in southern China and Singapore. Clinical records, voice messages, and fundus and slit-lamp images were transmitted from Xiamen, and an off-line dialogue by e-mail and Internet-relay chat was conducted. The time delay from transmission to receipt was 30 minutes, which would be adequate to respond to most ophthalmic emergencies. This pilot project will promote computer literacy among doctors, and inter-institutional interaction in the health care profession. OphthWeb can provide telemedicine and electronic medical records at a low cost and great convenience.

Journal Article↗
PubMed1998

Peripapillary nerve fiber layer thickness measurement reproducibility using scanning laser polarimetry.

PURPOSE: The authors assess the reproducibility of retinal nerve fiber layer (RNFL) thickness measurements using scanning laser polarimetry. METHODS: The right eyes of five healthy individuals were scanned by two trained operators (S.T.H., H.I.) using the Nerve Fiber Analyzer II (Laser Diagnostic Technologies, Inc., San Diego, CA, U.S.A.). Each participant was scanned six consecutive times per session for five sessions carried out over separate days within a two-week period. Intra- and interoperator measurement reproducibility was assessed. RESULTS: Intraoperator reproducibility was high. Mean coefficients of variation for total RNFL thickness measurements were 4.48 +/- 1.76% and 4.92 +/- 2.32% for operators 1 and 2, respectively. Interoperator reproducibility was high (p = 0.20-0.93) if a single ellipse was applied to the images of both examiners. However, measurement reproducibility worsened if each operator created his own measurement ellipse (p < or = 0.05 for 3 out of 5 participants). CONCLUSION: Interoperator error in image analysis can be minimized by using a single ellipse for the baseline and all subsequent scans even if subsequent scans are acquired by different operators.

Adult↗
PubMed1998

Factors affecting image acquisition during scanning laser polarimetry.

BACKGROUND AND OBJECTIVE: To illustrate artifacts that may be encountered during measurement of the peripapillary retinal nerve fiber layer (RNFL) using scanning laser polarimetry (SLP). PATIENTS AND METHODS: A total of 426 patients with a variety of ocular diagnoses underwent RNFL measurements using SLP from June 1996 to April 1997. Scanning was performed by two operators whose reproducibility of measurements had been previously validated. Images were selected to illustrate clinical features that adversely affected measurement of the thickness of the RNFL. RESULTS: Image acquisition was difficult in eyes with corneal grafts or edema, keratic precipitates, anterior uveitis, posterior subcapsular cataract, vitreous opacity, peripapillary atrophy, posterior staphyloma, and high axial myopia. These scans resulted in poor clinical correlation with visual field tests and optic nerve examination, poor reproducibility of images, and unreadable images. CONCLUSION: Anterior and posterior segment pathologies, particularly those localized to the cornea and lens, may produce spurious RNFL measurements and should be carefully considered prior to clinical decision making.

Aged↗
PubMed1998

Muscarinic acetylcholine receptor antagonists inhibit chick scleral chondrocytes.

PURPOSE: Muscarinic acetylcholine receptors (mAChRs) have been implicated in the control of myopia in humans and in animal models. This study was conducted to determine whether mAChRs influence the growth of the chick sclera and, if so, which mAChR subtypes are involved. METHODS: Sclera and scleral chondrocytes from normal and form-deprived eyes of 10- to 14-day-old chicks were treated with a total of seven ligands: two agonists, carbachol (nonselective) and McN-A-343 (selective for the M1 mAChR subtype); and five antagonists, atropine (nonselective), pirenzepine and telenzepine (M1), gallamine (M2), and 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP; M1 and M3). Incorporation of sulfate into glycosaminoglycans and of thymidine into DNA were quantified and normalized to sample DNA content. Possible toxicity of ligands at high doses was examined by analysis of cell number (by cell counting), viability (by trypan blue exclusion), and cellular metabolic activity (by dehydrogenase activity). RESULTS: Cellular proliferation and extracellular matrix production were inhibited by atropine in whole sclera and in its cartilaginous layer. Sulfate incorporation by chondrocytes from normal and form-deprived eyes was inhibited by mAChR antagonists with a rank order of potency (atropine > pirenzepine = 4-DAMP >> gallamine) consistent with regulation by M1, rather than M3 or M2 mAChR subtypes. Pirenzepine inhibited sulfate incorporation by chondrocytes from form-deprived eyes more effectively than those from normal eyes. Chondrocyte cultures were not viable when grown in high doses of any of the ligands used except gallamine. CONCLUSIONS: In chick scleral chondrocytes, synthesis of DNA and glycosaminoglycans was inhibited by mAChR antagonists. This inhibition was probably mediated by the M1 subtype mAChR. Therefore in vivo the sclera may be a site of action for the mAChR antagonists previously used to influence myopia. Although at high concentrations mAChR antagonists tested seemed to be toxic to chondrocytes, at lower doses inhibition occurred without toxic effects.

Animals↗
PubMed1997

Ocular-hypertensive response to topical steroids in children.

OBJECTIVE: The purpose of the study is to investigate the rate and degree of ocular-hypertensive response to topical steroids in Chinese children. DESIGN: The study design was an institutional, randomized, clinical trial. PARTICIPANTS: A total of 19 consecutive patients were studied. INTERVENTION: Topical steroids were administered to Chinese children younger than 10 years of age who underwent bilateral strabismus surgery. One eye was randomized to receive topical 0.1% dexamethasone (DMS), whereas the fellow eye received 0.1% fluorometholone (FML) six times per day for up to 4 weeks. Intraocular pressure (IOP) was measured on the day before operation and at postoperative days 1, 3, 6, 10, 13, and 27, then every 2 weeks thereafter until the IOP fell to preoperative levels. Topical steroids would be stopped if IOP was 30.00 mmHg or greater. MAIN OUTCOME MEASURES: Peak IOP and maximal change of IOP from baseline were measured and categorized into low, intermediate, and high levels. Time to peak IOP also was studied. RESULTS: A total of 16 patients were included. The peak IOP for DMS-treated eyes was 30.66 +/- 8.35 mmHg (range, 13.00-48.00 mmHg), whereas that in FML-treated eyes was significantly lower at 20.66 +/- 6.03 mmHg (range, 11.30-36.30 mmHg) (P = 0.001). The maximal change in IOP ranged from -2.60 to +31.00 mmHg in DMS-treated eyes (mean, 15.48 +/- 8.71 mmHg), almost double that of FML-treated eyes (range, +1.00 to +17.00 mmHg; mean, 5.83 +/- 4.96 mmHg) (P = 0.001). When the ocular-hypertensive responses of both DMS and FML groups were categorized into three levels of severity, significant differences were found between the two treatment groups (P = 0.001). In the DMS group, nine patients (56.25%) were high responders and six patients (37.5%) were intermediate responders. In the FML group, only one patient (6.25%) was a high responder. CONCLUSIONS: The ocular-hypertensive response to topical DMS in children occurs more frequently, more severely, and more rapidly than that reported in adults. A total of 56% of the studied children, all younger than 10 years of age, were high responders to topical DMS. Of these, 89% attained their peak IOP within 8 days. Its use in children should best be avoided if possible. It would be desirable to monitor the IOP when it is being used. Conversely, FML produced a much less ocular-hypertensive effect and therefore poses an acceptable risk of clinically significant pressure elevation.

Administration, Topical↗