High-throughput and high-accuracy single-cell RNA isoform analysis using PacBio circular consensus sequencing.

Although long-read single-cell RNA isoform sequencing (scISO-Seq) can reveal alternative RNA splicing in individual cells, it suffers from a low read throughput. Here, we introduce HIT-scISOseq, a method that removes most artifact cDNAs and concatenates multiple cDNAs for PacBio circular consensus sequencing (CCS) to achieve high-throughput and high-accuracy single-cell RNA isoform sequencing. HIT-scISOseq can yield >10 million high-accuracy long-reads in a single PacBio Sequel II SMRT Cell 8M. We also report the development of scISA-Tools that demultiplex HIT-scISOseq concatenated reads into single-cell cDNA reads with >99.99% accuracy and specificity. We apply HIT-scISOseq to characterize the transcriptomes of 3375 corneal limbus cells and reveal cell-type-specific isoform expression in them. HIT-scISOseq is a high-throughput, high-accuracy, technically accessible method and it can accelerate the burgeoning field of long-read single-cell transcriptomics.

Integrative Single-Cell RNA-Seq and ATAC-Seq Analysis of Mouse Corneal Epithelial Cells.

Purpose: Corneal epithelial homeostasis is maintained by coordinated gene expression across distinct cell populations, but the gene regulatory programs underlying this cellular diversity remain to be characterized. Here we applied single-cell multi-omics analysis to delineate the gene regulatory profile of mouse corneal epithelial cells under normal homeostasis. Methods: Single cells isolated from the cornea epithelium (with marginal conjunctiva) of adult mice were subjected to scRNA-seq and scATAC-seq using the 10×Genomics platform. Cell types were clustered by the graph-based visualization method uniform manifold approximation and projection and unbiased computational informatics analysis. The scRNA-seq and scATAC-seq datasets were integrated following the integration pipeline described in ArchR and Seurat. Results: We characterized diverse corneal epithelial cell types based on gene expression signatures and chromatin accessibility. We found that cell type-specific accessibility regions were mainly located at distal regions, suggesting essential roles of distal regulatory elements in determining corneal epithelial cell diversity. Trajectory analyses revealed a continuum of cell state transition and higher coordination between transcription factor (TF) motif accessibility and gene expression during corneal epithelial cell differentiation. By integrating transcriptomic and chromatin accessibility analysis, we identified cell type-specific and shared gene regulation programs. We also uncovered critical TFs driving corneal epithelial cell differentiation, such as nuclear factor I (NFI) family members, Rarg, Elf3. We found that nuclear factor-κB (NF-κB) family members were positive TFs in limbal cells and some superficial cells, but they were involved in regulating distinct biological processes. Conclusions: Our study presents a comprehensive gene regulatory landscape of mouse cornea epithelial cells, and provides valuable foundations for future investigation of corneal epithelial homeostasis in the context of cornea pathologies and regenerative medicine.

Serum 25-hydroxyvitamin D is associated with stroke history in a reverse J-shape.

Background: 25-hydroxyvitamin D [25(OH)D], the major form of vitamin D in the body, has a non-linear association with stroke risk. However, the association is not fully understood. The specific shape of the association and the ideal value of 25(OH)D related to minimum risk of stroke remain unclear. Aim: We conducted the study to establish the correlation between circulating 25(OH)D and stroke history and determine the ideal value of 25(OH)D in relation to the lowest stroke prevalence. Methods: Data from the National Health and Nutrition Examination Survey (NHANES) were used for analyzes. We used multivariate logistic regression analysis with fitted smooth curves to explore the relationship between 25(OH)D and self-reported stroke history. Subsequently, 40,632 participants were enrolled in the study. Results: A reverse J-shaped association between 25(OH)D and stroke history was determined, where the lowest stroke prevalence for the 25(OH)D level was about 60 nmol/L. After adjusting for confounding factors, prevalence of stroke showed an increasing trend below and above the middle quintile (53.2-65.4 nmol/L) of 25(OH)D. Participants with 25(OH)D levels in the lowest quintile (≤ 39.3 nmol/L) had a 38% increased prevalence of stroke (OR 1.38, 95 %CI 1.12-1.70), while those in the higher level range of 25(OH)D (65.5-80.8 nmol/L) had a 27% higher stroke prevalence (OR 1.27, 95 %CI 1.03-1.57). Conclusion: Using data from a large, cross-sectional cohort program, we found that circulating 25(OH)D was related to stroke history in a reverse J-shaped manner. Given how the causal relationship between circulating 25(OH)D and history of stroke has not been established, more high-quality evidence based on the reverse J-shaped feature is needed to elucidate the link between vitamin D and stroke risk, and the effect of vitamin D supplements on stroke prevention.

Genomic Elucidation of a COVID-19 Resurgence and Local Transmission of SARS-CoV-2 in Guangzhou, China.

While China experienced a peak and decline in coronavirus disease 2019 (COVID-19) cases at the start of 2020, regional outbreaks continuously emerged in subsequent months. Resurgences of COVID-19 have also been observed in many other countries. In Guangzhou, China, a small outbreak, involving less than 100 residents, emerged in March and April 2020, and comprehensive and near-real-time genomic surveillance of SARS-CoV-2 was conducted. When the numbers of confirmed cases among overseas travelers increased, public health measures were enhanced by shifting from self-quarantine to central quarantine and SARS-CoV-2 testing for all overseas travelers. In an analysis of 109 imported cases, we found diverse viral variants distributed in the global viral phylogeny, which were frequently shared within households but not among passengers on the same flight. In contrast to the viral diversity of imported cases, local transmission was predominately attributed to two specific variants imported from Africa, including local cases that reported no direct or indirect contact with imported cases. The introduction events of the virus were identified or deduced before the enhanced measures were taken. These results show the interventions were effective in containing the spread of SARS-CoV-2, and they rule out the possibility of cryptic transmission of viral variants from the first wave in January and February 2020. Our study provides evidence and emphasizes the importance of controls for overseas travelers in the context of the pandemic and exemplifies how viral genomic data can facilitate COVID-19 surveillance and inform public health mitigation strategies.

Efficient assembly of nanopore reads via highly accurate and intact error correction.

Long nanopore reads are advantageous in de novo genome assembly. However, nanopore reads usually have broad error distribution and high-error-rate subsequences. Existing error correction tools cannot correct nanopore reads efficiently and effectively. Most methods trim high-error-rate subsequences during error correction, which reduces both the length of the reads and contiguity of the final assembly. Here, we develop an error correction, and de novo assembly tool designed to overcome complex errors in nanopore reads. We propose an adaptive read selection and two-step progressive method to quickly correct nanopore reads to high accuracy. We introduce a two-stage assembler to utilize the full length of nanopore reads. Our tool achieves superior performance in both error correction and de novo assembling nanopore reads. It requires only 8122 hours to assemble a 35X coverage human genome and achieves a 2.47-fold improvement in NG50. Furthermore, our assembly of the human WERI cell line shows an NG50 of 22 Mbp. The high-quality assembly of nanopore reads can significantly reduce false positives in structure variation detection.

Trends of Visual Impairment and Blindness in the Singapore Chinese Population over a Decade.

We evaluated the prevalence of visual impairment (VI) and blindness among Chinese adults in the Singapore Chinese Eye Study (SCES, 2009-2011), and compared the trends with the Tanjong Pagar Survey, Singapore (TPS), conducted a decade earlier. The SCES comprised of 3,353 Chinese adults aged ≥40 years (response rate, 72.8%). Participants underwent standardized examinations, including measurements of presenting, and best-corrected visual acuity (VA). Bilateral VI (VA < 20/40 to ≥20/200) and blindness (VA < 20/200) were defined based on the United States definition (better-seeing eye). Age-standardized prevalence was calculated using the 2010 Singapore Chinese Population Census. Primary causes and factors associated with VI and blindness were evaluated. In SCES, the age-standardized prevalence of presenting bilateral VI and blindness were 17.7% and 0.6%, respectively; the age-standardised prevalence of best-corrected bilateral VI and blindness were 3.4% and 0.2%, respectively. The previous TPS reported similar rates of best-corrected bilateral VI (3.8%) and blindness (0.3%). In SCES, cataract remains the main cause for both best-corrected bilateral VI (76.0%) and blindness (50.0%). Older age, female, lower income, lower educational level, and smaller housing type were associated with presenting bilateral VI or blindness (all P ≤ 0.025). These findings will be useful for the planning of eye care services and resource allocation.

The Prevalence and Types of Glaucoma in an Urban Chinese Population: The Singapore Chinese Eye Study.

IMPORTANCE: Glaucoma represents a major public health challenge in an aging population. The Tanjong Pagar Eye Study reported the prevalence and risk factors of glaucoma in a Singapore Chinese population in 1997, which established the higher rates of blindness in this population. OBJECTIVES: To determine the prevalence and associated risk factors for glaucoma among Chinese adults in Singapore and to compare the results with those of the 1997 study. DESIGN, SETTING, AND PARTICIPANTS: In a population-based survey of 4605 eligible individuals, we selected 3353 Chinese adults 40 years or older from the southwestern part of Singapore. Participants underwent examination at a single tertiary care research institute from February 9, 2009, through December 19, 2011. EXPOSURES: All participants underwent slitlamp ophthalmic examination, applanation tonometry, measurement of central corneal thickness, gonioscopy, and a dilated fundus examination. MAIN OUTCOMES AND MEASURES: Glaucoma as defined by the International Society of Geographical and Epidemiological Ophthalmology guidelines and age-standardized prevalence estimates computed as per the 2010 Singapore Chinese census. Blindness was defined as logMAR visual acuity of 1.00 (Snellen equivalent, 20/200 or worse). RESULTS: Of the 3353 respondents, 134 (4.0%) had glaucoma, including primary open-angle glaucoma (POAG) in 57 (1.7%), primary angle-closure glaucoma (PACG) in 49 (1.5%), and secondary glaucoma in 28 (0.8%). The age-standardized prevalence (95% CI) of glaucoma was 3.2% (2.7%-3.9%); POAG, 1.4% (1.1%-1.9%); and PACG, 1.2% (0.9%-1.6%). In a multivariate model, POAG was associated with being older and male and having a higher intraocular pressure. Of the 134 participants with glaucoma, 114 (85.1%; 95% CI, 78.1%-90.1%) were not aware of their diagnosis. Prevalence (95% CI) of blindness caused by secondary glaucoma was 14.3% (5.7%-31.5%), followed by 10.2% (4.4%-21.8%) for PACG and 8.8% (3.8%-18.9%) for POAG. We could not identify a difference in the prevalence of glaucoma compared with the 3.2% reported in 1997 (difference, -0.04%; 95% CI, -1.2 to 1.2; P = .97). CONCLUSIONS AND RELEVANCE: The prevalence of glaucoma among Singapore Chinese likely ranges from 2.7% to 3.9%, with secondary glaucoma being the most visually debilitating type. We could not identify a difference compared with previous studies approximately 12 years earlier. We report a high proportion of previously undiagnosed disease, suggesting the need to increase public awareness of this potentially blinding condition.

Body mass index and retinopathy in Asian populations with diabetes mellitus.

Body mass index (BMI) is an established risk factor for diabetes. However, the association between BMI and diabetic retinopathy (DR) has been inconclusive. We aimed to assess the association between BMI and DR in a large population-based sample of multi-ethnic Asian adults in Singapore. We examined 2,278 adults aged ≥40 years with diabetes who participated in three population-based studies conducted from 2004 to 2011: the Singapore Malay Eye Study, the Singapore Indian Eye Study, and the Singapore Chinese Eye Study. Retinal photographs taken from both eyes were graded for any and vision-threatening (VTDR) using the modified Airlie House Classification. BMI (kg/m(2)) was categorized into normal/underweight (<25), overweight (25-29.9), and obese (≥30). The prevalence rates of any and VTDR in the study population were 35.1 % and 9.1 %, respectively. The prevalence of any and VTDR decreased with increasing categories of BMI (P trend <0.001 and 0.005). In multivariable models adjusted for potential confounders, compared to those with normal weight, the odds ratio (95 % confidence interval) of any DR was 0.71 (0.57-0.88) for overweight and 0.70 (0.53-0.92) for obese. Corresponding estimates for VTDR were 0.84 (0.59-1.21) for overweight and 0.58 (0.35-0.94) for obese. The inverse association between BMI and any DR was consistently present when BMI was analyzed as a continuous variable and in analyses stratified by ethnicity and age. In a population-based sample of multi-ethnic Asian adults, BMI levels were inversely associated with any DR and VTDR.

ABCC5, a gene that influences the anterior chamber depth, is associated with primary angle closure glaucoma.

Anterior chamber depth (ACD) is a key anatomical risk factor for primary angle closure glaucoma (PACG). We conducted a genome-wide association study (GWAS) on ACD to discover novel genes for PACG on a total of 5,308 population-based individuals of Asian descent. Genome-wide significant association was observed at a sequence variant within ABCC5 (rs1401999; per-allele effect size =  -0.045 mm, P = 8.17 × 10(-9)). This locus was associated with an increase in risk of PACG in a separate case-control study of 4,276 PACG cases and 18,801 controls (per-allele OR = 1.13 [95% CI: 1.06-1.22], P = 0.00046). The association was strengthened when a sub-group of controls with open angles were included in the analysis (per-allele OR = 1.30, P = 7.45 × 10(-9); 3,458 cases vs. 3,831 controls). Our findings suggest that the increase in PACG risk could in part be mediated by genetic sequence variants influencing anterior chamber dimensions.

Ethnic differences in undercorrected refractive error in Asians.

PURPOSE: To describe the ethnic variations in the prevalence and risk factors for undercorrected refractive error and its impact on vision-specific functioning (VF) in a multiethnic Asian population. METHODS: A total of 3353 Chinese, 3400 Indians, and 3280 Malays in Singapore participated in this population-based cross-sectional study. Distance presenting visual acuity (VA) was measured using a logarithm of the minimum angle of resolution number chart. Best-corrected VA was assessed using the same test protocol as presenting VA. Undercorrected refractive error was defined as an improvement of at least 0.2 logarithm of the minimum angle of resolution (two lines equivalent) in the best-corrected VA compared with the presenting VA in the better eye when presenting VA was less than 20/40 in the better eye. The VF-11 questionnaire measured participants' VF. Multivariate linear regression was performed to assess the impact of undercorrected refractive error on the overall VF score. RESULTS: Regardless of ethnicity, participants with undercorrected refractive error had a reduction in VF score compared to those with normal vision in both eyes. The overall prevalence of undercorrected refractive error was highest in Indians (25.1%), followed by Malays (22.2%) and Chinese (19.7%). Undercorrected refractive error was less common in spectacles or contact lenses wearers than in non-spectacle wearers or non-contact lenses wearers. Adults with mild to moderate refractive errors were most likely to have undercorrected refractive error (p < 0.001). In multivariate analysis, increasing age (p < 0.001), Indian race (p < 0.001), lower education level (p < 0.001) or poorer housing (p < 0.001), having refractive errors (p < 0.001), and not wearing optical corrections (p < 0.001) were significantly associated with increasing undercorrected refractive error. CONCLUSIONS: In Singapore, undercorrected refractive error is most prevalent in Indians and least prevalent in Chinese. The impact of undercorrected refractive error on VF was consistent across all three ethnicities. There may be higher barriers to visual correction among Malays or Indians compared with Chinese in Singapore.

The economic cost of myopia in adults aged over 40 years in Singapore.

PURPOSE: To estimate the economic cost of myopia among adults aged 40 years and older in Singapore. METHODS: A substudy of 113 Singaporean adults aged 40 years and older with myopia (spherical equivalent refraction of at least -0.5 diopters) in the population-based ancillary study of Singapore Chinese Eye Study (SCES) was conducted. A health expenditure questionnaire was used to assess the direct cost of myopia. RESULTS: A total of 113 (90.4%) of 125 myopic subjects participated in the survey. The mean cost was approximately SGD$900 (USD$709) per person per year. The lifetime per capita cost ranged from SGD$295 (USD$232) for those with 0 year's duration to SGD$21,616 (USD$17,020) for those with 80 years' duration. Costs of spectacles, contact lenses, and optometry services were the major cost drivers, contributing to an average of 65% of total costs. Seven subjects (6.2%) had undergone LASIK surgery, resulting in a cost of SGD$4891 (USD$3851) per patient per year. Three subjects (2.7%) reported annual costs of (SGD$33 or USD$26) for complications due to LASIK surgery or contact lenses. There was an increasing cost of myopia in adults who started to wear glasses at earlier ages. By applying our cost data to age-specific myopia prevalence data in the whole population in the country, the total cost was estimated to be approximately SGD$959 (USD$755) million per year in Singapore. CONCLUSIONS: Myopia is associated with substantial out-of-pocket expenditure, imposing considerable economic burden for patients. Myopia is a disorder with immense societal costs and public health impact.

Prevalence of refractive errors in a multiethnic Asian population: the Singapore epidemiology of eye disease study.

PURPOSE: To determine the prevalence of refractive errors in a multiethnic Asian population aged over 40 years and to examine secular trends and racial differences. METHODS: A total of 10,033 adults (3353 Chinese, 3400 Indians, and 3280 Malays) participated in this study. Refractive error was determined by subjective refraction. Ocular biometric parameters were determined by partial coherence interferometry. Myopia and high myopia were defined as spherical equivalent (SE) of less than -0.5 diopters (D) and -5.0 D, respectively. Hyperopia was defined as SE of more than 0.5 D. Astigmatism was defined as cylinders less than -0.5 D. RESULTS: The prevalence of myopia, high myopia, hyperopia and astigmatism in Singapore adults aged over 40 years was 38.9% (95% confidence interval [CI] 37.1, 40.6); 8.4% (95% CI 8.0, 8.9); 31.5% (95% 30.5, 32.5); and 58.8% (95% CI 57.8, 59.9), respectively. Compared with the Tanjong Pagar Survey 12 years ago, there was a significant increase in the prevalence of astigmatism and mean axial length (AL) in Chinese adults aged over 40 years in Singapore. Chinese were most likely to be affected by myopia, high myopia, astigmatism, and had the longest AL among the three racial groups. CONCLUSIONS: The prevalence of myopia in Singapore adults is lower compared with the younger "myopia" generation in Singapore. The prevalence of astigmatism and mean AL have been increasing significantly within the past 12 years in the Chinese population. Chinese adults had higher prevalence of myopia, high myopia, astigmatism, as well as the longer AL compared with non-Chinese adults in Singapore.

Branch retinal vein occlusion and optic nerve head topographic parameters: the Singapore Indian eye study.

AIM: To examine the association between branch retinal vein occlusion (BRVO) and quantitative optic disc topographic parameters. METHODS: The Singapore Indian Eye Study (SINDI) is a population-based study of 3400 Singapore Indians aged 40+ years. BRVO was defined and graded from retinal photographs. Optic disc parameters were quantified using the Heidelberg Retinal Tomograph III (HRT III). Associations were evaluated for individual eyes; the generalised estimating equation was used to account for correlation between fellow eyes. RESULTS: 6173 eyes (comprising 19 BRVO) had gradable retinal photographs and HRT images. After controlling for age, gender, and systemic (hypertension, diabetes, myocardial infarction) and ocular factors (intraocular pressure, glaucoma, central corneal thickness, axial length, previous laser photocoagulation), BRVO was associated with larger optic disc area (OR highest vs lowest tertile, 4.70; 95% CI 1.00 to 22.01; p=0.036), larger cup area (OR highest vs lowest tertile, 4.80; 95% CI 1.03 to 22.35; p=0.029) and larger cup-disc area ratio (OR highest vs lowest tertile, 4.44; 95% CI 0.95 to 20.66; p=0.037). After excluding glaucoma eyes, BRVO remained significantly associated with these parameters (p=0.027, p=0.018, p=0.024, respectively). CONCLUSIONS: Quantitative optic disc parameters (optic cup and disc area) are associated with BRVO, even in non-glaucomatous eyes. Optic nerve head morphology may play a role in BRVO pathogenesis.

Differential associations of myopia with major age-related eye diseases: the Singapore Indian Eye Study.

PURPOSE: To determine the associations of myopia and axial length (AL) with major age-related eye diseases, including age-related macular degeneration (AMD), diabetic retinopathy (DR), age-related cataract, and primary open-angle glaucoma (POAG). DESIGN: Population-based, cross-sectional study. PARTICIPANTS: A total of 3400 Indians (75.6% response rate) aged 40 to 84 years in Singapore. METHODS: Refractive error was determined by subjective refraction, and AL was determined by noncontact partial coherence laser interferometry. Age-related macular degeneration and DR were defined from retinal photographs according to the Wisconsin Age-Related Maculopathy Grading System and Airlie House classification system, respectively. Age-related cataract was diagnosed clinically using the Lens Opacity Classification System (LOCS) III system. Glaucoma was defined according to International Society for Geographical and Epidemiological Ophthalmology criteria. MAIN OUTCOME MEASURES: Age-related macular degeneration, DR, age-related cataract, and POAG. RESULTS: Myopic eyes (spherical equivalent [SE] <-0.5 diopter [D]) were less likely to have AMD (early plus late AMD) (odds ratio [OR], 0.45; 95% confidence interval [CI], 0.25-0.79) or DR (OR, 0.68; 95% CI, 0.46-0.98) compared with emmetropic eyes; each millimeter increase in AL was associated with a lower prevalence of AMD (OR, 0.76; 95% CI, 0.65-0.89) and DR (OR, 0.73; 95% CI, 0.63-0.86). Myopic eyes were more likely to have nuclear (OR, 1.57; 95% CI, 1.13-2.20) and posterior subcapsular (OR, 1.73; 95% CI, 1.10-2.72) cataract, but not cortical cataract (P = 0.64); each millimeter increase in AL was associated with a higher prevalence of posterior subcapsular cataract (PSC) (OR, 1.29; 95% CI, 1.07-1.55), but not nuclear (P = 0.77) or cortical (P = 0.39) cataract. Eyes with high myopia (SE <-6.0 D) were more likely to have POAG (OR, 5.90; 95% CI, 2.68-12.97); each millimeter increase in AL was associated with a higher prevalence of POAG (OR, 1.43; 95% CI, 1.13-1.80). CONCLUSIONS: Myopic eyes are less likely to have AMD and DR but more likely to have nuclear cataract, PSC, and POAG. The associations of myopia with AMD, DR, and POAG are mostly explained by longer AL. However, the association between myopia and nuclear cataract is explained by lens refraction rather than AL.

Genome-wide association analyses identify three new susceptibility loci for primary angle closure glaucoma.

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 significant associations at three new loci: rs11024102 in PLEKHA7 (per-allele odds ratio (OR)=1.22; P=5.33×10(-12)), rs3753841 in COL11A1 (per-allele OR=1.20; P=9.22×10(-10)) and rs1015213 located between PCMTD1 and ST18 on chromosome 8q (per-allele OR=1.50; P=3.29×10(-9)). Our findings, accumulated across these independent worldwide collections, suggest possible mechanisms explaining the pathogenesis of PACG.

Variation in prevalence of myopia between generations of migrant indians living in Singapore.

PURPOSE: To assess the influence of factors related to migration and acculturation on myopia in migrant Indians in Singapore. DESIGN: Population-based cross-sectional study. METHODS: A total of 3400 Singaporean Indians (75.6% response rate) aged over 40 years participated in this study. Information regarding country of birth, migration age, and language of interview were collected from interviews. Indians born outside of Singapore were defined as "first-generation" immigrants, while Indians born in Singapore were defined as "second-generation (or higher)" immigrants. Refraction was determined by autorefraction and refined by subjective refraction. Ocular biometry including axial length (AL), anterior chamber depth (ACD), and corneal radius (CR) were measured by partial coherence interferometry. Myopia and high myopia were defined as spherical equivalents (SE) of less than -0.5 diopter (D) for myopia, and < -5 D for high myopia, respectively. RESULTS: The prevalence of myopia (30.2% vs 23.4 %) and high myopia (4.8% vs 2.5%) were higher in second-generation immigrants compared with first-generation immigrants. Second-generation immigrants had longer AL (23.50 mm vs 23.37 mm, P = .004) than first-generation immigrants after multivariate adjustment. The excess prevalence of myopia was reduced by 37.5% but remained statistically significant (P = .02) after further controlling for educational level. Among first-generation immigrants, those migrating to Singapore before the age of 21 had significantly higher prevalence of myopia (odds ratio [OR]: 1.85; 95% confidence interval [CI]: 1.32, 2.59) and longer AL (regression coefficient: 0.27; 95% CI: 0.11, 0.43) than those migrating after 21 years of age. Also, first-generation immigrants interviewed in English had higher prevalence of myopia (OR: 1.46; 95% CI: 1.00, 2.17) than their non-English-interviewed counterparts. CONCLUSIONS: The prevalence of myopia among second-generation (or higher) Indian immigrants in Singapore is higher than first-generation immigrants. Country-specific environmental factors may be important for the increasing prevalence of myopia in Asia.

The impact of bilateral or unilateral cataract surgery on visual functioning: when does second eye cataract surgery benefit patients?

AIM: To examine the impact of bilateral or unilateral cataract surgery on visual functioning. METHODS: The Singapore Malay Eye Study is a population-based study of 3280 Singapore Malay patients aged 40-80 years, of which 3225 had data available for inclusion. Cataracts were graded from digital lens photographs according to the Wisconsin scale. Study subjects were categorised as having: bilateral cataract surgery performed; unilateral cataract surgery performed with minimal cataract in the fellow eye; unilateral cataract surgery performed with significant cataract in the fellow eye; and bilateral cataract. Visual functioning was assessed using the modified VF-9 scale culturally adapted for Singaporean individuals, validated by Rasch analysis. The overall Rasch-modified vision-specific functioning score was compared across the four groups after adjusting for confounders such as age, gender, ocular and systemic comorbidities. RESULTS: Persons with bilateral cataract had poorer visual functioning than those who had bilateral cataract surgery (mean visual functioning scores 3.38 vs 3.11, respectively, p=0.029). When compared with bilateral surgery, visual functioning improvements among patients with unilateral cataract surgery depended on the status of the fellow eye, with improvements only seen if the fellow eye had significant cataract (mean visual functioning scores 2.81 vs 3.25, p=0.019) or poor visual acuity (mean visual functioning scores 2.78 vs 3.25, p=0.018) after adjusting for confounders. CONCLUSIONS: Bilateral cataract surgery was associated with greater visual functioning over unilateral cataract surgery when the fellow eye had a significant cataract or poor presenting visual acuity, supporting the current practice of second eye surgery depending on the fellow eye's cataract status and visual acuity.

Classification algorithms enhance the discrimination of glaucoma from normal eyes using high-definition optical coherence tomography.

PURPOSE: To evaluate the diagnostic performance of classification algorithms based on Linear Discriminant Analysis (LDA) and Classification And Regression Tree (CART) methods, compared with optic nerve head (ONH) and retinal nerve fiber layer (RNFL) parameters measured by high-definition optical coherence tomography (Cirrus HD-OCT) for discriminating glaucoma subjects. METHODS: Consecutive glaucoma subjects (Training data = 184; Validation data = 102) were recruited from an eye center and normal subjects (n = 508) from an ongoing Singaporean Chinese population-based study. ONH and RNFL parameters were measured using a 200 × 200 scan protocol. LDA and CART were computed and areas under the receiver operating characteristic curve (AUC) compared. RESULTS: Average RNFL thickness (AUC 0.92, 95% confidence interval [CI] 0.91, 0.93), inferior RNFL thickness (AUC 0.92, 95% CI 0.91, 0.93), vertical cup-disc ratio (AUC 0.91, 95% CI 0.90, 0.92) and rim area/disc area ratio (AUC 0.90, 95% CI 0.86, 0.93) discriminated glaucoma better than other parameters (P ≤ 0.033). LDA (AUC 0.96, 95% CI 0.95, 0.96) and CART (0.98, 95% CI 0.98, 0.99) outperformed all parameters for diagnostic accuracy (P ≤ 0.005). Misclassification rates in LDA (8%) and CART (5.6%) were found to be low. The AUC of LDA for the validation data was 0.98 (0.95, 0.99) and CART was 0.99 (0.99, 0.994). CART discriminated mild glaucoma from normal better than LDA (AUC 0.94 vs. 0.99, P < 0.0001). CONCLUSIONS: Classification algorithms based on LDA and CART can be used in HD-OCT analysis for glaucoma discrimination. The CART method was found to be superior to individual ONH and RNFL parameters for early glaucoma discrimination.

Early retinal arteriolar changes and peripheral neuropathy in diabetes.

OBJECTIVE: To examine the association between early retinal arteriolar abnormalities and diabetic peripheral neuropathy (DPN). RESEARCH DESIGN AND METHODS: Data from 608 people (aged 40-80 years) with diabetes from the population-based Singapore Malay Eye Study were analyzed. Participants underwent binocular two-field digital retinal photography and quantitative sensory testing. DPN was defined as an abnormal response to a monofilament or neurothesiometer test. Quantitative changes of retinal vascular caliber and arteriolar bifurcation geometry were measured using a computer-based program. Qualitative retinal signs of retinopathy and retinal arteriolar wall signs were graded by standardized methods. RESULTS: DPN was present in 155 people (25.5%). After adjusting for age, sex, diabetes duration, HbA(1c), cardiovascular risk factors, antihypertensive medication use, and peripheral arterial disease, people with suboptimal arteriolar caliber (odds ratio 1.94 [95% CI 1.22-3.10]), larger arteriolar branching coefficient (1.58 [1.03-2.42]), diabetic retinopathy (1.82 [1.20-2.75]), and focal arteriolar narrowing (2.92 [1.48-5.76]) were more likely to have DPN. Participants with a greater number of retinal microvascular signs were more likely to have DPN than those without retinal changes (6.11 [2.11-17.71] for two or more signs and 3.47 [1.18-10.21] for one sign compared with none). CONCLUSIONS: Individuals with diabetes with early retinal arteriolar abnormalities are more likely to have DPN, independent of hyperglycemia and major vascular risk factors. These data support the hypothesis that early microvascular dysfunction, evident in the retina, is an independent risk factor for DPN.