John A. Landers

Prevalence of refractive error in rural Myanmar: the Meiktila Eye Study.

OBJECTIVE To determine the prevalence of refractive error and associated risk factors in the Meiktila District of central rural Myanmar. DESIGN Population-based cross-sectional study. PARTICIPANTS Randomized stratified cluster sampling of the inhabitants 40 years or older from villages in Meiktila was performed; 2481 eligible participants were identified, 2076 participated in the study, and adequate refractive data were obtained on 1863 individuals (75.1%). METHODS Demographic data including age, gender, and education level were obtained from all participants. The ophthalmic examination included autorefraction, nuclear opalescence (NO) grading at the slit lamp, and applanation tonometry. MAIN OUTCOME MEASURES Refractive errors were classified by type of ametropia and their prevalence was determined. Univariate and multivariate analyses were performed and odds ratios were calculated for the predictors of refractive error within the statistical models. RESULTS Mean refractive error measured -1.3 diopters (D) (standard deviation [SD], 2.9) and mean cylindrical error measured 1.1 D (SD, 1.5). Myopia of >-1.0 and >-6.0 D occurred in 42.7% (95% confidence interval [CI], 40.4%-44.9%) and 6.5% (95% CI, 5.4%-7.6%) of subjects, respectively. Myopic refractive error was associated significantly with a higher degree of NO (P<0.001) and age. Hypermetropia of >+1.0 D occurred in 15% (95% CI, 5.4%-7.6%) of the population and was associated with higher education levels (P<0.001). Astigmatism worse than 1.0 D occurred in 30.6% (95% CI, 28.5%-32.7%) of the population and was associated with age (P<0.001) and NO (P<0.001). CONCLUSION Myopia was more prevalent in older subjects and in those with increased NO. The prevalence rates of myopia in the > or =40 age group are higher than those found in other Asian regions and are likely to contribute to visual impairment.

Heritability of central corneal thickness in nuclear families.

PURPOSE Many ocular parameters show strong heritable tendencies. The significance of central corneal thickness (CCT) in the context of glaucoma has been the subject of much debate recently, but its heritability has not been extensively explored. This study was designed to investigate the parent-child heritability of CCT among groups who have CCT considered to be at the extreme ends of the normal range. METHODS Index cases were recruited through a tertiary referral center if their CCT was greater than 578 microm (thick) or less than 510 microm (thin), representing +/-1 SD from a previously published meta-analysis mean of 544 microm (34 microm SD). Subsequently, CCT was measured in all available family members of the index cases. Family units were then analyzed to establish the degree of heritability of CCT from parent to child. RESULTS Thirty-three index cases were included in the analysis (10 >1 SD and 23 <1 SD from the meta-analysis CCT mean). The mean CCT of the children of index cases with a CCT more than 1 SD from the mean (n = 15) and less than 1 SD from the mean (n = 40) was 568 microm (32 microm SD) and 521 microm (22 microm SD), respectively (t = 6.14; P < 0.0001). The parent-child heritability estimate for CCT was h(2) = 0.68 (95% CI, 0.64-0.73). CONCLUSIONS These results indicate that CCT shows strong parent-child heritability, with offspring likely to demonstrate CCT similar to the parental index case.

Factors affecting awareness and knowledge of glaucoma among patients presenting to an urban emergency department

Background: Until advanced, glaucoma is asymptomatic. For early diagnosis to occur, patients may need to be aware of it and seek assessment regularly. People who have risk factors for glaucoma may have a greater awareness of the disease.

The prevalence and causes of visual impairment in indigenous Australians within central Australia: the Central Australian Ocular Health Study

Aim To determine the prevalence and causes of visual impairment and blindness among indigenous Australians living in central Australia. Methods 1884 individuals aged 20 years or older, living in one of 30 remote communities within the statistical local area of “Central Australia”, were recruited for this study, from which 1883 were assessable. This equated to 36% of those ≥20 years old and 67% of those ≥40 years old within this district. Participants were recruited as they presented to the eye clinic at each remote community. Patients underwent Snellen visual acuity testing and subjective refraction. After this, an assessment of their anterior and posterior segments was made. Rates and causes of bilateral visual impairment (vision worse than Snellen visual acuity 6/12 in the better eye) and bilateral blindness (Snellen visual acuity worse than 6/60 in the better eye) were presented. Results 19.4% (365/1883) had bilateral visual impairment (25.1% of those ≥40 years old) and 2.8% (53/1883) had bilateral blindness (3.6% of those ≥40 years old). Refractive error followed by cataract were the main causes for bilateral visual impairment and blindness. Following these, diabetic eye disease and trachomatous corneal opacification were the main causes of bilateral visual impairment and bilateral blindness, respectively. Conclusion This study indicates that bilateral visual impairment and blindness are, respectively, 25.1% and 3.6% among indigenous Australians, four to seven times higher than among the non-indigenous Australian population. Trachoma is the leading cause of bilateral blindness after refractive error and cataract.

Optic nerve head parameters of an indigenous population living within Central Australia.

Purpose:  Clinical examination of the optic disc is an essential element in the assessment of its health. Previous work has described normal optic disc appearance among different races. No such description of optic discs exists for indigenous Australians, who are at low risk of developing glaucoma. This study was designed to evaluate optic disc parameters of indigenous Australians.

A Comparison of Global Indices between the Medmont Automated Perimeter and the Humphrey Field Analyzer

Background: Two commonly used perimeters in Australia are the Humphrey Field Analyzer II (HFA) and the Medmont Automated Perimeter (MAP). Each device describes the visual field in terms of numerical values called global indices; however, these values are not interchangeable between devices. This study was designed to directly compare the global indices of HFA and MAP visual fields. Methods: 63 subjects who had suspected glaucoma, ocular hypertension or glaucoma, or were normal controls were recruited selectively. Each patient was tested with the MAP and HFA. Global indices were then compared between tests. These included mean deviation (MD) and pattern standard deviation (PSD) from the HFA and average defect (AD) and pattern defect (PD) from the MAP. Results: The MD and PSD results were strongly correlated with the AD and PD results, respectively. The relationship between them could be described in terms of two polynomial equations: AD = 0.94+1.31(MD)+0.02(MD)2 and PD = 2.21(PSD)–0.05(PSD)2–0.006. These non-linear relationships may be the result of differences in testing method (test stimulus spectrum, number of testing locations or background luminance) or differences in the way each global index was calculated. Conclusion: The AD and PD results obtained from the MAP may be substituted for the MD and PSD results from the HFA after appropriate conversion.

Topography of the frequency doubling perimetry visual field compared with that of short wavelength and achromatic automated perimetry visual fields

Background: Traquair described the topography of visual field sensitivity as a “hill” or “island” of vision. Achromatic automated perimetry (AAP) demonstrates this shape of the visual field in photopic conditions. Techniques claimed to target the magnocellular pathway (frequency doubling perimetry, FDP) and those using a stimulus targeting the koniocellular pathway (short wavelength (or blue on yellow) automated perimetry, SWAP), might produce one that is different. The authors compared the visual field topography from FDP with those of SWAP and AAP, to investigate whether there were significant differences in their shape. Method: A sample of 51 patients with previously confirmed normal perimetry were recruited; either low risk glaucoma suspects or normal controls. AAP, SWAP, and FDP perimetry was performed in random order on the same day. The topography of each field was analysed to determine its average shape and to compare results in the same individuals. Results: The topography of the visual field produced by each perimeter differed significantly. While all three had maximal sensitivity centrally, over the 24 degrees from the centre to the periphery, mean sensitivities decreased by 4.9 decibels (dB) for AAP and 7.3 dB for SWAP, while FDP sensitivities by just 1.8 dB over 20 degrees (the extent of the FDP field). FDP mean sensitivities decreased by approximately 0.3 dB with every 10 year increase in age, compared with 1 dB for AAP and 2 dB for SWAP. Conclusion: While the topography of the SWAP (koniocellular) field is steeper than corresponding AAP fields, that of the FDP (magnocellular) visual field was considerably flatter. The difference in this shape may reflect retinotopic or cortical mechanisms, which are specific to the magnocellular pathways.

Genome-wide association study of intraocular pressure uncovers new pathways to glaucoma

Intraocular pressure (IOP) is currently the sole modifiable risk factor for primary open-angle glaucoma (POAG), one of the leading causes of blindness worldwide1. Both IOP and POAG are highly heritable2. We report a combined analysis of participants from the UK Biobank (n = 103,914) and previously published data from the International Glaucoma Genetic Consortium (n = 29,578)3,4 that identified 101 statistically independent genome-wide-significant SNPs for IOP, 85 of which have not been previously reported4–12. We examined these SNPs in 11,018 glaucoma cases and 126,069 controls, and 53 SNPs showed evidence of association. Gene-based tests implicated an additional 22 independent genes associated with IOP. We derived an allele score based on the IOP loci and loci influencing optic nerve head morphology. In 1,734 people with advanced glaucoma and 2,938 controls, participants in the top decile of the allele score were at increased risk (odds ratio (OR) = 5.6; 95% confidence interval (CI): 4.1–7.6) of glaucoma relative to the bottom decile.A combined analysis of participants from the UK Biobank and the International Glaucoma Genetic Consortium identifies 85 new loci for intraocular pressure (IOP). Pathway analysis uncovers new pathways associated with both IOP and glaucoma.