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.

Prevalence and causes of visual impairment in rural myanmar: the Meiktila Eye Study.

OBJECTIVE: To determine the prevalence and causes of visual impairment in the Meiktila district of central, rural Myanmar. DESIGN: Population-based cross-sectional study. PARTICIPANTS: Random, stratified, cluster sampling of the inhabitants 40 years of age and older from villages in the Meiktila district was performed; 2481 eligible participants were identified and 2076 participated in the study. METHODS: The ophthalmic examination included presenting and pinhole Snellen visual acuity with an illiterate E chart, slit-lamp examination of the anterior segment, and dilated stereoscopic fundus examination. The principal cause of visual impairment was recorded. MAIN OUTCOME MEASURES: Visual impairment and blindness were defined by both presenting and corrected visual acuity according to World Health Organization criteria: better eye < 6/18 and < 3/60, respectively. RESULTS: Comprehensive examinations, including Snellen visual acuity, were performed on 2073 participants (83.6%) The prevalence estimate of presenting visual impairment was 40.4% (95% confidence interval [CI], 36.1-44.7) and of presenting blindness was 8.1% (95% CI, 6.5-9.9). After pinhole correction, the corresponding prevalences were 26.8% (95% CI, 23.5-30.1) and 5.3% (95% CI, 4.0-6.6). Cataract, uncorrected refractive error, and glaucoma were the most common causes of visual impairment. CONCLUSIONS: Visual impairment and blindness remain major public health problems in rural Myanmar. Specific programs directed toward reducing the cataract burden need to be implemented.

Prevalence of glaucoma in rural Myanmar: the Meiktila Eye Study.

AIM: To determine the prevalence of glaucoma in the Meiktila district of central, rural Myanmar. METHODS: A cross-sectional, population-based survey of inhabitants > or =40 years of age from villages in Meiktila district, Myanmar, was performed; 2481 eligible participants were identified and 2076 participated in the study. The ophthalmic examination included Snellen visual acuity, slit-lamp examination, tonometry, gonioscopy, dilated stereoscopic fundus examination and full-threshold perimetry. Glaucoma was classified into clinical subtypes and categorised into three levels according to diagnostic evidence. RESULTS: Glaucoma was diagnosed in 1997 (80.5%) participants. The prevalence of glaucoma of any category in at least one eye was 4.9% (95% CI 4.1 to 5.7; n = 101). The overall prevalence of primary angle-closure glaucoma (PACG) was 2.5% (95% CI 1.5 to 3.5) and of primary open-angle glaucoma (POAG) was 2.0% (95% CI 0.9 to 3.1). PACG accounted for 84% of all blindness due to glaucoma, with the majority due to acute angle-closure glaucoma (AACG). CONCLUSION: The prevalence of glaucoma in the population aged > or =40 years in rural, central Myanmar was 4.9%. The ratio of PACG to POAG was approximately 1.25:1. PACG has a high visual morbidity and AACG is visually devastating in this community. Screening programmes should be directed at PACG, and further study of the underlying mechanisms of PACG is needed in this population.

Gonioscopy findings and prevalence of occludable angles in a Burmese population: the Meiktila Eye Study.

AIM: To determine the prevalence of preglaucomatous angle-closure disease in central Myanmar. METHODS: A population-based survey of inhabitants >or=40 years in the Meiktila District was carried out; 2481 subjects were identified, 2076 participated and 2060 underwent gonioscopy of at least one eye. Eyes with angles traditionally described as "occludable" were recorded as primary angle-closure suspects (PACS); eyes with PACS and peripheral anterior synechiae (PAS), or an increased intraocular pressure but without primary angle-closure glaucoma, were recorded as primary angle closure (PAC). RESULTS: The prevalence of PACS in at least one eye was 5.7% (95% CI 4.72 to 6.62); prevalence increased with age and was more common in women (p<0.001). The prevalence of PAC in at least one eye was 1.50% (95% CI 1.47 to 1.53). All participants with PAS had at least 90 degrees of closure (range 90-360 degrees). CONCLUSION: The prevalence of preglaucomatous angle-closure disease (PACS and PAC) in this population was 5.7% and 1.5%, respectively. PACS was more common in women, and its prevalence increased with age.

Retinal detachment neuropathology and potential strategies for neuroprotection.

Understanding the neuropathology of retinal detachment from postmortem and animal models allows identification of cellular targets, receptors and mediators for pharmacological manipulation. In this review, concepts of retinal detachment and neuropathology are examined at cellular and structural anatomical levels using postmortem and animal model data. Possible neuroprotective strategies are reviewed in the setting of the new environment created by successful retinal reattachment surgery.

Use of photographic techniques to grade nuclear cataracts.

Methods for objectively documenting and grading different varieties of lens opacities are needed in order to conduct research on risk factors for cataracts. This study tested the feasibility and reliability of using two different photographic methods to grade nuclear opacities. Photographs were taken of 41 eyes using a regular Topcon SL-5D photo slit lamp, and using a Topcon SL-45 (Scheimpflug) camera. The photographs were graded against a set of four standard photographs of increasing nuclear opacification. Densitometric analyses were also performed on both sets of photographs. The clinical grade, on examination, of the nucleus was compared to the examiner's grade of each photograph. Agreement was fair between the examination results and the grading of the photographs. Inter-observer reliability was high (kappa = 0.71) with photographs taken using the photo slit lamp. Moreover, the severity grading of the photographs showed a good correlation with the severity of opacity as determined by densitometric analyses. On the basis of these data, and on the field experience, the use of photographs of the nucleus obtained by photo slit lamp may be used in epidemiological surveys.

Lack of evidence for aspirin use and prevention of cataracts.

A population-based cross-sectional survey of 838 men aged 30 years and over was conducted to examine the effect of aspirin, and other potential risk factors, on the prevalence of cataracts. Lens opacities were graded on clinical examination for location (cortical, nuclear, and posterior or subcapsular) and severity. The results do not support the claim that large doses of aspirin, or frequent use of aspirin, protects against or retards the growth of lens opacities.

Corneal changes associated with chronic UV irradiation.

The association between exposure to UV radiation and corneal disease was investigated in 838 watermen who work on the Chesapeake Bay, Maryland. Individual ocular exposure was calculated by combining a detailed occupational history with laboratory and field measurements. Pterygium was found in 140, climatic droplet keratopathy in 162, and pinguecula in 642. Logistic regression analysis showed that pterygium and climatic droplet keratopathy were significantly associated with a broad band of UV radiation exposure (UV-B, 290 to 320 nm; A1, 320 to 340 nm; and A2, 340 to 400 nm), but the association with pinguecula was weaker. Simple measures such as wearing a hat or spectacles protect the eye and could potentially reduce the amount of pterygium and climatic droplet keratopathy attributable to UV radiation exposure.

Treatment of onchocerciasis. The ocular effects of ivermectin and diethylcarbamazine.

The ocular changes that occur with diethylcarbamazine treatment of onchocerciasis seriously restrict its usefulness. Ivermectin, a newly developed antifilarial drug, was compared with diethylcarbamazine for treatment of onchocerciasis in a double-masked, placebo-controlled trial. Thirty men with moderate to severe infection and ocular involvement were randomly assigned to receive ivermectin as a single oral dose (200 micrograms/kg), diethylcarbamazine (administered for eight days), or placebo. Detailed ocular examinations were performed serially over a 12-month period. Diethylcarbamazine treatment caused a marked increase in living and dead microfilariae in the cornea, punctate opacities, and limbitis during the first week of therapy. Ivermectin had no such effect. However, ivermectin therapy resulted in a long-term reduction in intraocular microfilariae comparable to that seen with diethylcarbamazine. Ivermectin appears to have few ocular complications and be a better-tolerated and more effective microfilaricidal agent than diethylcarbamazine for the treatment of onchocerciasis.

Ivermectin prophylaxis against experimental Onchocerca volvulus infection in chimpanzees.

Ivermectin was tested for possible prophylactic action against the third and fourth larval stages (L3 and L4) of Onchocerca volvulus inoculated into chimpanzees. The infective larvae (L3) were obtained from laboratory-raised black flies. Eighteen chimpanzees were inoculated, each with approximately 250 L3. Six were treated with ivermectin (200 micrograms/kg) on the day of inoculation, 6 were treated with ivermectin on day 28, and 6 were not treated. Monthly skin snips were taken for the next 30 months to detect patent infection. One of the chimpanzees treated with ivermectin on the day of infection developed a patent infection as did 4 of the 6 treated at day 28 and 4 of the 6 control animals. The results suggest that ivermectin may have a partial in vivo effect against the L3 of O. volvulus but has no effect against later larval stages of the parasite.

Ivermectin treatment of patients with severe ocular onchocerciasis.

The treatment of onchocerciasis with diethylcarbamazine and suramin is associated with an exacerbation of ocular disease. This occurs more frequently in patients with severe onchocercal ocular disease. We assessed ocular changes following ivermectin treatment in 39 patients with severe ocular onchocerciasis. Patients were treated with 100, 150, or 200 micrograms/kg of ivermectin at either 1 or 2 year intervals and followed for 3 years. There was no evidence for an acute exacerbation of either anterior or posterior segment eye disease, and there was a marked improvement in ocular status in the group as a whole. There was a significant decrease in onchocercal involvement which was maintained for at least 3 years. Annual treatment with ivermectin can be used safely in patients with severe ocular disease and is beneficial over a prolonged period of time.

Epidemiology of blindness and visual impairment in the kingdom of Tonga.

Data on the prevalence and causes of blindness and visual impairment in Polynesians are not readily available nor are they population based. This survey was designed to obtain an accurate estimate of blindness and its causes in Tonga. A sample of 4056 persons, aged 20 years and over, was selected by stratified cluster sampling. Participants received a screening, visual acuity examination, and, if visually impaired, were referred for detailed ophthalmic examination to determine the cause. The prevalence of bilateral blindness in the study population was 0.47% and all affected were aged over 50 years. It is estimated that the national prevalence of bilateral blindness, adjusted for the sample weight applied in the selection procedure, is 0.56% (95% confidence interval 0-1.13). Monocular blindness was three times more frequent. Cataract was responsible for 68.4% of bilateral and 30.3% of monocular blindness. Risk factors for life time experience of cataract included age and diabetes (self-reported). Neither smoking nor the presence of pterygium were independently associated with cataract. Increasing years of education were protective against cataract for women, but not men. Corneal opacity from infection or trauma, and diabetes were responsible for most of the remaining visual impairment. While these results do not represent a significant public health problem by world standards they do provide a basis for planning blindness prevention programmes in the region.

Ocular manifestations of onchocerciasis in a rain forest area of west Africa.

The epidemiology and natural history of onchocerciasis and its ocular complications in rain forest areas are poorly understood. The present study was conducted on a rubber plantation in a hyperendemic area in the rain forest of Liberia, West Africa, where 800 persons were examined. The prevalence of infection was 84% overall 29% had intraocular microfilariae, and 2.4% were blind in one or both eyes. Onchocerciasis was the cause of all binocular blindness and one-third of all visual impairment. Over half of the visual impairment caused by onchocerciasis was due to posterior segment diseases. Chorioretinal changes were present in 75% of people, and included intraretinal pigment clumping in 52% and retinal pigment epithelium atrophy in 32%. Atrophy of the retinal pigment epithelium was associated with increasing age and severity of infection. Intraretinal pigment was strongly associated with anterior uveitis. There was a strong correlation between uveitis and the inflammatory chorioretinal sequelae: retinitis, intraretinal pigment, subretinal fibrosis, and optic neuropathy. These findings indicate that considerable visual impairment associated with rain forest onchocerciasis is common and is due largely to chorioretinal disease.

Effect of single-dose ivermectin therapy on human Onchocerca volvulus infection with onchocercal ocular involvement.

Ivermectin has shown promise as a potentially safe and effective microfilaricidal drug for the treatment of onchocerciasis. Several limited studies have shown it to have fewer side effects, especially ocular complications, than the currently available drug, diethylcarbamazine. The detailed ocular findings in 200 moderately to heavily infected Liberians who were enrolled in a safety and dose-finding study are presented. They received either 0, 100, 150, or 200 micrograms/kg of ivermectin and were followed up for 12 months. In clinical studies so far carried out ivermectin in a dose of 100, 150, or 200 micrograms/kg has not been associated with any major adverse reactions nor were there any sight-threatening effects even in the presence of severe ocular disease. Each of these doses significantly reduced the ocular microfilaria load for at least 12 months when compared with either the placebo (p less than 0.05) or pretreatment values (p less than 0.001). However, the 100 and 150 micrograms/kg doses caused fewer minor side effects than the higher dose. These results confirm that ivermectin in a single oral dose may be a safe and effective microfilaricidal drug for the treatment of onchocerciasis and that it appears to be free of major ocular side effects.

Prevalence and causes of blindness in the South Australian population aged 50 and over.

PURPOSE: To conduct a population based study examining the prevalence and causes of blindness and visual impairment in the South Australian population aged 50 and over. METHODS: A random stratified cluster sample of 2115 persons was recruited from geographically exhaustive local government areas within South Australia. All participants underwent distance visual acuity measurements. In those participants with corrected visual acuity < 6/18 in the better eye a cause was determined. RESULTS: Cataract and macular degeneration were the most common causes of monocular and binocular blindness. The prevalence of monocular and binocular blindness in South Australia in the population aged 50 and over is calculated to be approximately 3.7% and 1.3%, respectively. These rates increase significantly in the elderly (70 years of age and over) subgroups. CONCLUSIONS: Degenerative conditions are the principal causes of visual impairment in South Australia. The number of visually impaired persons in South Australia is likely to increase over the coming decades. Accurate data are essential in order to optimise the use of limited resources.

Technology assessment applied: a comparison of ophthalmic diagnostic techniques to detect diabetic retinopathy among Aboriginal people in central Australia.

Diabetes mellitus is one of the non-communicable diseases that has accompanied Aboriginal exposure to Western life style. The prevalence of diabetes mellitus is higher in the Aboriginal population than in non-Aboriginal Australians (Holding, 1985) and many Aboriginals who have diabetes mellitus develop diabetic retinopathy. Early detection facilitates treatment and prevention of blindness, a sequela of diabetic retinopathy. This paper describes the use of technology assessment as a framework for comparing two diagnostic technologies, fundal camera and ophthalmoscope, for use with Aboriginal people in central Australia.

Risk factors for early angle-closure disease in a Burmese population: the Meiktila Eye Study.

PURPOSE: To determine risk factors for early angle-closure disease (AD) in a Burmese population. METHODS: A cross-sectional, population-based survey of the inhabitants, 40 years of age and over, from villages in the Meiktila District was performed; 2481 eligible participants were identified, 2076 participated in the study, and 2050 could be categorized as having early AD (defined by the presence of so-called occludable angles (<90 degrees of posterior trabecular meshwork visible on gonioscopy), but without glaucomatous optic neuropathy). The ophthalmic examination included Snellen visual acuity, slit-lamp examination, tonometry, gonioscopy, biometry, and dilated stereoscopic fundus examination. RESULTS: The mean axial length (AL) and anterior chamber depth (ACD) in those with occludable angles were 21.9 and 2.60 mm, respectively; in those with non-occludable angles, the corresponding lengths were 22.74 and 2.84 mm, respectively (P<0.001 for both comparisons). In the univariate analyses, age, female gender, nuclear and cortical cataract, steeper corneal curvature, more anterior lens position, and myopia were also significantly associated with occludability. In the multivariate analysis, age, AL, ACD, and nuclear cataract were significantly associated with occludability. CONCLUSION: In this Burmese population, those with occludable angles had significantly shorter ALs, ACDs, and thicker lenses than those without occludable angles. In multivariate analysis, increasing age, decreasing AL, decreasing ACD, and nuclear cataract were significant predictors of early AD. The presence of nuclear cataract per se should raise clinical suspicion of the possibility of AD in this population.

The prevalence, severity and risk factors for pterygium in central Myanmar: the Meiktila Eye Study.

AIMS: To determine the prevalence, severity and risk factors associated with pterygium in adults in central Myanmar. METHODS: Population-based, cross-sectional survey of the people 40 years and over residing in rural Myanmar. Pterygium was graded for severity (T1 to T3) by visibility of episcleral vessels, and the apical extent was recorded. An autorefractor was used to measure refractive error. RESULTS: There were 2481 subjects identified, and 2076 (83.7%) participated. The prevalence of pterygium in either eye was 19.6% (95% confidence interval (CI) 16.9 to 22.2) and of bilateral pterygium 8.0% (95% CI 7.7 to 8.3). Outdoor occupation was an independent predictor of pterygium (p<0.01). The mean apical extent from the limbus was 2.2 mm (95% CI 2.05 to 2.35). Higher-grade pterygia did not have a significantly greater apical extent (p = 0.35). The presence of pterygium was associated with astigmatism, (p = 0.01), and the amount of astigmatism increased as both the severity (p<0.01) and apical extent increased (p<0.01). Two people of the 84 people blinded in both eyes were bilaterally blind from pterygium (1.7%; 95% CI 0.2 to 6.1), and pterygium accounted for 2.2% (95% CI 0.7 to 5.0) of blindness in at least one eye. No participant had low vision in both eyes due to pterygium, but pterygium led to 0.8% (95% CI 0.3 to 1.6) of low vision in at least one eye. Pterygium was therefore associated with 0.4% (95% CI 0.04 to 1.3) of binocular visual impairment and 1.0% (95% CI 0.6 to 1.8) of visual impairment in a least one eye. CONCLUSIONS: There is a high prevalence of pterygium in central Myanmar, and the risk of developing this condition increases with outdoor occupation. Pterygium in this population is associated with considerable visual morbidity, including blindness.

Anisometropia in an adult population in rural myanmar: the Meiktila Eye Study.

PURPOSE: To determine the prevalence and risk factors for anisometropia in a rural adult population in central Myanmar. METHODS: A population-based ophthalmic survey was conducted in rural villages in central Myanmar. Ansiometropia was assessed in subjects with phakic eyes. The severity of anisometropia was defined as the absolute difference of the spherical equivalent between the two eyes. RESULTS: Prevalence of anisometropia (> or =1.0 D) in all participants was 35.3% (95% CI 32.7-37.9%); severe anisometropia (> or =2.0 D) was present in 18.9 % (95% CI 16.8-21.0%). There was no significant gender difference in anisometropia prevalence or severity. Prevalence and severity of anisometropia were significantly associated with age. Multiple logistic regression analysis revealed that cataract, myopia, but not age, were associated with anisometropia. The between-eye differences in axial length (r = 0.15, p < 0.001) and corneal curvature (r = 0.19, p < 0.001) were significantly correlated with the severity of anisometropia. CONCLUSIONS: Prevalence of anisometropia is relatively high in this rural adult population in Myanmar. Myopia and cataract, but not increasing age, are the potential risk factors of anisometropia in this population.