Cataract in rural Myanmar: prevalence and risk factors from the Meiktila Eye Study.

AIMS: To determine the prevalence of and risk factors for cataracts in a rural region of central Myanmar. METHODS: A cross-sectional, population-based survey of inhabitants >or=40 years of age from villages of central Myanmar; 2076 participated, and 2044 (82.3%) had an examinable lens in at least one eye. Data recording included smoking history, occupation, education level, betel-nut chewing, height and weight, and dilated lens assessment using Lens Opacities Classification System III grading: nuclear (>or=4), cortical (>or=2) and posterior subcapsular (>or=2) cataracts. Aphakic and pseudophakic eyes were included as operated cataracts for statistical analysis. RESULTS: The prevalence of any cataract including operated eyes was 40.39% (95% CI 37.30 to 43.48%): 27.35% nuclear, 20.91% cortical and 11.34% posterior subcapsular cataracts. No significant association was found between cataract and betel-nut use, gender, smoking or outdoor occupation. The likelihood of all cataract types increased with age (multivariate analysis including operated eyes: OR 1.154, CI 1.13 to 1.18, p<0.001). Low level of education and low body mass index were associated with nuclear cataracts. Large village size was associated with increased risk for nuclear cataract (OR 3.23, CI 1.989 to 5.250, p<0.001) and decreased risk for cortical cataract (OR 0.20, CI 0.08 to 0.47, p<0.001). CONCLUSIONS: The prevalence of cataract in rural Myanmar is similar to that in other developing Asian regions. Cataracts are strongly associated with increasing age, and are more common in those with lower education and lower body mass index.

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.

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.

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.

[Roles of posterior parietal cortex in stereopsis: characteristics of responses of axis-orientation-selective neurons in monkey caudal intraparietal area].

Patients with parietal lesions may fail to adjust the orientation of their hand to that of a target object, or may make errors in judging the orientation of a bar. This suggests that the parietal cortex has a function in the discrimination of the orientation of objects. In this study we investigated the responses of axis-orientation-selective neurons in caudal intraparietal (CIP) area to stereoscopic stimuli. Among the characteristics we investigated responses to the length and thickness of objects, sensitivity to binocular disparity, and position invariance in depth. Computer generated stereoscopic stimuli were presented to the monkey on a 70 inch screen. Most of the neurons responded better to long or narrow stimuli. All neurons which were orientation selective only in the frontal plane were not disparity sensitive. Most of the neurons which were orientation selective in the sagittal or horizontal plane were sensitive for binocular disparity. The majority of these neurons had wide receptive fields and their responses were position-invariant. These results suggest that the axis-orientation-selective neurons in CIP area encode the orientation of the longitudinal axis of objects in 3-dimensional space.

[Effects of different types of disparity cues on the response of axis-orientation selective cells in the monkey parietal cortex].

PURPOSE: To specify the cues for the discrimination of orientation in depth in axis orientation selective (AOS) neurons. METHODS: We analyzed the responses of AOS neurons in the monkey caudal intraparietal sulcus (cIPS) region using binocular disparity stimuli generated by stereoscopic 3 D computer graphics. RESULTS: Most AOS neurons (20/27) were sensitive to binocular disparity and showed tuning to the orientation of a slit in the sagittal plane with orientation disparity cues. For 12 neurons we also used an array of discs or dots instead of slits to eliminate orientation disparity. Half of the neurons (6/12) responded better to the slits than to the discs or dots, suggesting that they were sensitive to orientation disparity. Five neurons (5/12) responded equally well to the discs or dots suggesting that they were more sensitive to the gradient of horizontal disparity than to the orientation disparity. CONCLUSION: Both orientation disparity and disparity gradient were likely to be integrated in the cIPS area to represent axis orientation of an object in space.

Neural representation of three-dimensional features of manipulation objects with stereopsis.

In the first part of this article, we review our neurophysiological studies of the hand-manipulation-related neurons in the anterior part of the lateral bank of the intraparietal sulcus (area AIP). We describe the properties of visually responsive neurons in area AIP. Object-type visual-dominant neurons responded to the sight of objects and showed selectivity not only for simple geometrical shapes, but also for complex objects such as a knob-in-groove and a plate-in-groove. Some of the object-type visual-dominant neurons showed selectivity for the orientation of the longitudinal axis or the plane (surface) of a plate or a ring. In the second part of this article, we review our study of binocular visual neurons in the caudal part of the lateral bank of the intraparietal sulcus (c-IPS area), in particular, of axis-orientation-selective (AOS) neurons and surface-orientation-selective (SOS) neurons. AOS neurons preferred long and thin stimuli, were sensitive to binocular disparity, and tuned to the axis orientation in three-dimensional (3D) space. SOS neurons preferred broad and flat stimuli and were tuned to the surface orientation in depth. Some SOS neurons responded to a square in a random dot stereogram (RDS) with orientation tuning, suggesting that they encode surface orientation from a disparity gradient. Others responded to solid figure stereograms with orientation disparity and/or width disparity. It was concluded that the c-IPS area is a higher center for stereopsis, which integrates various binocular disparity signals received from the V3 complex and other prestriate areas to represent the neural code for 3D features. It may send projections to the AIP area and contribute to visual adjustment of the shape of the handgrip and/or hand orientation for manipulation and grasping. Neurons of the AIP area may also receive monocular cues of depth from the ventral visual pathway to discriminate the 3D shape of the object of manipulation.

Modulation of behavioral inhibition in appetitive extinction following manipulation of adrenal steroids in rats: implications for involvement of the hippocampus.

Corticosterone, the principal glucocorticoid in the rat, binds selectively to the CA1 pyramidal neurons of the hippocampus where the hormone has been demonstrated to exert a moderate chronic suppression of spontaneous activity. In the first experiment of the current study, the functional behavioral significance of this hormone--brain interaction was investigated in the extinction of an appetitive runway response in normal rats and those with lesions of the hippocampus. During extinction, half of the animals in each group were given daily subcutaneous injections of corticosterone. Whie the classical retardation effect of hippocampal lesions on appetitive extinction was replicated, hormone treatment was without effect in normal or hippocampally damaged subjects. The absence of a hormone effect in normals was primarily attributed to a saturated limited-binding system operating in the normal animal. Experiment 2 tested this notion, repeating the first experiment, with adrenal-ectomized (ADX), ADX + corticosterone replacement, and normal groups of animals. Adrenalectomy produced a striking facilitation of extinction which was speculated to be the result of a hyperactive inhibitory neural organ free from an inhibitory endocrine feedback. Corticosterone treatment normalized the progress of extinction in ADX animals, providing support for the afore-mentioned speculation. In the normal animal, it appears that a stress-induced surge in hormone level interacts with a limited-capacity neural binding to produce a transient dynamic range of behavioral disinhibition, perhaps promoting persistence during initial stages of frustrative nonreward in moderate stress tasks.