Prevalence, causes and socio-economic determinants of vision loss in Cape Town, South Africa

Purpose

To estimate the prevalence and causes of blindness and visual impairment in Cape Town, South Africa and to explore socio-economic and demographic predictors of vision loss in this setting.

Methods

A cross sectional population-based survey was conducted in Cape Town. Eighty-two clusters were selected using probability proportionate to size sampling. Within each cluster 35 or 40 people aged 50 years and above were selected using compact segment sampling. Visual acuity of participants was assessed and eyes with a visual acuity less than 6/18 were examined by an ophthalmologist to determine the cause of vision loss. Demographic data (age, gender and education) were collected and a socio-economic status (SES) index was created using principal components analysis.

Results

Out of 3100 eligible people, 2750 (89%) were examined. The sample prevalence of bilateral blindness (presenting visual acuity <3/60) was 1.4% (95% CI 0.9–1.8). Posterior segment diseases accounted for 65% of blindness and cataract was responsible for 27%. The prevalence of vision loss was highest among people over 80 years (odds ratio (OR) 6.9 95% CI 4.6–10.6), those in the poorest SES group (OR 3.9 95% CI 2.2–6.7) and people with no formal education (OR 5.4 95% CI 1.7–16.6). Cataract surgical coverage was 68% in the poorest SES tertile (68%) compared to 93% in the medium and 100% in the highest tertile.

Conclusions

The prevalence of blindness among people ≥50 years in Cape Town was lower than expected and the contribution of posterior segment diseases higher than previously reported in South Africa and Sub Saharan Africa. There were clear socio-economic disparities in prevalence of vision loss and cataract surgical coverage in this setting which need to be addressed in blindness prevention programs.     

The molecular genetics of color vision and color blindness

Recent reports from several laboratories have changed our thinking about the molecular genetics of normal color vision and color blindness. The impact of these new findings can be best appreciated by examining them in the context of the historical development of color vision theory.     

Zooplankton associations in the swamps of southern Sudan

Samples from the main Nile channel yield a poor zooplankton, deficient in species and heavily laden with organic debris. Samples from side arms and floodplain lakes yield a richer zooplankton, often containing 15–20 species of rotifers and ten or more species of Crustacea. When the floodplain lakes are heavily vegetated the number of species increases. For the Crustacea the index of diversity () normally varies between 0.6 and 2.4, but in a side arm of the Bahr el Zeraf it reaches 6.1 and in Lake Ambadi on the Bahr el Ghazal it reaches 8.4. The diversity of the rotifers is somewhat higher, normally ranging between 2 and 4.5, but reaching 23 in Lake Ambadi. The zooplankton of Lake Ambadi is the most distinctive and contains several species not found at other stations. The reasons for the peculiar zooplankton of Lake Ambadi are discussed.     

Child mortality levels and survival patterns from southern Sudan

Data from a 1985 survey in two major population centres in Southern Sudan, Juba and Wau, were analysed in order to assess childhood mortality levels and the effect of UNICEF's health care programme. There are continuing high levels of childhood mortality. Logistic regression analysis shows significant positive associations between child survival and immunization, oral rehydration therapy and maternal education.     

Plasticity of monocular and binocular vision following cerebral blindness: evoked potential evidence

Using monocular and dynamic random dot correlogram (DRDC) stimuli, sequential visual evoked potentials changes were demonstrated in 2 patients following cerebral blindness. The recovery of binocular vision was delayed in comparison to the recovery of monocular vision. The results are not due to simple acuity impairment or convergence deficiency, and thus provide evidence for the vulnerability of postsynaptic cortical mechanisms of human binocular vision.     

Statistical and molecular analyses of evolutionary significance of red-green color vision and color blindness in vertebrates

Red-green color vision is strongly suspected to enhance the survival of its possessors. Despite being red-green color blind, however, many species have successfully competed in nature, which brings into question the evolutionary advantage of achieving red-green color vision. Here, we propose a new method of identifying positive selection at individual amino acid sites with the premise that if positive Darwinian selection has driven the evolution of the protein under consideration, then it should be found mostly at the branches in the phylogenetic tree where its function had changed. The statistical and molecular methods have been applied to 29 visual pigments with the wavelengths of maximal absorption at approximately 510-540 nm (green- or middle wavelength-sensitive [MWS] pigments) and at approximately 560 nm (red- or long wavelength-sensitive [LWS] pigments), which are sampled from a diverse range of vertebrate species. The results show that the MWS pigments are positively selected through amino acid replacements S180A, Y277F, and T285A and that the LWS pigments have been subjected to strong evolutionary conservation. The fact that these positively selected M/LWS pigments are found not only in animals with red-green color vision but also in those with red-green color blindness strongly suggests that both red-green color vision and color blindness have undergone adaptive evolution independently in different species.     

Fish communities in the perennial wetland of the Sudd, southern Sudan

SUMMARY. 1. Cyperus papyrus and Typha domingensis swamps were recognized as the major ecological zones in the perennial wetland of the Sudd.
2. Fish sampling, chiefly by gill-netting and electric fishing, was concentrated in the open-waters of channels and lakes together with submerged, fringing and marginal vegetation in the accessible papyrus zone. Sixty-two species were recorded including fifteen catfishes. thirteen characoids, seven cyprinids, seven mormyrids and seven cichlids.
3. The highest diversity and abundance of tishes was obtained in the shallow Sudd lakes which revealed considerable uniformity in population structures. The most numerous species in gill-nets were Alestes dentex, Synodontis frontosus and S. schall , whereas Heterotis niloticus, Mormyrus cashive and Distichodus rostratus assumed importance in terms of biomass. Micralestes avutidens and cichlids were abundant among the small fishes inhabiting fringes of Eichhornia crussipes , and air-breathing species occurred beneath the vegetation mat.
4. Flowing-water habitats exhibited a similar but restricted fauna. Catches were dominated by Synodontis frontosus in open-water and by Micralestes acutidens and Chelaethiops bibie in the margins. The latter species was shown to have a clear preference for running water.
5. Peak catches in a representative river-lake could be interpreted as the arrival of fish for breeding or their migration through the lake for reproduction elsewhere. The capture of fry or juveniles of many species in fringing or marginal vegetation indicates that the permanent floodplain of the Sudd provides suitable spawning and rearing grounds.
6. Access to the extensive Typha zone was limited but from available evidence it was inferred that air-breathing fishes, notably Heterotis and Gymnarchus , may penetrate the swamps to reach areas remote from perennial transmission channels.     

Some causes of blindness seen at Noor Eye Institute, Afghanistan

This is a survey of the causes of blindness recorded by three students of The City University during a six-week stay at NOOR Eye Institute in Kabul, Afghanistan. The nature of the sample used makes it unsuitable for direct comparison with surveys from other countries. Nevertheless, broad conclusions can be drawn. Severe eye disease is a considerable problem in Afghanistan, in common with other developing countries. The survey included all new patients seen in the outpatient clinic, blind to the extent of being unable to count fingers at more than three metres, in one eye or both. The sample of patients was examined by an ophthalmologist working with our team. A diagnosis was made and various social and demographic questions were asked with the help of an interpreter. In all, 473 patients were examined and included in our survey sample, a very high proportion of the new patients attending the clinic (40.46 per cent). The main causes of blindness were found to be cataract (31.12 per cent), corneal scarring (19.8 per cent), chorioretinal degenerations (6.79 per cent), glaucoma (6.65 per cent) and aphakia (5.52 per cent). Of the major causes of blindness, about forty per cent of the cases were considered remediable, and about thirty per cent could have been prevented. An outstanding difference between the causes of blindness in developed nations and those seen in Afghanistan was the amount of blindness caused by infection, especially in the younger age groups (up to 30 years). Cataract is a major cause of blindness in the older age groups of both societies. People suffering from ocular disease in Afghanistan wait until their sight is badly impaired or lost completely before seeking treatment. This results from a lack of knowledge of what could be done to conserve sight, the irreversible nature of many eye diseases, the distances involved in travelling to the clinic, and even a lack of knowledge of its existence.     

Prevalence and risk factors for Plasmodium falciparum malaria in pregnant women of eastern Sudan

Background

Pregnant women are more susceptible to malaria, which is associated with serious adverse effects on pregnancy. The presentation of malaria during pregnancy varies according to the level of transmission in the area. Our study aimed to demonstrate the prevalence and risk factors for malaria (age, parity and gestational age) among pregnant women of eastern Sudan, which is characterized by unstable malaria transmission.

Methods

The prevalence and possible risk factors for Plasmodium falciparum malaria were investigated in 744 pregnant Sudanese women attending the antenatal clinic of New Haifa Teaching Hospital, eastern Sudan, during October 2003-April 2004.

Results

A total 102 (13.7%) had P. falciparum malaria, 18(17.6%) of these were severe cases (jaundice and severe anaemia). Univariate and multivariate analysis showed that, age and parity were not associated with malaria. Women who attended the antenatal clinic in the third trimester were at highest risk for malaria (OR = 1.58, 95% CI = 1.02–2.4; P < 0.05). Women with malaria had significantly lower mean haemoglobin (9.4 g/dl, 95% CI 9.1–9.7 versus 10.7, CI 10.6–10.8, P < 0.05). A significantly lower haemoglobin was observed in those with severe falciparum malaria compared to non-severe form (8.3 g/dl, 95% CI 7.6–9.1 versus 9.4, 95% CI 9.1–9.7, P = < 0.05).

Conclusion

The results suggest that P. falciparum malaria is common in pregnant women attending antenatal care and that anaemia is an important complication. Preventive measures (chemoprophylaxis and insecticide-treated bednets) may be beneficial in this area for all women irrespective of age or parity.     

Retrolental fibroplasia; blindness in infants of low weight at birth

Retrolental fibroplasia is today the principal cause of blindness in children of preschool age, exceeding all other causes combined. The disease occurs in infants of low weight at birth, commonly those born prematurely. The incidence of the disease is rising at an alarming rate. Vitamin E deficiency, corticotropin (ACTH) deficiency, the use of cow's milk in place of mother's milk, and improper oxygenation have been suggested as etiologic factors but the cause remains a mystery. Often the incidence is high in institutions in which maximal care is given premature infants.Clinically, the disease advances through an "active" phase during which regression is possible, and a "subsiding" or "cicatricial" phase which terminates with the formation of a disorganized opaque mass behind the lens. The earliest manifestations are noted in the fundi. Hemorrhages, neovascularization, transudation commencing in the periphery, and retinal separation contribute to the formation of the characteristic retrolental membrane. The diagnosis may be made when the retrolental membrane is observed in the eye of an infant whose weight at birth was low. Differential diagnosis is required occasionally. Thus far, no form of therapy has prevented or reversed the pathologic changes successfully. Use of vitamin E, corticotropin and mother's milk has not influenced the incidence of the disease. Avoidance of premature delivery if possible is indicated.     

Osmotic cataract causes reduced vision in wild Atlantic salmon postsmolts

Osmotic cataracts were diagnosed in all of 191 Atlantic salmon Salmo salar L. postsmolts caught during 8 trawl hauls on the western side of the V?ringsplateau, Norwegian Sea, in June 2001. The changes varied from a hazy opacity in the anterior part of the lens to cataracts affecting the whole lens. Severely affected lenses appeared swollen and large vacuoles were visible in the opaque areas. Large vacuoles in otherwise clear lenses were diagnosed in 1 of 4 adult salmon examined. Histologically, widened sutures, vacuolation of lens epithelium and cortex, and proteinaceous lakes subjacent to the epithelium were the most frequent changes, while extensive cortical necroses and epithelial proliferation were seen in a few cases. UV-absorbance of the aqueous humor was determined and levels compared to plasma levels and also to levels in farmed Atlantic salmon of the same developmental stage. Wild salmon generally showed higher levels of protective factors than farmed fish. The osmotic type of cataract diagnosed leads to poor vision and is a potential cause of reduced survival in postsmolts. The cause of the cataracts could not be determined, but defective osmoregulation is suspected.     

Ten days of darkness causes temporary blindness during an early critical period in felines

Extended periods of darkness have long been used to study how the mammalian visual system develops in the absence of any instruction from vision. Because of the relative ease of implementation of darkness as a means to eliminate visually driven neural activity, it has usually been imposed earlier in life and for much longer periods than was the case for other manipulations of the early visual input used for study of their influences on visual system development. Recently, it was shown that following a very brief (10 days) period of darkness imposed at five weeks of age, kittens emerged blind. Although vision as assessed by measurements of visual acuity eventually recovered, the time course was very slow as it took seven weeks for visual acuity to attain normal levels. Here, we document the critical period of this remarkable vulnerability to the effects of short periods of darkness by imposing 10 days of darkness on nine normal kittens at progressively later ages. Results indicate that the period of susceptibility to darkness extends only to about 10 weeks of age, which is substantially shorter than the critical period for the effects of monocular deprivation in the primary visual cortex, which extends beyond six months of age.     

Prevalence and causes of chronic energy deficiency and obesity in Indian women

We investigate the nutritional status of women in India and its relation to the prevalence of chronic energy deficiency (CED) and obesity. To do this, we have used the data from the Indian National Family Health Survey, 1998-1999, on body mass index (BMI) of ever-married women, ages 15-49 years, along with several socioeconomic factors, such as level of education, religion or caste, occupational status, and standard of living index. The study was based on 81,712 women from 26 states and 6 zones, which were grouped according to geographic proximity of the states of India. A multiple linear regression analysis was done to see the relation between nutritional status of women and different socioeconomic factors. The data reveal that the prevalences of CED, overweight, and obesity in India are 31.2%, 9.4%, and 2.6%, respectively. The incidences of CED and obesity are negatively related. The prevalence of CED is the lowest in Arunachal Pradesh and highest in Orissa. Punjab has the highest prevalence of obesity, and Bihar has the lowest. For the zonewise distribution the Northeast zone has the lowest degree of prevalence of CED and the East zone is at the bottom of the list with the highest degree of malnutrition. We also found that the nutritional status of women goes together with the enhancement of their educational status, standard of living, and so on. There are also significant differences between rural and urban sectors and among castes, religions, and occupations. Furthermore, regression analysis shows that all the socioeconomic variables considered here significantly affect BMI in Indian women.     

Association Between the Prevalence of Schistosomiasis in Elementary School Students and Their Parental Occupation in Sudan

Global efforts to identify groups at high risk for schistosomiasis have mainly concentrated on identifying their geographical distribution. Investigations on the socioeconomic characteristics of high-risk groups are relatively scarce. This study aimed to explore the associations between schistosomiasis among students and their parents’ occupations. A nationwide cross-sectional survey was conducted targeting 105,167 students in 1,772 primary schools across Sudan in 2017. From these students, 100,726 urine and 96,634 stool samples were collected to test for Schistosoma haematobium and S. mansoni infection. A multi-level mixed effect analysis was used with age and sex as fixed factors, and school as a random factor. The odd ratios (ORs) of practicing open defecation among farmers’ children were almost 5 times higher than their counterparts whose parents were government officials (OR=4.97, 95% confidence intervals (CIs): 4.57–5.42, P<0.001). The ORs of contacting water bodies for watering livestock among farmers’ children were more than 4 times higher than those of children whose parents were government officials (OR=4.59, 95% CIs: 4.02–5.24, P<0.001). This study shows that schistosomiasis represents a disease of poverty and that farmers’ children constituted a high-risk group.