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A cataract is a clouding of the lens in the eye affecting vision. It develops with age (Hodge ,W,G 1995) but may also occur due to other reasons postulated in the study below. Due to the long standing view of a correlation between the quality of light one is exposed to and the vision, most believed that UV light plays a major role in the development of cataracts. Sunlight has both thermal and photochemical effect on the eyes occurring with risk levels depending on which type of UV radiation is present.
UV light is easily absorbed into the body and serves to produce immense amounts of vitamin D, necessary for growth. However over-exposure leads to sunburn and some forms of cancer . High intensities of UV to the eyes cause arc eye thus the basis of the postulation that it does contribute to formation of cataracts in the long run.
UV light can be mapped into three categories UVA ,UVB and UVC. Wavelength characteristic of UVB and UVA enable them to permeate the cornea into the lens. Experimental research has established that the UV radiation accelerates ionization and oxidation of contents of the lens. Increased ionization overtakes repair thus leading to clouding of the lens. Sustained clouding blurs vision and leads to cataract formation.
Research work and studies into the causation of cataracts is key in formulation and implementation of policies in prevention of cataracts. Speculation into this field of medicine has been rife but not conclusive. Many studies have dwelt on factors put forth as risk magnifiers such as use of protective gear(hats and glasses),exposure to sunlight during leisure and occupational activities,history of residence ( L Wong 1993),dietary constituents (Roberton, J.M 1991),age (Zhonghua Yi Xue Za Zhi. 2008), and genetic factors.
Most of the studies I analyzed dwelt on most but not all the factors posted as increasing the risk factors. Faults were portrayed in the studies in relation to reliability of data used to come up with,sample characteristics, time quality of the data, control measures to validate the data, as ell as presence of contribution of other factors separate from the mainstay of the study.
Experimental studies based on use of animal models(rats,rabbits) as well a research activities on human beings have been designed to investigate the effect on lens opacities after exposure to UV under varying conditions.
In a study by Michael. R., et. al. (1990) and Hightower K(1995) lens specimen from rats was used to estimate the difference in lens opacities under different levels of UV exposure. Standard preparation and storage modes were used so to maintain quality, before and after results were analyzed using sophisticated equipment to capture the before and after exposure scenario.
By comparing the average results with control experiment data, both research groups reported positive inclination between exposure to UV light and deterioration of th contents of the lens. The opacity resulting from the lens increased with increase in amount and length of exposure. The lens used were from rats and the study aimed at investigating the impact of length and intensity of exposure to UV on the lens.
The study was faulted along lines of appropriateness of model and intensity of UV light used. Difference in human and rat characteristics came into play. To dispel any further uncertainties Ning Zhu et al (2008) and Jun Heo,MD et al (2008) used epithelial cells from a human lens in a study to reveal the impact of UV light on the human lens. Their study also dug into protective characteristics of certain flavonoids. Using cultured sampled with well spread experiments so as to achieve a balanced outcome, the findings complimented each other.
UV light played a major function in deterioration of cells present in the eye lens. The level of damage observed was both dependent on amount and timing of exposure. The specific damage was in form of degeneration of the cells resulting from oxidation after ionization caused by the UVA and UVB light.
Both studies broke ground in prevention and repair of damage caused through UV light exposure by flavonoids. Marked regeneration(after application of flavonoids) in previously depreciated cells(after exposure to UV light) gave light to their impact. Present in green tea and some fruits ,Flavonoids are known to aid in prevention of oxidation resulting from UV light.
Occupational and residence characteristics contributing to exposure to sunlight were found not to be consisted along all spheres of comparison. Studies in Maryland(2007) and the Beaver dam(1992) focused on the exposure intensity resulting from the occupation and leisure activities of the participants in the group. The occupational factors were supported by literacy levels in the study in Valencia by Fletcher E et al (2007). The individuals who had outdoor occupations were found to have higher prevalence than those who worked indoors due to educational background.
Studies in Beaver dam by Barbara E. K. Klein (1992) and Maryland(2007) water-men all came up with finding that there was increased prevalence of certain types of cataracts prevalent only in males. Use of protective gear during young age contributed to reduced risk in severity of cortical and nuclear cataracts.
A different study carried out in Nepal(2008), found magnificent relation between exposure to sunlight and gender with risk of developing cataracts higher in women but more correlation between UV exposure and cataracts observed in men.
In determining the impact of residential history, dependability of data is hampered by the recall factors. However through use of data relating to height,weight medical, drug use and outdoor exposure the study groups are able to estimate the exposure. During analysis of the
findings they estimate exposure to UV radiation using outdoor exhibition during leisure and occupation, meteorological data, terrain and protective gear used. Ecological factors and latitude as explained by MC Michael et al (1997) affect the exposure hours to sunlight. In Nepal study (1992) it was found that cataract prevalence was less in higher altitudes, a scenario which was observed in Valencia by Fletcher et al(2002).
Cosmic radiation was put forth as a possible cause with airline pilots being more prone to developing cataracts than non pilots. In Valencia(2002), the occupational factors were not directly supported by the study. However it was found that those who worked outdoors had higher prevalence than those who worked indoors. This was attributed to educational level owing to the fact that most highly educated participants worked indoors.
Studies and experiments carried out in Maryland (2007), Chesapeake bay(1988) , and Beaver bay(1992) affirmed the prevalence of cataracts with sustained exposure to UV light. The correlation between development of cortical cataracts and exposure to UV light has largely been duplicated in superbly conducted studies.
In the Beaver Dam study it was discovered that despite women having lesser exposure to UVB light ,they had high chances of developing cortical opacities than men, bringing in the discussion of whether gender had an important role to play. Despite the reduction of light entering th eye achieved through use of glasses and hats as observed by Rosenthal et al (1986), the participants in Valencia (1986) were not privy to any campaigns to start use of such. Collman et al (1988) found a strong association between exposure to sunlight in prevalence of both posterior sub-capsular and cortical cataracts. An index constructed by Rosmini et al (1998)to measure the exposure to sunlight came up with no association between the PSC cataract levels and sunlight score.
In addition to other detrimental conditions the lens is exposed to, widespread deterioration was observed under conditions of UV radiation exposure combined with nutritional deficiencies by Wegener A,et al (2002). During the experiment they used rats which had been exposed to similar diet routines either deficient in zinc or in vitamin E. After sustained exposure to UV following three weeks on the diet on all samples except for the control,the lens opacities were investigated. Body weight and cornea condition data was incorporated into the findings.
Increase in density of cornea in the irradiated specimen with a diet deficient of zinc and vitamin C showed close relationship between UVA and UVB effect on the lens and dietary deficiencies. Studies were base on the exposure length by measuring the length of sunlight exposure.
Age factors were considered during the study by Hodge ,W,G et al (1995). Opacity of lens occurs at advanced ages due to inefficiency in the repair process. As indicated earlier the characteristics of the participants during formative years greatly influenced the age at which cataracts developed. Congenial and traumatic factors not withstanding,those exposed to UV radiation at at younger ager(20 years) had higher prevalence as compared to exposure dating 40 years as observed in the Beaver Dam study(1992).
Dietary factor have also come into play after discovery that flavonoids have anti-oxidation capabilities. High vitamin content is associated with delayed cataract formation. Suzen MM et al(2008) found a magnificent decrease in nuclear cataract prevalence among women whose diet was composed of vitamins and minerals,similar to finding in the Beaver Dam study(1992). Other risk factors include cigarette smoke (Christan, W.G et al 1993) and heavy alcohol consumption. Chasen-Taber et al (1999)found possibility of congenital cataracts resulting from lack of vitamin D however the assessment of the levels were controversial.
Medical history of the individual plays a role in the occurrence of cataracts. Trauma to the eyes as well as surgeries can contribute to some forms of cataracts. Diabetes melitus has also been found to compound the prevalence (Kunisaki M 1995). During the Beaver Dam study(1992) all participant with conflicting medical history were not considered due to the underlying factors. Other studies suggest people with diabetes are at risk for developing a cataract. Reports of increased prevalence in users of steroids (Jia LY, 2008), diuretics and major tranquilizers have not yet been studied. Research is needed to distinguish the effect of the disease from the consequences of the drugs themselves.
Taylor HR (1986) found that use of glasses to aid vision in men during younger years decreased the risk of severe cortical and nuclear opacities which can be attributed to regulation of UV transmission to the lens while reported that it could actually trigger occurrence of an array of cataracts.
Other risk factors notwithstanding,such as diabetes, heat levels,hormonal abnormalities and certain drugs,ultra violet light was found to be a primary contributor to development of cataracts,longterm accumulation of DNA damage induced by UV light as well as reaction between the membranes and ions present in the air.
Catherine McCarty (2007) found a close relationship between cataracts and genetic factors after observing its occurrence among twins in Australia. A similar observation was made at the Framingham eye Clinic by Marvin J.P (1995) after reported magnification of cases of increased opacities among siblings,which was not duplicated among spouses.
The relation between sunlight exposure and type of cataract was not explored by the study. Age of exposure was considered with age bundles of twenty being used. it was found that there was increased risk with exposure to sunlight during twenties than during the forties.
In the Beaver Dam study,the authors of the report following a study posted a strong association between occupational exposure to sunlight with prevalence of cataracts in age range of 20 to 29 years ,with reduction in prevalence in cataracts later in life after reduction of exposure during the same ages.
The effect of UV radiation in the quality of sight cannot be downplayed. Other risk factors considered ,prevalence of most forms of cataracts have been found to carry an association with continued exposure to sunlight. Both study and experimental data has always converged towards the premise that exposure to UV light compounds the occurrence of cataracts.
However, none of the findings have conclusively proven that exposure to sunlight is a causative factor to cataracts. The studies were challenged by insufficient and unreliable data to base the observation on. However,the experimental data, albeit facing procedural faults, is a wake up call to mankind since prevention is better then care. Since a perfect scenario for study is beyond reach due to interference from other risk factors,