Cataract in relation to UV radiation

The World Health Organization (WHO) has developed an internationally recognized system of colors corresponding to levels of the UVI" (Ultraviolet (UV) Radiation.) as shown in [graph 4]. As shown in [graph 5], the UV indexes are collected from three different online sources from the internet: Weather Altas, World Weather Online and Weather WX. The UVI is then averaged from the three sources and presented in [graph 5]. The UVI is very similar throughout the three chosen years, thus only showing the average from the three sources is valid enough.

The calculations from the three different sources are found in appendix c. From [graph 4 and 5], it is derived that Dar es salaam is associated with a very high risk of harm from unprotected sun exposure, while Gaocheng is associated with low risk of arm from unprotected sun exposure. The level of UV radiation is impacted by:

Geographical location: UV exposure is greater in tropical areas near the earth's equator because the sun is directly over the equator thus having the shortest distance to travel.

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Altitude: UV exposure is greater at higher altitudes because there is less atmosphere to absorb UV rays.

Time: The sun's angle in relation to earth varies according to seasons. A greater amount of UV radiation is experienced in the summer months, because the sun is in a more direct angle. UV exposure is also the most intensive during noon when the sun is at its highest point in the sky (Ultraviolet Radiation and Health).

Setting: UV exposure is generally greater in open spaces, especially when there are high reflective surfaces such coastal areas.

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It is also possible to cause long-term damage under cloudy weather, because of the scattering from patchy cloud covers.

Since Dar es salaam and Gaocheng is located in opposite hemispheres, their seasons and uv index is also the other way around. Dar es salaam being in the southern hemisphere has winter during the middle of the year with the lowest UV radiation (6.7), but Gaocheng being in the northern hemisphere has summer during the middle of the year with the highest UV radiation (8). All the factors that impact the UVI have a positive association with Dar es salaam than Gaocheng - closer to the equator, same altitude at sea level, always in summer, has more open space and a greater reflective surface (Indian ocean) - thus Dar es salaam has a greater UVI due to its geographical features. Dar es salaam has a concave up structure and Gaocheng has a concave down structure, hence proven by the seasons affected by the opposing hemispheres.

Cataract in relation to UV radiation

The eye is able to absorb UV radiation incidents by the tear film (covers the outer mucosal surface of the eye), the cornea and the lens. The cornea is transparent to visible light but absorbs a significant portion of UVB radiation and a very small portion of UVA radiation, while also being responsible for approximately ? of the eye's total optical ability (Addepalli, Uday Kumar, et al.). The anterior layers of the cornea (epithelium and bowman layer) are twice as effective at absorbing UVB radiation than posterior layers. The incident of cataract is high in countries with excessive sunlight - "this could be because of the photochemical generation of reactive oxygen species (ROS)" (Varma, Shambhu Dayal, et al). Since the lens comprises a large percentage of proteins, therefore, it is potentially the major target for photooxidation. Yellow (weak) to brown (severe) coloration of cataract were noted in countries with higher solar intensities due to photooxidation of proteins such as tryptophan moieties when compared to people living in higher latitude (Addepalli, Uday Kumar, et al.). Photooxidation is the process of oxidation (chemically combined with oxygen) caused by the effect of light. In this process, light is absorbed by a pigment in the eye then produces ROS, such as singlet oxygen and superoxide, whereby these damages ocular tissue (Addepalli, Uday Kumar, et al.). "Damage to the ocular tissue by UV irradiation occurs by many mechanisms such as protein cross-linking, dysfunction of enzymes, ion pump inhibition, genetic mutations, and membrane damage" (Addepalli, Uday Kumar, et al).

The crystalline lens is a protective pigment that filters UV radiation in the lens. The germinative area of the crystalline lens is located equatorially [figure 2] and is also the most sensitive area to UV radiation, hence the cataract is mostly spoke shaped. Since epithelial cells are in the anterior area of the lens, they are a likely target for UVB damage (Andley, Ushua P., et al). Epithelial cells serve as transport functions for the entire lens, are key sites of enzymes systems that protect the lens from oxidative stress. Exposure of cells to UVB radiation induces DNA damage and triggers alternation in the synthesis of specific proteins. Thus, the lens is likely to be influenced by the long terms effects of stressors such as UV radiation. There's a positive correlation between age and UV absorption by the lens.

A concentration of cortical cataract was found in the lower nasal quadrant of the lens [figure 6] (Damage of the Ultraviolet on the Lens). The most likely viewed position during peak sunlight hours suggests that the lower nasal lens region receives the highest dose of UVB (Pastor-Valero, Maria, et al). UVB is also proven to be an established risk factor for cortical cataract, due to the fact that the differential exposure by region could account for dimensional variations in cataract severity (Pastor-Valero, Maria, et al). Age-related cataract changes caused in the deep equatorial cortex of the lens are most likely worsen by UVB exposure through mechanisms such as increased oxidative radical burden and lipid peroxidation. UVB exposure had a variable effect on cataract severity, with little to no effect in the upper nasal regions of the lens and a maximum effect in the lower regions (Abraham, Alison G., et al).

Data Interpretation

As displayed in [graph 1], Dar es salaam has a total of 2,851 cataract patients in the year 2016, 2,829, and 2941 in the year 2017 and 2018 respectfully. With an average of 2,874 patients amongst the three years that are diagnosed with cataracts, with the majority average of 35.1% of the patients being 70 years of age and over. From [graph 3], the life expectancy for Tanzania is only 64.9, Dar es salaam's life expectancy can be considered a bit higher hence it is the capital city. As shown in [graph 6], the comparison of cataract patients with the UV index is relatively similar, having a similar concave up structure. With the most number of patients in March, September to November, and with the least patients from April to August, where January and December can be seen as outliers. A portion of the local income is based on the fishery, and fishermen have a greater chance of cataract formation because of the intensive reflection of UV radiation from the sea, the contact with the sea is also very common and inevitable, hence it may suggest a possible reason for the greater amount of cataract patients. .

As displayed in [graph 2], Gaocheng has an average of 958 patients per year that are diagnosed with cataracts, with 58.1% of the patients being 70 years of age and over, thus showing the severity of this eye disease amongst elders in Gaocheng, and having a higher correlation with the term 'age-related'. It is also noticed that the total number of patients have decreased from 1,222 (in 2016) to 915 (in 2017) to 738 (in 2018), thus showing that the action taken towards this disease in Gaocheng is more effective or more distributed between the population than in Dar es salaam. Since Gaocheng is not even a leading city in China, the same principle can also be applied to other cities in China, hence their movement towards a more developed country with better health support. As shown in [graph 7], the relationship between the number of cataract patients and UVI amongst the months seems to be random. Unlike Dar es salaam having a relatively positive correlation between the two variables, Gaocheng doesn't follow the same concept. Such that the highest number of cataract patients is given in March when the UVI is 4 and lowest number of cataract patients is given in June when the UVI is 8. This may suggest that the UV radiation is not a considerable impact factor towards cataract formation in Gaocheng, and it is more age-related.

Dar es salaam is a bigger city with a higher population compared to Gaocheng, but the difference amongst the cataract patients can be viewed by the percentages given in [graph 1] and [graph 2]. The data suggests that most cataract patients from both cities are aged 70 or more. Thus meaning the concept of cataract being age-related is proven to be valid, but with a higher correlation in Gaocheng having more than 50% of the patients aged 70+. The distribution of cataract patients with age is very similar amongst the three years with both cities, thus showing that the pattern of cataract patients is consistent, with a positive correlation between age and cataract patients. The same correlation can also be derived from the relationship between UVI and cataract patients in Dar es salaam, but not Gaocheng.

Evaluation of Method

The time period for the cataract formation cannot be determined with the information given, because the data is only collected by the hospitals when the patients arrive at the designated hospital and are then diagnosed with the disease with the confirmation from doctors. Although the information given can be used to determine the number of cataract patients with their correlation to age and UV radiation. The data does not specify between different ethnic groups and cataracts, as they might conclude with different outcomes. As shown from a study: "2010 U.S. age-specific prevalence rates for cataract by age and race/ethnicity" (Cataract Data and Statistics), does show that the vast majority (80%) of cataract patients in the US were white. Also with the acknowledgment that in Tanzania, not everyone has access to medical attention therefore it is difficult to know the actual number of people with cataract.

Possible Preventions

Dietary intakes of vitamin E, carotenoid lutein, zeaxanthin from food supplements were associated with a decreased risk in cataract formations (What Are Cataracts?).

With the negative correlation between age and the normal production of antioxidants, increasing the intake of fruits and vegetables can delay age-related cataracts and macular degeneration (What Are Cataracts?).

Antioxidant vitamins such as vitamin C and foods containing omega 3-fatty acids.

Sunglasses and protection of skin from solar exposure (Cataract.).


The human eye is constantly exposed to sunlight and artificial lighting. Light transmission through the eye is fundamental to its natural biological functions of directing vision, and therefore, light absorbed by the eye is inevitable. Considering that cataracts and other conditions, together with glaucoma, are not unusual in older adults, it's essential to get your eyes checked often. That is without a doubt critical if you have a family history of eye troubles or have been uncovered to things that would purpose trouble with your eyes. Adults need to see an ophthalmologist at least every 2 years until age 50, and then every 12 months after that.

"The lower nasal areas had the highest cortical cataract severity in both the right and left eyes" (Abraham, Alison G., et al.). In an evaluation of the high and low concentration of ultraviolet light groups (represented by the average exposure level), higher radiation had the maximum effect inside the decreased areas of the lens (Abraham, Alison G., et al).

In eastern countries such as China, "cataracts are the main public health issue in relation to increased ambient ultraviolet radiation (UVR)" (Wang, Yang, et al.). Therefore the awareness of cataracts in China is greater than it is in Tanzania, thus proven by the data collected with Dar es salaam having a greater distribution of cataract patients within the given age groups.

A study conducted by the National Eye Institute (NEI) in 2014 confirms that there is a firm link between UV radiation and oxidative stress (New Research Sheds Light on How UV Rays May Contribute to Cataract). Since the oldest cells in the lens get little to no oxygen, and oxidative stress only occurs with the presence of oxygen. The study suggests that UV light can be a substitute for oxygen to trigger harmful oxidative reactions in the lens, by showing glycation that is also typically seen in cataracts and cells that are damaged by oxidative stress. In addition, the natural antioxidant in our body, glutathione, only offered little protection against UV radiation, therefore increases the known threat of UV radiation.

With the depletion of the ozone layer caused by factors such as human activities, the UV radiation is filtered less through the atmosphere, thus increasing the intensity of UV radiation and the risk of UV induced skin cancer and cataracts. However, cataracts are the main public health concern for people of color that applies for both chosen countries, "because this population is less likely to develop skin cancer due to the protective properties of their skin" (Wang, Yang, et al.). The main type of cataract caused by UV radiation is the cortical cataract, and the odds have increased due to an increase of ocular exposure to UVB. With the estimation, "that 167,000-830,000 additional cases of cortical cataracts would be identified by 2050 in the U.S. with 5-20% ozone depletion resulting in an increase of UVB rays " (West, Sheila K., et al.), the same principle can be applied to other nations because ozone depletion is a global issue.

Updated: May 19, 2021
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Cataract in relation to UV radiation. (2019, Nov 29). Retrieved from

Cataract in relation to UV radiation essay
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