Eyes diseases in elderly people
1) Why do cataracts and macular degeneration occur during aging?
2) Which environmental factors impact on the eyes which lead to cataract and macular degeneration and why these are more evident in the aged eyes?
Biology Extended Essay
Personal code: gxw225
Content page ………………………………………………………………P.3
Aim and background information…………………………………………P.9-10
Hypothesis, variables, equipment, procedures…………………………P.10
Human eye is an organ which allows us to see, it has been known as the most complex organs in the body because it is made up of many different components such as cornea, iris, pupil, lens, retina, optic nerve, conjunctiva and ciliary muscles. All of these small structures have connections with each other, in terms of functioning, which gives us an opportunity to look/appreciate the outer world.
How does the human eyes work?
The human eye acts like a camera with lots of different small components working together. The cornea helps to focus the light, which is at the front surface of the eye. The iris then controls the amount of light reaching into our eyes by adjusting the size of the pupil automatically. If the outer environment is too bright, the iris will adjust the pupils and reduces the amount of light going into the eyes. When the environment is dark, the pupil will be enlarged by the iris to allow more light entering the eye. After receiving light from the outer environment into our eyes, the cornea helps to transmit the electric impulses up to the brain. (National Keratoconus Foundation 2018). Our brain is connected with optic nerve, which helps us to perceive the images. However, the image received by the retina is upside down and our brains help to flip the images back to original, therefore the images could be properly seen.
Diagram 1: Anatomy of the eyes (Griffin 2018)
-2572759700Diagram 2: How messages from the outer environment are transferred to our brain. (Image source: The Eyewear Boutique 2017)
The retina also helps for visual recognition, it is a thin layer located near the optic nerve. When the lens has focused on the light, the responsibility of the retina is to obtain the light and then transforms it to neural signals. The retina that sends these neural signals to the brain and allows us to recognise the visual. The retina plays a vital role in vision, if the retina is damaged, it has the chance to cause permanent blindness. (Healthline Medical Team 2015)
At the same time, a specialised type of neuron is also found in the retina, known as the photoreceptor cell. The main function of the photoreceptor cell is to respond to light. A large amount of photo pigment rhodopsin is found inside the photoreceptor cell membrane. These photopigments are tightly packed to allow a large number of light photons to be absorbed when reaching the photoreceptor. The photopigments are responsible for absorption of light and consists of a type of protein known as opsin and a small molecule called chromophore. The chromophore is responsible for the absorption of photons of light. When photopigments detect light, they will begin to change shape and start to trigger some chemical reactions. Meanwhile, the photopigments also send signal towards the visual cortex of the brain, informing the brain about how much light there is inside the retina. Different kinds of photopigments are contained inside different types of photoreceptor. (Twaddell 2014)
In the human eye, there are two different kinds of photoreceptor cells called rods and cones. The cones only function in light (during daytime), as they require a large amount of light to be stimulated. Cones are responsible for colour vision, while rods are quite sensitive to light, therefore it only function in dim light (night time). However, rods do not have the ability to distinguish colour, except for black and white colour only. There are around 6 million cone cells and 125 million rod cells inside a human retina. The photoreceptive cones and rods are arranged in a way where they produce the best combination during day and night vision. However, people with colour-blind cannot tell the differences between some colours. A person with colour-blind does not have the particular cone cells inside the retina or that particular type of cone cells may be weaker. (Chudler 2017)
When light enters into our eyes, it is first refracted by the cornea – which is located on the front outer surface of the eyeball. The purpose of the cornea is to provide light-bending ability in our eyes. The light is bent again, after it passes through the cornea; while the crystalline lens in our eyes will help to adjust the focus on light. The ciliary muscles in our eyes helps to alter the shape of the lens, either by flattening or bending and therefore the light rays can be focused by the lens on the retina. (Easton Eye Care 2018)
The lens is another important part in our eyes, it is composed of flexible tissue and is located behind the pupil and the iris. The main function of our lens is to help focusing images and light on our retina. As our lens is flexible, it can change the shape to help focusing on objects that are nearby or further away from us. Attached to the lens are the ciliary muscles which help to change the shape of the lens. When we are looking at nearby objects, the lens becomes rounded to focus on the image. Since the ciliary muscles helps to release tension on the ligaments and as a result, the lens become more curved. While the lens will become more elongated when we are looking at objects that are further away. Over time, the lens starts to lose some of its flexibility and therefore having difficulties to focus on nearer objects, that’s the time when people need to have a reading glasses when they get older. (Encyclopaedia Britannica 2018)
Specific eye disorders that will happen during aging
1) Age macular degeneration (AMD) happens when the macula in our eyes are damaged that could lead to severe vision loss. People with age macular degeneration will have blurred vision compare to a normal vision, images may not be as clear. It may have an impact on their daily life, such as reading or writing. This disease usually starts to happen on people aged 40 or above. (National Health Service 2018)
2) Glaucoma is a disease of too much pressure in the eye which results in damage to the retina. Vision will be lost also due to the damaged optic nerve. In Australia, around 300,000 people suffer from glaucoma. As the eye pressure level starts to increase, a severe blurred vision will occur. There are no treatments for glaucoma at the moment unfortunately. (Hoste 2018)
3) Cataract are caused by the protein that clouds the lens, which results in blurred vision and blindness. Cataracts are often thought that it only happens on older people, however cataract may also happen on children as some children are born with it. (National Eye Institute (NEI) 2015) Cataracts can develop due to eye injuries or other problems after an eye surgery. Statistics indicate that approximately 20 million of people in the world are blind due to suffering from cataracts. (Sightsavers 2017)
4) Diabetic Eye Disease, also known as diabetic retinopathy, it is a disease where the retina is damaged due to diabetes and may leads to blindness. 80% of people who suffer from diabetes are also diagnosed with diabetic eye disease. People who suffer from diabetes from a long period of time will have a higher chance of getting diabetic eye disease. The age range of people suffer diabetic eye disease is from aged 20 until around 65 years old. (National Eye Institute (NEI) 2015)
5) Presbyopia is process that occur naturally during aging, where the eyes loss the ability to change its focus in order to see objects that are near, and it is also an example of refractive errors. Refractive errors are a type of eye disorders due to the irregularity in the eye shape, and therefore vision become impaired and blurred. (Bixler 2018) Statistics illustrate that about 42% of people having visual impairment is caused by refractive error. Usually presbyopia starts to happen starting from 40 years old onwards, where a blurred vision develops at a normal reading distance. People have presbyopia may also have headaches from if reading from a close distance for a long time. (Sightsavers 2017)
6) Trachoma is one of an infectious disease that can cause blindness, and it is also known as neglected tropical disease. Bacterial infection such as conjunctivitis is the main cause to trachoma. If it is not treated immediately, it will cause scarring to the eyelid and leading to the eyelashes turn inward, thus they scrape against the eye with every blink. Trachoma infections may spread around rapidly through having contact with infected flies as well as personal contact (e.g. hands or clothes), thus it disproportionately impacts on children and women. Statistics also show that approximately 182 million of people in the world were at risk of blindness due to trachoma in 2017. (Sightsavers 2017)
Above all of these disease, the two most common eye disorders that appear on older people are age macular degeneration and cataract. Therefore, these two eye disorders are investigated in the following essay.
Why is this topic worth investigating?
This topic is significance and worth investigating because finding out more information of the causes of these two common eye diseases would be helpful to some of the older people in the family as to understand their sufferings. It is also worth investigating of whether age is the only main factor that cause cataracts and macular degeneration or not. It would also be interesting to study about other factors such as genetics factor, diet, diabetes and environmental factors also contribute to these two eye disorders or not. I also have a strong passion on looking into the eyes, for example how do we see images, why can we detect different colours and what is happening to the cells inside our eyes. Since this topic has not been done in the past, it is worth undertaking a deeper investigation on one of the most complex organs in the human body – the eyes. It is also best to gain more knowledge about what is happening to the eyes when people are getting older. Therefore, I have chosen this particular topic area to research on.
1) Why do cataracts and macular degeneration occur during aging?
2) Which environmental factors impact on the eyes which lead to cataract and macular degeneration and why these are more evident in the aged eyes?
Aim and background information
To evaluate why cataracts and macular degeneration occur more often in later years.
As people reach middle ages, the ciliary muscles in their lens start to weaken. As a result, light rays are converging together behind the retina and this decreases the ability to focus on nearby objects. When a person suffers from cataract, the proteins in the lens start to clump together, which results in vision loss. In a healthy lens, the proteins remain dissolved inside the lens cells. The proteins start to clump together, and lens will become “cloudy” due to getting separated out of the solution or due to external damage and the patience will get cataract. Some common symptoms of cataract include: blurred vision or double vision and sensitivity to light.
Age macular degeneration is one of the most common eye disorders for people aged over 50, it occurs when cells start to damage in the macula. The yellow deposits under the retina, known as drusen will start to form and accumulate and eventually continue to grow. A type of fatty protein known as lipids made up these drusen. (Porter 2018) The growth of drusen will have a negative impact on the cells in the retina. Cells death may happen and leads to a loss of vision, which is the main cause of macular degeneration. (Peiliang 2016)
The macula is the small and yellowish proportion, located in the central part of the retina. When a person is looking at an object directly, an image will form on his/her macula from the light of that object. In the centre part of the macula is known as fovea centralis, it contains photoreceptors without any rods containing in the fovea. Since there are no rods in the fovea, we will not be able to look at small and dim objects when we are in the dark. The photoreceptors in the retina are responsible for absorbing incoming light. To detect any colours, tiny photons must stimulate the cone cells – which are located in the fovea centralis and in the macula. (Ted Montgomery 2018) Damaged macula will affect the central vision which impact on people’s daily activities such as reading, writing and recognising other people’s faces. During ageing, new tiny blood vessels will grow underneath the macula on some people, however these blood vessels may leak blood and fluid into people’s eyes, which causes damage to the macula and loss of vision. Some other factors that also causes macular degeneration are high blood pressure & heart disease, obesity, exposure to sunlight, smoking and family history.
Environmental factors such as exposure to sunlight and lack of Vitamin D are the primary cause of cataracts and macular degeneration respectively in people over the age of 80.
Independent variable: the target age group of participants
Dependent variable: the percentage of people across different countries suffer from cataract and macular degeneration within the age group
Control variable: keeping the same five countries for research
1) Research for statistics on the amount of people from different countries that have cataract and age macular degeneration.
2) Put all the statistics in a table format and graph the results.
3) Analyse and discuss the statistics
Countries The estimation percentage of people over aged 80 suffer from cataract: The estimation percentage of people aged between 50 to 80 suffer from cataract
Australia 70% 31%
China 17% 13%
United Kingdom 19% 11%
Canada 16% 6.9%
United States 50% 13.5%
Table 1: Statistics for cataracts
– (Khairallah et al. 2015)
-14557949879000- (Canada National Institute for the Blind (CNIB) 2018)
Diagram 3: Cataracts statistics graph
Countries The estimation percentage of people over aged 80 suffer from macular degeneration The estimation percentage of people aged between 50 to 80 suffer from macular degeneration
Australia 3.1% 13.5%
China 4% 15%
United Kingdom 10% 3.6%
Canada 15.2% 3.8%
United States 48% 24%
Table 2: statistics for macular degeneration
Age-Related Macular Degeneration: Facts & Figures, 2016
Diagram 4: Macular degeneration statistics graph
It was found that the estimated percentage of people aged over 80 suffer from cataract is mostly higher than people aged 50-80 except for Australia and China. Australia has 3.1% of people aged over 80 suffering from macular degeneration and 13.5% of people aged 50-80 have macular degeneration. (The Fred Hollows Foundation 2013) Most of the statistics shows that as the age increases, the chance of getting cataract and macular degeneration will also increase. However, other than aging factor, environmental factor, such as exposure to naturally occurring radiation (sunlight) is also another major cause of cataract and macular degeneration. Statistics indicate that Australia has the most people suffering from cataracts in both age groups. There are approximately 70% of people aged over 80 have cataracts and 31% of people aged between 50 and 80 have cataracts. (Australia Institute of Health and Welfare 2005) Since Australia is a country where it always experiences high levels of UV radiation as the country is close to the equator, therefore most Australians often expose to sunlight for a long period of time, which damages the lens capsule, lens cells and their membranes. (Cancer Council 2016)
Research indicates that when our lens absorbs ultraviolet (UV) radiation (sunlight), a type of chemical known as free radical may form inside our lens, which would damage our lens eventually and this may cause cataracts. (WebMD 2018) Our lens is mainly made up protein, known as crystalline. Free radicals, also known as reactive oxygen species (ROS), an example of ROS is superoxide anion radical, lead to the cause of cataracts and structurally damaging the crystalline lens. Another example of free radicals is hydrogen peroxide (H2O2), it is formed naturally when sunlight is connecting with water, which can also cause opacification to the lens. When hydrogen peroxide gets into our eyes, it will cause oxidation of proteins inside the lens (Jain et al. 2003) and oxidation of proteins may decrease the protease activity in the lens. If the lens cells gradually lacking protease activity, then they may not have the ability to handle with crystallin damages. While the crystallin are starting to denature, there is a chance that they will accumulate, which contribute to the development of cataracts. (Davies et al. 1987) Therefore, research demonstrates that hydrogen peroxide is the major oxidant that involves in the causations of cataracts. (Rahman et al 2012) While US is the country with the most amount of people over age 80 having cataracts after Australia, which is approximately 50% (Laser Eye Surgery Hub, 2014) as it is also a country with the most sunshine in the world.
Some people are born with cataracts or develop cataracts during early childhood. These cataracts may be related to genetic factors or associated with a trauma. Personal behaviour may also lead to cataracts. Smokers increase the risk of developing cataract compared with non-smokers. (Robman et al. 2005) Studies show that the smokers double the chance of having cataracts, and the risk continues to increase if continuing to smoke. (WebMD 2018) Smoking is also one of the risk factor that contributes to the development of macular degeneration. Every cigarette smoked may causes damage to our vision. Smoking may narrow the blood vessels which reduces the blood supply to the eyes. Genetics also play an important role in causing macular degeneration. The risk of developing macular degeneration is 50% for people who have a relative with macular degeneration while the risk is 12% for people whose relatives do not have macular degeneration. (Bedell et al 2010).
Although research information illustrates that genetics, personal behaviour and aging are part of the factors that cause macular degeneration, the major cause is the environmental factor. Some of the researchers from the University of Buffalo recently found out that a lack of Vitamin D production may lead to the cause of macular degeneration. (Cannell 2015) A study published from the “Archives of Ophthalmology” in April 2011 found that people who often take foods with more vitamin D or taking vitamin D supplements, they are less likely to have macular degeneration (Cole 2017). Vitamin D deficiency will less likely to affect a younger person’s eyes, but instead our eyesight will be affected once it begins to decline throughout the time period.
Statistics illustrate that Canada has the most percentage of people (15.2% for people aged over 80) who suffer from macular degeneration after United States. (CNIB Seeing Beyond Vision Loss 2018) Since Canada is one of the countries in the world that has the least hours of sunlight, therefore the time that the Canadians stay under the sun would be shorter and thus they absorb less Vitamin D, which leads to a number of elderlies suffering from macular degeneration. There are many findings that suggest a lack of vitamin D could lead to macular degeneration. Researchers from the University of Buffalo stated that people with poor vitamin D are 6.7 times more likely to have macular degeneration compare to people with sufficient among of vitamin D. (Rutberg 2016) Recent studies have been done to investigate the connection between vitamin D and macular degeneration. The studies looked at the blood levels of vitamin D in a group of women between 50-79 years old in the Women’s Health Initiative Study Group. They concluded that high levels of vitamin D concentrations may protect women younger than 75 years old from getting macular degeneration. (Degner 2012)
Other than environmental factors causing macular degeneration, it could be the macular does not have the ability to get rid of the waste products or to absorb enough oxygen rich nutrients from the tissues. The development of drusen is the cause of macular degeneration. Macular drusen are the yellow deposits that start to expand between the choroid layer and the retinal pigment epithelium, in other words, it means the blood vessels layer that supply nutrients for the macula. Since the photoreceptor cells, the cones and the rods, they require a huge amount of oxygen. If they do not receive enough oxygen, they will start to degenerate and die. The macular is mainly formed by cone cells, and the purpose of cone cells is for our colour vision and central vision. By the time these cone cells start to degenerate, we will begin to see less vivid colours and our central vision becomes blurry and cloudy. Drusen are harmful to our eyes because they obstruct with waste products getting eliminated from our macula as well as oxygen nutrients getting into the macula. People with drusen may need more lights to read books or newspaper and a blurry spot may emerge in their central vision. (Degner 2018)
From the above statistics and facts, it is known that cataracts and macular degeneration are more prevalent in older years due to the environmental factors. As the older people experienced longer time to sunlight exposure, which could directly be harmful to the eyes. Therefore, other than aging factors, exposure to sunlight is the main factor of causing these eye disorders and leads to a number of people in older ages suffer from cataracts and macular degeneration. There are definitely many other factors combining together to cause cataracts and macular degeneration, but in personal point of view, a judgement was made – that is, environmental factor (exposure to sunlight) impact on the cells inside our eyes easily and causing these eye disorders. Although there are a few statistics indicate that the percentage of people in older age that have macular degeneration begins to decrease, however most of the other statistics support the hypothesis – that is cataracts and macular degeneration becomes prevalent in aged over 80.
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