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| The eye ball |
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To know what happens when cataract happens lets start with understanding the structure of the human eye ball.
The process of seeing something starts with the lens aiding our eye in focusing on that object. It's (the lens) a clear tissue found behind the iris, the colored part of the eye (see the picture). The lens of the eye works like the camera lens, focusing light onto the retina- a delicate, sensitive nerve layer of the eye, on which the image is formed.
Just like it happens in a camera, the lens of the eye adjusts the focus, letting us see things clearly both up close and far away. |
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| IMAGE FORMATION AND LENS |
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 This lens is mostly made up of water and protein. In normal conditions the eye lenses are clear, watery substances that can change shape as they focus. |
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| WHAT IS CATARACT? |
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The word cataract is derived from the Latin 'cataracta' meaning
"waterfall".
As rapidly running water turns white, the term may later have been used (metaphorically) to describe the similar appearance of the eye lens in cataract.
The structure of lens is interesting one. The proteins, in the lens, are arranged in such a precise manner that keeps the lens clear and yetlets light pass through it. WHAT IS CATARACT? IMAGE FORMATION AND LENS
But, everything is destined to change with age (primarily, but can occur earlier in ones life too). The process (of ageing or some other detriment causing factor) brings with it degeneration of the structure. What happens is some of the protein in the lens clumps together and starts to cloud a small area of the lens.This is a cataract, and over time, the clump can grow larger and cloud more of the lens, making itharder to see.
In brief, cataract is the clouding of the eye's lens that can cause vision problems, including blindness.
Usually cataract is formed in the center or nucleus of the lens. Sometimes it is formed at the periphery and extends its spokes from the outside of the lens to the center. And sometimes it begins at the back of the lens. Cataract can be of different types. |
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| SYMPTOMS |
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Cataract may affect one or both eyes. The condition usually takes a long time to progress and is painless (apart from the anguish of not being able to see clearly).SYMPTOMS
Following are the symptoms of cataract:
 Blurred vision
Double vision in one eye
Sensitivity to light
Spots in the vision
Trouble seeing in bright light
Reduced sight that cannot be corrected by wearing glasses |
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Cataract is one of the major causes of age-dependent visual 1 impairment and blindness.
In developing countries like India; the magnitude of the problem is overwhelming. Usually some degree of cataract is present 2 after the age of 50 years. |
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| TREATMENT |
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Surgical removal of the cataract is the primary treatment of the disease. This removal becomes necessary when symptoms, as mentioned earlier, become severe.
In this form of treatment, the cloudy lens is removed and then replaced by an artificial one. This new lens acts as the permanent lens, and thus helps the patient regain good eyesight. |
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| RISK FACTORS FOR CATARACT |
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Although cataracts are the leading causes of blindness, how it itself is caused is unclear. The exact cause of cataract (or how the process of clumping of protein starts) is not very clear. Nevertheless, extensive studies have identified some risk factors, which can predispose an individual to cataract formation.
The most common cause of cataract is ageing. Age relatedcataract is also called as senile cataract. Though age is the mostcommon cause of the cataract, one must be aware that it can also start developing earlier.
Following are the factors that are associated with higher risk of cataract formation: |
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Diabetes
Exposure to sun's UV rays
Prolonged consumption of steroids
Smoking
Alcohol consumption
Exposure to infrared radiation
Eye injury |
In addition to these factors scientists have identified one additional risk factor that could cause cataract. It not only works as an independent risk factor but also serves as a link between other risk factors and cataract. The factor is called as Oxidative Stress.
Let's see what “Oxidative Stress' is and how it plays a role in furthering or causing a disease/abnormality. |
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| OXIDATIVE STRESS |
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 To understand the role of oxidative stress one must know about free radicals. An atom has
protons and neutrons at its center and electrons revolving around the center in orbits. In normal conditions, these electrons are found in pairs. If an electron revolving around the center is not paired, the species is called as a free radical.
Free radicals are unstable and highly reactive. To achieve stability they 'rob' electrons from the surrounding molecules to produce an electron pair. Due to this, the molecule from which the electron is removed becomes unstable and turns into a free radical. This process of 'robbing' repeats with the new free radical and the chain progresses.
In this way, a single radical is capable of producing a sequence of electron transfer reactions. The process of the removal of electron is called as oxidation. And the stress thus generated by the free radicals is called as oxidative stress.
These free radicals attack fatty acids and proteins in cell membranes and cause damage to it. Free radicals also damage the DNA. The oxidative stress is implicated in the development of a variety of diseases like Cancer, Atherosclerosis, Diabetes mellitus, Alzheimer's disease, Parkinson's disease etc. Cataract is on the list! |
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| CATARACT AND OXIDATIVE STRESS |
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Various studies were conducted to explore the role of oxidative stress in the development of cataract. A study has found that extensive oxidation of the lens protein and lipid was present in the individuals who had developed cataract. The magnitude of oxidation was much less in individuals without cataract. Subsequently, a range of studies have proved the contribution of free radicals and oxidative stress in the 3,4,5,6,7,8 development of cataract.
The free radical induced damage of the lens cells has also been proved by an experiment conducted on animals. Lenses of rats were isolated from the eyes and were exposed to a significant burden of oxidative stress. It was observed that the loss of transparency of lenses CATARACT AND OXIDATIVE STRESSbegan in the equatorial region within 24 hours and the entire outer area was opaque by 96 hours. No involvement of the central nuclear region was observed initially. However after an additional 48 hours, the central nuclear region became opaque.
An eye lens is continuously exposed to light and air. Oxygen in the air and light work together to produce oxygen free radicals. When the cells in the lens are exposed to the action of these free radicals the damage starts. Cataract is thought to be a result of damage caused to various cell types in the eye lenses by oxidative stress.
It was found in a study that the free radicals impair the crystalline proteins present in the lens. It is the clumping of these very proteins that is responsible for the clouding that leads to cataract.
The eye lens contains a different enzyme called as proteolytic enzyme. These proteolytic enzymes are responsible for removing the damaged proteins in the lens. Free radicals also smash up these proteolytic enzymes and add to the damage. |
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The damage caused by oxidative stress is irreversible and there is an inverse relationship between the stress period and the time required for the damage. This means that if the oxidative stress has been occurring for a longer period, the time required for the damage of the lens is less.
Diabetes and smoking, another two additional risk factors causing cataract are also associated with higher oxidative stress. Oxidative stress has been implicated in the development of cataract in both these conditions
We have seen that surgical removal of the cataract is the primary treatment of the disease.
But after all that is just a treatment! Do we have any tool to delay the development of cataract? The answer is yes. And the tool is ANTIOXIDANTS. |
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| What are ANTIOXIDANTS? |
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 Antioxidants are substances whose presence, in relatively low concentrations, significantly inhibits the rate of oxidation. It is the counter to the process of oxidation. Antioxidants deal with these free radicals and control oxidative stress. Every person, in old age or with a risk factor for cataract, is exposed to additional oxidative stress due to an excessive burden of free radicals. To neutralize this oxidative stress human body has a store of natural antioxidants present in the form of various secretions such as albumin, bilirubin, estrogen, etc. These arthe Natural (physiological) antioxidants that human body uses to fight off the potential (damage) threat posed by oxidative stress. Human eye is also well equipped to take care of the local free radicals. Antioxidant enzymes like glutathione peroxidase, superoxide dismutase, and 9 catalase can counteract the oxidative stress generated in eye.
But, these natural antioxidants that are synthesized in human bodies may not be always sufficient to take care of the additional burden of free radicals in the eye. So, one needs to extract antioxidants from the diet.
Thus nutrition is one promising means of protecting the eyes from cataract. But there are limitations, especially in old age! As the age advances the dietary intake is usually reduced. Decreased efficiency of digestive system is another problem of old age. And above all the supposedly “modern”, and deviously unhealthy, food habits preventthe sufficient intake of the much needed dietary antioxidants. |
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| Why antioxidant supplements? |
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 This is the reason why individuals who are predisposed to the development of cataract need additional supply of antioxidants. Therefore supplementation with antioxidants appears to be an attractive possibility to delay the onset of cataract.
Various herbal antioxidants present in nature have the potential to offer a range of advantages in delaying development of cataract. Any nutritional supplement, which offers ingredients having significant antioxidant activity, can have positive impact on development of cataract. Studies also claim that optimal intake of antioxidant nutrients may contribute to enhanced quality of life and 10 decelerated Ageing. |
