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A cataract is defined as clouding or opacification of an otherwise clear lens of the eye or its surrounding transparent membrane, the capsule. According to Dr. Lawrence Woodard, MD at Omni Eye Services, Atlanta, “The eye is similar to a camera; just as a camera’s lens focuses light onto a film, the eye’s lens focuses light onto the retina.”
Another important function of the lens is its ability to adjust an eye’s focus at all distances by the process of accomodation; this allows us to see things clearly both up close and far away. The opacification of the lens blocks the passage of light making the formation of a clear image on the retina blurred, while hardening of the lens makes accommodation difficult thereby causing numerous visual disturbances.
This disease is progressive and so are the visual symptoms. According to Mr Vincenzo Maurino- a renowned ophthalmologist, “Normally, a cataract starts forming at the age of 50-60 when the lens starts to become a little less transparent and then as the patient ages further, it starts affecting the quality of the vision itself and requires removal.” WHO regards it as the most common preventable cause of blindness worldwide along with uncorrected refractive errors.
According to World Health Organization, (2010) 20 million people go blind because of cataract which represents 51% of all the blind people worldwide. Studies suggest that cataract is responsible for clinical blindness i.e. visual acuity of <3/60 in approximately 570,000 adults in Pakistan.
Patients with cataract may present with or more of the following symptoms:
The lens is composed of fibers enclosed by a thin capsule, and is maintained by zonules on both sides. The lens fibers are made from the lens epithelium and migrate from the margin towards its center. The central part of the lens is called the nucleus and is made up of the oldest fibers, while the newly formed lens fibers are deposited in layers around it, called the cortex. The lens fibres are made up of water and protein, called crystallins. The clarity of lens is dependent on the fine arrangement of the three-dimensional structure of these proteins and their hydration. With increasing age, the metabolic efficiency of lens reduces, thus increasing its predisposition to noxious factors; oxidative stress breaks down the three-dimensional structure of proteins allowing them to aggregate or clump together, along with damage to the cell membranes of lens fibres. This results in clouding or discoloration of lens in that area and scattering of light, noted as an early cataract. The process continues gradually till the whole lens becomes cloudy, making it harder to see.
Based on location of opacification within the lens, cataracts are classified into three types: cortical, nuclear, and posterior sub-capsular opacities. The type of cataract affects the type and severity of patient’s symptoms:
A sub-capsular cataract occurs at the back of the lens and noted in diabetics or in people taking high doses of steroid medications. Such an opacity may not produce any symptoms until it is well-developed.
A nuclear cataract forms deep in the central zone (nucleus) of the lens and are associated with ageing. It affects the brightness of colours as the earliest symptom. As the nuclear cataract develops, it causes an index myopia which results in a temporary improvement in near vision, called the “second sight.”
A cortical cataract is characterised by whitish, wedge-like opacities that start in the periphery of lens and move to the center in a spoke-like fashion, surrounding the central nucleus. These opacities particularly cause symptoms of glare while driving at night.
Some factors, discussed below, may provoke the above mechanisms and a cataract is noticeable at an early age.
Experts have identified numerous risk factors and preventable causes of cataract that need to be looked for to ensure an early detection of disease. The risk factors may be divided into those that can be modified and those that cannot.
Treatment of cataract is almost always surgical. A trial of conservative management may, however, be given if visual acuity is more than or equal to 6/24. Commonly performed surgical procedures include:
Dr. Jeff Taylor gives hope to all individuals suffering from the disease as he states, “Cataracts are one of the most treatable eye diseases.” Furthermore, Mr Vincenzo Maurino claims, “…removal of the cataract will give most patients 99% perfect vision, with the added benefit of reducing of their dependence on glasses.” The most evident and straight-forward benefit is better vision. Due to the recent technological advancements, intraocular lens (IOL) come in great varieties allowing those with other co-existing conditions like myopia, hyperopia, presbyopia, and astigmatism to see better than before they had cataract as these conditions may also be addressed during cataract surgery. As a result, patients attain complete independence from spectacles given the right type of IOL is employed. Overall, there is marked improvement in quality of life and high levels of patient satisfaction after cataract surgery with a success rate ranging between 70-80% in light of recent studies.
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