Cataract – Written by Purrven Bajjaj, B Optom, MSc Clinical Optom.
A cataract occurs when an opaque or cloudy area develops in the normally clear lens (responsible for the focusing mechanism) of the eye. This cloudy area scatters and blocks the light as it passes through the lens, preventing a clear image from reaching the retina (light-sensitive tissue at the back of the eye). Clouded vision caused by cataracts is often described as seeing through a frosty or foggy window. When the cloudy vision interferes with daily activities such as reading or driving a car, undergoing surgery is recommended to remove the cataract.
The following sections will briefly outline the global problem and economic impact of cataract, how it forms, its various types, its risk factors, its signs and symptoms, and some insights into its treatment options.
Globally, is the leading cause of blindness and the second cause of partial vision loss. A large study conducted in 21 countries reported that in 2020, cataract was the leading cause of blindness in those aged 50 years and older .
Global estimates show that approximately 2.2 billion people suffer from total or partial vision loss, out of which, about 65 million is due to cataract. According to the National Eye Institute in the United States (US), the number of people with the condition in the US is expected to double from 24.4 million to about 50 million by the year 2050 .
Cataract is known to cause blindness or partial vision loss, potentially affecting an individual’s ability to work. Surgery is available to treat and remove cataracts to prevent blindness or partial vision loss. Barriers in low-income countries such as the lack of health insurance, inability to afford surgery, or lack of suitable eye health facilities hinders the treatment of cataracts through surgery.
Researchers have found that people who have undergone cataract surgery are able to increase their economic productivity by approximately 15 times the cost of the surgery during the first year after surgery . A study done at a large chain hospital in India, the Aravind Eye Hospital, reported that about 6 in 10 women who lost their jobs as a result of becoming blind due to cataract regained their jobs after cataract-removal surgery .
Cataracts form when proteins in the lens of the eye clump together, making the lens cloudy. The lens of the eye is normally clear, allowing light to pass through. The lens allows the focusing of light on the retina (light sensitive tissue at the back of the eye) to produce clear vision, and mostly consists of water and proteins.
In an eye without cataract, the proteins line up in a manner such that it enables the lens to be completely clear, allowing light to pass through easily. If proteins in the lens clump together, the lens gets cloudy and light cannot pass through the clumps of protein in the lens easily, resulting in decreased vision. Over time, as the clumps of protein become larger and thicker, vision is further decreased.
The following section covers the various types of cataracts.
A nuclear cataract refers to the hardening of the nucleus or center of the lens of the eye. Nuclear cataract may cause an increase in the onset of myopia (short-sightedness). In the initial stages of nuclear cataract, the lens becomes cloudy and yellow. As the condition progresses, the lens may turn brown and harden. People with nuclear cataract may have difficulty distinguishing between shades of colour due to yellowing or browning of the lens.
In cortical cataract, areas of white cloudiness develop in the outer edges of the lens called the cortex. These areas of cloudiness spread inward and appear like spoke wheels or in a star pattern. People with cortical cataract experience blurred vision and glare as light entering the eye is scattered and a decrease in contrast is observed as well.
Posterior subcapsular cataract (PSSC) begins as a cloudy or opaque area on the back surface or posterior of the lens. PSSC develops below the lens capsule, hence the name ‘subcapsular’. The lens capsule is a sac-like membrane that holds the lens in place. When PSSC begins to develop, it usually does so rapidly and symptoms such as glare, presence of haloes around light, and difficulty reading are noticed a few months after PSSC begins to develop.
Children can get cataracts too and they may be present at birth (congenital cataracts) or develop as they grow (paediatric cataract).
Congenital cataract is the clouding of the lens of the eye that is present at birth. Clouding of the lens causes blurring of vision as light cannot reach the retina (light-sensitive tissue at the back of the eye). Without early intervention, this can affect children’s visual development, causing other sight-threatening conditions such as lazy eye, nystagmus, inability to fix and focus on objects, and even blindness.
If the cataract only affects a small part of the lens and does not interfere with vision, surgery is not required. However, if the cataract is dense and affects vision, congenital cataracts may need to be removed during infancy.
Among children with congenital cataracts, 1 in 4 cases is attributed to genetics , which means that they probably inherited the genes from either parent. Other congenital cataracts may occur due to trauma, diabetes, myotonic dystrophy, galactosemia, neurofibromatosis or rubella. To detect congenital cataracts, it is important to ensure that children undergo routine eye checkups.
Children may also develop another type of cataract known as paediatric cataract, which may also occur due to trauma, diabetes, or may be inherited from either parent. Trauma directly to the eye accounts for 40% of the paediatric cataract cases .
Traumatic cataract is clouding of the lens that may occur after a blunt trauma (when an object collides with the eye but does not cut the eye or face with force) or sharp trauma (when an object collides with the eye and face with force, hitting the eye and disrupting the lens fibers). It is essential to avoid eye injuries and trauma as much as possible by taking appropriate measures like using protective eyewear such as glasses and eye shields when dealing with potentially hazardous situations.
The lens is the most radiosensitive structure of the eye. Radiation cataract is clouding of the lens resulting from damaged cells, covering the posterior (back) surface of the lens. Cell damage occurs due to over exposure to radiation. Ultraviolet rays from the sun and radiation treatment for cancer can cause radiation cataracts. Blurring of vision from radiation cataracts may occur 1 or 2 years following high radiation exposure and many years after exposure to low radiation doses .
Cataracts can be present at birth or may develop as a natural part of the ageing process. Age-related cataracts (nuclear cataracts, cortical cataracts and posterior subcapsular cataract) are known to develop faster and risk factors contributing to these types of cataracts are mentioned below.
Studies have found that smokers are twice as likely to develop cataracts as compared to those who do not smoke .
Studies indicate that cataract is about 4 times more common among people under the age of 65 who have diabetes . For people over the age of 65 with diabetes, cataracts are twice as prevalent than those with no diabetes . The longer the duration of someone suffering from diabetes and the poorer the control of their diabetes, the higher the risk of developing cataract.
Taking high doses of steroids for prolonged periods can cause posterior subcapsular cataracts to form.
According to the World Health Organization, 1 out of 5 cataracts could be prevented with proper eye protection or reduced exposure to direct sunlight.
Radiation treatment for cancer or other diseases can result in an earlier onset of cataract. Symptoms can either appear as early as 1 to 2 years following high doses of exposure or many years after exposure to lower doses.
Cataracts are not usually dangerous to eye health until they become completely white, referred to as overripe or hypermature cataract. This can cause an increase in eye pressure and present suddenly with redness, pain in the eye, and/or headaches, and will need to be removed.
When cataract initially develops, it may only affect a small part of the lens and symptoms may not be present or mild, if any. As the condition progresses, it clouds more of the lens and scatters the light passing through the lens, making symptoms more noticeable.
If you experience any of these signs and symptoms, schedule an appointment with an eye health professional to get your eyes checked. It is also important to note that the development of eye conditions may even start before symptoms appear, which makes going for regular and timely eye checks that much more essential.
Cataract is diagnosed by trained eye health professionals through a comprehensive eye health check. To allow for better and wider examination of the eye, drops are often used to dilate or widen the pupil (dark spot in the centre of the eye) and the eye health professional will then do a dilated eye exam. Dilation drops take about 30 minutes to effectively dilate the pupil for examination and will cause a temporary blurring of vision that resolves after about 4 to 6 hours.
After assessing the health of the eye, the eye health professional will then grade the cataract by following a grading scale which categorises the types of cataracts according to their severity. Grading scales differ between countries. When the cataract is deemed to be severe or causing a significant decrease in vision and ability to perform daily activities, the eye health professional will then recommend surgery.
Surgery is the only known treatment for cataract. It is where the surgeon removes the clouded lens and replaces it with a new, artificial lens, also known as an intraocular lens (IOL) that becomes a permanent part of the eye. Cataract surgery is performed as a day surgery and is usually performed with topical instead of general anaesthesia.
Most cataract surgeries are performed with a technique referred to as phacoemulsification, which removes the need for stiches. The procedure involves making a small incision on the cornea (transparent jelly like layer protecting the front of the eye). An instrument that vibrates is then introduced in the eye via this incision in a process called emulsification or softening of the lens. The clouded lens is then sucked out through the instrument and the capsule of the lens remains to receive the artificial lens implant or IOL. There are various types of IOLs available and after discussing your needs and expected visual outcome after surgery, the eye health professional will recommend the most suitable option accordingly.
Cataract surgery is known to improve the quality of life of patients by approximately 40% when performed in both eyes . 9 in 10 people report better vision after undergoing surgery to remove cataracts .
In the initial stages, before surgery is recommended, the following are some tips that can be useful for people with cataract:
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