Any opacity in the lens of the eyes is called a cataract. It is a common cause of visual impairment, especially in the elderly. It results in visual impairment. On clinical examination, it appears as white opacity in the pupils. The density of the opacity depends on the severity of the cataract.
How does cataract occur?
The mechanism of occurrence of cataracts is not understood completely. A normal lens is made of protein fibers arranged in such a fashion that light rays pass through without being affected. In certain diseases, there is an alteration in the protein structure which results in the scattering of light. This reduces the lens transparency. Some protein alterations result in yellow or brown discoloration. On microscopic examination, fluid-filled vesicles have been noticed between the lens fibers. These changes are related to free radical-induced oxidative damage, the effect of ultraviolet rays, and malnutrition. Once a change occurs in the lens fibers, no amount of medical treatment can reverse those chemical changes of cataract formation.
What are the causes of cataract?
The commonest cause of cataracts is old age. Aging brings about degenerative changes in proteins which result in the appearance of lens opacities. Scientific studies have shown that the prevalence of cataract is 50% in people aged 65 and reaches nearly 70% in those above 75 years of age. The other risk factors or causes include direct trauma, toxic chemicals, smoking, hereditary factors, and diabetes mellitus.
What are the types of cataract?
A cataract is classified into two types depending on the opacity of the lens. A mature cataract is one in which the whole lens is opaque. The immature cataract has areas of opacity with the remaining transparent lens. Sometimes the proteins liquefy and leak out of their capsule. The resulting shrunken lens results in hyper mature cataract. The various types of cataract depending on their cause are discussed below.
Age-related cataract
After middle age, the central part of the lens called the nucleus becomes harder and is called a nuclear cataract. In these patients, the near vision improves due to an increase in the focusing power of the central area of the lens. These patients usually remain asymptomatic. Some patients develop opacities in the outer layers of the lens called the cortex. This is due to increased hydration of lens proteins which results in their separation and an alteration of vision. This is called a cortical cataract. Age-related cataract progresses slowly and usually, surgery is not required. When indicated, surgery for extraction of lens improves vision dramatically.
Traumatic Cataract
Traumatic cataract occurs due to a blow to the eyeball where the lens is damaged or displaced. There may be a foreign body stuck inside the lens. Some of the common causes include injuries from fireworks, air rifle pellets, rocks, arrows, exposure to heat or x-rays. Most of these injuries are preventable. Simple use of protective glasses saves many eyes. Any injury to the lens capsule results in the entry of fluid (aqueous or vitreous) between the lens fibers. The lens becomes white very soon associated with pain and visual impairment.
Complicated Cataract
A cataract due to another eye disease is called a complicated cataract. It results in a complication of the intraocular disease. Conditions like uveitis, glaucoma, retinitis pigmentosa, and retinal detachment result in cataract formation. These cataracts usually affect one eye and deterioration of vision occurs. The recovery of vision is poor if at all it occurs.
Cataract Associated with Systemic Disease
Cataract in both eyes occurs in many diseases like diabetes mellitus, hypocalcemia due to any cause, allergic dermatitis, galactosemia, and Down syndromes.
Drug-Induced Cataract
Prolonged use of steroids, whether systemic or instillation of eye drops can result in cataract. Other drugs which may cause this condition include phenothiazines, amiodarone, and phosphocholine iodide eye drops.
A cataract is a common disorder of the aged. It may occur early in certain occupations or due to the causes discussed above. Reduction in visual acuity affects the quality of life, hence one should take precautions to avoid trauma or exposure to harmful agents.
