- A cataract is a clouding of the lens of the eye.
- Cataracts are prevalent, and most cataracts are a result of the aging process.
- Although many cataracts are not significant enough to require treatment, surgical removal of cataracts is usually safe and effective, resulting in improved vision.
- Cataract surgery should be performed when the cataract’s visual loss significantly impacts the individual patient’s lifestyle.
A cataract is an eye disease in which the eye’s clear lens becomes cloudy or opaque, causing a decrease in vision. Although the word cataract to describe this condition has been part of the English language since only the 15th century, the eye disease has been recognized and surgically treated since ancient times.
The lens is a portion of the eye that is usually clear. It focuses rays of light entering the eye onto the retina, the light-sensitive tissue at the back of the eye. To get a clear image onto the retina, the portions of the eye in front of the retina, including the lens, must be clear and transparent.
The light striking the retina initiates a chemical reaction within the retina. In turn, the chemical reaction creates an electrical response carried to the brain through the optic nerve. The brain then interprets what the eye sees.
In a normal eye, light passes through the transparent lens to the retina. The lens must be clear for the retina to receive a sharp image. Suppose the lens is cloudy from a cataract. In that case, the image striking the retina will be blurry or distorted, and the vision will be blurry. The extent of the visual disturbance is dependent upon the degree of cloudiness of the lens.
Most cataracts are related to aging. Cataracts are prevalent in older people. By age 80, more than half of all Americans have some degree of cataract or have already undergone cataract surgery in one or both eyes. By age 95, this percentage increases to almost 100%. A cataract can occur in either or both eyes. Individuals with a cataract in one eye usually go on to develop a cataract in the other eye. A cataract is not contagious and cannot spread from one eye to another or from person to person. Cataracts do not cause the eye to tear abnormally. They are neither painful nor make the eye itchy or red.
Although vision can be restored in most people with cataracts, age-related cataracts are still the most common cause of blindness globally, primarily because many third-world nations lack appropriate and available surgical services.
As life span increases in the developed world due to modern technology and new treatment methods of acute and chronic disease, age-related cataracts will continue to increase.
Different types of Cataracts
Cataracts can be classified by anatomical location within the lens, degree of clouding of the lens, or the cataract’s cause.
The lens of the human eye is shaped and sized similar to an M&M candy. It has a front (anterior) part and a back (posterior) part. The lens’s central portion is called the lens nucleus, and the outer portion is called the lens capsule. Between the inner nucleus and the outer capsule is a part of the lens called the cortex.
Clouding of the lens can occur only in the nucleus, in which case the term “nuclear cataract” or “nuclear sclerosis” is used. If the clouding occurs in the lens cortex only, the cataract is termed a “cortical cataract.” If the lens’s loss of clarity is primarily in or adjacent to the capsule, the term “subcapsular cataract” is used.
The clouding location can also be defined as being anterior or posterior, central, or peripheral. Often the clouding of the lens may affect multiple portions of the lens. The most common type of cataract related to age is sometimes termed a “senile cataract.” This type of cataract primarily involves the nucleus of the lens. Cataracts that develop in the posterior subcapsular area (in the rear region of the lens capsule) are known as posterior subcapsular cataracts and are more common in younger age groups.
Any degree of loss of the normal transparency of the lens is called a cataract. The cloudier the lens, the more advanced the degree of cataract. A cataract may be mild, moderate, or severe. It may be early or advanced. If the lens is opaque, it is termed a “mature” cataract. Any cataract that is not opaque is therefore termed an “immature” cataract. Most mature cataracts are white in color.
Risk Factors for Cataracts
Advanced age is a significant risk factor for the development of cataracts. Family history for early development of cataracts, diabetes, tobacco use, and prolonged exposure to sunlight are also risk factors, as is trauma to the eye.
Causes of Cataracts
The lens is made of mostly water and protein. The protein is arranged in a specific way that keeps the lens clear and allows light to pass through it to focus a clear image onto the retinal surface. Some of the protein may clump together and start to cloud a small lens area as we age. This is our understanding of the cause of age-related cataract. Over time, the cataract may become denser or cover more lens areas, making it more difficult to see through. A cataract is not a growth or tumor.
There are many other causes of cataracts beyond advancing age. Whatever the reason, all cataracts result from similar changes to the protein of the lens, similarly resulting in visual blurring or visual loss.
Blunt or penetrating injury to the eye may result in cataract, either immediately after the injury or some weeks to years afterward. A cataract following an injury may appear and then not increase in density (be stationary) or be progressive. Eye surgery for other conditions can also cause cataracts. Excessive exposure to ionizing radiation (X-ray), infrared radiation (as in glass blowers), or ultraviolet radiation may also cause cataracts.
Diabetes is associated with the development of cataracts. Inflammatory disease of the eye, such as iritis or uveitis, may cause or accelerate cataract development in the involved eye.
Many genetic illnesses are associated with the development of cataracts. These include myotonic dystrophy, galactosemia, homocystinuria, Wilson’s disease, Down syndrome, and many others. Congenital infections with herpes simplex, rubella, toxoplasmosis, syphilis, and cytomegalic inclusion disease may also result in cataracts.
When taken over a long time, many medications can cause secondary cataracts. The most common of these are oral corticosteroids, such as prednisone, currently used for various medical conditions.
The term “congenital cataract” is used when a baby is born with any lens clouding. This may be present in one or both eyes, be stationary or be progressive. Causes include genetic disorders or infectious or non-infectious intrauterine developmental disorders, both often associated with the baby’s other physical abnormalities.
Atopic dermatitis, other skin and mucous membranes, hypothyroidism, and hyperparathyroidism are associated with cataracts’ early development.
Patients who develop cataracts in both eyes at an early age often have family members who have also developed cataracts prematurely, implying a genetic cause, even in the absence of a recognized underlying disease.
Symptoms of Cataracts
You may not notice any symptoms with early cataracts. As a cataract becomes more advanced, a decrease in vision clarity, not fully correctable with glasses, is noticed. There is a loss of contrast sensitivity so that shadows and color vision are less vivid. Disturbing glare may be noted as light is into the eye scattered by the cataract. Haloes may be observed around lights. Night vision will be diminished.
In certain types of cataracts, double vision may be noted in the affected eye. Some patients report that they require frequent changes in their eyeglass or contact lens prescriptions and may be aware that their near vision improves as their distance vision declines.
A cataract does not routinely cause discomfort or pain in the eye or alter the eye’s external appearance.
Family members of a person affected by cataracts in both eyes may notice that they appear not to see as well as before. The eye will appear normal to the untrained observer unless the cataract is mature and white. In that situation, the eye’s pupil, which typically appears black, will look grey or white to the observer.
The examining physician will find diminished visual acuity in the affected eye or eyes. A change in the glasses does not seem entirely correct for this vision loss. An ophthalmologist can quickly examine the lens of the eye. The lens characteristics of cataracts can be seen using a slit lamp, an illuminating and magnifying device used to painlessly inspect the structures within the eye’s front, including the lens.
The standard cataract surgical procedure is performed in a hospital or an outpatient surgery center. There is no overnight stay at the facility. The most common form of cataract surgery today involves a process called phacoemulsification. After numbing the eye with drops or an injection, your surgeon will make a minimal incision in the eye’s surface in or near the cornea with the use of an operating microscope. A thin ultrasound probe, often confused with a laser by patients, is inserted into the eye and uses high-ultrasonic vibrations to break up (phacoemulsify) the clouded lens. These tiny fragmented pieces are then suctioned out of the eye using the same ultrasound probe. Once the cataract is removed, an artificial lens is placed into the thin capsular bag that the cataract previously occupied. This lens is essential to help your eye focus after surgery.