By Jordana M. Smith
Cataracts are one of the most well-known ailments that affect the eye. Approximately 20.5 million Americans carry this diagnosis, and an estimated 2.5 million surgeries per year are performed to correct this condition. Worldwide, this condition afflicts 48 percent, or approximately 18 million people of the world's blind, making it the leading cause of preventable blindness. Studies from the 1990s estimate that almost 40 percent of men and 45 percent of women aged 74 years and older suffer from cataracts that significantly impair their vision.
The human eye has two main components, the cornea and the lens, that allow light to enter the eye unchanged so that it may be processed into crisp colors and sharp contours. Cataract is a condition where a normally clear lens becomes cloudy and thus produces a distorted picture. A common comparison is with a window that has been frosted. Manifestations include blurry vision, difficulty with night vision or glare, diminished color perception and double vision.
Cataract types are classified as nuclear, cortical and posterior subcapsular. In nuclear cataracts, the opacification occurs in the center part of the lens and with time, the lens may change color from opaque white to yellow or even brown. Cortical cataracts begin on the outermost edges of the lens and extend in towards the center in a pattern of "spokes," similar to the wheels on a bicycle. Posterior subcapsular cataracts form on the backmost portion of the lens, much like ivy may cover the outside wall of a house. The different types are important as symptoms from each may differ significantly. Nuclear cataracts tend to distort distance vision whereas posterior subcapsular cataracts tend to distort near vision. Cortical cataracts manifest mainly as difficulty with glare, from sunlight or oncoming headlights during nighttime driving.
The most prevalent type is age-related cataract. This type of cataract tends to develop over years as the lens hardens and slowly builds up protein deposits. Although the exact cause of age-related cataract development is not known, an estimated 30-50 percent of risk is due to genes. Cataracts also can be caused by therapy with certain drugs, including corticosteroids, phenothiazines, amiodarone and anticholinesterases. Traumatic damage to the lens through physical force or direct injury also can cause cataract formation. Blunt and penetrating trauma, including certain surgical procedures, can cause opacification at the site of injury and may even extend throughout the entire lens. Other traumatic forces to the eye include radiation, ultraviolet light and chemical injuries. The last major category includes cataract caused by diseases such as diabetes, Wilson's disease and myotonic dystrophy.
Initially, cataracts may be treated with prescription glasses if vision is minimally blurred. However, when vision becomes significantly impaired or affects the performance of enjoyable activities, definitive treatment, surgery, is recommended. Surgery is performed on an outpatient basis, and typical procedure length is 20 minutes. Patients are made comfortable with mild sedation and topical anesthetic eye drops. A small incision is made at the edge of the clear part of the eye to allow access to the lens. A small instrument is introduced and utilizes ultrasonic technology to break apart the cataract and suction the lens from the eye. Then, the lens implant is placed at the same location as the previous natural lens. Typically patients are then given ointment and a temporary shield to protect the eye and, after observation, are allowed to return home.
Vision typically returns to pre-cataract clarity within 48 hours of surgery. Patients are followed by the surgeon to ensure continuing good position of the lens implant and proper healing.
Jordana M. Smith is a resident in the department of ophthalmology, Penn State Hershey Eye Center at Penn State Milton S. Hershey Medical Center.