The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017
The term “cataract” is used to describe a condition when the lens of the eye becomes opaque over time, often resulting in decreased visual acuity and overall visual function, which commonly results in increased falls, difficulty reading, difficulty driving, or decreased night vision. In most cases, the cataract (lens of the eye) can be removed using minimally invasive surgery and replaced with a new artificial lens that is inserted below the cornea of the eye, providing increased visual acuity postoperatively.
Types of Cataracts
There are two primary categories of cataracts. They are defined by (1) their location and (2) their point of origin.
Cataracts Defined by Location
Nuclear sclerotic cataracts are the most common type and are based on age. They often develop very gradually, resulting in the lens becoming more yellow in color and much more rigid in consistency. What is unique about nuclear sclerotic cataracts is that a patient’s near vision may actually improve for a period of time before all vision becomes more difficult. Cortical cataracts usually present as a cloudiness or opaqueness in the cortical region (outer ring) of the lens. They tend to have a “wheel” appearance with spokes that project from the outer portion of the lens to the center, causing light to refract or scatter as it enters the eye and resulting in impaired vision. Posterior subcapsular cataracts occur when the opacity or cloudiness of the lens develops on the back side of the lens, which results in increased sensitivity to light, decreased near vision, and haloing of light.
Cataracts Defined by Their Point of Origin
These types of cataracts include (1) age-related cataracts, which start to develop as a function of aging, often beginning at age 40, but not really becoming significant until after age 70; (2) secondary cataracts, which are frequently a secondary effect of surgery for some other type of eye pathology, most commonly after surgery to release intraocular pressure associated with glaucoma or in patients who are on steroids for an extended period of time; and (3) traumatic cataracts, which can develop as a result of direct trauma to the eye. These types of cataracts can develop either very shortly after an injury or, more often, develop many years after an injury, probably in association with aging. In addition to direct trauma, exposure to chemicals or other caustic agents can also cause rather immediate cataracts.
There are a number of health and environmental factors that often result in the development and onset of cataracts or that can increase the severity of cataracts. Individuals with long-term diabetes mellitus are thought to have an increased risk of developing cataracts due to the buildup of sorbitol, a sugar that is a breakdown product of glucose. The exact mechanism of how this might work is not well understood. Smoking and the long-term use of alcohol have also been shown to increase a person’s risk for cataracts. In fact, both males and females who are heavy smokers double their risk of developing cataracts. This is thought to be due to the increased number of free radicals that can be found in the circulating blood of smokers. Smokers also experience a decrease in oxygen flow to the cornea and lens of the eye, resulting in a decrease in the turnover of nutrients necessary for proper function of the eye. Third, long-term use of corticosteroids is also being looked at closely now as a potential cause of cataracts. In fact, a recent study showed that individuals with asthma who have a history of long-term use of inhaled corticosteroids have a 90 percent greater risk for developing cataracts than nonasthmatics. Lastly and probably the most common cause of cataracts is overexposure or prolonged exposure to bright sunlight, which exposes the lens of the eye to high doses of ultraviolet light.
Treatment for cataracts can be either nonsurgical or surgical in nature. Nonsurgical treatment is an option with the very early onset of cataracts. These treatments include using various types of corrective lenses to decrease light intensity, or the use of high-intensity reading lamps and other behavioral activities. It also includes trying to decrease or eliminate the factors that might be contributing to the onset of cataracts.
There are two primary surgical treatments. The first and most common procedure used today is called phacoemulsification, in which sound waves (ultrasound) are used to break up the lens of the eye, and then the debris is simply removed from the eye capsule. The removed lens is then replaced with an artificial lens, which often gives a patient nearly normal vision. The second surgical procedure uses an extracapsular approach: the lens is removed from the eye as a single entity. It is not broken up by chemical or ultrasound procedures. This procedure has more risk involved due to the larger incision that needs to be made to remove the lens.
Charles A. Ferguson
See also: Blindness; Visual Fields; Visual System
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Neale, Rachel E., Jennifer L. Purdie, Lawrence W. Hirst, & Adele C. Green. (2003). Sun exposure as a risk factor for nuclear cataract. Epidemiology, 14(6), 707—712.