Home > Encyclopedia of Nursing & Allied Health > Cataracts

Definition

The lens of the eye is normally transparent. A cataract is a condition in which the lens of the eye becomes cloudy or opaque. This cloudiness can impair vision and may lead to eventual blindness.

Description

The human eye has several parts. The outer layer of the eyeball consists of a transparent dome-shaped cornea and an opaque, white sclera. The cornea and sclera help protect the eye. The next layer includes the iris, pupil, and ciliary body. The iris is the colored part of the eye and the pupil is the small, dark, round hole in the center of the iris. The pupil is primarily responsible for allowing light into the eye. The ciliary body contains muscles that help the eye focus. The lens, which lies behind the pupil and iris, is covered by a cellophane-like capsule. It is normally transparent, elliptical in shape, and somewhat elastic. Due to this elasticity, the lens can focus on both near and far objects. The lens is attached to the ciliary body by fibers (zonules of Zinn). Muscles in the ciliary body act on the zonules, which then change the shape of the lens. This process is called accommodation—the lens focuses images to help make vision clear. As people age, the lens hardens and changes shape less easily. As a result, accommodation becomes more difficult, making it harder to see things up close. This normal aging condition, called presbyopia, generally occurs around age 40 and continues until about age 65. Individuals with this condition generally need reading glasses.

The lens is made up of approximately 35% protein and 65% water. As people age, degenerative changes in the lens's proteins occur. Changes in the proteins, water content, enzymes, and other chemicals are some of the reasons for the formation of a cataract.

The major areas of the lens are the nucleus, the cortex, and the capsule. The nucleus is in the center of the lens, the cortex surrounds the nucleus, and the capsule is the outer layer. Opacities can occur in any area of the lens, and cataracts can be classified according to their location (nuclear, cortical, or posterior subcapular cataracts). The density and location of the cataract determines the amount of vision affected. If the cataract forms in the area of the lens directly behind the pupil, vision may be significantly impaired. A cataract that occurs on the outer edges or side of the lens causes less visual impairment.

Cataracts in the elderly are so common that they are thought to be a normal part of aging. Cataracts affect about 50% of individuals between the ages of 52-64, while at least 70% of those 70 and older are affected. Cataracts associated with aging (senile or age-related cataracts) are usually bilateral (occur in both eyes) with asymmetric progression (different rates of progression). Initially, cataracts may not affect vision. If the cataract remains small or at the periphery of the lens, the visual changes may be minor.

Cataracts are much less common in younger people. Congenital cataracts are rare in newborns. When they do occur, they may be due to genetic defects or an infection or disease in the mother during pregnancy. Traumatic cataracts may develop after a foreign body or trauma injures the lens or the eye. Systemic illnesses, such as diabetes, also may result in cataracts. Cataracts can occur secondary to other eye diseases—for example, uveitis or glaucoma. Such cataracts are called complicated cataracts. Toxic cataracts result from chemical toxicity, such as steroid use. Cataracts also can result from exposure to the sun's ultraviolet (UV) rays.

Causes and symptoms

Recent studies have investigated the effect of nutrition on cataract formation. The results have been mixed, with some studies finding that there is a connection between nutrition and cataract formation and other studies finding none. Much interest has been focused on the use of antioxidant supplements as a protection against cataracts. Antioxidants, such as vitamins A, C, E, and beta-carotene, help the body neutralize oxygen-free radicals.

Smoking and alcohol intake, however, have been implicated in cataract formation, as have the use of oral corticosteriods and antihypertensive agents. Some studies have determined that a diet high in fat increases the likelihood of cataract formation, while an increase in foods rich in antioxidants reduces the incidence. More research is needed to determine the precise role played by diet, smoking, alcohol consumption, and antioxidants in the formation of cataracts.

Some unrelated physical conditions, such as diabetes mellitus, also may contribute to cataracts. Eye injuries and sun exposure also are causative factors.

There are several common symptoms of cataracts:

• gradual, painless onset of blurry, filmy, or fuzzy vision
• poor central vision
• frequent changes in eyeglass prescriptions
• changes in color vision
• increased glare from lights, especially oncoming headlights when driving at night
• "second sight" improvement in near vision (no longer needing reading glasses)
• poor vision in sunlight
• presence of a milky whiteness in the pupil as the cataract progresses

Diagnosis

Ophthalmologists and optometrists detect and monitor cataract growth and prescribe prescription lenses for visual deficits. Ophthalmologist perform cataract extraction.

Cataract diagnosis begins with a complete eye exam. The ophthalmic assistant, technician, or nurse gathers information to determine the progression of the vision loss. It is unusual for cataracts to cause rapid vision loss, but sometimes patients believe the vision problem is acute because vision in the better eye has only recently been compromised. Patient history includes a review of refractive history, previous ocular disease, ambylopia, eye surgery, and trauma. Ophthalmic personnel also question patients about difficulties driving, reading, and performing daily activities, and record any medication the patient currently uses.

The ocular exam determines the severity of the cataract and assesses other factors that might contribute to the potential for good vision after surgery. The exam includes measurement of visual acuity under both low and high illumination, biomicroscopy with pupillary dilation, stereoscopic fundus examination with pupillary dilation, assessment of ocular motility and binocularity, visual fields, evaluation of pupillary responses, refraction, and measurement of intraocular pressure (IOP).

Treatment

No treatment may be necessary for cataracts that cause no symptoms or that cause only minor visual changes. It is important for an ophthalmologist or optometrist to continue to monitor and assess the cataract during regular office visits. Increased strength in prescription eyeglasses or contact lenses may be diagnostic and beneficial.

Cataract surgery—the only option for patients whose cataracts interfere with vision to the extent that their daily activities are affected—is the most frequently performed surgery in the United States. It generally improves vision in more than 90% of patients. Most cataracts are removed before the lens is completely opaque or mature. This is done to minimize the impact of

the cataract on the patient's daily life and also to decrease the risk of other eye complications. Sometimes cataracts need to be removed so the surgeon can examine the back of the eye more carefully. This is important in patients with diseases that may affect the eye. If cataracts are present in both eyes, surgery is performed on one eye at a time. The first eye heals before the second cataract is removed, sometimes as soon as the following week. A final eyeglass prescription is usually given about four to six weeks after surgery. Patients will still need reading glasses. The overall health of the patient must be considered in making the decision to have undergo cataract surgery. However, age alone need not preclude effective surgical treatment of cataracts, and people in their 90s can have successful return of vision after cataract surgery.

Surgery to remove cataracts is generally an outpatient procedure. A local anesthetic is used, and some newer techniques take only minutes to complete. Removal of the cloudy lens can be accomplished with one of the three types of cataract surgery available:

• Extracapsular cataract extraction. In this type of cataract extraction, the lens and the front portion of the capsule are removed. The back part of the capsule remains in place.
• Extracapsular cataract extraction by phacoemulsification. This type of extracapsular extraction requires only a very small incision, resulting in faster healing. Ultrasonic vibration is applied to the lens to break it up into very small pieces, and the ophthalmologist then aspirates the pieces out of the eye with suction. As of 2001, this is the most commonly performed type of cataract surgery.
• Intracapsular cataract extraction. The lens and the entire capsule are removed. This method carries an increased risk for detachment of the retina and swelling after surgery, and, as a result, it is rarely used.

A replacement lens is inserted at the time of the surgery. A plastic artificial lens called an intraocular lens (IOL) is placed in the remaining posterior lens capsule of the eye. When the intracapsular extraction method is used, an IOL may be clipped onto the iris. Contact lenses and cataract glasses (aphakic lenses) are prescribed if an IOL cannot be inserted due to complications. A folding IOL is used with the phacoemulsification procedure to allow it to pass through the small incision.

Antibiotic drops to prevent infection and steroids to reduce inflammation are prescribed after surgery. An eye shield or glasses protect the eye from injury while it heals. During the night, an eye shield is worn. The patient returns to the doctor the day after surgery for assessment, with several follow-up visits over the next two months to monitor the healing process. Return visits at three and six months are optional.

Prognosis

The cataract extraction success rate is very high with a good prognosis. A visual acuity of 20/40 or better is expected as a result of cataract extraction. If an extracapsular cataract extraction was performed, a secondary cataract may develop in the remaining back portion of the capsule. This can occur one to two years after surgery. YAG capsulotomy is most often used for this type of cataract. YAG stands for yttrium aluminum garnet, the name of the laser used for this procedure. This is a painless outpatient procedure and requires no incision. The laser beam makes a small opening in the remaining back part of the capsule, allowing light through.

Complications occur in a very small percentage (3-5%) of surgical cataract extractions. Possible complications include infections, corneal edema (swelling), diplopia, bleeding, retinal detachment, iris prolapse or vitreous in the wound, intraocular lens dislocation, and the onset of glaucoma. Some problems may occur one to two days, or even several weeks, after surgery. Follow-up examinations should check the patient for haziness or redness in the eye, decrease in vision, nausea, and pain.

Health care team roles

Skilled ophthalmic technicians and assistants record the patient history and perform many of the preliminary tests. Depending on skill level, these ophthalmic assistants may perform measurement of visual acuity under both low and high illumination, biomicroscopy with pupillary dilation, assessment of ocular motility and binocularity, visual fields, evaluation of pupillary responses to rule out afferent pupillary defects, refraction, and measurement of intraocular pressure (IOP).

Before the surgery, nurses and assistants also prepare the operating room (OR). Many ophthalmologists now have their own ambulatory surgery centers (ASCs) where skilled technicians and ophthalmic nurses play a critical role in preparing the OR and patients for the surgery. Ophthalmic nurses also assist the ophthalmologist during surgery and discuss outcomes with patients postoperatively.

Patient education

When a cataract is found, the patient should be informed, even if surgery is not immediately indicated. The optometrist or ophthalmologist should discuss the different treatment options, as well as the risks and benefits of surgery with the patient.

Prevention

The eyes should be protected from UV radiation by wearing glasses with a special coating. Dark lenses alone are not sufficient, but the lenses must be coated to filter out UV light (specifically, UV-A and UV-B). Antioxidants also may help prevent cataracts by reducing free radicals that can damage lens proteins. A healthy diet rich in sources of antioxidants, including citrus fruits, sweet potatoes, carrots, green leafy vegetables, and/or vitamin supplements, may be beneficial. When taking certain medications, such as steroids, more frequent eye exams may be necessary. Patients should also be told not to smoke.

---

KEY TERMS

---

Glaucoma—Disease of the eye characterized by increased pressure of the fluid inside the eye. Untreated, glaucoma can lead to blindness.

Ultraviolet radiation (UV)—Invisible light rays that may be responsible for sunburns, skin cancers, and cataract formation.

Uveitis—Inflammation of the uvea. The uvea is a continuous layer of tissue which consists of the iris, the ciliary body, and the choroid. The uvea lies between the retina and sclera.

---

Mary Bekker