Astigmatism is a condition in which either the cornea or the lens of the eye has an abnormal curvature, causing out-of-focus vision. Astigmatism is a common refractive error in which a person cannot see objects with complete clarity. In some cases the person can see vertical lines more clearly than horizontal lines; this is called with-the-rule astigmatism. In other cases the person can see horizontal lines clearly while vertical lines look blurred; this is called against-the-rule astigmatism. Children are more likely to have with-the-rule astigmatism while adults are more likely to have against-the-rule astigmatism.
Astigmatism is a very common visual defect. It often exists together with nearsightedness (myopia) or farsightedness (hyperopia). It is estimated that as many as a third of the general American population has some degree of astigmatism. Mild astigmatism is considered normal and may not require corrective lenses. Astigmatism is equally common in men and women and in all races and ethnic groups.
Nursing Care Plan Signs and Symptoms
The exact cause of astigmatism is not known; it is usually present from birth. In a few cases, astigmatism may result from an injury to the eye or from keratoconus, an eye disorder that causes the tissue of the cornea to become thinner over time. In an astigmatic eye, the irregularly shaped cornea or lens prevents light from focusing properly on the retina, the light-sensitive tissue layer that lines the back of the eye. When the cornea is irregularly curved, the eye focuses light on two different points inside the eye rather than one. If the person is nearsighted, one of the two focal points will lie in front of the retina; if the person is farsighted, the second focal point will lie behind the retina. In simple astigmatism, one of the two focal points will lie on the retina itself. If the person has compound myopic astigmatism, however, both focal points lie in front of the retina. Similarly, in compound hyperopic astigmatism, both focal points lie behind the retina.
A few people have what is called mixed astigmatism, in which one focal point falls in front of the retina and the other behind it. The basic symptom of astigmatism is that objects look blurred at any distance. People who are severely astigmatic may also develop headaches, eye strain, and fatigue along with blurring of vertical, diagonal, or horizontal lines if their refractive error is not corrected.
Nursing Care Plan Diagnosis
Astigmatism and other refractive errors are evaluated by a series of vision tests. After the examiner takes a history of the patient’s symptoms (including a family history of eye problems), the patient is usually asked to read the letters on an eye chart known as a Snellen chart. The examiner may also shine lights into the eyes or administer eye drops that allow him or her to see all the structures inside the eye clearly. examination allows the doctor to evaluate the patient for nearsightedness or farsightedness.
To determine the degree of astigmatism, the examiner will use a keratometer, a device that measures the curvature of the cornea. The examiner will measure the steepest and flattest curves on the cornea. Another technique that can be used to evaluate astigmatism is called corneal topography and uses a device called a videokeratoscope. The keratoscope part of the machine projects rings of light onto the cornea while the examiner studies the pattern of the reflected light and records it with a video camera. Corneal topography provides a more detailed picture of the shape of the patient’s cornea and can be used to determine the proper fit for contact lenses.
Nursing Care Plan Treatment
Mild astigmatism may not need corrective treatment. A person should see their eye doctor, however, if they are developing headaches or eye strain, or if blurry vision is interfering with daily activities.
People whose astigmatism is severe enough to require correction have several options:
• Eyeglasses. These can be used to correct astigmatism caused by uneven curvature of the lens as well as the cornea. Eyeglasses are prescribed by an optometrist or ophthalmologist but made and fitted by an optician.
• Hard contact lenses. These usually provide more effective correction of astigmatism than soft contact lenses.
• Orthokeratology (Ortho-K). This is a procedure in which the person wears hard contact lenses for several hours overnight in order to gradually correct the curvature of the cornea. The lenses are removed during the day. Ortho-K is also referred to as corneal molding. It does not permanently improve vision; if the patient stops wearing the retainer lenses, their vision may return to its original condition.
• Laser surgery. An ophthalmologist can use lasers to reshape the cornea either by making a flap in the surface of the cornea and reshaping the tissue of the cornea under the flap, or by completely removing the upper layer of tissue in the cornea before reshaping the lower layers of tissue. There are drawbacks to surgical correction of refractive errors, however. These include the risks of infection, development of haze in the cornea, or dry eyes. In some cases the surgeon may need to perform a second operation if the first one either overcorrected or undercorrected
the shape of the patient’s cornea. It is important for a patient with astigmatism to discuss all the treatment options with the optometrist or ophthalmologist, as no two people will have exactly the same degree of visual blurring or the same lifestyle.
Nursing Care Plan Prognosis
Astigmatism may either improve over time or grow worse; it also changes from with-the-rule astigmatism in childhood to against-the-rule astigmatism in adulthood in some people. Most people with astigmatism who need corrective lenses or other types of treatment, however, do very well. About 20 percent of people with keratoconus, however, will eventually need a corneal transplant.
Nursing Care Plan Prevention
Astigmatism is largely a matter of heredity and cannot be prevented. People can, however, live comfortably with it by visual screening in childhood, regular eye checkups at all ages, and wearing corrective lenses if necessary.
The Future
Astigmatism is such a common refractive error in the general population that it is not likely to disappear in the near future. It is possible that the present variety of treatment options will be improved or expanded by further research.
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