NURSING CARE RELATED TO THE SENSORY AND
NEUROLOGICAL SYSTEMS
1-18
Section IV. DISORDERS OF THE EYE
1-18. VISUAL DEFECTS
a. Myopia. Also referred to as "nearsightedness", myopia is a refractive error caused by a structural defect of the eye.
(1) The eyeball is too long from front to back, causing light rays to focus in front of the retina rather than on it.
(2) Close objects can be seen more clearly than distant objects, which appear blurred and unfocused.
(3) Vision may be corrected with the use of a concave lens, which will cause the light rays to focus on the retina.
b. Hyperopia. Also known as hypermetropia and "farsightedness", hyperopia is a refractive error caused by a structural defect of the eye.
(1) The eyeball is too short from front to back, causing light rays to focus behind the retina rather than on it.
(2) Distant objects can be seen more clearly than those close up. Near objects are blurred and unfocused.
(3) Vision may be corrected with the use of a convex lens, which will cause the light rays to focus on the retina.
c. Presbyopia. Presbyopia is a refractive error caused by a decrease
in the power of accommodation of the crystalline lens, due to weakening of the ciliary muscles with aging.
(1) The near point of distinct vision becomes further from the eye. (This is why you may see someone reading while holding the reading material at arm's length.)
(2) Vision may be improved with the use of corrective lenses such as bifocals, which have a small lens for near vision placed within the lower half of a larger lens for distant vision.
d. Astigmatism. This is a refractive error caused by uneven curvature of the refractive surfaces of the eye.
(1) Light rays are not focused along equal planes because of the curvature, causing vision to be unfocused.
(2) Vision can be improved with the use of a lens called a cylinder lens, which compensates for the uneven curvature and allows the light rays to focus sharply.
e. Cataract. A cataract is an opacity of the crystalline lens or its capsule. It is the leading cause of blindness in the United States.
(1) Vision becomes distorted and/or unfocused. Bright lights produce a glare.
(2) Vision is improved by surgical removal of the opaque lens. The missing lens is compensated for by the use of special eyeglasses or contact lenses, or by intraocular implant
of an artificial lens.
f. Glaucoma. Glaucoma is a condition in which there is increased pressure within the eyeball. If uncorrected, glaucoma will lead to blindness.
(1) Increased pressure is caused by faulty drainage of aqueous fluid.
(2) Drug therapy is used to promote drainage of the aqueous fluid, or decrease the production rate of the aqueous fluid, or both.
(3) When drug therapy is not effective, surgical intervention is indicated. There are many different procedures used, but the objective of all is to decrease intraocular pressure by facilitating the filtration and drainage of the aqueous fluid.
