Chapter 9 The senses Pathophysiologic Concepts Amblyopia The loss of visual acuity in an eye that appears to be structurally intact is known as amblyopia. With amblyopia, the central nervous system becomes unable to identify visual stimuli; that is, the signals are sent from the eye but are not recognized in the brain. Strabismus The condition called strabismus is a deviation in the position of the eyes relative to each other. With strabismus, the eyes may appear to be crossed. An individual who has strabismus often complains of double vision.

Nystagmus The involuntary, rhythmic movement of one or both eyes is called nystagmus. The movement may be jerking, rotating, or pendular. Myopia Myopia, also called nearsightedness, occurs when the eye is unable to accommodate sufficiently to objects that are far away. Myopia may result from developmental elongation of the eyeball that causes the image to be focused in front of the retina. Hyperopia Hyperopia, also called farsightedness, occurs when the eye is unable to accommodate sufficiently to close objects, causing the object to be focused past the retina. Hyperopia may be present early in life or may develop later, typically after the fourth decade of life (presbyopia).

Astigmatism In astigmatism, light rays are scattered rather than focused on the retina because of an asymmetric curvature of the cornea. The image is distorted or blurred. Astigmatism may occur with myopia or hyperopia. Papilledema Papilledema is the swelling of the optic disk where the optic nerve leaves the eye and enters the brain. Because the optic disk is in communication with the brain, papilledema can occur in any condition that causes severely increased intracranial pressure. Such conditions may include brain tumor, infection, or injury. Papilledema is often an important diagnostic clue in severe brain pathology.

Conductive Hearing Loss Conductive hearing loss is a decrease in hearing caused by a blockage in the conduction of sound waves in the external or middle ear. Conductive hearing loss may be caused by: -foreign object is present in the ear -an excessive wax or fluid buildup in the external or middle ear. -middle-ear infections (otitis media). *A hearing aid may offer improvement. Sensorineural Hearing Loss Sensorineural hearing loss is a decrease in hearing caused by dysfunction of the organ of Corti, the auditory nerve, or the brain.

Tinnitus Described as a ringing in one or both ears.tinnitus may accompany: - ear wax buildup or presbycusis. -aspirin overdose -middle-ear infection, or - otosclerosis (irregular ossification of middle-ear bones). Vertigo The sensation of motion or spinning, or feeling of being off balance. Vertigo is sometimes accompanied by nausea, weakness, and mental confusion. Inner-ear inflammation, especially of the semicircular canals, is the most common cause of vertigo..

Conditions of Disease or Injury Conjunctivitis Is inflammation of the conjunctiva of the eye. Causes :infectious process, physical irritation, an allergic response -The conjunctiva becomes red, swollen, and tender. -Conjunctivitis stemming from a bacterial infection is sometimes called pink eye. Cataracts Is a progressive loss in the transparency of the lens. The lens becomes cloudy or gray-white in color, and visual acuity is reduced. Cataracts occur when proteins in the normally transparent lens break down and coagulate on the lens.

Glaucoma Glaucoma is a condition of the eye usually caused by an abnormal increase in intraocular pressure (to greater than 20 mm Hg). The high pressures, sometimes reaching 60 to 70 mm Hg, cause compression of the optic nerve as it leaves the eyeball, leading to death of the nerve fibers. Otitis Otitis is an inflammation of the ear. Inflammation may be of the external ear canal, called otitis externa, or of the middle ear, called otitis media.