Disorders of the Eyes and Ears (BIO 181-201)

a refraction abnormality in which either the cornea of the lens has an irregular curve. As a result, parts of the image are cut out of focus and vision is blurred or distorted.

A loss of transparency of the lens. Lens becomes cloudy due to changes in the structure of the lens proteins. Occur with aging but also by injury, excessive exposure to ultraviolet rays, medications, disease (diabetes) and smoking.

A abnormally high intraocular pressure due to buildup of aqueous humor within the anterior cavity. Fluid compresses the lens into the vitreous body and puts pressure on the neurons of the retina. Persistent pressure results in a progression from mild visual impairment to irreversible destruction of neurons of the retina, damage to the optic nerve and blindness. It is the most common cause of blindness.

Farsightedness (hypermetropia). A refraction disorder. Eyeball length is short relative to the focusing power of the lens and cornea. Lens may be too thin. In either case, the image conveys BEHIND the retina. People with hyperopia can see distant objects clearly, but not close objects.

Nearsightedness. A refraction abnormailty in which the eyeball is too long relative to the focusing power of the cornea and lens. Lens may be too thick. So the image converges in front of the retina. People with myopia can see close objects clearly but not distant objects.

Due to prolonged vitamin A deficiency. Results in subnormal amount of rhodopsin and the inability to see well at low lights.

The site where CN II exits the eyeball

a degenerative disorder of the retina in the region of the macular lutea. Since the macula lutea is the site of acute vision, individuals with the disease retain their peripheral vision but lost the ability to see straight ahead. Usually begins around age 50 and is more common in smokers.

a rapid involuntary movement of the eyeballs possibly due to CNS disease. It is also associated with vertigo.

A sensation of spinning or movement in which the world seems to revolve or person revolves in space. Associated with nausea or vomiting. May be caused by cervical arthritis, infection of the vestibular apparatus or chemical exposure.

Results from an increased amount of endolymph that enlarges the membranous labyrinth, or high pressure ruptures the membranous labyrinth and mixes the endolymph and perilymph. Receptors are highly stimulated. Among the symptoms are fluctuating and hearing loss (distortion of the basilar membrane) and roaring tinnitus (ringing), spinning or whirling vertigo (dizziness).

Caused by impairment of the hair cells in the cochlea or damage to the cochlear branch of CN VIII. May be caused by atherosclerosis, repeated loud noise, certain drugs (aspirin, streptomycin).

Caused by impairment of the external and middle ear mechanisms for transmitting sound to the cochlea. Causes are: otosclerosis, thickening of the eardrum, injury to the eardrum, impacted cerumen, and aging.

Used to distinguish between conduction and sensorineural deafness. Stem of vibrating tuning fork is held to the center of the forehead. In individuals with normal hearing, the sound is heard equally in both ears. If the sound is heard best in the affected ear, the deafness is conduction. If the sound is heard best in the normal ear, the deafness is sensorineural.