Hyperopia (far-sightedness) occurs when the parallel light rays from distant objects are focused behind the retina. Hyperopic individuals can see distant objects perfectly well because their ciliary muscles contract almost continuously to increase the light-bending power of the lens, which moves the focal point forward onto the retina. However, diverging light rays from nearby objects are focused so far behind the retina that the lens cannot bring the focal point onto the retina even at its full refractory power. Thus close objects appear blurry, and convex corrective lenses are needed to converge the light more strongly for close vision. Hyperopia usually results from an eyeball that is too short or a lazy lens with poor refractory power.
Diabetic retinopathy is a disorder of retinal blood vessels. It is characterized by capillary microaneurysms, hemorrhage, exudates, and the formation of new vessels and connective tissue. The disorder occurs most frequently in patients with long-standing poorly controlled diabetes mellitus. Repeated hemorrhage may cause permanent opacity of the vitreous humor, and blindness may eventually result. Photocoagulation of damaged retinal blood vessels by a laser beam may be performed to prevent hemorrhaged from the vessels. (Mosby’s)
Glaucoma is an abnormal condition of elevated pressure within an eye caused by obstruction of the outflow of aqueous humor. Acute glaucoma occurs if the pupil in an eye with a narrow angle between the iris and cornea dilates markedly, causing the folded iris to block the exit of aqueous humor from the anterior chamber. Primary open-angle glaucoma is much more common, often bilateral; it develops slowly and is genetically determined. The obstruction is believed to occur within the Schlemm’s canal.
Extreme ocular pain, blurred vision, redness of the eye, and dilation of the pupil accompany acute glaucoma. Nausea and vomiting may occur. If untreated, acute glaucoma causes complete and permanent blindness within 2 to 5 days. Chronic glaucoma may produce no symptoms except gradual loss of peripheral vision over a period of years. Sometimes present are headaches, blurred vision, and dull pain in the eye. Cupping of the optic discs may be noted on opthalmoscopic examination. Halos around lights and central blindness are late manifestations. Both types are characterized by elevated intraocular pressure indicated by tonometry. Acute glaucoma is treated with eye drops to constrict the pupil and draw the iris away from the cornea; osmotic agents such as urea, mannitol, or glycerol given systemically to lower intraocular pressure; acetazolamide to reduce fluid formation; and surgical iridectomy to produce a filtration pathway for aqueous humor. Chronic glaucoma can usually be controlled with eye drops such as betablockers, topical carbonic anhydrase inhibitors, and prostaglandin analogs. Other treatment includes carbonic anhydrase inhibitors, epinephrine eye drops, and timolol, a beta-adrenergic blocking agent.
Cataracts are an abnormal progressive condition of the lens of the eye, characterized by loss of transparency. A gray-white opacity can be observed within the lens, behind the pupil. Most cataracts are caused by degenerative changes, often occurring after 50 years of age. The tendency to develop cataracts is inherited. Trauma, such as a puncture wound, may result in cataract formation; less often, exposure to such poisons as dinitrophenol or naphthalene (moth balls) causes them.
Eye strain is commonly a problem for people who work on computers. To lessen eye strain, you can adjust the brightness of the computer monitor to the surroundings of the room so that you avoid high levels of light. Computer users who are farsighted should take extra caution, as they may experience eye fatigue because of the extra focusing efforts.
Sports-related injuries are common in children under 18, and especially in children under the age of 14. Before the age of 14, hand-eye coordination, balance, and reflexes are still developing. Basketball and baseball are common sports for eye injuries. Wearing properly fitting protective eye gear designed for specific sports (like racquetball, and hockey) can help reduce risk of injury to the eyes.
For more information on eye health, visit the American Optometric Association’s website.
2. Research color blindness on the Internet. Describe what occurs in the eyes to cause the condition, what people see, what groups of people are more likely to have it, if it is genetically linked, and list the web address of your source.
3. Briefly research information on diseases of the eye. Name the disease, briefly explain what it is and discuss any prevention/treatment that is available.
4. List any other hearing problem. Describe it; list its causes, what risk factors make it more likely, etc. List the web address of your source.
5. Do you or have you ever had problems with your eyes or ears? Was it something that was preventable? If yes, what can be done to prevent it from occurring again? If no, what treatment helped?
To get a 10: Your answers need to be correct and you can have no grammatical errors, within the second revision of this lesson. Questions are posted with answers; answers are correct, complete, and clear; all lesson requirements have been met. All answers are in complete sentences.
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