7.8: Diseases of the Eyes

In many people, one or more diseases compound the adverse effects of aging of the eyes. The incidence of such diseases increases with age, so that the risk for those over age 75 is 2.5 times greater than the risk for those between ages 50 and 65. Some of these diseases are little more than a nuisance, while others drastically reduce the quality of vision and in severe cases cause blindness. To see the effects of the more serious diseases on vision, go to the National Eye Institute (https://www.nei.nih.gov), the American Academy of Opthamology (https://www.aao.org/eye-health), or the https://www.emedicinehealth.com site "Eye Diseases and Conditions" at https://www.emedicinehealth.com/image-gallery/age-related_macular_degeneration_picture/images.htm. (Suggestion 162.02.02a) (Suggestion 162.02.02b)

Minor Diseases

Lacrimal Fluid

The production of lacrimal fluid may decline so far that the eyes become dry, causing irritation. The application of wetting solutions can largely relieve this problem. Other individuals experience what seems to be an excessive production of lacrimal fluid because the fluid pours out of the eye, forming tears.

In most cases the cause of the tearing is not excess production of fluid but some factor that prevents the fluid from draining properly into the nasal cavity. One common cause of such tearing is excessive weakening of the circle of muscle surrounding the eyelids. When it is weak, the muscle allows lacrimal fluid to accumulate behind the eyelid until it overflows onto the face. Tearing may also be caused by infection or other factors that block the lacrimal ducts that lead from the eyes to the nasal cavity.

Eye Muscles

Weakening of the eye muscles may cause problems other than tearing. For example, inadequate contraction of the circular muscle surrounding the eyelids may cause drying of the eye if the eyelids are not closed completely during sleep. Also, weakening of the muscle that raises the upper eyelid causes drooping of the lid. Besides producing the appearance of drowsiness, a drooping lid may obstruct part of the field of view.

The circular eye muscle sometimes contracts excessively, causing the lower eyelids to turn inward. The edge of the lid and its eyelashes then scrape on the eye, producing irritation. If this condition is severe and is not corrected, the scar tissue that forms can drastically reduce vision by blocking and scattering light.

Cataracts

Cataract formation is the most common serious eye disease among the older population. However, its impact in the United States has been lowered considerably by the high rate of success in treating this disease surgically. Cataract surgery is the most common surgical procedure in the U.S. There are one million surgeries per year, accounting for 12% of annual Medicare expenses.

Cataracts are the most common age-related eye disease and the main cause of blindness in "third world" locations.

Recall that aging causes the formation of opacities in the lenses. Free radicals and glycation are main contributing factors. At first opacities usually develop toward the periphery of the lens, where they scatter light and cause glare, but eventually they form toward the center of the lens. Central opacities cause glare and decrease visual acuity because they scatter and block light. An affected individual is said to have cataracts when central opacities reduce visual acuity substantially.

Main risk factors for cataract formation in descending order of importance are increasing age; exposure to UV-B light; and topical or internal corticosteroids. Other risk factors include being female; having diabetes mellitus; smoking; family history; low socioeconomic status; malnutrition or low levels of AOXs (e.g., vit A, vit C, vit E, carotenoids); dehydration; and eye trauma or internal eye inflammation. Diabetes mellitus is a disease involving hormone imbalances and abnormally high levels of a sugar called glucose in the blood. Opacities in the lenses of diabetics seem may be caused by glycation and by the conversion of glucose to another sugar, sorbitol, which accumulates in the lenses. Estrogen supplements in postmenopausal women seem to reduce their risk of developing cataracts.

When cataracts are treated by surgical removal of the affected lens, the ability of the eye to refract light is restored by implanting an artificial lens or by wearing eyeglasses or contact lenses. However, not all individuals with cataracts can or should undergo eye surgery.

Age‑Related Macular Degeneration

The second most common serious eye disease among the elderly is age‑related macular degeneration (AMD), also called senile macular degeneration. It accounts for about 25 percent of visual loss among those under age 80 and about 40 percent among those over age 80. As the name indicates, this disease causes deterioration of the retina. Though the cause of AMD is not known, factors that increase the likelihood of its occurrence include being of advanced age, having high blood pressure, having family members with the disease, and having atherosclerosis.

The mechanism by which AMD causes retinal damage is not clear, but it seems to involve *FR damage and formation of lipid peroxides (LPs). It seems that age changes in the pigmented epithelium and Bruch's membrane begin to occur in excess near the edge of the macula. These changes substantially reduce the passage of nutrients from the choroid to the sensory retina, leading to degeneration of the cones. There is no treatment for this disease at this stage.

If the disease progresses no further, there will be decreased visual acuity in the center of the field of view. However, in about 10 percent of cases blood leaks from choroid vessels and passes between the pigmented epithelium and the macular region of the sensory retina. Phagocytic cells from the choroid also invade the retina. These changes cause more severe degeneration, and about 90 percent of these advanced cases result in macular blindness.

The onset of AMD is indicated by gradual deterioration of vision in the central region of the field of view. Sudden rapid distortion of vision in this area is a warning sign that bleeding and rapid macular degeneration are occurring. Professional help should be sought at once. Treatment with lasers can slow or stop further vessel damage and bleeding in about 50 percent of advanced cases. If treatment is not obtained or is unsuccessful, macular blindness is likely.

Since AMD affects only the macula, peripheral vision is not appreciably altered. When central vision is affected, activities such as driving and reading become difficult or impossible.

Glaucoma

Glaucoma is the third leading serious eye disease among older people. It causes diminished vision because the high pressure that develops from accumulation of aqueous humor inside the eye damages the retina and optic nerve. The pressure inside the eye is called intraocular pressure (IOP). About 9 percent of people over age 65 have one of the three types of glaucoma.

Open‑Angle Glaucoma

About 80 percent of all patients with glaucoma have open‑angle glaucoma. Its risk factors include being of increasing age, having relatives with glaucoma, being black, and being male.

The cause of and the mechanism producing high IOP are unknown. Pressure in both eyes is affected. When the pressure remains somewhat high for extended periods, it slowly damages the retina and optic nerve. The damage may be noticed by the affected individuals as a gradual shrinkage in the width of the field of view. Unfortunately, this narrowing may go undetected until permanent injury has occurred. If left unchecked, open‑angle glaucoma leads to total blindness.

Fairly simple procedures that are normally part of a complete eye examination can detect the presence of open‑angle glaucoma long before significant eye damage has occurred. These procedures include measurement of IOP and visual examination of the optic nerve using an ophthalmoscope. The combination of the two tests identifies about 80 percent of all affected people.

Though there is no cure for open‑angle glaucoma, the IOP can be controlled and the effects of the disease can be prevented with appropriate medications.

Angle‑Closure Glaucoma

Angle‑closure glaucoma or narrow‑angle glaucoma gets its name from the accompanying abnormally narrow space between the lens and the cornea. It accounts for about 10 percent of all cases of glaucoma.

With angle‑closure glaucoma, the IOP may rise quite high within a matter of minutes or hours. Affected individuals often experience eye pain, headache, nausea and vomiting, halos around lights, and blurred vision. If this is not treated within 2 to 3 days, permanent eye damage and blindness can result. Treatment usually involves surgery that reestablishes normal drainage of the aqueous humor.

Secondary Glaucoma

The remaining 10 percent of glaucoma cases involve secondary glaucoma. This condition is characterized by elevated IOP resulting from another disorder such as diabetes, tumor, or disease of the vessels in the eye. Each type of secondary glaucoma is treated according to its specific cause.

Diabetic Retinopathy

Diabetic retinopathy (DR) means "disease of the retina associated with diabetes." The form of diabetes involved is diabetes mellitus. While DR is not nearly as common as cataracts, AMD, or glaucoma, it is the third leading cause of blindness in the United States and the most common cause of blindness in those with diabetes mellitus. The incidence of DR among diabetics increases with the length of time since the onset of diabetes. For example, only 7 percent of those who have had diabetes for less than 10 years have developed DR, while more than 62 percent of those who have had it for more than 15 years have developed DR.

Diabetic retinopathy seems to develop because some of the extra glucose in the blood is converted to sorbitol, which weakens retinal capillaries so much that they are overly dilated by normal blood pressure. Some weak spots in the capillaries bulge outward as aneurysms that leak and bleed. Injured vessels and hemorrhaged blood can be seen when the inside of the eye is examined with an ophthalmoscope. Fluids and blood from the leaking dilated capillaries injure the retina.

As more blood flows through the dilated capillaries, unaffected capillaries receive less blood flow and eventually shrink and close. The areas of the retina that were served by these shrunken capillaries are injured because they receive inadequate blood flow. Such ischemic areas can be seen with an ophthalmoscope. As the number of abnormally dilated and shrunken retinal vessels increases, more of the retina is adversely affected and vision deteriorates.

In more advanced cases of DR, retinal vessels near the optic nerve grow into the vitreous humor. Since these proliferating vessels are weak, they rupture easily, especially when the vitreous humor moves. Hemorrhaging near or into the vitreous humor often leads to blindness from secondary glaucoma or from detachment of the retina from the choroid.

The best treatment for diabetic retinopathy is to maintain blood sugar levels within the normal range. Once vessels become dilated, the progressive destruction of the retina can be slowed by destroying the dilated vessels with laser surgery.