While James Taylor saw fire and rain and Peter Gabriel saw the red rain coming down, an increasing number of American adults are seeing only a touch of grey. In fact, the American Foundation for the Blind (AFB) estimated more than 25 million American adults have significant vision loss, including individuals who are blind and those who have trouble seeing even when wearing corrective lenses. A report from Prevent Blindness America, “Vision Problems in the U.S.”, further noted 20.5 million Americans older than 40 have cataract, 5.3 million have diabetic retinopathy, 2.2 million have glaucoma and 1.6 million have late-stage age-related macular degeneration (AMD).1
Add to this the fact that more than 90 percent of adults surveyed recently by Transitions Optical said sight is their most important sense and the one they feared losing the most, and it’s easy to see why more attention is focused on preserving vision. However, vision is a fine-tuned, complex process involving the eye, nerves and brain. Light first hits the corneal surface and is focused to pass through the pupil and lens; it travels through the vitreous humor to the retina, a light-sensitive layer covered with photoreceptor cells that absorb the light and turn it into nerve impulses that are fed through the optic nerve into the brain for interpretation. The peripheral retina distinguishes light from dark and permits peripheral vision, while the macula focuses on fine detail and colors.
The retina is an ideal environment for the generation of free radicals since it has high levels of blood (and thus oxygen) supply, high-light exposure and cell membranes rich in polyunsaturated fatty acids. Therefore, environmental factors and simple ultraviolet (UV) radiation lead to oxidative stress, while nutritional imbalance can exacerbate visual impairment.
Two degenerative conditions of the eye have been linked to nutritional factors: AMD and cataract. AMD is among the leading causes of blindness in Western countries, affecting about 20 percent of all people older than 65; it is believed to be the leading cause of irreversible blindness in the elderly in Western populations. AMD is characterized by irreversible progressive degeneration of the macula lutea, the site of the highest visual acuity of the retina. Dry AMD, the more common form, occurs when light-sensitive cells in the macula slowly break down, blurring central vision. Its most common early symptom is the presence of drusen, yellow deposits under the retina. Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula, raising the macula from its normal position and causing rapid damage.
Cataract remains the leading cause of blindness in the world. The lens becomes cloudy or opaque due to damage caused by oxidative stress, exposure to UV light and genetics; aging and inflammation are also associated risk factors. The two most common types of age-related cataracts are nuclear (center of the lens) and cortical (in the lens periphery).
Glaucoma is the second leading cause of blindness globally. The term refers to a group of eye diseases that cause vision loss through damage to the optic nerve. The two primary types of glaucoma are open-angle glaucoma (also known as primary open-angle glaucoma—POAG) and angle-closure glaucoma. POAG is the most common form and occurs when the eye’s drainage canals become clogged, increasing intraocular pressure (IOP). While vision loss from glaucoma is irreversible, it can be managed with medication or surgery.
One additional cause of blindness is diabetic retinopathy, whereby the disease damages the blood vessels that nourish the retina, causing the vessels to leak or break. It affects more than 4 million Americans. Macular edema (swelling) in diabetic retinopathy can be treated with laser surgery to slow fluid leakage and reduce the fluid levels in the retina.
