To see or not to see

When I was in college in the mid-1960s, my basketball coach forced me to see an eye doctor for glasses. Apparently, I was constantly squinting on the court. Sure enough, I needed glasses (contacts were unavailable for my Rx). No big deal, I thought. Oh, boy, was I wrong! Playing basketball with glasses was/is a miserable experience. I experienced headaches, sweat dripping into my eyes, injuries to my nose, and blurry vision. It seemed like every year, I had to return to get a new, more powerful Rx. And the cost was ridiculous – examinations, lenses, frames, and coatings were out-of-this-world.

I still wear glasses today, and they’re more expensive than ever, particularly designer frames that fit better, have thinner lenses, and don’t break. And now I need four pairs: regular wear, sunglasses, driving glasses, computer glasses, and, oh yes, golf glasses. I know that’s five, but I don’t really need golf glasses. That said, they do help with reading the greens (without them, my putting would be really bad instead of just bad!). To complicate matters, now I need surgery to replace a lens since I appear to have cataracts. I’m not alone. The number of people who wear glasses increases year after year. Reasons range from airborne pollution to genetic mutations. The latest data reveal that more than 75% of people over age 55 wear eyeglasses.

Anatomy of an eye

(Image courtesy of Victor Katch.)

Your eye includes the cornea, the clear front window that transmits and focuses light into the eye. It acts like a windshield and partly bends light as it enters the eye. Tear fluid keeps the cornea lubricated.

The sclera is the white part of the eye that forms the general eyeball shape and structure. The conjunctiva is the thin layer that covers the sclera and lines the eyelids inside.

The aqueous humor is a fluid that fills the anterior chamber of the eye and helps maintain its shape.

The iris contains the muscles that control pupil size and is also responsible for eye color. The pupil is the black circle inside the iris. It is like an adjustable window to the eye inside. It widens and narrows to control how much light enters the eye.

The lens focuses light that enters the eye and directs it to the back of the eye.

The vitreous humor is the clear, gel-like fluid that fills the space between the lens and retina. The retina is the thin layer of light-sensitive cells at the back of the eyes that converts light into electrical signals. It contains rods, which help see in low light, and cones, which help see colors.

The macula, a small area of the retina, is critical to vision. It is responsible for the center of the visual field and helps you see color and fine details. The optic nerve connects the retina to the brain. It transmits signals from the eye, with connection points linking to multiple brain areas.

The external muscles control the eye’s position, alignment, and movement and contribute to its shape. This enables the ability to switch one’s focus between near and far objects.

How the eye works

(Image courtesy of Victor Katch.)

“Seeing” requires light from the outside world. The eye allows light to enter and pass through a series of clear components and sections, including the cornea, aqueous humor, lens, and vitreous humor. Those structures bend and focus light, adjusting how far the light will travel before it comes into focus on the retina. Eye muscles can make subtle changes to eye shape, moving the focus point so it lands at the “correct” location on the retina. When light lands on retina cells, they send signals to the brain – like coded messages describing the color, intensity, and other relevant details about the light. The brain decodes and processes these signals and uses them to “build” the image you perceive.

Making a spectacle

The major reasons why humans need glasses include refractive errors that can occur when the eye shape or structure prevents light from focusing on the retina the way it’s supposed to. The following are the major refractive errors.

• Astigmatism — People with astigmatism, like me, have an irregular curve to their cornea that bends light abnormally. This prevents light from focusing on the retina with precision. Without a pinpointed focus on the retina, objects viewed at certain distances appear blurred. About 14% of children and 40% of adults have an astigmatism. Common symptoms include poor night vision, squinting to focus, blurry vision, headaches, and eye strain.
• Hyperopia (farsightedness) — The eyes focus light on a point past the retina (see “How the eye works” image). This makes close objects and text appear blurry while faraway objects appear clear. About 5% of children and 31% of adults have hyperopia. Common symptoms include difficulty seeing up close, headaches (especially when reading), and eye strain.
• Myopia (nearsightedness) — The eyes focus light on a point in front of the retina. This makes distant objects look out-of-focus while close objects look clear. About 12% of children and 27% of adults are nearsighted. Common symptoms include difficulty seeing far away, squinting to focus, and eye strain.
• Presbyopia — Similar to hyperopia, close-up objects and text appear blurry, but unlike hyperopia, it occurs naturally with aging as the eye lens loses its flexibility and functionality. Roughly 1.8 billion people in the world have presbyopia. Common symptoms include headaches, eye strain, holding reading materials farther away to read them, and difficulty seeing materials up close.

Other eye disorders and diseases

The major causes of vision loss include age-related eye diseases such as macular degeneration, cataracts, diabetic retinopathy, and glaucoma. Other common eye disorders include amblyopia and strabismus.

(Image courtesy of Victor Katch.)

Age-related macular degeneration (AMD) is an eye disorder that results in distorting central vision, which is necessary to see objects clearly and to execute common daily tasks such as reading and driving (see AMD image). AMD affects the macula, the central part of the retina that allows the eye to perceive fine details. About 1.8 million Americans aged 40 and older are affected by AMD. An additional 7.3 million are at substantial risk of developing it. AMD is the leading cause of permanent impairment of reading and fine or close-up vision among people aged 65 years and older.

There are two forms of AMD: wet and dry. Wet AMD is when abnormal blood vessels behind the retina start to grow under the macula, ultimately leading to blood and fluid leakage. Bleeding, leaking, and scarring from these blood vessels cause damage and rapid central vision loss. An early symptom of wet AMD is that straight lines appear wavy.

AMD occurs when the macula thins over time as part of the aging process, gradually blurring central vision. The dry form is more common and accounts for 70-90% of AMD. The dry form progresses more slowly than the wet version. Over time, as less of the macula functions, central vision gradually declines. Dry AMD generally affects both eyes. Drusens are among the most common early signs of dry AMD. They are small yellow deposits of fatty proteins (lipids) that accumulate under the retina and appear as tiny pebbles of debris that build up over time.

(Image courtesy of Victor Katch.)

Cataract represents eye clouding (of the lens) and is the leading cause of blindness worldwide. Cataracts can occur at any age due to a variety of causes and can be present at birth. An estimated 30+ million Americans aged 40 and older have a cataract in one or both eyes.

Diabetic retinopathy (DR) is a common complication of diabetes and is the leading cause of blindness in American adults. It results from progressive damage to the retina’s blood vessels. Diabetic retinopathy usually affects both eyes.

Glaucoma is a group of diseases that can damage the eye’s optic nerve and usually results in vision loss and/or blindness. Glaucoma most often occurs when the normal fluid pressure inside the eyes slowly rises. Symptoms include severe headaches, severe pain, nausea or vomiting, blurred vision, and eye redness. There are two types of glaucoma — open angle and closed angle. Open angle represents a chronic condition that progresses slowly over a long period of time while angle closure can appear suddenly and is often very painful.

Amblyopia (lazy eye) is the most common cause of vision impairment in children. It occurs when the vision in one eye degrades because the eye and the brain don’t work together properly. Conditions leading to amblyopia include an imbalance in the positioning of the two eyes (termed strabismus) and more nearsighted, farsighted, or astigmatic issues in one eye than the other.

Dry eye disease (DED) occurs when tears cannot adequately lubricate the eyes. Mostly, DED occurs if not enough tears are produced, or are of poor quality. Tear instability leads to inflammation and damage of the eye’s surface. Dry eyes feel uncomfortable, sometimes stinging or burning. Blurred vision and eye fatigue are also symptoms. DED can be chronic or may only occur in certain situations, such as on an airplane, in an air-conditioned room, or after looking at a computer screen for a long period of time.

Optometrists, ophthalmologists, and opticians, oh my!

Optometrists perform eye exams and vision tests, detect vision problems, and prescribe corrective treatments such as glasses, contact lenses, and medications. Optometrists complete four years of professional training after college to earn a Doctor of Optometry degree (O.D.). They also may complete additional training or specialty fellowships.

Ophthalmologists complete medical school, followed by a one-year internship and three-year residency. Ophthalmologists address all medical and surgical eye issues and can treat eye-related issues due to complex medical conditions. They also provide pre- and post-surgical care, much like a primary-care eye doctor.

Opticians fill prescriptions written by optometrists and ophthalmologists; they help individuals choose and fit eyeglass frames.

Take care of your eyes

• Good eye health starts with obtaining the necessary nutrients proven to protect the eyes. This includes omega-3 fatty acids; antioxidants like lutein and zeaxanthin as well as other carotenoids; and zinc, vitamin C, and vitamin E. Regular consumption of green leafy vegetables (spinach, kale, Swiss chard); salmon, tuna, and other oily fish; eggs, nuts, beans, and other nonmeat protein sources; and lots of citrus fruits will ensure adequate intake of all the nutrients the eyes need.
• Quit smoking to decrease the risk of getting cataracts and damaging the optic nerve.
• Wear sunglasses to protect the eyes from the sun’s ultraviolet (UV) rays. Too much UV exposure boosts the chance of developing cataracts and macular degeneration.
• Use safety eyewear when needed.
• Look away from the computer screen. Stop staring at your phone.
• Visit an eye doctor regularly.

 
 
References

(Lead image credit: Michigan Photography.)