Education & Terminology
How the Eye Works
Light rays enter the eye through a transparent layer of tissue, known as the cornea. The cornea bends light through a watery substance called the aqueous humor. As light continues on its pathway it passes through the dark, round opening in the center of the colored iris known as the pupil. The iris, the part of the eye that gives the eye its color, also changes the size of the pupil from very small to large in order to regulate the amount of light that is entering.
Light then passes through another structure, called the lens. The lens is attached to muscles which contract or relax in order to make adjustments which allows light to be focused for clarity. Once through the pupil and lens, light then passes through the larger posterior portion of the eye that is filled with a clear, jelly-like substance called the vitreous humor. Continuing through, light comes to the retina, the membrane that lines the back wall of the eye, containing photo- receptor (rod and cone) cells. These cells convert light to electrical impulses.
The cone cells (about 7 million in number) are in greatest concentration in the small, central part of the retina, called the macula. This area is responsible for producing sharp, detail vision and color vision. The rod cells (numbering about 100 million), in the peripheral retina, provide vision in dim light. Electrical impulses are sent through the optic nerve, the bundle of retinal fibers that exits the back of the eye, and transported to the brain where they are interpreted in the primary visual cortex and an image is perceived.
Importance of Eye Exams
Vision screenings that are performed by a school nurse or your employer are not the same as comprehensive eye exams. Eye doctors check for ocular and other diseases that have no early symptoms, but should nevertheless be treated as early as possible to avoid vision loss. It is recommended that healthy adults under 40 have an eye exam every 1-2 years, and those over 40 are urged to have an exam every year. The American Optometric Association recommends that chidren receive their first eye exam at 6 months of age, a second at 3 years of age, and another before beginning school. Children under the age of 18 should be seen once a year. Vision and ocular health can vary greatly from month to month as children grow and change.
A contact lens is a thin plastic lens that is fitted over the cornea of the eye to correct various vision defects. There are two main types of contact lenses prescribed today, both of which are described below:
- Gas Permeable Lenses
Gas permeable contact lenses are more rigid and smaller in diameter than are soft contact lenses. One of their chief advantages is breathability: Your cornea needs oxygen for optimal health and function. Gas permeable lenses allow more oxygen to pass through them than do soft lenses, so corneal irritation is less likely. Their disadvantage is that they’re initially less comfortable than soft lenses. Most people get used to them quickly, but if you stop wearing them for more than a few days, you’ll have to readapt. Gas permeable lenses can correct certain vision problems — such as refractive errors that require high spherical or cylindrical powers — more accurately than can soft lenses.
- Soft, Disposable Contact Lenses
Soft disposable contact lenses were designed to be a healthier and more convenient approach to contact lens wear. Their introduction revolutionized the way people wore contact lenses. The majority of today’s lenses are disposable because they are convenient and affordable. Throw them away daily, weekly, or monthly. Disposable or frequent replacement contact lenses are a healthy, time-saving option. Colored disposable contact lenses look great on light and dark eyes, whether you need vision correction or not. Silicone hydrogel contact lenses are a relatively new lens material that delivers high amounts of oxygen to your eyes, enabling 30-day continuous wear for some people. Please consult your optometrist for your particular wearing schedule and maintenance instructions.
Glasses are a device that compensate for defective vision or to protect the eyes from light, dust, and the like, consisting usually of two glass or plastic lenses set in a frame that includes a nosepiece for resting on the bridge of the nose and two sidepieces extending over or around the ears. Glasses are made to accommodate a specific visual or occupational need and require a written prescription from an optometrist.
LASIK is a surgical procedure intended to reduce a person’s dependency on glasses or contact lenses. LASIK stands for Laser-Assisted In Situ Keratomileusis and is a procedure that permanently changes the shape of the cornea, the clear covering of the front of the eye, using an excimer laser. A knife, called a microkeratome, is used to cut a flap in the cornea. A hinge is left at one end of this flap. The flap is folded back revealing the stroma, the middle section of the cornea. Pulses from a computer-controlled laser vaporize a portion of the stroma and the flap is replaced. LASIK treats nearsightedness, farsightedness and astigmatism. We do not provide LASIK surgery, but we offer consultations, referrals, as well as pre and post-op care.
Terms & Definitions
Eye allergies are no different than allergies that affect your sinuses, nose or lungs. When an allergen comes in contact with your eyes, your body releases histamine – a chemical produced in reaction to a substance that the immune system can’t tolerate. Special cells called mast cells make histamine. These cells are present throughout the body but are highly concentrated in the eyes. Ocular allergens tend to be airborne (as are most other allergens). The most frequent allergic triggers include pollen, pet hair or dander and dust.
Lazy eye, or amblyopia, is the loss or lack of development of central vision in one eye that is unrelated to any eye health problem and is not correctable with lenses. It can result from a failure to use both eyes together. Lazy eye is often associated with crossed-eyes or a large difference in the degree of nearsightedness or farsightedness between the two eyes. It usually develops before age six and it does not affect side vision.
Anti-reflective coating is a thin layer(s) that is applied to a lens to reduce the amount of reflected light and glare that reaches the eye. It not only improves visual acuity, but is cosmetically more attractive.
A vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance. It is a very common vision condition. Most people have some degree of astigmatism. Slight amounts of astigmatism usually don’t affect vision and don’t require treatment. However, larger amounts cause distorted or blurred vision, eye discomfort and headaches.
A bifocal lens has one segment for near vision and one segment for far vision. There are several variations including executive (lined), progressive (no line), and specialty bifocals. Bifocal contact lenses are also available.
Blepharitis is an inflammation of the eyelids and eyelashes causing red, irritated, itchy eyelids and the formation of dandruff like scales on eyelashes.
A cataract is a cloudy or opaque area in the normally clear lens of the eye. Depending upon its size and location, it can interfere with normal vision. Most cataracts develop in people over age 55, but they occasionally occur in infants and young children. Usually cataracts develop in both eyes, but one may be worse than the other.
Computer Vision Syndrome - CVS
Collection of problems, mostly eye- and vision-related, associated with computer use. Symptoms include eyestrain, dry eyes, blurred vision, red or pink eyes, burning, light sensitivity, headaches and pain in the shoulders, neck and back.
Conjunctivitis is an inflammation of the conjunctiva, the thin, transparent layer that lines the inner eyelid and covers the white part of the eye. The three main types of conjunctivitis are infectious, allergic and chemical. The infectious type, commonly called “pink eye” is caused by a contagious virus or bacteria.
Diabetes is a disease that interferes with the body’s ability to use and store sugar and can cause many health problems. One, called diabetic retinopathy, can weaken and cause changes in the small blood vessels that nourish your eye’s retina, the delicate, light sensitive lining of the back of the eye. These blood vessels may begin to leak, swell or develop brush-like branches.
Dry Eye Syndrome
The tears your eyes produce are necessary for overall eye health and clear vision. Dry eye means that your eyes do not produce enough tears or that you produce tears which do not have the proper chemical composition.
Farsightedness, or hyperopia, as it is medically termed, is a vision condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly.
Glaucoma is an eye disease in which the internal pressure in your eyes increases enough to damage the nerve fibers in your optic nerve and cause vision loss. The increase in pressure happens when the passages that normally allow fluid in your eyes to drain become clogged or blocked. The reasons that the passages become blocked are not known.
A high index lens has a higher index of refraction than other lenses, meaning that light travels faster through the lens to reach the eye than with traditional glass or plastic. It is denser, so the same amount of visual correction occurs with less material so the lens can be thinner. This is an attractive option for patients with higher prescriptions.
Macular degeneration is the leading cause of blindness in America. It results from changes to the macula, a portion of the retina that is responsible for clear, sharp vision and is located at the back of the eye.
Multifocal is a type of spectacle or contact lens design that includes more than one focal area, such as bifocals or trifocals.
Nearsightedness, or myopia, as it is medically termed, is a vision condition in which near objects are seen clearly, but distant objects do not come into proper focus. Nearsightedness occurs if your eyeball is too long or the cornea has too much curvature, so the light entering your eye is not focused correctly.
Presbyopia is a vision condition in which the crystalline lens of your eye loses its flexibility, which makes it difficult for you to focus on close objects. This usually becomes present after the age of 40.
Strabismus occurs when one or both of your eyes turn in, out, up or down. Poor eye muscle control usually causes strabismus. This misalignment often first appears before age 21 months but may develop as late as age 6.
A stye develops when a gland at the edge of the eyelid becomes infected. Resembling a pimple on the eyelid, a stye can grow on the inside or outside of the lid. Styes are not harmful to vision, and they can occur at any age.
Vitreous Detachment & Floaters
Spots called floaters are small, semi-transparent or cloudy specks or particles within the vitreous, the clear, jelly-like fluid that fills the inside of your eyes. They appear as specks of various shapes and sizes, threadlike strands or cobwebs. Since they are within your eyes, they move as your eyes move and seem to dart away when you try to look at them directly. Spots are often caused by small flecks of protein or other matter trapped during the formation of your eyes before birth. They can also result from deterioration of the vitreous fluid, due to aging; or from certain eye diseases or injuries. Most spots are not harmful and rarely limit vision and many fade over time. However, suddenly seeing new floaters, or floaters accompanied by flashes of light or peripheral vision loss, may indicate a retinal detachment. Any dramatic changes should be addressed to an optometrist or ophthalmologist immediately.