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Who does what? | Your prescription | Frames | Lenses | Getting your money's worth | Protective eyewear

Who does what?

The ophthalmologist or optometrist writes a prescription. The optician grinds or manufactures lenses according to the prescription.

Your prescription

When the ophthalmologist or optometrist hands the patient the prescription for glasses, it generally appears very confusing to the patient. However, if the patient develops an understanding of each term on the prescription, it isn't so difficult to interpret. A typical prescription form may look something like this chart.

	Sphere	Cylinder	Axis
O.D.
O.S.

One of the first things on the prescription is a set of initials - O.D. or O.S.

O.D. stands for oculus dextrus and represents the right eye. Sometimes there will be the abbreviation R.E. for right eye instead of O.D.

O.S. or oculus sinister represents the left eye. Sometimes the doctor will substitute L.E. for O.S. If there are no initials, the numbers for the right eye will be listed first

The sphere column describes how nearsighted (myopic) or farsighted (hyperopic) a person is. A plus (+) in front of the first two numbers means the patient is farsighted. A minus (-) means the patient is nearsighted.

The degree of farsightedness or nearsightedness is measured in diopters. A diopter is a unit that measures lens power. A diopter is based on how much a light ray passing through the glass will be bent. The thickness of the lens will increase as the power increases. People with one diopter of myopia have about 20/50 vision (they see objects at twenty feet that a person with normal vision would be able to see at fifty feet) and objects would begin to blur three to four feet away. People with three diopters of myopia have about 20/400 vision (they see at twenty feet what a person with normal vision would be able to see at four hundred feet) and objects would begin to blur about a foot away.

The cylinder column refers to astigmatism. It measures the dioptric difference or the difference between the cornea's steepest and lowest curves. In a person who is suffering from astigmatism, the cornea is shaped like the back of a spoon instead of a sphere. The orientation of the spoon shape can differ from person to person. The orientation in one person may be like the spoon is standing on its end, and in another person as if the spoon were lying on its side.

The axis column describes the orientation in degrees from the horizontal. It can be anywhere from one to 180 degrees with ninety degrees being vertical. Usually the left and right eyes in a person with astigmatism are symmetrical.

The following prescription is for a hyperopic eye or farsighted eye.

	Sphere	Cylinder	Axis
O.D.	+2.50	+1.00	180
O.S.	+1.75	+1.50	180
		+2.00

The patient's right eye has 2.5 diopters of farsightedness with one diopter of astigmatism and an axis of 180 degrees. The left eye has 1.75 diopters of farsightedness with 1.5 diopters of astigmatism and an axis of 180 degrees.

This patient also has presbyopia (aging eyes) and needs bifocals. This is indicated with +2.00, which indicates the strength of the reading part of the lens. This patient needs two diopters of power for reading.

The following prescription is for a myopic eye or nearsighted eye.

	Sphere	Cylinder	Axis
O.D.	-1.25	-2.50	90
O.S.	-0.75	-2.25	90
		+1.50

The patient's right eye has 1.25 diopters of nearsightedness with 2.5 diopters of astigmatism with an axis of ninety degrees. The left eye has .75 diopters of nearsightedness and 2.25 diopters of astigmatism with an axis of ninety degrees. The patient has presbyopia and will need 1.5 diopters of power for the reading part of his or her glasses.

Frames

Most people who wear glasses don't spend a lot of time selecting their frames. However, their glasses are something they are going to have to live with (and be happy with) day in and day out for many months, or even years. In addition to correcting vision, a person's glasses should be comfortable, durable, and attractive.

Patients should start selecting their frames by having the optician look at their prescription. Some prescriptions work better in certain frames. For example, thin, oval, wire frames aren't sturdy enough to support thick lenses.

In addition, the frames should suit the size of the person's face. The frame should cover twenty to thirty percent of the person's face, and the top of the frame should follow the line of the eyebrows. If the frame is too large, it can catch glare and create distortions in the vision. If the frame is too small, side vision may be limited. A person who needs strong lenses should look at small frames with rounded edges. They will reduce distortions created by having too much lens outside the line of vision.

People are often confused about the material they should select for their frames - metal or plastic. Metal is usually the lightest and most stylish material, but plastic is more durable and may be better for thick lenses. Titanium and carbongraphite are very resistant to damage and are a good choice for people with an active lifestyle.

Eyeglasses should fit comfortably and securely. They shouldn't rub behind a person's ears or irritate the bridge of the nose. If, after a few days, the patient finds his eyeglasses aren't comfortable, he should let the optician know. The optician can usually make minor adjustments in the hinges, bridges, or temples to make the glasses fit more comfortably. Opticians can also adjust the "tilt" of glasses on the person's face or the "wrap" of the glasses around the face to make sure the patient is seeing well and the fit is comfortable.

The hardest part of buying glasses may be finding a frame that suits the patient's face. The first thing patients should do is look in the mirror and determine the shape of their face - round, square, triangular, heart-shaped, or oval. Then they should try to find a frame that is the opposite of their face shape. A person with a round face should try square shaped glasses to minimize roundness. Frames for a person with a heart-shaped face should have low temples and the lenses should get wider at the bottom. This will add fullness to the lower half of the face. A person with a square face should select round frames that soften the lines of his or her face. Cat's eye shaped frames that compliment a wide jaw line are good for triangular shaped faces. People with oval faces can use almost any frame.

Lenses

There are three types of lenses. The convex lens is thicker in the middle than at the edges, sort of like a magnifying glass. Light rays are gathered towards a central point. Convex lenses are used to correct farsightedness or hyperopia. The requirement for a convex lens is indicated with a plus (+) on the prescription.

The concave lens is thinner at the center than at the edges so it spreads the light rays apart. Concave lenses are used for nearsighted eye or myopic eyes. The requirement for a concave lens is indicated with a minus (-) on the prescription.

The cylindrical lens is curved more in one direction than it is in the other direction. It is used for astigmatism and is part of a prescription for nearsightedness or farsightedness.

Lenses are available in safety glass, regular plastic, and polycarbonate. The safety glass can be heavy and cause pressure on the nose or cause the glasses to slide down the nose. Regular plastic is lighter than glass, but scratches easily. Polycarbonate is very strong and lightweight, and it won't shatter.

Single powered lenses

Single powered lenses deal with only one vision deficiency. They correct myopia (nearsightedness), hyperopia (farsightedness), or astigmatism. They can be used in glasses that are worn all the time or in glasses that are worn part-time - just for reading or for computer use. Half glasses that people with presbyopia (aging eyes) use for reading usually have single power lenses.

Multi-focal lenses

Multi-focal lenses are used for people with presbyopia (aging eyes) and generally require some adjustment. Bifocals have two-part lenses. The top part is for distance and the bottom section is for reading. There is a line between the two sections.

Trifocals have three segments with two lines. The middle section allows the person to see mid-range images.

Progressive lenses have no lines. There is a gradual transition between the various parts of the lens, and that may create some distortion.

Lens enhancements

When a person shops for eyeglasses, he or she can choose a variety of lens enhancements. People who likes to wear sunglasses when they are outside and don't want to switch back and forth between regular glasses and sunglasses may want to select photochromatic lenses, which darken automatically in sunlight and get lighter when the person goes inside. They are available in plastic or glass. Plastic loses its darkening power after a few years, but glass keeps it forever. Photochromatic lenses have ultra-violet (UV) protection. This means they block out harmful ultraviolet rays, which are suspected of causing age-related eye diseases such as cataracts and macular degeneration. UV protection is good for anyone who spends much time out doors.

Another lens enhancement people often select is scratch protection. This is needed for plastic lenses, especially if a person is hard on lenses. However, the anti-scratch coating can crack in extreme temperatures.

Anti-reflective coating can reduce glare, reflections, and ghost images. It is useful for people with strong prescriptions and people who drive at night. It makes the glass almost invisible in frames. As a result, it is a good option for people who do a lot of public speaking. The coating is hard to keep clean and can rub off with frequent cleaning or rubbing.

Lenses can be tinted. This enhancement is mostly cosmetic, but can help with light sensitivity. The tint can add color to a person's face and hide wrinkles and dark circles under the eyes.

Finally, the edge of your lenses can be treated. To eliminate the blocky appearance of thick lenses, the optician grinds down the edges of the lenses until they are even with the frame. This eliminates sharp edges and reduces the weight of the lens.

Taking care of lenses

Eyeglasses will last longer if they are taken care of. Glasses should always be removed using both hands. This will reduce wear and tear on the temple, which is the part of the glasses that bends the most if they are pulled off with one hand. Eyeglasses should never be placed face down on any surface when they are removed from the face. They should always be placed in a protective case. Water or liquid soap should be used to clean glasses; tissues and paper towels are too rough and may scratch the lenses.

Getting your money's worth

When you select a new pair of glasses, compare both price and value. Many optical centers advertise bargain prices, but they don't always provide the service and guarantee the patient needs. When buying glasses, the consumer should always consider the quality of the frames and lenses, the amount of time and care taken fitting glasses, professional know-how, and the service and guarantee. Surveys show that glasses purchased from a doctor's office are more likely to be more trouble-free, higher in quality, and more accurate to the prescription.

There are ways to keep costs down. Avoid paying for lens enhancements twice. Polycabonate lenses already have UV and scratch protection, there shouldn't be an additional charge for those features. Don't purchase lens enhancements you don't need. If you normally wear sunglasses instead of regular glasses outside, you won't need to have UV protection for your regular glasses. By purchasing a higher quality frame initially, you may save the cost of having to replace an inferior frame in a few months. Inexpensive frames often have weak hinges that can loosen, come apart, or break with usage. If you take reading glasses off frequently, keep them on a chain or cord around your neck. This will prevent them from getting lost or damaged because they were repeatedly laid down on a surface.

Protective eyewear

Your eyes are one of the most important assets you have. You use them constantly. They are irreplaceable and must be protected from injury. Whether your eyes are at risk from sports or work, protection is available.

When playing sports, regular glasses won't protect your eyes from blows from elbows or hard, fast-moving objects. Sports glasses that have heavy frames made from strong, durable material can help protect the eyes against injury. They generally have a strap that fastens around the head so they won't fall off. Some sports, such as baseball and hockey, require additional protection. Players at certain positions need helmets with a safety shield to protect their eyes from flying objects.

Many people are exposed to hazards at work that can damage their eyes including flying particles, dust, fumes, vapors and harmful light rays. Protective eyewear is available to protect the eyes from potential hazards. Safety glasses have lenses that are impact resistant. They have frames that are stronger than regular glasses. Safety glasses must meet ANSI (American National Standards Institute) standards. They should have ANSI Z87.1 and ASTM F803-88 printed on the frame or lens. This means the frames meet rigorous safety testing. If the frames don't have those numbers, they may not be strong enough to protect your eyes. Safety glasses are available in prescription glasses. Additional protection such as side shields, cups, and tinted lenses can be added if needed.

Workers must wear appropriate eyewear for the hazard they work with. Safety goggles, which provide a secure shield around the entire eye, provide protection from hazards coming from any direction. They are impact resistant and can be tinted.

Face shields and helmets are used for welding or working with molten materials. They may also be worn if there is risk of exposure to chemicals, heat, or glare hazards. They do not offer enough protection for the eyes by themselves and must be used in combination with safety glasses or goggles.