Some are disposable and others need to be cleaned. When you learn which type you're going to get, you can start becoming an expert in how to wear them safely and keeping them clean. The most important thing about contact lenses is good hygiene to prevent infections in your eye. But the really fun part of new glasses or contact lenses is how well you can see. They can make your whole world look better! Reviewed by: Jonathan H.
Salvin, MD. Larger text size Large text size Regular text size. Why do some people need glasses and others don't? How Eyes Work The eyeball includes: the cornea say: KOR-nee-uh , clear tissue that helps the eye focus the iris , the colored part the pupil the black circle in the center of the iris, which is really an opening in the iris, that lets light enter the eye the lens , which also helps the eye focus the retina , at the very back of the eye.
It's easy to get the two confused: Nearsighted also called myopia means someone can see stuff that's near, like a book, but has trouble seeing stuff that's far away. Farsighted also called hyperopia means someone can see stuff that's far away clearly, but has more trouble seeing up close like reading the print in a book. Some farsightedness in kids is normal because they can focus their eyes to make up the difference. But some kids are very farsighted and need glasses or contact lenses.
What's the difference? An ophthalmologist is a medical doctor trained to treat vision problems; this includes prescribing eyeglasses and contact lenses, but also doing eye surgery for other eye-related problems. An optometrist is a licensed professional who specializes in eye exams and in figuring out the right prescriptions for eyeglasses and contact lenses.
An optician makes or sells eyeglasses and contact lenses according to an ophthalmologist's or optometrist's prescription. Convex lenses. These lenses are thickest in the center, like a magnifying glass. They are used to correct farsightedness hyperopia. Cylindrical lenses. These curve more in one direction than in the other. They are used to correct astigmatism.
If your child is old enough, let them play an active role in choosing their own glasses. Think about the features below when buying eyeglasses for children:. Ear pieces that wrap around the ear cable temples are advised for children under 4 years. Straps may also be advised to hold the glasses in place.
About 45 million Americans wear contact lenses. About 9 out of 10 people who wear contact lenses use soft lenses. In general, there are 2 types of contact lenses:. A contact lens prescription includes more information than an eyeglass prescription. Special measurements are taken of the curvature of the eye.
In addition, your child's healthcare provider will determine if their eyes are too dry for contact lenses. The provider will also see if there are any corneal problems that may prevent your child from wearing contact lenses. Trial lenses are often tested on the eyes first to ensure the correct fit. This spreads the light away from the center of the lens and moves the focal point forward.
The stronger the lens, the farther the focal point is from the lens. To make a plus lens above on the right , the thickest part of the lens is in the middle and the thinnest part on the outer edges. The light is bent toward the center and the focal point moves back.
The stronger the lens, the closer the focal point is to the lens. Placing the correct type and power of lens in front of the eye will adjust the focal point to compensate for the eye's inability to focus the image on the retina.
The strength of a lens is determined by the lens material and the angle of the curve that is ground into the lens. Lens strength is expressed as diopters D , which indicates how much the light is bent. The higher the diopter, the stronger the lens. Plus and minus lenses can be combined, with the total lens type being the algebraic sum of the two. To make a lens, the first thing you need is a lens blank. Blanks are made in factories and shipped to individual labs to be made into eyeglasses.
The bottom of the mold forms a spherical curve on the front face. A small segment with a stronger curve may be placed in the mold to form the segment for bifocals or progressive lenses.
And in case you've ever wondered, OD means right eye and OS, left eye. The lab technician selects a lens blank that has the correct segment called an add and a base curve that is close to the prescribed power. Then to make the power match the prescription exactly, another curve is ground on the back of the lens blank. See the illustration below. If it is needed, the cylinder curve is also ground at the same time. To create a lens with the strength of Corrective lenses can be made with glass or plastic, but nowadays, plastic is the most common.
While several different types of plastic are used in making lenses, all of them follow the same general manufacturing procedures. Most of the steps outlined also apply to glass, although a few important differences are noted at the end.
Step 1: The technician chooses a lens blank of the desired material with the proper base curve and, if needed, add power. Step 2: If the prescription calls for a cylinder, a line is marked on the front of the lens to define degrees, and then another line is drawn that matches the axis of the second curve.
If there is a segment, the segment edge is used as the degree line. Often the optical center of the lens is made slightly above the segment edge, and the line is marked the appropriate distance. Note: When there is no segment or induced prism, the lens may be left unmarked and the cylinder axis determined after the lens is ground. Step 3: Since the front of the lens will be left as is, it is covered by a special tape to protect it.
Step 4: Depending on the type of equipment, the lens must be prepared to fit onto the generator , which is commonly a compound surface grinder capable of grinding two curves at once. A chuck receiver called a block is placed on the front of the lens over the protective tape. If there is a cylinder curve, the lens is oriented so the cylinder axis matches the cylinder sweep axis of the generator. The center of the block will become the optical center of the lens.
Depending on the equipment, the lens may be held in place by special adhesive pads, with a special alloy that "glues" the lens to the block or with plastic. The lens might need other processing besides the compound curves produced by the generator, so the lens may also be tilted in the chuck. This tilt will offset the optical center called induced prism often used to allow thinner lenses or to accommodate special requirements of the prescription. Step 6: The curves are set on the machine and the lens is generated ground.
This step may either be fully automated or operated by hand, where the operator manually sweeps the quill grinding wheel across the lens, gradually advancing the lens until the desired lens thickness is achieved. Lens thickness is determined by curve type plus or minus , lens material some plastics are tougher and may be ground thinner , or other considerations safety glasses, for instance, are made thicker than lenses for everyday use.
If the lens gets too hot during the operation it may warp or tear, so it is cooled by water, which also washes away the cut material called scarf. Step 7: The lens is taken off the generator and placed in a special sanding machine called a cylinder machine to remove any marks left by the generator. Meanwhile the lenses are kept cool and cleaned with water. Following the sanding operation, the lenses are polished on an identical machine, except that felt polishing pads washed with polishing compound are used instead of sandpaper and water.
When this step is completed, the lens is optically clear without visible scratches. Step 8: The block is removed from the lens, and the lens is washed and inspected.
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