It is required when eye alignment needs assistance. It is indicated as follows:. Each one of these indicators provide information about the base direction or the thickest edge of the prism.
Coastal does not offer prism prescription glasses. In addition to the general parameters, eyeglass prescriptions can require a Pupillary Distance PD. Your PD is the distance between the center of one pupil the central black dot of your eye to the center of the other pupil.
It is measured in millimeters and is an important part of your prescription. PD indicates where the optical center of your lenses should be placed, so you can have the best, most comfortable vision. If you see a — , it indicates nearsightedness. In the sample below, the right eye is prescribed This eye needs a cylinder of The ADD value is usually present in a multifocal prescription.
The left eye is prescribed with a sphere of Without the ADD value, it is a single vision prescription. The differences between each type of glasses are not always clear. To understand how to correctly read a prescriptions for glasses, here is an overview of the main categories of lenses that can be written on your prescription. Single vision lenses : a large majority of glasses come with single vision correction. This common type of lens is generally used to correct nearsightedness, farsightedness or used as reading glasses.
Bifocal lenses : these glasses come with two vision corrections. One is on the lower part of the lens to help you read or see from near, and the other on the upper part includes a distance prescription. Progressive lenses : multifocal lenses offer multiple corrections in one pair. These prescriptions have a no-line lens and offer intermediate distance vision, which can be adapted for certain specific uses, such as computer work. You may also find additional information on your glasses prescription such as the suggestion of certain types of lens coating and special comments from your optometrist.
If you have questions about anything on your prescription, feel free to give a call to our customer service team. Vision enhancement: a special treatment for one or both lenses used to improve vision and clarity through your glasses. You could find different options such as:. Anti-reflective coating : enhances clarity and concentration by allowing more light to come in and reduces reflection.
When the sun comes up, your glasses turn into sunglasses! Polarized : improved glass technology designed to filter and reduce glare. Polarized lenses offer more clarity and a sharper vision to their wearers. Although roughly 3 out of every 4 people in America require corrective lenses, according to research from the Vision Council, many do not understand what their eye prescription means. A person with any questions about what their prescription means should speak to their optician who can answer any questions and help explain the numbers.
Usually, these differences are not due to illness. For example, children do not fully develop the ability to focus both eyes on one object at the same time until they are 7 years old. Although not all older adults will have eye problems, several eye conditions have associations with age, including:. The most common age-related change is presbyopia. More than one-third of Americans experience this condition, which develops as the aging eye lens becomes less flexible and stiffer.
People can start developing presbyopia when they are in their 20s. As people age, the muscles that control the size of their pupils become weaker, which makes it more difficult for the eyes to adjust to changes in light. The pupils generally become smaller, which makes it more difficult for a person to see in low light conditions, such as driving at night.
People can take steps to protect and enhance their vision. Key recommendations from the National Eye Institute include:. According to the Centers for Disease Control and Prevention CDC , 61 million adults in the United States face a high risk of vision loss, but only half of them have seen an eye doctor in the past year.
Regular, thorough eye exams play a crucial role in maintaining and improving vision because they can catch potential eye problems early. According to the American Academy of Ophthalmology , a complete eye exam should include:. A small chuck receiver is placed where the geometrical center of the finished lens will be, and the lens is then oriented on the axis.
Usually, only an adhesive pad is needed to hold the receiver on the lens. The lens is chucked in the edger and held in place by a pressure pad that presses on the opposite side of the lens like holding a very large coin between your thumb and forefinger at its center.
Step A pattern in the shape of the frame is inserted in the edger. Patterns are commonly plastic and may be supplied by the frame manufacturer or made in the lab.
Newer edgers do not use patterns; instead, the shape is determined by a probe that measures the frame and stores the information in a computer, which in turn controls the edging operation. As it operates, the slowly turning lens is brought into the fast turning cutting surface, which is either a grinding wheel or steel blades, until a guide contacts the pattern, which is rotating to match the lens.
If the frame has a complete rim surrounding the lens, a bevel, or ridge, is cut along the edge of the lens that will fit into a groove in the frame; otherwise, the edge is left flat. Step The lens is inserted into the frame.
Fit and orientation is double checked, any worn screws or hinges are replaced as needed, and the frame is made square. The finished eyeglasses are then thoroughly cleaned and packaged for delivery to the patient.
Glass lenses are ground and polished much the same way as plastic except that diamond cutting surfaces are used, and some details may vary. The blanks are made of relatively soft glass and must be tempered, either by chemicals or heat, to strengthen them before inserting into the frame.
Advances in automation are rapidly changing how lenses are made. For example, the vast majority of labs now use computers to determine curve parameters and lens choice, and equipment is available that will combine several steps or even do the entire operation automatically. For more information about corrective lenses and related topics, check out the links on the next page. Bob Broten is an American Board of Opticianry-certified optician and certified laboratory technician at Lenscrafters Inc.
He holds a bachelor's degree in biology and did extensive research in fish vision while pursuing his degree. Author's note: I am indebted to Erik Schopp, A. O-certified optician and general manager of Lenscrafters , and Dr. Dawne R. Griffith, O. Robert D.
Optics and optometry are complex subjects beyond the scope of this article. In presenting the basic principles of these two disciplines, I've oversimplified somewhat for the sake of brevity. For this I apologize. Any errors in fact or theory are entirely mine. I encourage interested readers to seek professional advice, as this article is a brief overview and not intended as a guide to diagnoses. Also, I am grateful to Lenscrafters store in Portland and to Joshua Boyd, lens technician, for help in taking the photos used with this article.
Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Everyday Innovations. How Corrective Lenses Work. Test your eyes. How Your Eye Focuses On the back of your eye is a complex layer of cells known as the retina. When you look at something, three things must happen: Advertisement.
The image must be reduced in size to fit onto the retina. The scattered light must come together -- that is, it must focus -- at the surface of the retina.
The image must be curved to match the curve of the retina. Read More. Out of Focus Sometimes, for different reasons, the eye doesn't focus quite right: The surfaces of the lens or cornea may not be smooth, causing an aberration that results in a streak of distortion called astigmatism.
The lens may not be able to change its curve to properly match the image called accommodation. The cornea may not be shaped properly, resulting in blurred vision. Myopia nearsightedness occurs when a distant object looks blurred because the image comes into focus before it reaches the retina. Myopia can be corrected with a minus lens, which moves the focus farther back. Hyperopia farsightedness occurs when a close object looks blurred because the image doesn't come into focus before it gets to the retina.
Hyperopia, which can also occur as we age, can be corrected with a plus lens. Bifocal lenses, which have a small plus segment, can help a farsighted person read or do close work, such as sewing. Astigmatism is caused by a distortion that results in a second focal point. It can be corrected with a cylinder curve. How a Lens Works " ".
Determining Lens Strength The strength of a lens is determined by the lens material and the angle of the curve that is ground into the lens. A spherical lens looks like a basketball cut in half. The curve is the same all over the surface of the lens. A cylindrical lens looks like a pipe cut lengthwise. The direction of a cylinder curve's spine axis defines its orientation. It will only bend light along that axis.
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