What Is The Formula For The Area Of A Sphere Which Prescriptions Go With Which Lenses?

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Which Prescriptions Go With Which Lenses?

You order glasses online.

You enter your prescription and the distance to the student. (Pupillary distance (abbreviated PD) is the distance from the center of one pupil to the center of the other pupil. Getting your glasses online is as necessary as your prescription.)

The website you order from reads these items and recommends lenses for your glasses.

How does it know which lens is right for you?

Here’s how. Every optical lens, from standard index to high index, single vision to multifocal, accommodates a range of prescriptions.

Let’s take a look at the different prescription lenses that opticians offer, the different types of prescriptions, and the types of prescriptions that the lenses cover.

The two broad prescription categories are single vision and multifocal. Multifocal prescriptions include bifocals and progressive medications.

Nearsightedness and farsightedness are corrected according to the numbers in the Sphere section of the prescription. Prescriptions for nearsightedness can be filled up to -20.00, for distance vision up to +12.00.

If you have astigmatism, it will be shown on your prescription with numbers in the Cylinder (CYL) and Axis (sometimes abbreviated “X”) fields. For single-vision prescriptions, ie those without numbers in the Near-Vision Reading ADDition section (NV-ADD or simply ADD), prescriptions in the CYL section can be filled up to + or – 6.00. The numbers under Axis or X simply refer to the angle at which the CYL, the actual cylinder invisible to the wearer, is placed on the lens.

A small number of eyeglass wearers have prism corrections in their prescription. They can be filled for single vision (non-multifocal) prescriptions up to 5:00 in any cardinal direction (base up, base down, base in, or base out).

Myopia prescriptions can be filled for people with numbers in the NV-ADD section of their prescription who want to get multifocal glasses, known as bifocals, which are glasses with a reading insert lined at the bottom of the lens. up to -9.00 and in case of farsightedness up to +6.00. You can go up to +3.50 on NV-ADD.

A type of multifocal glasses called progressives are glasses that have no visible line between the three different focus segments, which are distance vision (driving and watching TV) at the top of the lens, intermediate (computer) vision in the middle of the lens, and near (reading) vision at the bottom of the lens.

Prescriptions can be filled with larger corrections for progressives than for bifocals. Most progressives go up to -10.00 for nearsightedness and up to +8.00 for farsightedness. As with bifocals or single vision glasses, the CYL correction goes up to + or -6.00. And as with bifocals, the NV-ADD goes up to +3.50.

Here are the specific single vision lenses with their prescriptions.

For the mildest single vision prescriptions with SPH between -2.00 and +1.00 or lower and CYL +/- 2.00 or lower, the recommended lens is a 1.50 standard index lens.

This lens is made of CR-39 plastic. CR-39 plastic is a polymer (a polymer is a large molecule made up of many repeating subunits called monomers) that got its name because it was the 39th formula of the plastic developed in the Columbia Resins (hence the “CR”) project. 1940. This plastic was first used in the creation of glass-reinforced plastic fuel tanks for the B-17 bomber in World War II.

CR-39 plastic has a refractive index of 1.498, which is rounded to 1.50 in the optical world.

Another lens available for single vision prescription is the 1.57 medium index lens. This lens is often described as “polycarbonate composite” because in addition to the polycarbonate, the lens is made up of other polymers and resins that keep the lens thinner than a 1.50 lens. Its range is -4.00 /+2.00 or lower on SPH and +/- 6.00 or lower on CYL.

With an average index of 1.53, the Trivex lens is a polymer lens that is the most impact resistant lens available. It covers the same range as a 1.57 average index lens: -4.00/+2.00 or lower on SPH and +/- 6.00 or lower on CYL. It is recommended for rimless, children’s and sports glasses due to its exceptional impact resistance. However, unlike the 1.50 and 1.57 lenses, it cannot be tinted.

If $29.95 is more than you want to spend on an impact-resistant single-vision lens, a $1.59 clear polycarbonate lens for $9.00 might be preferable. It covers the same range as 1.57 Polycarbonate Composite and 1.53 Trivex lenses, with SPH of -4.00/+2.00 or lower and CYL of +/- 6.00 or lower. In addition, it is the second lens available in terms of impact resistance, a step down from the 1.53 Trivex lens in terms of impact resistance, making it a good and cheaper alternative to rimless, children’s and sports glasses.

Like the 1.53 Trivex lens, it can’t be tinted though, although it’s available as anti-glare polarized sunglasses and photochromic “auto tinting” lenses that darken in bright sunlight and clear again when you’re out of the sun. .

Occasionally, some people wearing rimless or half-frame glasses with 1.59 clear polycarbonate lenses have reported chromatic aberration, which means a rainbow-like reflection around the outer edge of the lens.

Additionally, the 1.59 pure polycarbonate lens tends to scratch more easily than the 1.50, 1.57, and 1.53 lenses because it is a softer lens material.

1.61 high index polymer single vision lenses offer a thinner lens for stronger prescriptions than medium and standard index optical lenses. It is suitable for SPHs of -6.00/+3.00 or lower, and like all the others except the 1.50 standard index lens, CYLs that go up to +/- 6.00.

A high-index lens reduces the edge thickness of myopic (-) prescriptions and the center thickness of far-sighted (+) prescriptions. Additionally, it has a flatter aspherical lens surface that improves the visual quality the wearer experiences while reducing eye distortion when others are looking at you.

Next up is the 1.67 high index polymer single vision lens. It offers a thinner prescription lens than standard 1.50, 1.53 Trivex, 1.57 mid-index, 1.59 polycarbonate and 1.61 high-index lenses. This includes SPHs of -20.00/+10.00 or lower and CYL of +/- 6.00 or lower.

Just like the 1.61 high index lens, the 1.67 lens reduces the edge thickness of myopic (-) prescriptions and the center thickness of farsighted (+) prescriptions. And like 1.61 high-index lenses, its aspherical lens surface improves the wearer’s visual quality while reducing the distortion of the wearer’s eyes that others see.

The highest index single vision plastic lens is a 1.74 high index polymer lens. This is for myopic (-) single vision prescriptions only. It offers a thinner lens for SPHs of -8.25 to -10.00 or lower and covers CYLs of +/- 4.00 or lower.

Just like the 1.53 medium index Trivex and 1.59 polycarbonate lenses, the 1.74 lens cannot be tinted. It is not available as a polarized or photochromic lens. Like the 1.61 and 1.67 high index lenses, it has an aspherical surface that improves the visual quality of the wearer while reducing the distortion of the wearer’s eyes that others see.

Anti-reflective coatings are suitable for all optical lenses, but are especially recommended if you are getting a high index lens. They reduce glare and reflection and let more light through the lens, improving contrast, which improves visual acuity.

This includes single vision lenses.

The most common type of bifocal lens is the 28 D-style near-sighted reading segment lens. This means that the top of the bifocal segment lens is flat and the bottom is curved, which is why the bifocal lens looks like a big D on its side. It is called “flattop 28” because the widest part of the bifocal segment lens is 28 millimeters (mm).

One of the bifocal lenses is a CR-39 plastic bifocal lens with a standard index of 1.50. It is just like a 1.50 standard index single vision lens, except it has a bifocal segment. This lens is suitable for SPH of -3.00/+1.50 or lower when CYL is +/- 6.00 and ADD is +3.50 or lower.

The bifocal segment line is located 2 mm below the center of the lens. So if you have a 30mm high lens, the bifocal segment is 13mm from bottom to top, 2mm below the 15mm centerline.

1.61 high index aspherical bifocal polymer lens provides a thinner lens for prescriptions with SPH of -9.00/+6.00 or less, CYL of +/- 6.00 or less and ADD of +3.50 or less .

As with single vision high index lenses, an anti-reflective coating is recommended for high index bifocals.

Now let’s look at progressive lenses.

Progressive (no-line multifocal) glasses follow the same pattern as single vision lenses in terms of the index of the distance part of the lens. They deviate slightly from bifocals in the nearsighted reading segment. “Free-form” style progressive lenses have a reading corridor of approximately 14 mm, which is approximately half the width of a bifocal lens.

The 1.50 standard index progressive CR-39 plastic lens covers SPHs of -2.00/+1.00 or lower, CYLs of +/- 6.00 or lower, and ADD powers of +3.00 or less. The 1.57 average index progressive polymer lens covers SPHs of -4.00/+2.00 or lower, CYLs of +/- 6.00 or lower, and ADD power of +3.50 or lower.

With a 1.53 average index, the Trivex progressive lens, like the single vision Trivex lens, has the highest impact resistance of our included lenses. Like the single vision Trivex lens, this lens cannot be tinted. It is slightly thinner than the standard 1.50 index lens. It covers SPHs of -4.00/+2.00 or lower, CYLs of +/-4.00 or lower, and ADD power of +3.00 or lower. It is recommended for rimless and sports glasses, but unlike the single vision Trivex lens, it is not recommended for children who are only rarely prescribed multifocal glasses.

The properties of the following progressive lenses, the 1.59 medium index pure polycarbonate progressive lens and the high index 1.61 and 1.67 lenses, follow the same pattern as the single vision lenses. 1.59 progressive lens, which, like the Trivex lens, cannot be tinted (although it can be ordered as polarized, anti-glare sunglasses or with photochromic, “auto-tint” lenses), covers SPHs of -4.00/+2.00 or lower , CYL -id +/- 4.00 or less and ADD +3.00 or less.

The high-index 1.61 progressive polymer lens covers SPHs of -6.00/+3.00 or lower, CYLs of +/- 6.00 or lower, and ADDs of +3.00 or lower. The high-index 1.67 progressive polymer lens covers SPHs of -10.00/+8.00 or lower, CYLs of +/- 6.00 or lower, and ADDs of +3.00 or lower. As with single vision lenses, anti-reflective coatings are recommended for high index lenses.

Now you know all the features of all prescription lenses.

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