The axis of the eyeglass prescription is the distance between the eyeball and the lens. There are several different distances for this, including the IPD or Pupillary Distance and the BVD Back Vertex distance. Those are the two major kinds, but there are many others as well.
PD or IPD Pupillary Distance
If you have been prescribed eyeglasses or bifocals, you may have been given a number for the pupillary distance (PD) or IPD. This is important for getting a pair of glasses that are the right size. Incorrect PD values can cause double vision images, headaches, and fatigue.
It is recommended that you visit an eye specialist in order to get an accurate measurement of your pupillary distance. However, you can also measure your own PD.
To do this, you will need a ruler. You can also take a picture of your face with a smartphone camera.
You should stand about 8 inches from a well-lit mirror. When you are done, you should measure several times. Try to do this several times each day.
If you do not have a ruler, you can use a piece of paper or cardboard. You can also ask a friend for help. Make sure you have a good mirror and a clean background.
Sphere Cylinder and Axis
When an eye doctor prescribes glasses for a patient, it's important to know the different parts of the prescription. Among them, Sphere Cylinder and Axis are important. These numbers are used to determine how well the lenses correct astigmatism. They also determine the strength of the lenses.
The sphere is the most basic element of an eyeglass prescription. It describes the strength of the lens needed to produce clear vision. This number is commonly called the SPH value. It's measured in 0.25 diopters. For example, if a patient has a sphere of +1.00, it means that the person has farsightedness. If the sphere is -1.00, it means that the person has nearsightedness.
Cylinder power is the other major element of an eyeglass prescription. It's the amount of power needed to correct astigmatism. Typically, the cylinder power is written in minus form, but it can be converted to a plus form if a doctor wishes.
Astigmatism is a condition that causes blurred vision in all directions. It's caused by an irregularity of the cornea and the retina. In most cases, the axis and cylinder are included in an eyeglass prescription.
BVD Back vertex distance
The back vertex distance on an eyeglass prescription is a very important measurement. It allows for the adjustment of the power of the lens. This is especially important when the prescription goes above +/- four diopters.
If you need a little help with your eyeglass prescription, an optician is a great resource. They can explain what the numbers on the prescription mean, and can explain the difference between eyeglasses and contact lenses.
Back vertex distance is a measure of distance between the back of the eyeglasses lens and the apex of the cornea. The higher the vertex distance, the stronger the lenses.
When a person needs a high powered lens, the Back Vertex Distance is one of the first measurements to be taken. A small change in the vertex distance can affect the strength of the lens, and even reduce the field of view.
Having a good understanding of the back vertex distance on an eyeglass prescription can help you avoid readjustments or problems with your frame selection. Especially if you are ordering progressive powered lenses, it is critical to know what your Back Vertex Distance is.
Near, Inter, and Dist
The axis on eyeglass prescription is near, inter, and dist. They are used to describe the distance from the patient's eyes to the lens. This information is necessary to determine how strong the prescription should be.
AXIS is an acronym for Angle of Astigmatism in the Eye. It is a number between one and 180 degrees. Usually, people have astigmatism in one or two of their eyes. Having astigmatism can result in blurred vision. Using an axis is important to help your eye care provider position the cylinder power properly.
ADD, also called reading addition, is an abbreviation for added correction needed to correct close work such as reading. Generally, the ADD value is written as a positive (+) value. However, a doctor may put a minus sign or 'DS' in the cylinder field. Normally, a plus sign or 'DS' indicates that no astigmatism is present. If the ADD box is empty, this is a sign that the patient has no astigmatism.
