The stronger your prescription is, the further the number is from zero. The back curve of the contact lens is measured in millimeters. This number is usually between 8 and 10mm. – this referrethance curve is calculated by measuring the distance between the lens and the cornea. The distance is measured from the center of one eye to a point on the other eye, which is called the “base curve”.
The base curve can be used to determine the strength of a prescription, but it is not a good indicator of how well the prescription is working. For example, if a person has a very strong prescription for their left eye and a weak one for the right eye (which is the case for most people), then the person’s left-eye prescription will be stronger than the one on their right.
However, this does not necessarily mean that the two prescriptions are the same strength. In fact, it may be that one of them is weaker, or that both are equally strong, depending on how the eye is positioned in relation to each other.
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How do you read a contact container prescription?
The distance from one edge of the contact lens to the other is called the diameter. The power of the lens strength may be different for each eye. For example, if you have a lens with a power of 1.5 DIA, and you are wearing eyeglasses, you will need to wear a pair of glasses that are at least 2 times stronger than this lens.
If you do not know the size of your eye, use a ruler to measure it. If the ruler is too big, it will not be able to fit in the eye socket, so you may have to use tape to hold it in place.
What is the BC number on contact lenses?
The back curve of your contact lens is measured using the ‘BC’ or base curve measurement. BC of your contact lenses should match your eye’s natural curve as closely as possible to ensure a better fit when you wear them. To measure your BC, take a piece of paper and write down the distance between your eyes and the centre of the lens.
You can use a ruler or a tape measure to measure this distance, or you can measure it with a digital caliper. If you are wearing contacts, you will need to take them out of their case and place them on a flat surface, such as a desk or table, to make sure they are in the correct position.
Then, place the contact in front of you and look at it from the side. BC should be between 0.5mm and 1.0mm, depending on the type of lens you have. For example, if your lens has a BC measurement of 2.2mm then you should have an eye-relief of between 2 and 3cm (1.8-2.4 inches). If this is not the case, please contact your optician or ophthalmologist for advice.
What is the cylinder and axis on contacts?
For contact lens production, the cylinder value is required. The exact position of the cornea is described in a range of values from 0 to 90. This angle is measured in degrees.
The axis is defined as the distance from the center of a lens to a point on a line that is perpendicular to that lens. For example, the axis of an eyeglass frame is the line from center to center, or the point at which the eyepiece is centered in the frame.
How do I know my contact lens power?
GP lens is selected with a base curve radius that’s one-half diopter flatter (less curved) than the cornea, a contact lens power of -2.75D would be predicted. A contact lens power less than 1.5D is predicted if the base curve radius is a half diopter steeper than the cornea.
The formula for calculating the power required for a lens to achieve a given corneal curvature is given in the table below. Note that this formula is based on the assumption that the lens has the same diameter as the eye, which is not always the case.
For example, if you are wearing contact lenses that have a diameter of 0.8mm, the formula would predict that a 0D lens would require -0.2D contact power, while a 1.0D one would need +1D. In fact, it is common for lenses to have different diameters at different times of life, with some lenses having a larger diameter at one time than at another.
