Base Curve (BC): The base curve determines what type of fit is required for the lens to meet the curve of your eye; this is usually written in millimeters or sometimes with the words: flat, median or steep.

What is normal BC for contacts?

Typical base curve values range between 8.0 and 10.0 mm, though it can be flatter (from 7.0mm) if you have a rigid gas-permeable lens. A person with a higher base curve number has a flatter cornea (the clear, front surface of the eye) compared to someone with a lower base curve number, which indicates a steeper cornea.

Is there a difference between 8.4 and 8.6 BC?

Studies show that a single base curve of 8.4mm managed a “good or better” fit in approximately 90% of individuals,¹ and base curves of 8.4mm and 8.6mm together encompassed 98% of individuals.

Does the BC on contacts matter?

You should never order contact lenses with a base curve that is different from your prescription. This can damage your eyes and cause problems with vision. This is especially important for people who purchase cosmetic coloured contact lenses, which are often of a standardised size.

What is BC and DIA in contact lenses?

1. Base Curve (BC): the number that indicates your contact lens' shape. According to the steepness or flatness of your cornea, your prescription indicates how large your contact lens should be. 2. Diameter (DIA): a number indicating your contacts' length to make sure they'll cover your cornea properly.

The numbers on your contact lens (what do they mean) | Lens Parameters

What is DIA in eye prescription?

Diameter: This stands for Diameter and is the length of the contact lens from one edge of the lens to the other. This is effectively the size of the contact lens and is used to make sure the contact lens covers the correct parts of your eye. E.g. DIA 13.8.

What happens if you wear the wrong base curve?

If your lenses have the wrong diameter or base curve, you'll likely feel that something is always in your eye. If the lenses are too flat, your eyelids will tend to dislodge them when you blink. The wrong size lenses can even cause an abrasion of your cornea.

How do you calculate BC for contact lenses?

1. For plus power use the spherical equivalent (SE) and add 4.00 diopters to that. For example, if you have an Rx of + 2.00 sphere, the base curve for the lens will be approximately 6.00.
2. Rx +2.00Sph -> [+2.00 +4.00D] = 6.00BC.

What is the difference between 14.1 and 14.2 diameter contacts?

14.0mm and 14.2mm contacts

In fact, there is not much difference between these two. Some manufacturers only make 14.2mm diameter contacts, and some others produce 14.0mm diameter contacts. ... In other words, the predominant size for the small contacts is between 14.0mm to 14.2mm.

What base curve should I choose?

The most basic rule is that you always want the base curve to be as close to +6.00 as you can get and still have the Rx work. ... The more minus the power (less plus power to minus power) the lower plus the base curve will become. A high minus Rx may even have a base curve of +0.25 or even 0.00.

How do you know the diameter of your eye?

For accuracy and consistency, always measure from the white part of one side of the eye directly across to the white part of the other side of the eye. Reference the example image below; the corneal diameter or visible iris diameter measures 12.01mm.

How important is BC contact lenses?

The 'BC' or base curve measurement indicates the back curvature of your contact lens, in millimetres. This is important for comfort, as the BC of your contact lenses should match your eye's natural curve as closely as possible to ensure a better fit when you are wearing your contact lenses.

Is there a big difference between 8.6 and 8.8 base curve?

A base curve of 8.6 mm of radius is more curved, and therefore a tighter fit, compared to the 8.8 mm base curve. People who have steeper corneas require tighter fitting contacts. If a contact is too loose, it may be uncomfortable, fold, or come right out.

What is the most common BC for contact lenses?

The base curve, or BC, is the radius of the back of the contact lens, the part that sits on your eye 3. According to Laser Eye Surgery Review , the average measurement of a base curve is between 8.0 and 10.0 3. An example of a common base curve would be BC 8.7mm.

What is the difference between 8.4 and 8.8 BC?

The 8.4mm base curve is still the likely best fit for the majority of eyes. In instances when the 8.4mm lens is too steep, the 8.8mm lens allows a flatter option. This is more likely needed in smaller eyes, and possibly in some very flat corneas. ... Oasys lenses are approved for up to six nights of continuous wear.

How do you find the base curve?

How To Measure The Base Curve? The base curve of any lens can be measured with a tool called a radius gauge, also known as a lens clock. A lens clock has three prongs that can measure the curvature of lenses (and other surfaces). When those 3 prongs are place against a flat surface, the gauge should read zero.

How do I choose a contact lens base curve?

Adjusted base curve in mm + 0.3mm = soft lens base curve.
...
Still another method is to use the following as a guide for selecting base curves:

1. If Low K is >45.00D, then fit the steeper BCR.
2. If Low K ranges from 41.00D to 45.00D, then fit the median BCR.
3. If Low K is <41.00D, then fit the flatter BCR.

Does base curve have to be exact?

The base curve number would be a number between 8.0 and 10.0 millimeters and would be more precise because these lenses need to fit just right. Now that most contact lenses dispensed are soft lenses, this measurement doesn't need to be quite as precise.

How do you tell if your contacts are not the right size?

Place the contact lens between the tips of your thumb and forefinger, grasping it near the center so the entire edge is free. Gently squeeze the lens, as if you are about to fold it in half. If the edge of the lens points upward (resembling a hard-shell taco), the lens is correctly oriented.

Is cylinder and BC the same?

Astigmatism can be corrected by toric contact lenses. Base Curve. Abbreviated “BC,” the base curve of a lens indicates the curvature on the inside of a lens. ... The cylinder is an oval band on a lens that enables an individual to see all ranges clearly at once and is measured in diopters, like spherical power.

What is SPH and CYL and axis?

SPH “sphere” indicates the amount of lens power prescribed for nearsighted or farsighted vision. It is measured in diopter and uses (+) for farsightedness (hyperopia) and (-) for nearsightedness (myopia). 4. CYL & AXIS: a Cylinder (CYL) and Axis number (between 0 and 180 degrees) are required to correct Astigmatism.

What does 0.0 mean for contacts?

0.00x means that there is no magnification....they are plain glass lenses.

What is the average PD for a woman?

An average PD measurement is about 62mm for women and 64mm for men. For children the measurement usually ranges from 41 to 55 mm.