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.

Is there a big difference between 8.4 and 8.6 base curve?

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.

What is the normal BC for contact lenses?

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.

Does the BC of contact lenses 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 the 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.

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

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 if the BC is wrong in contacts?

Lenses with the wrong base curve feel like they won't settle right on your eyes. If the lens is too curved for example, it may just slide around in your eye. Every time you blink, it may shift its position. This will make the lens extremely uncomfortable to wear.

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.

Can your base curve change?

In fact most labs today will not allow you to change or request a base curve at all. ... This completely overrides any use of the nominal lens formula or simple base curve calculations. 3) Never attempt to change the lens base curve to match a frame base curve.

What is BC 8.4 on contacts?

Basecurve (BC): This number indicates how curved your contact lens is. Your optician will try and match the curve of your contact lens to the curve of your eye to find the best fitted contact lens for you. E.g. BC 8.4.

What does power and BC mean for contacts?

Here's what those abbreviations mean: OD: Oculus dexter, the Latin term for right eye. OS: Oculus sinister, the Latin term for left eye. PWR: Power (also referred to as Sphere or SPH) BC: Base Curve (usually a number between 8 and 10)

How do I know the base curve of my eye?

Corneal Curvature

Generally, your eye doctor will use a keratometer to measure the curve of your cornea, which is the front surface of the eyes – where contacts rest. These numbers help to determine the lens diameter and base curve that appear on your contact lenses prescription.

Does base curve affect vision?

The base curve of a lens may affect certain aspects of vision, such as distortion and magnification, and wearers may notice perceptual differences between lenses with different base curves.

What is the astigmatism?

Overview. Astigmatism (uh-STIG-muh-tiz-um) is a common and generally treatable imperfection in the curvature of the eye that causes blurred distance and near vision. Astigmatism occurs when either the front surface of the eye (cornea) or the lens inside the eye has mismatched curves.

How important is diameter in contact lenses?

It's very important because it shows in which part of your eye the edges of the contact lens will rest. If the diameter is wrong, too small or too large it wont be stable on your eye and move around too much or it can be too tight and cause eye irritation and corneal abrasions.

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.

What is the smallest contact lens diameter?

The smallest sclerals are approximately 14.5 mm in diameter, and the largest can be up to 24 mm. Lenses that are 18 mm or smaller are subcategorized as mini-sclerals. The average human cornea is approximately 11.8 mm in diameter so even the smallest… Read More » The post What are scleral contact lenses?

How do I know the base curve of my contacts?

Base curve = 0.95 * 34.82 D = 33.07 D and then round up or down to the nearest whole diopter to arrive at the following final base curve to use for a contact lens over-refraction: Base curve = 33.00 D (actual measured base curve is 32.95 D)

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.

What is the best base curve for a lens?

To give eyeglass wearers close to the same range of vision, the backside of an optical lens should be close to a 6 base curve. Much flatter or steeper will affect the field of view and result in more head-turning.

What does BC and diameter mean for contacts?

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. ... Diameter (DIA): a number indicating your contacts' length to make sure they'll cover your cornea properly.

How do I choose a base curve for soft contact lenses?

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.

What is the base curve on glasses?

The base curve is the measurement of the lens curvature or how much the lens curves to the shape of the face. Depending on how high or low the base curve is indicates how curved or flat the frame and lenses will be.