The base curve of a contact lens is **the curvature of the back surface of the lens**. It determines the type of fit the lens must have to match the natural curvature of your eye.

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**.

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**Is there a big difference between 8.4 and 8.8 base curve?**

**A BC of 8.4 mm of radius is more curved**, and therefore a tighter fit, than 8.8 mm base curve. People who have steeper corneas require tighter fitting contacts.

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

The part of the lens that comes in contact with the eye. For soft contacts **there is not much difference between an 8.6** and 8.8 BC. The 8.8 BC is “flatter” than the 8.6 lens, meaning that the 8.6 lens has slightly more curvature or “steeper”. The 8.6 base curve will be a better fit for most people.

**How do I choose the right base curve for contacts?**

Figuring out the proper base curve based upon Rx is fairly simple: **Plus Power – Use the Spherical Equivalent (Sphere power plus half the cylinder power) and add 4.00 diopter to that**. Example – Rx of +2.50, the base curve will be approximately 6.50.

## What happens if you get 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.

## What is the most common base curve 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 big difference between 8.5 and 8.6 base curve?

**No there is not a big diff between the two base curves**. However, it’s the relationship between diameter and base curve that is more important. Also, the material of the lens can also affect the fit. You can have 3 diff contact lenses with the same BC, Diameter and power and they will all fit differently.

## What is the difference between 14.0 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. … Many 14.0mm contacts users use 14.5mm or 14.8mm contacts to demonstrate dolly effects on their eyes.

## Does base curve and diameter matter?

The diameter and base curve are **important factors** in determining what the optimum fit is for you. A proper fit ensures full coverage of the cornea, optimum edge alignment, and adequate movement of the lens for tear exchange.

## 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**.

## What does 8.7 mean on contacts?

The 8.7 curve is **.** **1mm flatter**, but since these are soft lens curvatures, and soft lenses assume some of the shape of the cornea, the fitting value won’t be changed dramatically. However, if you were prescribed an 8.7 B.C., and you purchased an 8.4 B.C., you might run into some comfort issues.

## What does axis mean for contacts?

The axis indicates **the angle (in degrees) between the two meridians of an astigmatic eye**. The axis is defined with a number from 1 to 180. The number 90 corresponds to the vertical meridian of the eye, and the number 180 corresponds to the horizontal meridian.

## 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.

## How do I figure out my contact lens base curve?

**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)

## Does base curve matter in contacts?

**Yes they do matter**. The BC, or base curve, is measured based on your cornea’s curvature. If the base curve is too small, it’ll squeeze your eye, and if it is too big, it won’t stay on your cornea. These both may cause damage to your eye.

## 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:**

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

## 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 happens if I wear the wrong prescription contacts?

One of the most common effects of wearing the wrong contact lens prescription is **blurry vision**. Since contacts are meant to improve vision, the wrong prescription will typically cause impairment in a person’s vision, says the U.S. Food and Drug Administration.

## What size are normal contacts?

The diameter of regular contact lenses that are sold in the United States are on average **14mm–16mm**. Similar to the diameter of regular contact lenses, circle lenses have no more than 15mm diameter since larger sizes would be harmful to the eyes at daily wear.

## What is the average power for contacts?

The power of your lens in measured in dioptres and this indicates the level of correction your lens must provide to correct and sharpen your vision. The correct power should normally give you **20/20 vision**.

## What is a normal eye diameter?

Conclusion. The size of a human adult eye is **approximately 24.2 mm (transverse) × 23.7 mm (sagittal) × 22.0-24.8 mm (axial)** with no significant difference between sexes and age groups. In the transverse diameter, the eyeball size may vary from 21 mm to 27 mm.

## What does BC and DIA mean for contacts?

**BC – Base Curve (usually a number between 8 and 10)** **DIA – Diameter (usually a number between 13 and 15)** Brand – The brand/type of contact lens that your doctor has fitted you for.

## Is there a difference between 14.2 and 14.3 diameter contacts?

**Yes they do matter**. The BC, or base curve, is measured based on your cornea’s curvature. If the base curve is too small, it’ll squeeze your eye, and if it is too big, it won’t stay on your cornea.

## How do you know the diameter of your eye?

Technique 1: Corneal Topographer

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.

## How is base curve measured?

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.

## What does median base curve mean?

Base Curve. … BC median refers to a **base curve 8.7 mm**. Diameter. Abbreviated “DIA” the diameter of a lens measures the width of a lens in millimeters, from end to end. The average size of a contact lens is between 13.5 and 15 millimeters.

## What is base curve radius of contact lens?

Typical values for a contact lens are from **8.0 to 10.0 mm**. The base curve is the radius of the sphere of the back of the lens that the prescription describes (the lower the number, the steeper the curve of the cornea and the lens, the higher the number, the flatter the curve of the cornea and the lens).

## Why are my eye axis so different?

However, **if one has astigmatism, their cornea and lens are not equally curved** and, therefore, they might have a different eye axis in comparison to that of a normal cornea. For example, if you have an axis 180 eye, your astigmatism is horizontal. Research shows that 1 in every 3 people have astigmatism.

## What does 180 axis mean in eye prescription?

Axis – The third number indicates the direction of your astigmatism. For example, an axis of 180 degrees means **the astigmatism is horizontal**. If your prescription doesn’t have a second or third number, you most likely don’t have astigmatism.

## What does 150 axis mean in eye prescription?

The axis for both eyes falls between 150 and 180, so this prescription would correct “with-the-rule astigmatism,” (see sidebar, above) meaning **the vertical meridian of each cornea is steeper than the horizontal meridians**. Meridians and Rx’s.

## What does D mean on contacts?

Sphere (SPH): The amount of lens power, measured in diopters (D), which **corrects nearsightedness or farsightedness**. If the number under this heading features a minus sign (–), this means you’re nearsighted, if it has a plus sign (+), this means you’re farsighted.

## What is the strongest contact lens prescription?

What is the strongest contact lens prescription? Contact lenses can be prescribed for extreme degrees of myopia, even for those who need correction of more than -20 Dioptres. Some lenses can go over -30 Dioptres. For monthly soft contact lenses, the highest level of corrective power is about **-12 Dioptres**.

## FAQs

### Does base curve on contacts really matter? ›

Yes they do matter. The BC, or base curve, is measured based on your cornea's curvature. If the base curve is too small, it'll squeeze your eye, and if it is too big, it won't stay on your cornea. These both may cause damage to your eye.

**What base curve should I choose for contact lenses? ›**

Their pliability and flexibility allows to them to fit virtually the entire population, making them nearly one-size-fits-all. 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.

**Should I get 8.4 or 8.8 base curve? ›**

**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.

**How do I figure out my contact lens base curve? ›**

Figuring out the proper base curve based upon Rx is fairly simple: Plus Power – **Use the Spherical Equivalent (Sphere power plus half the cylinder power) and add 4.00 diopter to that**. Example – Rx of +2.50, the base curve will be approximately 6.50.

**What if my base curve is off? ›**

A base curve that is too small can cause the contact lens to sit too tightly on the cornea. Mild symptoms might include **discomfort or dry/itchy/red eyes, but it can also block off oxygen supply or even damage the cornea**.

**What base curve do I need? ›**

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. In theory +6.00 should always give you the best possible combination of curves for weight, optics, etc.

**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. Consequently, some practitioners may specify "match base curves" on a new prescription.

**Does base curve change over time? ›**

**Base curve can also change as you wear a contact lens** based on environmental factors like the lens drying out, temperature changes, and exposure to makeup or soaps.

**Is there a difference between 8.4 and 8.5 BC? ›**

**No there is not a big diff between the two base curves**. However, it's the relationship between diameter and base curve that is more important. Also, the material of the lens can also affect the fit. You can have 3 diff contact lenses with the same BC, Diameter and power and they will all fit differently.

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

**The 8.8 BC is “flatter” than the 8.6 lens, meaning that the 8.6 lens has slightly more curvature or “steeper”**. The 8.6 base curve will be a better fit for most people. In general, 8.8 BCs are more likely to fit loose and move excessively on the eye.

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

...

**Still another method is to use the following as a guide for selecting base curves:**

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

**Is there a big difference between 8.6 and 8.7 base curve? ›**

“Is there a big difference between 8.6 and 8.7 base curve in contact lenses?” **No, the difference is small**. The 8.7 curve is . 1mm flatter, but since these are soft lens curvatures, and soft lenses assume some of the shape of the cornea, the fitting value won't be changed dramatically.

**How do I figure out my contact lens prescription from my glasses prescription? ›**

Can I use my glasses prescription for contact lenses? The simple answer to this question is no – **you cannot and should not use your glasses prescription to try to calculate your contact lens prescription**.

**What is the strongest contact lens prescription? ›**

What is the strongest contact lens prescription? Contact lenses can be prescribed for extreme degrees of myopia, even for those who need correction of more than -20 Dioptres. Some lenses can go over -30 Dioptres. For regular soft contact lenses, the highest level of corrective power is about **-12 Dioptres**.

**Can I wear normal contact lenses with astigmatism? ›**

Q: Can you wear regular contact lenses if you have astigmatism? A: **No, if you have astigmatism, it's essential that you wear specialized contact lenses because your condition can worsen if not**. Regular contact lenses do not cover your cornea's entirety, which will impair your ability to see even further.

**How do I know if my base curve is too big? ›**

What happens if the base curve size is wrong? If you realize that you've gotten contact lenses with an incorrect base curve, you may feel it. **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.

**Can contacts be too big for eyes? ›**

Even a slight difference in the diameter measurement (even less than a centimeter) can affect how your contact lens feels in your eye. Wearing a contact lens that doesn't fit is not only uncomfortable; it can affect your vision.

**What is the base curve of my eye? ›**

The base curve refers to **the degree of curvature of the contact lens, or how closely it fits against the eyeball**. A lower BC, like 8.40, means the lens is more curved and will fit snugly against the eye. Higher BCs like 8.70 indicate a flatter lens.

**What is the average eye size for contacts? ›**

Contact lens fitting

The average HVID in the general population is 11.8mm.

**How does decreasing the base curve impact the fit of a contact lens? ›**

Flattening the base curve by increasing the base curve value or decreasing the overall diameter of the contact lens will **decrease the sagittal depth** and correct for a tight fitting lens.

### How do contacts correct astigmatism? ›

Toric contact lenses are often the best choice for contact lens wearers with an astigmatism, because they're specifically designed to address the problem. **The special shape of a toric lens creates different refractive, or focusing, powers that can help correct either a corneal or a lenticular astigmatism**.

**What does 6 base curve mean? ›**

A 6-base curve is **a medium base with a minimal curve**. If you have a high prescription, the flatter base curve will accommodate the stronger correction. However, the lower the base curve, the more light will be let in through the sides of your sunglasses.

**What does BC mean when ordering contacts? ›**

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 does base mean on an optical prescription? ›**

The base **relates to the standard curvature of the frame, also known as wraparound effect**. The higher your prescription number, the more wraparound the frame is. On average, eyeglasses should have no more than a base of 4-6. However, the base can go as high as 8, especially for non-prescription sunglasses.

**How do you measure your eyes for contacts at home? ›**

Contact Lenses - Ocular measurements - YouTube

**What is the smallest size of contact lenses? ›**

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 scleral contact lens is designed to cover the entire corneal surface.

**Is BOZR the same as base curve? ›**

Back optic zone radius (BOZR); **sometimes referred to as the base curve (BC)**, the historic general rule of thumb describes a choice of BOZR within the range of flattest keratometry readings plus 0.7 to 1.0 mm, however, little correlation has been seen between BOZR and optimal fitting.

**What it is astigmatism in the eye? ›**

Astigmatism **occurs when the cornea or lens is curved more steeply in one direction than in another**. You have corneal astigmatism if your cornea has mismatched curves. You have lenticular astigmatism if your lens has mismatched curves. Either type of astigmatism can cause blurred vision.

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

**The 8.8 BC is “flatter” than the 8.6 lens, meaning that the 8.6 lens has slightly more curvature or “steeper”**. The 8.6 base curve will be a better fit for most people. In general, 8.8 BCs are more likely to fit loose and move excessively on the eye.

**Is there a big difference between 8.6 and 8.7 base curve? ›**

“Is there a big difference between 8.6 and 8.7 base curve in contact lenses?” **No, the difference is small**. The 8.7 curve is . 1mm flatter, but since these are soft lens curvatures, and soft lenses assume some of the shape of the cornea, the fitting value won't be changed dramatically.

### Is there a difference between 8.4 and 8.5 BC? ›

**No there is not a big diff between the two base curves**. However, it's the relationship between diameter and base curve that is more important. Also, the material of the lens can also affect the fit. You can have 3 diff contact lenses with the same BC, Diameter and power and they will all fit differently.

**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. Consequently, some practitioners may specify "match base curves" on a new prescription.

**Can your base curve change over time? ›**

**Base curve can also change as you wear a contact lens based on environmental factors like the lens drying out, temperature changes, and exposure to makeup or soaps**.

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

...

**Still another method is to use the following as a guide for selecting base curves:**

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

**Is 8.4 or 8.6 base curve? ›**

8.6 is standard base curve used by most soft contact lens company. If you were been advised 8.4 base curve I would suggest to stick to same base curve as flatter curve (8.6) may cause discomfort.

**How does base curve affect contact lenses? ›**

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.

**How do contacts correct astigmatism? ›**

Toric contact lenses are often the best choice for contact lens wearers with an astigmatism, because they're specifically designed to address the problem. **The special shape of a toric lens creates different refractive, or focusing, powers that can help correct either a corneal or a lenticular astigmatism**.

**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 8.6 base curve normal? ›**

**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.

**What is the normal contact lens size? ›**

Most traditional soft contact lenses have an overall diameter of **14.0 mm to 14.2 mm**, which may not provide adequate coverage or centration for a cornea that is larger than 12.0 mm.

### What is the smallest size of contact lenses? ›

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 scleral contact lens is designed to cover the entire corneal surface.

**How do I know if my base curve is too big? ›**

What happens if the base curve size is wrong? If you realize that you've gotten contact lenses with an incorrect base curve, you may feel it. **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.

**What is base curve on eye prescription? ›**

The base curve refers to **the degree of curvature of the contact lens, or how closely it fits against the eyeball**. A lower BC, like 8.40, means the lens is more curved and will fit snugly against the eye. Higher BCs like 8.70 indicate a flatter lens.

**What does 6 base curve mean? ›**

A 6-base curve is **a medium base with a minimal curve**. If you have a high prescription, the flatter base curve will accommodate the stronger correction. However, the lower the base curve, the more light will be let in through the sides of your sunglasses.