What does the base curve mean in contact lenses?
What is the base curve? 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. 1 It is usually expressed in millimetres and may be further characterised as steep, median, or flat.
How important is the base curve in contact lenses?
“ How important is the base curve of contact lenses? ” The base curve can be very important with RGP (rigid gas permeable) lenses, and a bit less important with soft lenses. The relationship between the curves of the cornea, and the curve of the lenses, will have impact on the dioptric power of the lens, as well as on the amount of movement the lens exhibits.
Can I wear contact lens of bigger base curve?
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. Can I order contact lenses with a different diameter?
How do you calculate base curve?
How do you calculate base curve? Simple Rule for estimating lens base curve on a MINUS POWER lens. For minus power lenses take half of the spherical equivalent and add 4 diopters to that. For example a -4.00 sphere power you would use -2.00 (half of the SE) + 4D, which would give you a 2BC. ie Rx -4.00sph -> [ (-4.00 x 0.50)+ 4.00D] = 2.00BC.
What is the normal base curve for contacts?
between 8.0 and 10.0 mmTypical 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's the difference between 8.4 and 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.
What is 8.6 base curve on contact lenses?
Contact Lens Base Curves and DiametersCONTACT LENSPOWER (SPH) RANGEBASECURVEBreeze+8.00 o -12.008.6Breeze XR+15.00 to +20.008.6Clariti 1 Day+8.00 to -10.008.6Clariti 1 Day Multifocal+8.00 to -10.008.4, 8.876 more rows
What happens if you wear contacts with a different base curve?
Mild symptoms might include discomfort or dry/itchy/red eyes, but it can also block off oxygen supply or even damage the cornea. That's why some people claim that contact lenses make their eyes feel dry or turn red, sometimes it's just because they are wearing a wrong base curve.
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. In theory +6.00 should always give you the best possible combination of curves for weight, optics, etc.
What is the most common 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.
How do I know my 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.
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 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 the base curve of contact lenses matter?
It is tempting to think that the base curve number will define how tight or loose (steep or flat) a contact lens will fit, but in actuality, how a contact lens fits is dictated by a relationship between the base curve and the diameter together, called the sagittal depth.
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.
How do I choose a base curve for soft contact lenses?
Base Curve Many lens fabricators suggest starting with a base curve radius (BCR) that is 4.00D to 5.00D flatter than flat K. Another method is to trial-and-error fit by selecting the middle BCR available. Most soft lens designs feature three BCRs: Steep, median and flat.
Is there a big difference between 8.6 and 8.7 base curve for contact lenses?
“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 convert my glasses prescription to contacts?
Can you convert glasses prescription to contact lenses? No – you cannot directly convert a glasses prescription to a contact lens prescription. Equally, you cannot convert a contact lens prescription to a glasses prescription.
How do I choose a base curve for soft contact lenses?
Base Curve Many lens fabricators suggest starting with a base curve radius (BCR) that is 4.00D to 5.00D flatter than flat K. Another method is to trial-and-error fit by selecting the middle BCR available. Most soft lens designs feature three BCRs: Steep, median and flat.
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.
What happens if the base curve size is wrong?
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 base curve?
The base curve is the measurement of the inside curve of your contact lenses. As part of your contact lens exam, your optometrist will do a Keratometer reading. This assessment helps the optometrist measure the shape of your cornea. This reading will result in a “K-reading” number that will give your optometrist a starting place for figuring out ...
Why do contact lenses not stay in place?
The same holds true with a base curve that’s too small, or not steep enough in its angle. The lens may not stay in place, and your eye may feel irritated. This is another reason why it’s always best to only get contact lenses through a licensed doctor of optometry and a licensed optical dispensary.
What does B.C.R. stand for?
The number you may not be familiar with on your prescription or contact lens box is the one designated B.C. or B.C.R. This number represents your base curve measurement.
Do contact lenses need to be precise?
Now that most contact lenses dispensed are soft lenses, this measurement doesn’t need to be quite as precise. Many soft contact lens brands only offer a few different base curve sizes in their lenses, so your optometrist will use your “K” reading to determine the size that’s best for your eye. Often contact lens manufacturers will only offer one ...
What Is The Base Curve?
The base curve is an important aspect of a lens, being the curvature on the surface of the back of the contact. The base curve is what determines the kind of fit the lens needs to have in order to match your eye’s natural curve. A base curve will vary from person to person, with those possessing a higher base curve figure having a flatter cornea (the clear outer layer at the front of the eye) and those with a lower number indicating a steeper cornea.
Should I Be Asking For Lenses With An Alternative Base Curve?
You should never wear contact lenses that have a different base curve from the one in your prescription, as your prescription has been specifically designed for you based on the measurements and health of your eyes – which is different for everyone.
Does The Base Curve Have An Impact On Comfort?
The reason it’s so important to have regular appointments with your optometrist is because the right kind of contact lens will differ from person to person. Having the correct lens that fits your eye is vital in not only ensuring your vision is clear, but also that you’re comfortable when wearing your contacts, too. The base curve, alongside the lens’s diameter, play a vital role in establishing which kind of fit you need to help correct your poor vision. The diameter of a contact lens refers to its width from edge to edge, defining where the lens will sit when in your eye.
What is the base curve?
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. 1 It is usually expressed in millimetres and may be further characterised as steep, median, or flat. 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.
Why are contact lenses so comfortable?
2 When the base curve and contact lens diameter are appropriate, there is adequate tear exchange from under the lens surface, which helps clear out debris. 2 All these factors contribute to your lenses being comfortable to wear and also to preventing eye damage and strain, thereby promoting overall eye health.
What is the diameter?
The diameter of a contact lens is the width of the lens from edge to edge. It is also expressed in millimetres. This number is usually between 13 mm and 15 mm, though it can be as small as 9mm if a rigid gas-permeable lens, and it determines where the lens will sit in your eye. 1 When you wear a contact lens with the appropriate diameter, the lens will remain stable in your eye, i.e. hold its position. If you wear a contact lens with the wrong diameter, it can cause discomfort and may even fall out.
Why is it important to fit your eyeglasses?
Having the right fit is essential for clear vision and long-term comfort and satisfaction with your lenses. 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.
Can a contact lens be damaged?
One of them is optimum fit, which is helped largely by making sure you order the exact prescription your optician has given you: this will ensure that the contact lens fits well on your eye. Wearing poorly-fitting contact lenses can damage the eye and cause problems such as blurred vision, headaches, and eye strain.
Can I order contact lenses with a different base curve?
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 base curve of a contact lens?
The base curve is a number from 8.0 to 10.0 on your prescription. Look at the last number on your prescription, which indicates the diameter of the lens. When you blink your eyes, your contact lenses move over the limbus, which is the part of your eye where the cornea meets the sclera.
How to tell if contact lens is stronger?
For those with a plus, the closer the lens is to the eye makes the lens weaker for the wearer. If you have a negative number , the closer the lens is to the eye, the stronger the lens is.
How to tell if you have astigmatism on your prescription?
Wearers with astigmatism may have additional columns on their prescription, with two numbers separated by an X. The cylinder should be a number between +4.00 and -4.00; this indicates the strength of your astigmatism. Those with severe astigmatism will have higher or lower cylinder numbers, which fluctuate over time as new technology breeds new products. The axis is a number between 0 and 180, and represents the orientation of your astigmatism.
What does a plus mean on a lens?
For those with a plus, the closer the lens is to the eye makes the lens weaker for the wearer. If you have a negative number, the closer the lens is to the eye, the stronger the lens is. Determine the base curve of your lenses. The next column represents the base curve (B.C. or B.C.R). This is the inside curve measurement of your lenses.
What is the axis of astigmatism?
The axis is a number between 0 and 180 , and represents the orientation of your astigmatism.
When was the contact lens rule published?
Federal Trade Commission. The contact lens rule: a guide for prescribers and sellers. Published June 2020.
Do contact lens prescriptions have a base curve?
These base curve values are similar to shoe sizes: With some brands, you may wear a different size. If your contact lens prescription does not have a base curve number, that brand only offers one base curve size.
What is the curve of a lens?
In modern lens design that curve is always plus (+) and has a convex shape.
What is the base curve?
In optical theory it is said that the base curve is, “The curve from which all other curves are measured.”
What is surfacing in optics?
Matching a base curve to a prescription is part of surfacing. Surfacing is the actual grinding away of the plastic on a lens to create the cur ves necessary to match a prescription. These days surfacing is done at the “lab” not at the “store” and is no longer part of the day-to-day work of an optician. Here is what I want you to know about base ...
What is the base curve of a high minus RX?
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 to find the spherical equivalent of RX?
The formula to determine the spherical equivalent of any Rx is: Rx sphere power added to 1/2 the cylinder power. If the Rx is a sphere like -2.50 then you work with the -2.50. Spherical equivalents are also used in other formulas and when working with contact lenses.
Can edgers overcome poor frame and RX matching?
A good edger can overcome many (but not all) poor frame and Rx matching problems. How to properly match lens and frame curves is covered in Course 3: All About Frames. Here is what you will need to know about base curve theory for the ABO or any practical exams you might need to take.
Can a computer determine the base curve of a lens?
1) In an upcoming lesson you will learn about free-form lens design. Only a computer can determine the correct base curve on a lens designed using free-form technology. In fact most labs today will not allow you to change or request a base curve at all.
Is A Fitted Contact Lens Important?
Maybe we did not realize it, but when buying any clothing or shoes we will require the sizes that fitted us, getting ourselves a pair of contact lenses doesn’t have the same reputation. Some did not aware that wearing poorly fitted contact lens can cause serious harm to your overall eye health.
Why do my contacts feel uncomfortable?
Apart from the wrong base curve or diameter, some other symptoms and factors that lead to contact lens discomfort are digital eye strain, dirty contact lenses & contact lenses with either too high or too low water content. You know the wrong size of contact lenses is causing you discomfort if it keeps falling out or restricts swift floating on the cornea.
What size lens do you need for cosplay?
But knowing that the larger diameter lens can create enlarging eyes effect, sizes ranging from 14.5-16mm are the choices for certain groups of people who wanted to look better with larger eyes or being used in some cosplay character. When some will go for 14.0mm that tends to lean towards a more natural and non-enlarging style.
What size are Iriz eyes?
The size eyes of an average person for adults are usually from 26mm to 28mm. Iriz size varies between 12 to 14mm, with 13mm being the most common. Hence, 14.0mm diameter is the size that best sit in your eyes.
What happens if you don't fit your eyeglasses?
If you wear lenses that don’t fit your eyes there’s a good chance you’ll develop contact lens intolerance. This condition can cause a person to be forced to wear eyeglasses or undergo laser vision correction.
Why do my contacts have a curve?
Wrong Base Curve Symptoms. If your lenses are too loose and keep moving up with every blink of eye, your contacts are a larger base curve. On the other hand, steeper or smaller base curves make your eyes feel tighter. An ill-fitted base curve also obstructs oxygen flow & causes discomfort.
How big should my contact lens be?
An average fit contact lens should cover past your iris, which is 1-2 millimetres bigger. If on the other hand your contact lens sits exactly on the edge of the iris called limbus; you may risk leaving it scratched. The size eyes of an average person for adults are usually from 26mm to 28mm.
How many base curves are there in soft contact lenses?
Soft contact lens manufacturers take advantage of the draping effect by only offering three or four base curves in their product line-up. If you find a manufacturer who only offers one B.C. (usually about 8.6), then be aware that about 30% of the potential wearers will have comfort issues with those lenses. Some will require a steeper curve, and some a flatter curve.
How does the base curve affect how a lens rides on your eye?
As others have said the base curve affects how a lens rides on your eye: good fit, too tight, too loose? While you may notice discomfort from a too-loose or too-tight fit, you also may not notice a tight fit in particular (a too-tight fit is also the main concern, as this may excessively-restrict the oxygen supply to the underlying cornea. Unlike with a too-loose fit (which is less concern medically), patients frequently don’t experience any discomfort despite a too-tight fit). The lens really needs to be seen on the eye via “slit-lamp” biomicroscope such as opto
Why do RGP lenses move with each blink?
Rgp lenses move with each blink and because rgp lenses are fitted larger than the old pmma lenses and are slippery they are fitted sometimes steeper to maintain lens centration on eye. Both soft and rgp lenses fit so drastically differently. In rgp lenses because they are total custom ordered for each patient there are no average base curves.The methodology for rgp lenses is different than fitting soft lenses.
What is the average width of a soft lens?
Most patients will fall in the range of 8.5 to 8.7 base curve (median) and 14mm would be averages. Typically its better for soft lenses to fit flatter than steeper. Soft lenses cover the entire cornea and actually extends past the limbal area by a few mm. If they are fit too steep, they may restrict tear exchange. Metabolic waste products must be able to get flushed out for new tears with each blink.
What measurements are taken during a contact lens fitting appointment?
During the fitting appointment, corneal curvature measurements will be taken, and they form the basis of the contact lens base curve selection.
How to know what size contacts to get?
You may get prescribed differently for different brands because every brand is different. Think about shoe brands and their sizes. A size 7 in one brand may be a size in another. If your eye doctor is the one prescribing you your contacts, then they will be fitting for your eye, since your doctor knows your eye and what fits it. If you want to get contacts from online, always check with your eye doctor first to see if the contacts will be good for the size and shape of you eye. Don’t base it off of one prescription because brands are different and your prescription may be different from the brand that your doctor prescribes you.
Do soft contact lenses fit corneas?
Very important with rigid gas permeable contact lenses. Not so important with soft contact lenses. Most soft contact lenses only come in one base curve today, although, a few brands do come in more than one base curve. For patients with flatter or more steep corneas the different base curve soft contact lenses are used. Usually, the one base curve of most soft contact lenses fit most corneas.
