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.
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?
Does the base curve on contact lenses matter?
Does base curve matter contact lenses? 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. Click to see full answer. Then, is Base Curve important with contact ...
Why are contact lenses better than glasses?
Why Contact Lenses are Better than Glasses
- Field of vision. Contact lenses adapt to the curvature of the eye, meaning you can have a wider field of vision than you can with glasses.
- Sport. Contact lenses make it a lot easier to play sport or exercise. ...
- Weather. ...
- Mask wearing. ...
- Toric lenses for astigmatism. ...
- Colored contact lenses. ...
- Outfit choice. ...
- Lens thickness. ...
- Frames. ...
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 happens if you wear the wrong base curve?
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.
How do I choose a contact 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.
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 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.
How do I know what my BC is for contacts?
Simple Rule for estimating lens base curve on a PLUS POWER lensFor 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.Rx +2.00Sph -> [+2.00 +4.00D] = 6.00BC.
What is the most common 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 is 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.
Can contacts be too big?
Many of them shrug and say, “What's the big deal?” However, wearing contacts too long is a big deal when you consider that it can damage your eyes and your vision. Wearing contacts too long is called “overwear,” and it can result in some serious issues: Red or irritated eyes. Eye pain.
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.
What does base curve mean for contacts?
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.
Does base curve of eye change?
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. As a doctor, selecting a contact lens for best fit is also challenging because the sagittal depth of any contact lens is not notated on the packaging.
Is it okay to wear a different base curve?
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.
What is 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.
Why are my new contacts blurry?
When you first wear contacts, it may take a few seconds for the lens to settle into the right place. This can cause blurred vision for a short moment in time. If your new contacts are blurry, this could also indicate that you are wearing the wrong prescription.
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 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 ...
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.
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 ...
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 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 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.
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.
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.
What determines the fit of contact lenses?
The most important thing that decides the fit of contact lenses in a patient’s eye is the base curve. Diameter is yet another factor but patients have reported problems of symptoms more with wrong base curve than size.
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 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.
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 much do gas permeable contacts move?
Compared with soft contact lenses, gas permeable contacts may move even a little more than that, which is two to three millimeters.
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 curve of a lens?
In modern lens design that curve is always plus (+) and has a convex shape.
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.
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.”
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 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.
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.