Why is the base curve of my contact lenses important?
11/05/2021 · What Is The Base Curve On A Contact Lens? What is contact lens base curve? It is the curvature of the back surface of the lens. The base curve determines the type of fit the lens must have to match the natural curvature of your eye. It is usually characterized as steep, median, or flat, and calculated in millimeters.
What is a base curve in glasses?
26/10/2021 · The base curve of a contact lens is the curvature of the back surface of the 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.
How do prescription lenses match base curves?
02/09/2016 · 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.
What is the curve of a lens?
07/01/2020 · The 'BC' or base curve measurement indicates the back curvature of your contact lens, in millimetres. It also means your contact lenses will be less likely to fall out. A lower BC number means a steeper curve of your cornea (the clear front surface of your eye). A higher BC number means your cornea is flatter.
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.01-Sept-2017
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.
How do I choose a contact lens base curve?
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.01-Aug-2005
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.
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. ... 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 happens if you wear contacts with 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?
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.
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.02-Sept-2016
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 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. ... In other words, the predominant size for the small contacts is between 14.0mm to 14.2mm.
Is there a big difference between 8.5 and 9.0 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 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.
Why do lenses feel uncomfortable?
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 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 ...
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 ...
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.
What are the measurements of a contact lens?
The diameter and base curve of a contact lens are two measurements that affect how well they fit your eye.
How small is a contact lens?
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.
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.
What does a higher base curve number mean?
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.
Can you order contact lenses with a 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 you wear contact lenses with a different diameter?
It is not recommended to wear contact lenses with a different diameter from your prescription. If the diameter is too wide, the lens will be loose in the eye and may slip out of place. If the diameter is too small, the lens will have a tight fit, causing discomfort.
Why is it necessary to trace the reasons for the discomfort?
It is necessary to trace the reasons for the discomfort so that you could make an intelligent choice the next time, you are offered vision correction lenses. No matter what is the sizes of the lens you are going for, the base curves & diameter of your eyes are the parameters that decide the lens sizes that sit in your eyes perfectly ...
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.
Can a wrong contact lens cause discomfort?
Wearing the wrong size of contact lens may not worsen your vision but definitely will cause discomfort. Here we will go through with you what will be the wrong base curve and wrong diameter symptoms.
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.
Can a wide eye lens cause itchiness?
Other than that some may even feel itchiness by wearing lenses that is too wide for their eyes.
What is the base curve of a lens?
Lenses are usually available in just a few base curves per style, such as 8.3, 8.6 or 8.9. The lower the number, the steeper of the curve, or angle, of the lens and your eye.
Where do contact lenses fit?
Contact lenses are designed to fit on the front surface of your eye , called the cornea. The back curves of a contact lens, measured in millimeters, should match the curve of your eye.
Is 8.6 a steep curve?
A lens with a base curve of 8.6 is steeper than a lens with a base curve of 8.9. Many factors affect the size of a lens, including the prescription and the diameter (size across the lens), so a base curve in one type of lens may be slightly different in another type or brand of contact 1. 00:00.
Why do you need an axis on a prescription?
The axis is measured in degrees. The axis is needed to compensate for the cornea’s non-spherical shape. The axis will indicate the orientation the cylinder power should sit.
What are the measurements of contact lenses?
The three main measurements on your contact lenses are power, base curve and diameter . Some peoples prescriptions will also include a cylinder, axis, add and in some cases, colour. When you go for an eye test your optician is legally obliged to give you a prescription and you are free to buy your contact lenses anywhere you like.
Is it cheaper to buy contact lenses online?
Buying them online is cheaper and ensures you receive the best deal on your contact lenses. We do not require you to send us your contact lens prescription before you order, but you make sure your contact lens prescription is up to date before making a purchase.
What does a minus sign mean on a prescription?
The correct power should normally give you 20/20 vision. If your prescription shows a minus sign (-) this means that you are short-sighted and have myopia. If your prescription shows a plus sign (+) ...
Do you see the color of your contacts?
Contact lenses and colour. If you have opted for colour contacts, you will also see the name of the colour on your lens package. Be aware, that depending on your own eye colour and the pigmentation of the lens, the appearance of coloured lenses will differ from person to person.
What does base curve mean on a contact lens prescription?
What does Base Curve on a contact lens prescription mean? The base curve is measured to ensure the correct fit of a contact lens on the eye. It should relate to the curvature of your cornea and is measured in millimetres. A lower number indicates a steeper corneal curve.
What does the diameter on a contact lens prescription mean?
What does Diameter on a contact lens prescription mean? The Diameter measures the length of your contact lenses from one edge to another and is measured in millimetres.
What is the shape of the base curve of a lens?
In modern lens design that curve is always plus (+) and has a convex shape. The corresponding curves that create the actual lens power (bend light) are placed on the back of the lens, are minus (-) and have a concave shape.
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.
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 ...
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.
