Why is the shape of the cornea important in contact lens fitting?
A Need for Predictable Fitting
First, lens diameter and base curve are the most important parameters controlling the lens design. Second, the most important corneal shape measurement is the corneal sagittal height because it defines the most appropriate contact lens-to-cornea fitting relationship.
How do I choose a contact lens base curve?
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 are the parameters required for contact lens?
Summary
| Contact lens Parameters | Unit of measurement | More information |
|---|---|---|
| Average | millimeter | from 13.00 to 15.00 |
| Cylinder | dioptre | from –0.25 to –10.00, toric contact lenses |
| Cylinder axis | degree | from 0 to 180, toric contact lenses |
| Addition | dioptre | from 1.00 to 3.00, multifocal lenses |
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.
How do I know if my contacts fit correctly?
Place the contact lens between the tips of your thumb and forefinger, grasping it near the center so the entire edge is free. Gently squeeze the lens, as if you are about to fold it in half. If the edge of the lens points upward (resembling a hard-shell taco), the lens is correctly oriented.
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.
What are the three important goals in contact lens assessment?
To perform techniques to verify and inspect contact lenses. To use auxiliary CL instruments and tests (e.g., trial set, fluorescein testing). To perform CL verification for vision correction, fit, and comfort.
What is BVP in contact lens?
To appropriately correct a patient with a toric soft contact lens, the back vertex power of the lens on the eye (BVP in situ) should equal the patient’s refraction at the ocular plane.
How do I know my base curve?
Simple Rule for estimating lens base curve on a PLUS POWER lens
- 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.
- Rx +2.00Sph -> [+2.00 +4.00D] = 6.00BC.
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.