Tvrda gas-propusna (RGP) kontaktna sočiva Koncepcija

Slide 29
Zadnja površina srednja periferija
Zahtev:
Treba da se poravna sa ravnajućom
korneom.
Uticaji:
Stabilnost fita.
Suzni tok.
Oblik kornealne periferije
Centriranje.
Rigid Gas Permeable Contact Lenses Design
Back Surface Mid-Periphery
Requirement:
Should align flattening cornea. Since the cornea flattens peripherally, the lens secondary
and peripheral zones must have curves which are flatter than the BOZR, preferably
flattening progressively. This can be achieved by a series of flattening blended spherical
curves, or by a continuous aspheric curve such as an ellipsoid or a paraboloid which
would match the corneal shape.
Affects:
Stability of fit.
If the mid-peripheral curves are significantly flatter than this corneal region, excessive
clearance, an unstable fit and excessive movement will result.
Tear flow.
This area of the lens can cause a restriction of tear flow if the bearing area is localized
(narrow) by sealing off the back optic zone region. This is also likely to produce a tight
fit and entrapment of debris or air bubbles within the optic zone area.
Corneal peripheral shape.
As with the central region, corneal shape can be affected by the lens fitting relationship.
Harsh and localized bearing on the mid-peripheral band may cause corneal indentation.
Centration.
If the mid-peripheral zone is flatter than the cornea resulting in excessive edge lift, the
lens is more likely to decentre.
Zadnja površina srednja periferija
Zahtev: