The answer is D.
The posterior optical zone will directly affect the lens to cornea relationship of a rigid
gas permeable lens. If the posterior
... [Show More] optical zone is steepened, it will increase the
sagittal depth. If it is flattened, it will decrease the sagittal depth. Changing the
power, which is accomplished by changing the anterior optical zone, will not affect
the sagittal depth of the lens, nor will changing its edge design. - Answer 1. The
sagittal depth of a rigid gas permeable contact lens can be altered without changing
the diameter by:
A. Changing the power
B. Changing the edge design
C. Changing the radius of curvature of the anterior optical zone
D. Changing the radius of curvature of the posterior optical zone
The answer is A.
A lens is truncated by removing a segment of the lower edge of a contact lens. This
creates a straight edge that interacts with the lower lid and aids in lens positioning.
Of the lens designs listed in the question, the only one that requires precise
positioning of its optical portions is a translating bifocal lens. - Answer 2. A truncation
is used on a rigid gas permeable contact lens to help enhance the performance of
which type of design?
A. Bifocal
B. Aphakic
C. Bitoric
D. Keratoconus
The answer is B.
A lenticular or myoflange design will decrease the mass of an aphakic lens as well
as increase the edge profile, which allows it to interact more with the upper lid and
aid in positioning of the lens. - Answer 3. The mass of an aphakic rigid gas
permeable contact lens can be reduced by making the lens design:
A. Spherical
B. Lenticular
C. Tricurve
D. Aspheric
The answer is B.
Increasing the optical zone diameter and increasing the overall lens diameter will
both tighten and steepen the relationship of the lens to the cornea. Decreasing the
optic zone diameter will serve to flatten and loosen the lens to cornea relationship.
Using a prism-ballasted lens design will not affect the lens to cornea relationship as it
relates to sagittal depth. - Answer 4. In order to tighten the fit of a rigid gas
permeable lens you can:
I. Increase the optical zone diameter
2. Decrease the optical zone diameter
3. Increase the overall lens diameter
4. Use a prism ballasted lens design [Show Less]