The posterior optical zone will directly affect the lens to cornea relationship of a rigid gas permeable lens. If the posterior 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 chang...
NCLE Advanced Certification Exam
Questions Answered Correctly.
The posterior optical zone will directly affect the lens to cornea relationship of a rigid gas permeable
lens. If the posterior 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
A. 3 only
B. 1&3
C. 2 only
D. 2&3
The answer is D.
A hyperflange will decrease edge thickness as well as lens awareness . Aspheric peripheral curves change
the posterior design of the lens but do not reduce edge thickness. A higher Dk material will not change
the overall lens edge thickness. A myoflange will actually add thickness to the lens edge and is used for
,high plus lenses not high minus lenses. - Answer 5. A high minus rigid gas permeable lens will be thin
centrally with relatively thick edges. To reduce the edge thickness, and increase overall comfort, use:
A. Aspheric peripheral curves
B. A myoflange
C. A higher Dk material
D. A hyperflange
The answer is C.
One would rarely polish or attempt to manipulate the central posterior surface of a rigid lens. Applying
polishing pressure to the mid-peripheral and the peripheral anterior surface would add plus power.
Applying polishing pressure to the central anterior surface would add minus power. - Answer 6. To add
minus power to a rigid contact lens with a rotating modifying spindle, one would:
A. Polish the posterior surface of the rigid lens
B. Polish the mid peripheral anterior surface
C. Polish the central anterior surface
D. Polish the peripheral anterior surface
The answer is A.
The keratometer readings indicate the need for a spherical back surface, which would rule out the use of
a bitoric lens. A soft spherical lens would not correct the moderate amount of refractive astigmatism that
is present, nor would the spherical rigid gas permeable lens. A front surface toric RGP would best meet
this patient's needs since it has a spherical back surface, but has a toric front surface which would
correct the residual astigmatism. - Answer 7. Which lens design would provide the best visual acuity for
a patient with the following information?
K's 42.00@ 180/ 42.50@90
Rx -6.75 +1.75 cx 90
A. Front surface toric rigid gas permeable
, B. Spherical rigid gas permeable
C. Soft sphere
D. Bitoric rigid gas permeable
The answer is A.
The wetting angle of a rigid gas permeable material describes how a fluid spreads over the surface. It is
important to remember, however, that wetting angle is a description of the material outside of the
patient's natural ocular environment. Within minutes of insertion, a rigid lens is encapsulated in the
natural tear mucin and the wetting angle of the material is no longer important. - Answer 8. Which of
the following describes the angle that the edge of a bead of water makes with the surface of a plastic?
A. Wetting angle
B. Surface angle
C. Bead angle
D. Reflection angle
The answer is B.
The back surface of a rigid lens will usually correct only the astigmatism that is found on the surface of
the cornea. Therefore, when there is significantly more astigmatism in the refraction than on the surface
of the cornea, residual astigmatism is anticipated. - Answer 9. If a patient has 1.50 D of refractive
cylinder and keratometer readings of 44.00@ 180/ 44 .50 @ 90, a spherical rigid gas permeable lens will:
A. Give the patient their best correctable vision
B. Usually result in residual astigmatism
C. Fit poorly
D. Be uncomfortable
The answer is C.
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