NCLE Advanced Certification Exam
Questions with Complete
Solutions170
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 - ANSWERS-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 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.
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 - ANSWERS-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.
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 - ANSWERS-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.
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 - ANSWERS-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.
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 - ANSWERS-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.
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 - ANSWERS-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.
, 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 - ANSWERS-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.
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 - ANSWERS-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.
Questions with Complete
Solutions170
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 - ANSWERS-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 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.
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 - ANSWERS-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.
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 - ANSWERS-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.
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 - ANSWERS-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.
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 - ANSWERS-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.
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 - ANSWERS-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.
, 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 - ANSWERS-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.
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 - ANSWERS-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.
