NOCE NOCE Contact Lens Fitting and Care 2 — Questions and Answers
Question 1: Which instrument is used to verify the base curve and power of a rigid gas-permeable (RGP) contact lens?
- Keratometer
- Lensometer (focimeter)
- Biomicroscope (slit lamp)
- Radiuscope (Correct answer)
Correct answer: Radiuscope
A radiuscope (also called an ophthalmometer or lens clock for RGPs) is used to measure the radius of curvature of the back surface of rigid contact lenses.
Question 2: When fitting a soft contact lens, which observation indicates an excessively STEEP (tight) fit?
- Excessive lens movement of 3–4 mm on blink
- Lens edge lifting and air bubbles visible at limbus
- Reduced or absent lens movement with a push-up test (Correct answer)
- Lens frequently falling out of the eye
Correct answer: Reduced or absent lens movement with a push-up test
A steep or tight soft lens fit shows reduced movement on blink and poor mobility on the push-up test because the lens is gripping the cornea too tightly.
Question 3: Vertex distance compensation in contact lens prescribing is generally required when the spectacle prescription exceeds what power?
- ±2.00 D
- ±4.00 D (Correct answer)
- ±6.00 D
- ±10.00 D
Correct answer: ±4.00 D
Vertex distance correction is clinically significant for prescriptions of ±4.00 D or greater, as the difference in back vertex distance between spectacles and contact lenses changes the effective power.
Question 4: What does lag (or lens lag) describe in contact lens fitting assessment?
- The time delay before a new lens stabilizes on the eye
- The movement of the lens in the opposite direction after an eye movement (Correct answer)
- The delay in vision improvement after lens insertion
- The amount the lens dehydrates over a wearing period
Correct answer: The movement of the lens in the opposite direction after an eye movement
Lens lag refers to the movement of a contact lens in the opposite direction to that of eye movement, used to assess lens fit by observing how the lens responds when the eye moves laterally.
Question 5: The push-up test during soft contact lens fitting is used to assess what parameter?
- Lens optical power
- Lens movement and fit tightness (lens mobility) (Correct answer)
- Corneal curvature changes
- Lens water content suitability
Correct answer: Lens movement and fit tightness (lens mobility)
The push-up test assesses lens mobility by using a finger to push the lower lid against the lens edge; a properly fitting lens should move smoothly and return to its original position.
Question 6: In contact lens prescribing, what is the recommended approach when there is a significant amount of residual astigmatism with a spherical soft lens?
- Prescribe a spherical RGP lens to mask all astigmatism
- Prescribe a toric soft contact lens to correct the residual cylinder (Correct answer)
- Increase the sphere power to compensate
- Recommend spectacles only and discontinue contact lens fitting
Correct answer: Prescribe a toric soft contact lens to correct the residual cylinder
When residual astigmatism remains uncorrected with a spherical soft lens, a toric soft contact lens should be prescribed to correct both the spherical and cylindrical components of the refractive error.
NOCE NOCE Contact Lens Fitting and Care 2
Which instrument is used to verify the base curve and power of a rigid gas-permeable (RGP) contact lens?