CPOT Contact Lens Fitting & Patient Care 2 — Questions and Answers
Question 1: What does keratometry (K-readings) measure during a contact lens fitting evaluation?
- Pupil diameter under dim illumination
- Curvature of the anterior corneal surface (Correct answer)
- Intraocular pressure in mmHg
- Anterior chamber depth in millimeters
Correct answer: Curvature of the anterior corneal surface
Keratometry measures the radius of curvature of the central anterior corneal surface in two primary meridians, which is essential for selecting the appropriate contact lens base curve.
Question 2: In contact lens fitting terminology, what does a 'steep' fit indicate?
- The lens base curve is flatter than the corneal curvature
- The lens base curve is more curved than the corneal curvature (Correct answer)
- The lens diameter is larger than the corneal diameter
- The lens power is stronger than the manifest refraction
Correct answer: The lens base curve is more curved than the corneal curvature
A steep fit occurs when the lens base curve is more curved than the cornea, resulting in restricted lens movement, central tear pooling, and potential corneal hypoxia.
Question 3: Which dye, viewed under cobalt blue light, is used to evaluate the tear film pattern beneath RGP contact lenses?
- Rose Bengal
- Lissamine Green
- Sodium fluorescein (Correct answer)
- Methylene Blue
Correct answer: Sodium fluorescein
Sodium fluorescein illuminated with cobalt blue light reveals the fluorescein pattern under RGP lenses, highlighting areas of bearing (dark), alignment (thin green), and clearance (bright green pooling).
Question 4: What does the acronym 'LARS' stand for in toric soft contact lens fitting?
- Left Add, Right Subtract (Correct answer)
- Left And Right Stabilization
- Lens Alignment Reference System
- Low Axis Rotation Standard
Correct answer: Left Add, Right Subtract
LARS guides axis adjustment when a toric lens rotates: if the lens rotates to the Left, Add that number of degrees to the axis; if it rotates Right, Subtract.
Question 5: What is the recommended contact lens movement with each blink during a soft lens fitting assessment?
- Less than 0.1 mm (essentially no movement)
- 0.25 to 1.0 mm (Correct answer)
- 2.0 to 3.0 mm
- 4.0 to 5.0 mm
Correct answer: 0.25 to 1.0 mm
Adequate soft lens movement of 0.25–1.0 mm per blink ensures proper tear exchange under the lens, supporting corneal oxygenation and preventing lens adherence.
Question 6: What does 'HVID' stand for in the context of contact lens fitting?
- High Visual Image Distance
- Horizontal Visible Iris Diameter (Correct answer)
- High-Volume Iris Dimension
- Horizontal Visual Inspection Data
Correct answer: Horizontal Visible Iris Diameter
HVID (Horizontal Visible Iris Diameter) measures the width of the visible iris from limbus to limbus and is used to select an appropriate contact lens overall diameter.
Question 7: What is the purpose of performing an 'over-refraction' during a contact lens fitting?
- To determine the corneal curvature for base curve selection
- To identify any residual refractive error beyond what the trial lens corrects (Correct answer)
- To measure the required change in lens diameter
- To assess whether a different base curve is needed
Correct answer: To identify any residual refractive error beyond what the trial lens corrects
Over-refraction is performed with the trial lens in place to measure any residual refractive error, indicating whether the lens power needs adjustment for optimal visual acuity.
CPOT Contact Lens Fitting & Patient Care 2
What does keratometry (K-readings) measure during a contact lens fitting evaluation?