ABO Contact Lenses 3 — Questions and Answers
Question 1: Which contact lens solution component is most associated with Acanthamoeba keratitis when patients use homemade saline or tap water?
- Hydrogen peroxide
- Povidone-iodine
- Sodium chloride contaminated with Acanthamoeba cysts (Correct answer)
- Polyhexamethylene biguanide (PHMB)
Correct answer: Sodium chloride contaminated with Acanthamoeba cysts
Tap water and homemade saline may harbor Acanthamoeba cysts; contact of lenses or cases with these sources is the primary risk factor for Acanthamoeba keratitis.
Question 2: When evaluating a fluorescein pattern for an RGP lens fit, a 'with-the-rule' corneal astigmat fitted with a spherical RGP will show:
- Pooling centrally and bearing superiorly/inferiorly
- Bearing centrally and pooling nasally/temporally
- Bearing centrally and pooling superiorly/inferiorly (Correct answer)
- Uniform alignment across the entire lens
Correct answer: Bearing centrally and pooling superiorly/inferiorly
In with-the-rule astigmatism, the vertical meridian is steeper; a spherical lens bears centrally along the flat horizontal meridian and shows pooling (fluorescein) along the steep vertical meridian.
Question 3: A patient's keratometry readings are 44.00/47.00 @ 090. What type of corneal astigmatism is present?
- With-the-rule astigmatism (Correct answer)
- Against-the-rule astigmatism
- Oblique astigmatism
- Regular astigmatism, unclassified
Correct answer: With-the-rule astigmatism
With-the-rule astigmatism means the vertical meridian (90°) is steeper; here 47.00 D at 090 confirms the steeper vertical meridian.
Question 4: Orthokeratology (ortho-K) lenses are fitted to achieve what primary effect?
- Correct presbyopia by changing lens power
- Temporarily flatten the cornea to reduce myopia (Correct answer)
- Increase corneal curvature for hyperopia correction
- Eliminate the need for toric lens designs
Correct answer: Temporarily flatten the cornea to reduce myopia
Orthokeratology uses reverse-geometry RGP lenses worn overnight to temporarily reshape (flatten) the central cornea, reducing myopia for daytime clear vision without spectacles.
Question 5: What is the recommended maximum time a conventional soft contact lens patient case should go before replacement?
- 1 month
- 3 months (Correct answer)
- 6 months
- 1 year
Correct answer: 3 months
Contact lens cases should be replaced every 3 months (or sooner if damaged) to reduce biofilm accumulation and contamination risk.
Question 6: A presbyopic patient who wears monovision contact lenses has the dominant eye corrected for distance. What is the typical approach for the non-dominant eye?
- Correct for intermediate distance
- Correct for near vision (Correct answer)
- Leave uncorrected
- Fit with a multifocal lens
Correct answer: Correct for near vision
In monovision, the dominant eye is corrected for distance and the non-dominant eye is corrected for near, allowing the brain to suppress the blurred image as needed.
Question 7: Which parameter most directly influences the tear exchange beneath a rigid gas-permeable contact lens?
- Center thickness
- Optical zone diameter
- Edge lift (axial edge clearance) (Correct answer)
- Lens diameter
Correct answer: Edge lift (axial edge clearance)
Edge lift determines the amount of clearance at the lens periphery, directly controlling how freely tears can pump beneath the lens with each blink.
ABO Contact Lenses 3
Which contact lens solution component is most associated with Acanthamoeba keratitis when patients use homemade saline or tap water?