AOA Contact Lens Practice 1 — Questions and Answers
Question 1: Which contact lens material parameter describes the amount of oxygen that actually reaches the cornea?
- Dk/t (oxygen transmissibility) (Correct answer)
- Water content
- Base curve radius
- Modulus of elasticity
Correct answer: Dk/t (oxygen transmissibility)
Dk/t (oxygen transmissibility) is the measure of oxygen flux through a specific lens thickness and determines how much oxygen reaches the corneal epithelium.
Question 2: Extended wear contact lenses are most associated with which serious complication?
- Microbial keratitis (Correct answer)
- Giant papillary conjunctivitis
- Superior epithelial arcuate lesions
- Contact lens-induced acute red eye
Correct answer: Microbial keratitis
Extended (overnight) wear dramatically increases the risk of microbial keratitis, particularly from Pseudomonas aeruginosa and Acanthamoeba.
Question 3: Orthokeratology (ortho-K) lenses work primarily by:
- Reshaping the corneal epithelium during overnight wear (Correct answer)
- Surgically flattening the stroma
- Increasing corneal thickness centrally
- Reducing aqueous production
Correct answer: Reshaping the corneal epithelium during overnight wear
Ortho-K uses reverse geometry RGP lenses worn overnight to temporarily flatten the central corneal epithelium, reducing myopia during the day.
Question 4: Giant papillary conjunctivitis (GPC) in contact lens wearers is best managed by:
- Switching to daily disposable lenses and reducing wear time (Correct answer)
- Increasing lens replacement frequency to monthly
- Switching to higher water content soft lenses
- Prescribing topical antibiotic drops
Correct answer: Switching to daily disposable lenses and reducing wear time
GPC is an immunological response to lens deposits and mechanical trauma; daily disposables eliminate deposit accumulation and reduce antigenic load.
Question 5: Which fitting relationship describes a rigid gas-permeable (RGP) lens that is steeper than the corneal curvature?
- Steep (vaulting) fit (Correct answer)
- Flat fit
- Alignment fit
- Interpalpebral fit
Correct answer: Steep (vaulting) fit
When a RGP lens base curve is steeper than the flattest corneal meridian (K), the lens vaults the cornea and causes apical clearance.
Question 6: What is the FDA oxygen transmissibility threshold for extended-wear soft contact lenses?
- Dk/t ≥ 87 ISO units (Correct answer)
- Dk/t ≥ 24 ISO units
- Dk/t ≥ 125 ISO units
- Dk/t ≥ 50 ISO units
Correct answer: Dk/t ≥ 87 ISO units
The FDA requires a minimum Dk/t of 87 ISO units for extended-wear (up to 30 nights) soft contact lens approval to support adequate corneal oxygenation.
AOA Contact Lens Practice 1
Which contact lens material parameter describes the amount of oxygen that actually reaches the cornea?