ABO Contact Lenses 4 — Questions and Answers
Question 1: A patient fitted with daily disposable contact lenses asks if they can wear the lenses for two days to save money. What is the most appropriate response?
- Acceptable if the patient uses a multipurpose solution overnight
- Acceptable for silicone hydrogel daily lenses only
- Not recommended; daily disposables lack the UV inhibitors needed for extended wear
- Not recommended; daily disposables are not designed for overnight storage or reuse (Correct answer)
Correct answer: Not recommended; daily disposables are not designed for overnight storage or reuse
Daily disposable lenses are manufactured for single-use only; they lack the coating durability and are not intended to be stored, cleaned, or reused.
Question 2: Which slit-lamp finding is most characteristic of giant papillary conjunctivitis (GPC) in contact lens wearers?
- Inferior punctate epithelial erosions
- Papillae greater than 0.3 mm on the upper tarsal conjunctiva (Correct answer)
- Follicles on the inferior palpebral conjunctiva
- Limbal injection with subepithelial infiltrates
Correct answer: Papillae greater than 0.3 mm on the upper tarsal conjunctiva
GPC is characterized by large papillae (≥0.3 mm, often ≥1 mm) on the upper tarsal conjunctiva caused by mechanical and immunological irritation from the lens.
Question 3: The over-refraction for a spherical RGP lens shows -0.75 D cylinder. This residual astigmatism most likely originates from:
- Corneal astigmatism not corrected by the lens
- Internal (lenticular) astigmatism (Correct answer)
- Lens flexure on the cornea
- Incorrect base curve selection
Correct answer: Internal (lenticular) astigmatism
A spherical RGP corrects corneal astigmatism via the tear lens; residual cylinder in over-refraction typically represents internal (lenticular) astigmatism arising behind the cornea.
Question 4: A patient with keratoconus is being fitted with contact lenses. Which lens type is generally considered the standard of care for moderate-to-advanced keratoconus?
- Soft toric lenses
- Spherical RGP lenses
- Scleral contact lenses (Correct answer)
- Hybrid contact lenses
Correct answer: Scleral contact lenses
Scleral lenses vault over the irregular cornea and rest on the sclera, providing excellent visual acuity and comfort for moderate-to-advanced keratoconus cases.
Question 5: What is the primary purpose of fenestrations (holes) in some rigid contact lens designs?
- Reduce lens weight
- Improve oxygen transmission through the lens
- Improve tear circulation and reduce bubble entrapment (Correct answer)
- Decrease lens flexure
Correct answer: Improve tear circulation and reduce bubble entrapment
Fenestrations allow improved tear exchange and prevent air bubbles from being trapped beneath the lens, though they are less commonly used with modern high-Dk materials.
Question 6: A patient reports lens awareness and foreign body sensation with a newly fitted RGP lens. Slit-lamp shows the lens riding high with limited blink-induced movement. What fitting relationship does this suggest?
- Flat fit
- Steep fit (Correct answer)
- Alignment fit
- Edge lift deficiency
Correct answer: Steep fit
A steep-fitting RGP lens has a base curve steeper than the cornea, causing suction, apical clearance, minimal movement, and significant lens awareness.
Question 7: Which preservative used in multipurpose contact lens solutions has been associated with a higher incidence of toxic anterior segment reactions in some patients, leading to reformulations?
- Polyquaternium-1 (Polyquad)
- Thimerosal (Correct answer)
- Polyhexamethylene biguanide (PHMB)
- Sodium perborate
Correct answer: Thimerosal
Thimerosal (a mercury-based preservative) was largely removed from contact lens solutions due to significant rates of hypersensitivity and toxic reactions in lens wearers.
ABO Contact Lenses 4
A patient fitted with daily disposable contact lenses asks if they can wear the lenses for two days to save money.
What is the most appropriate response?