COA Contact Lens Fundamentals 2 — Questions and Answers
Question 1: A patient complains of giant papillary conjunctivitis (GPC) after months of soft contact lens wear. What is the most likely cause?
- Corneal neovascularization from lens hypoxia
- Mechanical irritation and immune response to lens deposits or the lens edge (Correct answer)
- Bacterial infection from contaminated lens case
- Lens dehydration causing anterior surface dryness
Correct answer: Mechanical irritation and immune response to lens deposits or the lens edge
GPC (also called contact lens-induced papillary conjunctivitis, CLPC) is caused by repeated mechanical trauma from the lens edge and immune reaction to protein deposits on the lens surface, leading to papillae on the upper tarsal conjunctiva.
Question 2: What does 'Dk/t' represent in contact lens science?
- Lens diameter divided by thickness
- Oxygen transmissibility, calculated as permeability divided by lens thickness (Correct answer)
- Diffusion coefficient of the cleaning solution
- Dioptric power adjusted for lens thickness
Correct answer: Oxygen transmissibility, calculated as permeability divided by lens thickness
Dk/t is oxygen transmissibility, which accounts for both the material's oxygen permeability (Dk) and the actual thickness (t) of the lens, providing a measure of how much oxygen reaches the cornea.
Question 3: During a soft contact lens over-refraction, what is the primary purpose of this procedure?
- To measure the fit of the trial lens on the cornea
- To determine the final contact lens power needed by refracting over a trial lens (Correct answer)
- To assess corneal curvature changes from lens wear
- To evaluate the tear film stability under the lens
Correct answer: To determine the final contact lens power needed by refracting over a trial lens
Over-refraction determines the residual refractive error remaining while the patient wears a trial contact lens, allowing the practitioner to calculate the correct final lens power.
Question 4: What is orthokeratology (ortho-k)?
- Surgical reshaping of the cornea using a laser
- Use of specially designed rigid lenses worn overnight to temporarily reshape the cornea (Correct answer)
- An exercise regimen to strengthen extraocular muscles
- A method of measuring corneal curvature with a keratometer
Correct answer: Use of specially designed rigid lenses worn overnight to temporarily reshape the cornea
Orthokeratology involves wearing specially designed rigid contact lenses overnight to temporarily flatten the cornea, reducing myopia during the day without lenses.
Question 5: Which fluorescein staining pattern is commonly associated with a poorly fitting rigid gas-permeable lens causing 3 and 9 o'clock staining?
- Corneal hypoxia causing diffuse superficial punctate keratitis
- Desiccation of the corneal epithelium at the 3 and 9 o'clock limbal positions due to inadequate tear coverage (Correct answer)
- Bacterial keratitis from contaminated lens storage
- Allergic reaction to lens care solution preservatives
Correct answer: Desiccation of the corneal epithelium at the 3 and 9 o'clock limbal positions due to inadequate tear coverage
Three and 9 o'clock staining results from desiccation of the cornea at the nasal and temporal limbus, where the RGP lens edge causes inadequate blinking and tear film coverage.
Question 6: What is the recommended patient education regarding hydrogen peroxide contact lens care systems?
- Lenses can be inserted immediately after placing them in the peroxide solution
- Lenses must complete a full neutralization cycle (minimum 6 hours) before insertion (Correct answer)
- Hydrogen peroxide systems can be used with any contact lens type including daily disposables
- Rinsing with tap water is acceptable after the neutralization step
Correct answer: Lenses must complete a full neutralization cycle (minimum 6 hours) before insertion
Hydrogen peroxide must be fully neutralized (typically over 6 hours via a catalytic disc or tablet) before lens insertion, as un-neutralized peroxide causes severe ocular burning and damage.
Question 7: A keratometry reading is 44.00 D @ 180 / 46.00 D @ 090. When fitting a spherical soft contact lens, the effective lens power on the eye will primarily correct which component?
- The full astigmatic correction with no residual error
- The spherical equivalent, leaving residual astigmatism uncorrected (Correct answer)
- Only the steepest meridian power
- Only the flattest meridian power
Correct answer: The spherical equivalent, leaving residual astigmatism uncorrected
Spherical soft lenses drape over the cornea and correct mainly the spherical equivalent of the refraction; the corneal astigmatism is largely uncorrected, leaving residual astigmatism.
COA Contact Lens Fundamentals 2
A patient complains of giant papillary conjunctivitis (GPC) after months of soft contact lens wear.
What is the most likely cause?