Contact Lens Fundamentals Flashcards

A patient complains of giant papillary conjunctivitis (GPC) after months of soft contact lens wear. What is the most likely cause?

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.

What does 'Dk/t' represent in contact lens science?

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.

During a soft contact lens over-refraction, what is the primary purpose of this procedure?

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.

What is orthokeratology (ortho-k)?

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.

Which fluorescein staining pattern is commonly associated with a poorly fitting rigid gas-permeable lens causing 3 and 9 o'clock staining?

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.

What is the recommended patient education regarding hydrogen peroxide contact lens care systems?

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.

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?

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.