Contact Lens Practice Flashcards

The base curve of a contact lens is selected primarily based on:

Answer: Corneal curvature (keratometry readings)

Keratometry (or corneal topography) measures the anterior corneal curvature, which is used to select an appropriate base curve for proper lens-to-cornea fitting relationship.

Superior epithelial arcuate lesions (SEALs) in soft contact lens wearers are located at:

Answer: Superior limbal region, parallel to the limbus

SEALs are non-infective, sterile epithelial splits at the superior limbus caused by mechanical interaction of the lens edge with the superior limbal epithelium under the upper lid.

What does the 'plano' carrier design in a bitoric RGP lens achieve?

Answer: Minimizes lens rocking by correcting for corneal toricity mechanically

A plano carrier (back surface toric, front surface sphere) corrects corneal toricity mechanically to stabilize the lens and reduce rocking without introducing cylinder in the optic zone.

The minimum recommended wearing schedule for a new soft contact lens wearer during the adaptation period is:

Answer: Gradually increasing from 4–6 hours to full-time over 1–2 weeks

New wearers should adapt gradually, starting at 4–6 hours and increasing by 1–2 hours per day to allow corneal physiology and eyelid tolerance to adjust.

Which lens care system is contraindicated for use with silicone hydrogel lenses due to corneal staining?

Answer: Certain preserved multipurpose solutions (MPS) containing PHMB or Alexidine

Some MPS formulations containing PHMB or Alexidine interact with silicone hydrogel materials, causing preservative binding that leads to toxic epithelial staining.

What is the primary purpose of the 'fitting cross' used in multifocal soft contact lens evaluation?

Answer: To assess centration and zone alignment relative to the pupil

The fitting cross marking on multifocal lenses helps the practitioner verify that the distance and near optical zones are appropriately centered over the pupil.