Contact Lens Principles Flashcards
7 cards from real COT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Contact Lens Principles flashcards as text
When converting a spectacle prescription to a contact lens prescription, which step accounts for vertex distance?
Answer: Adjusting lens power for the 12 mm distance from the eye
Vertex distance conversion is needed for prescriptions above ±4.00 D because the corneal plane is approximately 12 mm closer to the eye than spectacle lenses.
Which term describes the zone of a rigid contact lens that creates the peripheral seal and allows tear exchange?
Answer: Peripheral curve
The peripheral curve (or blend zone) is flatter than the base curve and creates the edge lift needed for tear circulation under the lens.
A toric soft lens is rotating 20° counterclockwise from the intended axis. Which LARS rule applies?
Answer: Add 20° to the cylinder axis on the order
LARS (Left Add, Right Subtract): if the lens rotates left (counterclockwise), add the degrees of rotation to the ordered cylinder axis.
Which contact lens-related complication is characterized by upper tarsal conjunctival changes resembling cobblestones?
Answer: Giant papillary conjunctivitis
Giant papillary conjunctivitis (GPC) produces large papillae (>0.3 mm) on the upper tarsal conjunctiva, often from lens deposits or mechanical irritation.
What is the recommended replacement schedule for a 'daily disposable' contact lens?
Answer: Discarded after each single day of wear
Daily disposable lenses are designed to be worn once and discarded at the end of the day, eliminating the need for a lens care system.
When assessing RGP lens centration, a lens that consistently rides superiorly is most likely caused by:
Answer: Upper lid attachment due to lid anatomy or lens edge design
Superior decentration of RGP lenses is commonly caused by the upper eyelid capturing or attaching to the lens edge, especially with lid-attachment fitting philosophy.
Which solution type uses a chemical preservative system to disinfect soft contact lenses in a single step?
Answer: Multipurpose solution (MPS)
Multipurpose solutions combine cleaning, rinsing, and disinfecting in one bottle using preservatives such as PHMB or polyquaternium-1.