COT Contact Lens Principles 3

Question 1

When converting a spectacle prescription to a contact lens prescription, which step accounts for vertex distance?

Accepted Answer

Adjusting lens power for the 12 mm distance from the eye

Answer

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.

Question 2

Which term describes the zone of a rigid contact lens that creates the peripheral seal and allows tear exchange?

Accepted Answer

Peripheral curve

Answer

The peripheral curve (or blend zone) is flatter than the base curve and creates the edge lift needed for tear circulation under the lens.

Question 3

A toric soft lens is rotating 20° counterclockwise from the intended axis. Which LARS rule applies?

Accepted Answer

Add 20° to the cylinder axis on the order

Answer

LARS (Left Add, Right Subtract): if the lens rotates left (counterclockwise), add the degrees of rotation to the ordered cylinder axis.

Question 4

Which contact lens-related complication is characterized by upper tarsal conjunctival changes resembling cobblestones?

Accepted Answer

Giant papillary conjunctivitis

Answer

Giant papillary conjunctivitis (GPC) produces large papillae (>0.3 mm) on the upper tarsal conjunctiva, often from lens deposits or mechanical irritation.

Question 5

What is the recommended replacement schedule for a 'daily disposable' contact lens?

Accepted Answer

Discarded after each single day of wear

Answer

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.

COT - Certified Ophthalmic Technician Practice Test

COT - Certified Ophthalmic Technician Practice Test

COT Contact Lens Principles 3