COT Contact Lens Principles 2

Question 1

Which contact lens parameter describes the curvature of the back surface of the lens?

Accepted Answer

Base curve radius

Answer

The base curve radius (BCR) describes the curvature of the posterior (back) surface of a contact lens.

Question 2

A patient with keratoconus would most likely be best corrected with which type of contact lens?

Accepted Answer

Rigid gas-permeable lens

Answer

Rigid gas-permeable lenses mask the irregular corneal surface of keratoconus by creating a smooth refractive interface with the tear lens.

Question 3

What does the term 'oxygen transmissibility' (Dk/t) measure in contact lenses?

Accepted Answer

Oxygen passing through a lens of specific thickness

Answer

Dk/t (transmissibility) is calculated by dividing the oxygen permeability (Dk) by the lens center thickness (t).

Question 4

Which fluorescein pattern under a rigid lens indicates excessive apical clearance?

Accepted Answer

Bright central pooling with dark midperiphery

Answer

Excessive apical clearance produces a bright central pool of fluorescein (central pooling) with a dark (bearing) midperipheral ring.

Question 5

A soft contact lens is described as '38% water content.' What does this mean?

Accepted Answer

38% of the lens weight at equilibrium is water

Answer

Water content percentage refers to the proportion of the fully hydrated lens weight that is water at equilibrium.

COT - Certified Ophthalmic Technician Practice Test