COT - Certified Ophthalmic Technician Contact Lens Principles Questions and Answers

Question 1

A technician evaluating a rigid gas-permeable (RGP) lens with fluorescein observes a dark, central area of bearing on the cornea, surrounded by a bright green ring of pooling in the mid-periphery. What does this pattern indicate?

Accepted Answer

A flat fit (apical bearing)

Answer

A flat fit occurs when the base curve of the RGP lens is flatter (has a longer radius) than the central cornea. This causes the lens to rest heavily on the corneal apex, resulting in central touch or 'bearing' (which appears dark as it displaces the fluorescein dye), and to vault over the mid-peripheral cornea, causing a ring of dye 'pooling'.

Question 2

The term 'Dk/t' is a critical parameter for contact lens materials. What does this value represent?

Accepted Answer

The oxygen transmissibility of the lens

Answer

Dk/t represents the oxygen transmissibility of a contact lens. 'Dk' is the oxygen permeability inherent to the lens material, and 't' is the thickness of the lens. The combined value (Dk/t) indicates how much oxygen can pass through a specific lens to reach the cornea, which is vital for maintaining corneal health.

Question 3

A long-time soft contact lens wearer complains of increasing itchiness, mucous discharge, and a foreign body sensation that is worse after removing the lenses. Slit-lamp examination of the everted upper eyelid reveals large papillae. Which of the following conditions is the most likely diagnosis?

Accepted Answer

Giant Papillary Conjunctivitis (GPC)

Answer

Giant Papillary Conjunctivitis (GPC) is an inflammatory condition characterized by the formation of large papillae (>1mm) on the conjunctiva of the upper eyelid. It is commonly associated with an immunological and mechanical response to protein deposits on soft contact lenses, leading to symptoms of itching, mucus, and lens intolerance.

Question 4

A technician is assessing the fit of a new soft contact lens and observes minimal movement with the blink, conjunctival vessel blanching at the limbus, and the patient reports that vision is clear initially but becomes uncomfortable after a short period. What is the most appropriate adjustment?

Accepted Answer

Select a lens with a flatter base curve (larger BC number)

Answer

These are classic signs of a soft lens that is too tight (steep). A tight lens exhibits poor movement, can compress the blood vessels at the limbus, and often causes delayed discomfort. To loosen the fit, a lens with a flatter base curve (a larger radius of curvature, e.g., changing from 8.4 to 8.7) should be selected.

Question 5

Which type of contact lens care system requires a mandatory neutralization step to prevent severe chemical irritation to the cornea upon lens insertion?

Accepted Answer

Hydrogen peroxide-based system

Answer

Hydrogen peroxide systems are highly effective disinfectants, but unneutralized hydrogen peroxide is toxic to the cornea and will cause significant pain, burning, and potential injury. These systems require a neutralization step, typically using a special case with a catalytic disc or a neutralizing tablet, to convert the peroxide into harmless saline over several hours before the lens is safe to wear.

COT - Certified Ophthalmic Technician Practice Test

COT - Certified Ophthalmic Technician Practice Test

COT - Certified Ophthalmic Technician Contact Lens Principles Questions and Answers