COT - Certified Ophthalmic Technician Contact Lens Principles Questions and Answers — 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?
- A steep fit (apical clearance)
- A flat fit (apical bearing) (Correct answer)
- An ideal alignment fit
- Excessive peripheral clearance
Correct answer: A flat fit (apical bearing)
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?
- The lens's resistance to protein deposits
- The overall diameter divided by the central thickness
- The oxygen transmissibility of the lens (Correct answer)
- The percentage of water content in the material
Correct answer: The oxygen transmissibility of the lens
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?
- Microbial Keratitis
- Corneal Neovascularization
- Superior Limbic Keratoconjunctivitis (SLK)
- Giant Papillary Conjunctivitis (GPC) (Correct answer)
Correct answer: Giant Papillary Conjunctivitis (GPC)
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?
- Select a lens with a flatter base curve (larger BC number) (Correct answer)
- Increase the plus power of the lens
- Select a lens with a steeper base curve (smaller BC number)
- Decrease the overall diameter of the lens
Correct answer: Select a lens with a flatter base curve (larger BC number)
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?
- Multipurpose solution (MPS)
- Enzymatic protein removers
- Hydrogen peroxide-based system (Correct answer)
- Saline solution for rinsing
Correct answer: Hydrogen peroxide-based system
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.
Question 6: A patient requires a soft toric contact lens to correct their astigmatism. What is the primary purpose of the lens's stabilization design, such as prism ballast or thin zones?
- To increase the water content for better comfort
- To prevent the lens from rotating on the eye (Correct answer)
- To improve the lens's resistance to deposits
- To make the lens easier to see for handling
Correct answer: To prevent the lens from rotating on the eye
Toric lenses have different powers in different meridians to correct astigmatism. For this correction to work, the lens must maintain a specific rotational orientation on the eye. Stabilization designs, like making the bottom of the lens thicker (prism ballast), use gravity and eyelid forces to keep the lens from rotating out of position with each blink.
COT - Certified Ophthalmic Technician Contact Lens Principles Questions and Answers
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?