COT Contact Lens Principles 5 — Questions and Answers
Question 1: Which term describes the phenomenon where a soft contact lens tightens on the eye after extended wear, reducing movement?
- Lens warpage
- Lens binding (tight lens syndrome) (Correct answer)
- Dehydration-induced steepening
- Lid-wiper epitheliopathy
Correct answer: Lens binding (tight lens syndrome)
Lens binding occurs when mucus accumulates under the lens and adheres to the cornea, causing the lens to become immobile — particularly after extended or overnight wear.
Question 2: A patient wearing daily soft lenses develops a red eye immediately after insertion each morning. The most likely cause is:
- Giant papillary conjunctivitis from protein build-up
- Toxicity or hypersensitivity to the lens packaging solution or preservative (Correct answer)
- Corneal neovascularization
- Poorly fitting base curve
Correct answer: Toxicity or hypersensitivity to the lens packaging solution or preservative
Immediate-onset redness upon insertion of daily disposable lenses suggests a reaction to the packaging solution (e.g., phosphate buffer) rather than a chronic deposit issue.
Question 3: Which keratometry reading relationship is used as a starting guide when selecting an initial RGP base curve?
- Match the base curve exactly to the flattest K
- Select a base curve 0.25–0.50 D steeper than the flattest K (align or slightly steep) (Correct answer)
- Select a base curve 1.00 D flatter than the steepest K
- Base curve should equal the average of the two principal meridians minus 2.00 D
Correct answer: Select a base curve 0.25–0.50 D steeper than the flattest K (align or slightly steep)
A common starting guideline is to fit the RGP base curve on K (aligned) or slightly steeper than the flattest keratometry reading to achieve an aligned fluorescein pattern.
Question 4: What does a 'plus carrier' lenticular design in a rigid contact lens provide?
- Additional plus power to correct presbyopia
- A thicker peripheral zone to improve lid interaction and superior positioning (Correct answer)
- Increased optical zone size for large pupils
- Extra minus power in the periphery to reduce spherical aberration
Correct answer: A thicker peripheral zone to improve lid interaction and superior positioning
A plus carrier lenticular edge is thicker at the periphery, encouraging the upper lid to ride over and center the lens in a lid-attachment fit.
Question 5: Corneal neovascularization (pannus) associated with contact lens wear is primarily caused by:
- Mechanical trauma from lens edge lift
- Chronic hypoxia stimulating new blood vessel growth into the cornea (Correct answer)
- Allergic reaction to lens care solution preservatives
- Excessive lens movement abrading the limbal area
Correct answer: Chronic hypoxia stimulating new blood vessel growth into the cornea
Prolonged corneal hypoxia triggers angiogenic factors (VEGF) that stimulate limbal blood vessel growth into the normally avascular cornea.
Question 6: Which contact lens care step is considered the most critical in preventing Acanthamoeba keratitis?
- Using enzyme tablets weekly to remove protein deposits
- Avoiding tap water contact with lenses and lens cases (Correct answer)
- Applying rewetting drops before lens insertion
- Storing lenses in saline rather than multipurpose solution
Correct answer: Avoiding tap water contact with lenses and lens cases
Acanthamoeba organisms are present in tap water, so rinsing lenses or cases with tap water is a major risk factor for this devastating infection.
Question 7: What is the primary purpose of using sodium fluorescein during a rigid contact lens fitting evaluation?
- To measure intraocular pressure accurately
- To visualize the tear layer distribution between the lens and cornea (Correct answer)
- To stain corneal epithelial cells for cell count
- To identify the patient's corneal refractive index
Correct answer: To visualize the tear layer distribution between the lens and cornea
Fluorescein fills the tear layer under a rigid lens and fluoresces under cobalt blue light, revealing areas of bearing (dark) and clearance (bright) for fit assessment.
COT Contact Lens Principles 5
Which term describes the phenomenon where a soft contact lens tightens on the eye after extended wear, reducing movement?