NOCE Contact Lens Fitting and Dispensing

Question 1

In RGP contact lens fitting, a fluorescein pattern showing central touch (dark area centrally) with excessive edge lift indicates:

Accepted Answer

A flat lens fit

Answer

A flat-fitting RGP lens results in central bearing (dark area with fluorescein) and excessive peripheral edge clearance because the lens back surface is flatter than the cornea.

Question 2

When initially selecting a base curve for a soft contact lens, which measurement is most commonly used as the starting point?

Accepted Answer

The average of both K readings

Answer

For soft contact lens fitting, the base curve is typically selected based on the average keratometry reading because soft lenses drape over the entire cornea.

Question 3

A patient's spectacle prescription is -4.50 DS with a vertex distance of 12mm. What contact lens power would you expect to order?

Accepted Answer

-4.25 DS

Answer

Compensating for the 12mm vertex distance using the effectivity formula, the effective power at the corneal plane is approximately -4.25 DS (less minus than the spectacle Rx).

Question 4

Which lens parameter describes the peripheral edge design and tear exchange area of a rigid gas permeable contact lens?

Accepted Answer

Peripheral curve radius

Answer

The peripheral curve radius (and its width) defines the edge design of an RGP lens, governing tear exchange and lens-to-limbus relationship.

Question 5

What is the minimum oxygen transmissibility (Dk/t) recommended for daily wear soft contact lenses to prevent corneal hypoxia?

Accepted Answer

24 × 10⁻⁹

Answer

Holden and Mertz established that a minimum Dk/t of 24 × 10⁻⁹ is required for daily wear soft lenses to prevent significant hypoxic stress to the corneal epithelium.

NOCE - National Opticianry Competency Examination Practice Test

NOCE - National Opticianry Competency Examination Practice Test

NOCE Contact Lens Fitting and Dispensing