NBEO Contact Lenses & Fitting 3

Question 1

When evaluating a rigid gas permeable (RGP) lens fit on a normal cornea using sodium fluorescein, the ideal fitting relationship shows:

Accepted Answer

Alignment fit with minimal apical touch and moderate peripheral edge lift

Answer

An ideal RGP fit on a normal cornea demonstrates alignment with minimal apical touch and adequate peripheral clearance to allow tear exchange and prevent peripheral seal-off.

Question 2

Scleral contact lenses vault completely over the cornea and limbus, resting on which tissue?

Accepted Answer

The bulbar conjunctiva overlying the sclera

Answer

Scleral lenses bear entirely on the bulbar conjunctiva overlying the sclera, completely vaulting the cornea and limbus with a fluid reservoir beneath.

Question 3

Orthokeratology contact lenses are designed to achieve their primary refractive effect through which mechanism?

Accepted Answer

Temporarily reshaping the corneal epithelium via reverse geometry lenses worn during sleep

Answer

Orthokeratology uses reverse geometry RGP lenses worn overnight to temporarily redistribute and reshape the corneal epithelium, flattening the center and steepening the midperiphery to reduce myopia.

Question 4

Prism ballast stabilization used in soft toric contact lenses works by:

Accepted Answer

Adding base-down prism that weights the inferior lens, using gravity and lid forces to resist rotation

Answer

Prism ballast incorporates a wedge of base-down prism that makes the inferior portion of the lens thicker and heavier, using gravity and upper lid pressure to maintain rotational orientation.

Question 5

In a patient with keratoconus, rigid gas permeable contact lenses improve visual acuity primarily because they:

Accepted Answer

Create a smooth anterior refracting surface independent of the irregular cornea using a tear lens

Answer

RGP lenses mask irregular corneal astigmatism in keratoconus by creating a new smooth refracting surface; the tear lens between the flat posterior RGP surface and the irregular cornea fills in the irregularity.

NBEO - National Board of Examiners in Optometry Practice Test

NBEO - National Board of Examiners in Optometry Practice Test

NBEO Contact Lenses & Fitting 3