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

Full apical clearance with heavy edge bearing and no tear exchange

Answer

Three-point touch with no peripheral clearance

Answer

Central fluorescein pooling only with a sealed edge

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

The peripheral cornea at the limbal zone

Answer

The upper tarsal conjunctiva

Answer

The palpebral fissure margin

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

Permanently ablating the central corneal stroma during overnight wear

Answer

Providing multifocal correction to reduce accommodative demand

Answer

Stabilizing corneal ectasia by mechanical compression of the cone

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

Thinning the superior and inferior lens zones to allow lid attachment

Answer

Using a truncated inferior edge that aligns with the lower lid margin

Answer

Creating an aspherical back surface that locks onto the corneal toricity

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

Provide mechanical support that prevents cone progression

Answer

Deliver higher oxygen than soft lenses, allowing the cone epithelium to heal

Answer

Apply gentle pressure to flatten the apex of the cone permanently

Question 6

Which multifocal contact lens design presents both distance and near focal points to the retina simultaneously regardless of gaze direction?

Accepted Answer

Simultaneous vision concentric ring design

Answer

Alternating translating bifocal design

Answer

Modified monovision with distance-dominant lens

Answer

Aspheric single-vision lens with extended depth of focus

Question 7

Based on the Holden–Mertz criteria, what minimum Dk/t (×10⁻⁹) is required for a daily wear soft contact lens to prevent clinically significant corneal edema?

Accepted Answer

24

Answer

12

Answer

35

Answer

87