Ophthalmic Optics and Lenses Flashcards

A lens with a base curve of +6.00 D and a back surface power of -2.50 D has what front vertex power?

Answer: +3.50 D

Front vertex power equals base curve plus back surface power: +6.00 + (-2.50) = +3.50 D.

Which lens form produces the least amount of oblique astigmatism for a given prescription?

Answer: Best form (corrected curve) lens

Best form lenses are designed with optimal base curves to minimize oblique astigmatism and peripheral distortions.

A patient requires a prism of 4Δ base-in for the right eye. If split equally, how much prism is ground on each lens?

Answer: 2Δ base-in on each lens

When prism is split equally, half the total prism (2Δ) is placed base-in on each lens.

The critical angle in optics refers to the angle at which:

Answer: Total internal reflection occurs

The critical angle is the minimum angle of incidence at which total internal reflection occurs at the interface between a denser and less dense medium.

What is the effect of increasing a lens's center thickness on its optical performance?

Answer: Increases back vertex power

Increasing center thickness increases the back vertex power of a plus lens due to the lens clock effect.

A lens marked with a red dot indicates:

Answer: The temporal side for progressive lenses

Red dots on progressive lenses mark the temporal side to help with proper orientation during dispensing.

When measuring vertex distance, which surface of the lens is measured to the cornea?

Answer: Back surface (ocular side)

Vertex distance is measured from the back (ocular) surface of the lens to the front of the cornea.