Ophthalmic Optics and Principles Questions and Answers Flashcards

What is the dioptric power of a plano-convex lens with a front surface radius of curvature of 100 mm in air (n=1.00, n'=1.50)?

Answer: +5.00 D

Surface power = (n' − n) / r = (1.50 − 1.00) / 0.10 m = 0.50 / 0.10 = +5.00 D.

Which term describes the ability of a lens material to polarize light at a specific angle, known as Brewster's angle?

Answer: Polarization by reflection

At Brewster's angle, reflected light becomes completely polarized parallel to the surface, which is the basis for polarized ophthalmic lenses reducing glare.

When transposing −1.50 +2.00 × 090 into minus cylinder form, the result is:

Answer: +0.50 −2.00 × 180

Add sphere + cylinder = −1.50 + 2.00 = +0.50; reverse cylinder sign = −2.00; rotate axis 90° → 180°: result is +0.50 −2.00 × 180.

A prism of 5Δ is prescribed base-up OD. In which direction does the image appear displaced to that eye?

Answer: Upward

A base-up prism refracts light downward through the prism, making the image appear displaced upward (toward the apex).

What is the minimum vertex distance that must be accounted for when converting a spectacle prescription to contact lens power, according to standard practice?

Answer: Any prescription over ±4.00 D

By standard ophthalmic convention, vertex distance compensation is required when spectacle powers exceed ±4.00 D.

A bifocal add creates a prismatic effect at the reading level. For a +2.50 add with the reading zone 8 mm below the optical center, what is the prismatic effect using Prentice's Rule?

Answer: 2.0Δ base-up

Δ = D × c = 2.50 × 0.8 cm = 2.0Δ; a plus lens below its optical center produces base-up prism.

Which optical effect occurs when white light passes through a prism and is separated into its component wavelengths?

Answer: Dispersion

Dispersion is the separation of white light into its spectrum because different wavelengths are refracted by different amounts through the prism.