Ophthalmic Optics and Lenses Flashcards

What type of aberration causes light rays at different distances from the optical axis to focus at different points?

Answer: Spherical aberration

Spherical aberration occurs because peripheral rays focus at a different point than paraxial rays due to the spherical lens surface.

A high-minus lens is best fabricated with which base curve strategy to minimize edge thickness?

Answer: Flatter base curve

Flatter base curves on minus lenses reduce edge thickness by allowing the front surface to be less curved.

The Abbe value (V-number) of a lens material describes its:

Answer: Resistance to chromatic dispersion

The Abbe value measures how much a material disperses light into its spectral components; higher values mean less chromatic aberration.

A patient with -5.00 D prescription switches from glass (n=1.523) to polycarbonate (n=1.586). The new lenses will be:

Answer: Thinner at the edges

Higher index materials require less curvature to achieve the same power, resulting in thinner edges for minus lenses.

Prentice's Rule states that prism power at any point equals:

Answer: Distance from optical center (cm) × lens power (D)

Prentice's Rule: Prism (Δ) = distance in cm × power in diopters (P = cF).

Which of the following lens materials has the highest impact resistance?

Answer: Polycarbonate

Polycarbonate is the most impact-resistant ophthalmic lens material and is required for safety eyewear.

When transposing -2.00 -1.50 × 090, the result is:

Answer: -3.50 +1.50 × 180

To transpose: new sphere = sum of sphere and cylinder (-2.00 + -1.50 = -3.50), new cylinder = opposite sign (+1.50), new axis = 90° away (180).