Board Certified Ophthalmologist FREE Optics and Refraction Questions and Answers 2

Question 1

A patient with a cycloplegic refraction of +5.00 D requires a spectacle lens at a vertex distance of 12 mm. What is the effective power at the corneal plane?

Accepted Answer

+5.31 D

Answer

Using the effectivity formula, the effective power at a shorter vertex distance increases for plus lenses: +5.00 / (1 - 0.012 x 5.00) = +5.31 D.

Question 2

Which type of astigmatism is present when one focal line falls in front of the retina and the other falls behind it?

Accepted Answer

Mixed astigmatism

Answer

Mixed astigmatism occurs when the two principal meridians focus on opposite sides of the retina.

Question 3

What is the critical angle for total internal reflection at a crown glass-air interface if the refractive index of crown glass is 1.52?

Accepted Answer

41.1 degrees

Answer

The critical angle is calculated as sin^-1(1/1.52) = 41.1 degrees.

Question 4

A prism with an apical angle of 10 degrees and refractive index of 1.5 produces what amount of deviation?

Accepted Answer

5 prism diopters

Answer

Using the thin prism approximation, deviation = (n-1) x apical angle = (1.5-1) x 10 = 5 prism diopters.

Question 5

In retinoscopy, a with-the-rule movement is observed in the horizontal meridian. What type of lens should be added to neutralize this meridian?

Accepted Answer

Plus cylinder at 180 degrees

Answer

With movement in the horizontal meridian indicates relative hyperopia in that meridian, corrected by adding plus power at 180 degrees.

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Board Certified Ophthalmologist FREE Optics and Refraction Questions and Answers 2