Board Certified Ophthalmologist Optics and Refraction Principles 4

Question 1

A Galilean telescope uses a +5.00 D objective and a -20.00 D eyepiece. What is the separation between the lenses?

Accepted Answer

15 cm

Answer

The tube length equals the sum of focal lengths: 20 cm + (-5 cm) = 15 cm.

Question 2

In unilateral aphakia, which correction method produces the least aniseikonia?

Accepted Answer

Posterior chamber intraocular lens

Answer

An IOL near the eye's nodal point causes about 1-3% magnification, compared with about 7-10% for contact lenses and 25-33% for spectacles.

Question 3

Which bifocal segment design minimizes image jump?

Accepted Answer

Flat-top segment

Answer

The flat-top segment's optical center lies near its top edge, so little prism is introduced as the eye enters the segment.

Question 4

Which prism orientation is used in spectacles to relieve symptomatic exophoria at near?

Accepted Answer

Base-in

Answer

Base-in prism shifts the image outward, reducing the convergence demand for an exodeviation.

Question 5

What is the definition of one prism diopter?

Accepted Answer

Displacement of 1 cm at a distance of 1 m

Answer

One prism diopter deviates light 1 cm at 1 m, which is roughly 0.57 degrees for small angles.

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