Board Certified Ophthalmologist Optics and Refraction Principles 3

Question 1

An uncorrected -2.00 D myope has a near point of 10 cm. What is the amplitude of accommodation?

Accepted Answer

8.00 D

Answer

Near point vergence is 10 D and far point vergence is 2 D, so accommodation amplitude is 10 - 2 = 8 D.

Question 2

A +10.00 D spectacle lens worn at a 10 mm vertex distance is converted to a contact lens. What contact lens power is approximately needed?

Accepted Answer

+11.00 D

Answer

Effective power is 10 / (1 - 0.01 x 10) ≈ +11.1 D, since plus lenses moved closer to the eye need more power.

Question 3

Which is the correct minus-cylinder transposition of +2.00 +1.00 x 090?

Accepted Answer

+3.00 -1.00 x 180

Answer

Add the cylinder to the sphere, change the cylinder sign, and rotate the axis 90 degrees.

Question 4

Using a 67 cm working distance, retinoscopy neutralizes with a +4.00 D lens. What is the patient's refractive error?

Accepted Answer

+2.50 D

Answer

A 67 cm working distance corresponds to 1.50 D, which is subtracted from the gross retinoscopy finding.

Question 5

In with-the-rule astigmatism, at what axis is the minus cylinder correction typically placed?

Accepted Answer

180 degrees

Answer

With-the-rule astigmatism has the steeper vertical meridian, corrected by minus cylinder with axis near 180.

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