FREE COA Lensometry and Refractometry Questions and Answers

Question 1

While performing manual lensometry on a pair of glasses, you first focus the thin, single 'sphere' lines at -1.50 D.
You then turn the power wheel further until the thick, triple 'cylinder' lines come into focus at -2.75 D.
The axis wheel is set to 090.
How would this prescription be written in standard minus-cylinder format?

Accepted Answer

-1.50 -1.25 x 090

Answer

-2.75 +1.25 x 180

Answer

-1.50 +1.25 x 090

Answer

-2.75 -1.25 x 090

Question 2

What is the primary purpose of the Jackson Cross Cylinder (JCC) during a manual subjective refraction?

Accepted Answer

To refine the cylinder axis and power

Answer

To determine the initial sphere power

Answer

To measure the pupillary distance

Answer

To check for the presence of prism

Question 3

When neutralizing a lens in the lensometer, the target mires are perfectly clear and centered when the power wheel is at +3.00 D. However, to center the target in the reticle, the entire lens holder had to be moved down, causing the target to be displaced 2 units up on the prism scale. How should this prism be recorded?

Accepted Answer

2Δ Base Up

Answer

2Δ Base In

Answer

2Δ Base Out

Answer

2Δ Base Down

Question 4

A patient with a high myopic prescription of -11.00 D has their manifest refraction performed at a standard vertex distance of 14mm. Their new glasses are fit very close to their face, at a vertex distance of 10mm. Which of the following complaints is MOST likely?

Accepted Answer

The glasses feel too strong.

Answer

The glasses feel too weak.

Answer

The patient notices colored fringes around lights.

Answer

The patient feels no difference in power.

Question 5

Which of the following describes the correct procedure for measuring the 'add' power of a lined bifocal lens using a manual lensometer?

Accepted Answer

Measure the sphere power in the distance portion, then move to the near segment and re-focus the sphere lines. The add is the difference.

Answer

Measure the near segment first, then subtract the distance power.

Answer

Measure the distance power, then turn the glasses around and measure the front of the near segment.

Answer

Place the geometric center of the lens in the lensometer and take one reading.

Question 6

An automated refractor measures a young, asymptomatic patient's prescription as -3.00 D sphere in both eyes. However, a subsequent cycloplegic refraction reveals a true prescription of -0.75 D sphere. What is the MOST likely cause for this significant discrepancy?

Accepted Answer

Accommodative spasm

Answer

Instrument miscalibration

Answer

Poor patient fixation

Answer

Corneal surface irregularity