ABO Ametropia/Ophthalmic Optics 4

Question 1

A patient requires +2.50 D at the spectacle plane (12 mm vertex distance). What contact lens power is needed?

Accepted Answer

+2.44 D

Answer

F_contact = F_spec / (1 + d × F_spec) = 2.50 / (1 + 0.012 × 2.50) = 2.50 / 1.03 ≈ +2.43 D, rounded to +2.44 D.

Question 2

Oblique astigmatism refers to astigmatism with principal meridians oriented at:

Accepted Answer

Between 30–60 and 120–150 degrees

Answer

Oblique astigmatism is conventionally defined as astigmatism with the principal meridians between 30–60 degrees and 120–150 degrees.

Question 3

The Maddox rod test is used clinically to measure:

Accepted Answer

Heterophoria and vergence deviation

Answer

The Maddox rod converts a point source into a streak, dissociating the eyes to reveal and measure phoria or tropia.

Question 4

Which lens type is most effective at reducing oblique astigmatic error for off-axis gaze?

Accepted Answer

Corrected curve (best form) lens

Answer

Corrected curve (best form) lenses are designed with base curves that minimize oblique astigmatism during off-axis viewing.

Question 5

A patient's spectacle magnification is greater than 1.0. This indicates the patient is:

Accepted Answer

Hyperopic

Answer

Spectacle magnification >1.0 means the retinal image is larger than in the standard emmetropic eye, which occurs with plus (hyperopic) lenses.

ABO - American Board of Optometry Practice Test