ABO Ametropia/Ophthalmic Optics 2

Question 1

A patient has a prescription of -3.00 -1.50 x 090. What is the power in the 180-degree meridian?

Accepted Answer

-4.50 D

Answer

In the 180-degree meridian (perpendicular to axis 090), the full sphere plus cylinder power applies: -3.00 + (-1.50) = -4.50 D.

Question 2

Which type of astigmatism has one focal line in front of the retina and one behind it?

Accepted Answer

Mixed astigmatism

Answer

Mixed astigmatism has one principal meridian focused anterior to the retina (myopic) and the other posterior (hyperopic).

Question 3

A +2.00 D lens is placed 12 mm in front of the corneal plane. What is the equivalent power at the corneal plane?

Accepted Answer

+2.05 D

Answer

Using F' = F / (1 - dF) = 2.00 / (1 - 0.012 × 2.00) = 2.00 / 0.976 ≈ +2.05 D.

Question 4

The circle of least confusion in a Sturm's conoid is located:

Accepted Answer

Midway between the two focal lines

Answer

The circle of least confusion is the round cross-section of Sturm's conoid located equidistant between the two focal lines.

Question 5

A patient with 4.00 D of axial myopia has an eye axial length that is approximately how much longer than emmetropic?

Accepted Answer

1.4 mm

Answer

Each diopter of axial myopia corresponds to roughly 0.35 mm of excess axial length, so 4.00 D ≈ 1.4 mm.

ABO - American Board of Optometry Practice Test