ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers

Question 1

A patient's prescription is OD: -5.00 D sphere, OS: -2.00 D sphere. If their pupils are decentered 4 mm inwards from the optical centers of the lenses, what is the total amount and direction of induced horizontal prism?

Accepted Answer

2.8 prism diopters Base Out

Answer

Prentice's Rule (Prism = Power x Decentration in cm) is used for each eye. OD: 5.00 D x 0.4 cm = 2.0 p.d. For a minus lens, decentering IN induces Base OUT prism. OS: 2.00 D x 0.4 cm = 0.8 p.d. For a minus lens, decentering IN induces Base OUT prism. Since both eyes induce Base Out prism, the effects are additive: 2.0 p.d. BO + 0.8 p.d. BO = 2.8 p.d. Base Out total.

Question 2

A patient with anisometropia experiences vertical imbalance when reading. The prescription is OD: +1.00 D sphere, OS: +4.00 D sphere, with a +2.00 Add. Assuming a reading level 10 mm below the optical centers, which of the following is the most appropriate corrective action?

Accepted Answer

Order a slab-off (bicentric grind) on the right lens.

Answer

Vertical imbalance occurs when there's a significant power difference between lenses in the vertical meridian. Slab-off, a form of bicentric grinding, adds prism to correct this. The rule is to apply slab-off (Base Up prism effect) to the lens with the most minus or least plus power in the vertical meridian. In this case, the OD (+1.00 D) is the least plus lens and requires the slab-off correction.

Question 3

Which of the following lens materials has the highest index of refraction, resulting in the thinnest and lightest lens for a given high prescription?

Accepted Answer

High-Index Plastic 1.74

Answer

The index of refraction measures how efficiently a material bends light. A higher index means the material bends light more, allowing for a thinner and lighter lens design. High-Index Plastic 1.74 has one of the highest refractive indices available for ophthalmic lenses, significantly higher than Crown Glass (1.52), CR-39 (1.50), and Polycarbonate (1.59).

Question 4

A lens aberration that causes light of different colors (wavelengths) to focus at different points, resulting in colored fringes around objects, is known as:

Accepted Answer

Chromatic Aberration

Answer

Chromatic aberration is an optical effect where a lens fails to focus all colors to the same convergence point. This occurs because lenses have a different refractive index for different wavelengths of light. This dispersion of light results in colored halos or fringes around images.

Question 5

Using the 'minus cylinder' form, what is the correct transposition of the prescription +1.00 +1.50 x 090?

Accepted Answer

+2.50 -1.50 x 180

Answer

To transpose a prescription to minus cylinder form, follow three steps: 1. Algebraically add the sphere and cylinder powers to get the new sphere (+1.00 + 1.50 = +2.50). 2. Change the sign of the cylinder (+1.50 becomes -1.50). 3. Change the axis by 90 degrees (90 + 90 = 180). Therefore, the transposed prescription is +2.50 -1.50 x 180.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers