NOCE Ophthalmic Products and Materials Questions and Answers

Question 1

A patient with a high-minus prescription who is sensitive to peripheral color fringing would benefit most from a lens material with which of the following characteristics?

Accepted Answer

A low refractive index and a high Abbe value

Answer

The Abbe value is a measure of a lens material's chromatic aberration. A higher Abbe value indicates less chromatic aberration, meaning less color fringing, which is crucial for patient comfort in higher prescriptions. While a high refractive index creates a thinner lens, it is often associated with a lower Abbe value (more chromatic aberration). Therefore, prioritizing a high Abbe value is most critical for this patient's specific complaint. A low refractive index material like CR-39 often has a high Abbe value (58).

Question 2

A construction worker requires prescription safety glasses. According to ANSI Z87.1 standards, which lens marking indicates the eyewear has been tested for high-impact resistance?

Accepted Answer

Z87+

Answer

The ANSI Z87.1 standard specifies markings for safety eyewear. The '+' sign indicates that the lens has passed a high-velocity impact test, which involves a 1/4-inch steel ball traveling at 150 feet per second. The 'Z87' mark alone signifies basic impact resistance. 'Z87-2' indicates a prescription safety frame. 'D3' indicates protection from liquid splashes and droplets.

Question 3

An optician is designing a progressive addition lens for a patient with a high 'add' power who prefers a smaller, fashionable frame. To maximize the usable near vision area within the constraints of the small frame, which lens design characteristic should be prioritized?

Accepted Answer

A shorter corridor length

Answer

A shorter corridor length in a progressive lens allows the full add power to be reached more quickly, requiring less downward eye rotation. This is advantageous for smaller frames because it ensures the near zone is fully contained within the bottom of the lens shape. A longer corridor would place the near zone too low, potentially cutting it off.

Question 4

A patient with anisometropia of 2.50 D experiences vertical imbalance and diplopia when reading through their bifocal. To correct this, a slab-off is ordered. On which lens is a conventional slab-off typically ground?

Accepted Answer

The lens with the most minus or least plus power in the vertical meridian.

Answer

A conventional slab-off is a bicentric grind that adds base-up prism to the reading area of one lens to counteract vertical imbalance. It is always applied to the lens that has the most minus or least plus power in the 90-degree (vertical) meridian. This effectively neutralizes the excessive base-down prism induced in that eye at the reading level.

Question 5

When comparing polycarbonate and Trivex lens materials for a drill-mounted frame, Trivex is often preferred due to its superior:

Accepted Answer

Tensile strength

Answer

Trivex has a higher tensile strength than polycarbonate, making it more resistant to cracking and splitting around drill holes. This makes it an ideal choice for rimless or drill-mounted frames where the lens material itself must bear structural stress. While polycarbonate has excellent impact resistance, its lower tensile strength makes it more prone to stress fractures in this type of mounting.

NOCE - National Opticianry Competency Examination Practice Test

NOCE - National Opticianry Competency Examination Practice Test

NOCE Ophthalmic Products and Materials Questions and Answers