NOCE Dispensing Instrumentation Questions and Answers

Question 1

An optician uses a lens clock to measure the front surface of a lens and gets a reading of +6.50 D. The back surface measures -6.00 D in one meridian and -8.00 D in the perpendicular meridian. Assuming the lens clock is calibrated for the lens material, what is the nominal power of this lens?

Accepted Answer

+0.50 -2.00 x 180

Answer

To find the nominal power, add the front surface power to the back surface powers. Sphere power is the front curve plus the flattest back curve (+6.50 + (-6.00) = +0.50 D). Cylinder power is the difference between the two back curves (-8.00 - (-6.00) = -2.00 D). The axis is determined by the flattest meridian on the back surface. Since the powers are given without an axis, by convention, the first meridian is 180 and the second is 090. Thus, the prescription is +0.50 -2.00 x 180.

Question 2

When using a manual lensometer, if the sphere lines come into focus at +2.00 D and the cylinder lines come into focus at +3.50 D, and the axis wheel is set to 045, what is the correct prescription in plus-cylinder format?

Accepted Answer

+2.00 +1.50 x 045

Answer

In a manual lensometer, the sphere power is the first reading that comes into focus. The cylinder power is the difference between the second reading and the first reading (+3.50 - +2.00 = +1.50 D). The axis is the reading on the axis wheel when the cylinder lines are in focus, which is 045. Therefore, the prescription is +2.00 +1.50 x 045.

Question 3

A dispenser is fitting a patient with a new frame and needs to adjust the pantoscopic tilt. Which of the following tools is specifically designed for gripping the endpiece and temple to make this adjustment without damaging the frame?

Accepted Answer

Wide jaw angling pliers

Answer

Wide jaw angling pliers are designed to securely hold the endpiece and temple of a frame, allowing the dispenser to adjust the pantoscopic angle (tilt) without scratching or putting undue stress on the hinge or frame front.

Question 4

Which instrument is used to verify the base curve of a finished lens and can also detect surface warpage?

Accepted Answer

Lens Clock (Spherometer)

Answer

A lens clock, also known as a spherometer, has three probes that measure the surface curvature of a lens. This measurement is converted into diopters to indicate the base curve. By taking readings across the lens surface, it can also identify inconsistencies or warpage.

Question 5

A patient is being measured for single vision near glasses for reading at 40 cm. To ensure the optical centers are correctly placed for convergence, what setting should be adjusted on the corneal reflex pupillometer?

Accepted Answer

The vertex distance should be set to zero.

Answer

Modern pupillometers have a setting to account for the patient's convergence at near distances. By changing the dial from infinity (∞) to the patient's specific working distance (e.g., 40 cm), the instrument adjusts the measurement to provide an accurate near pupillary distance (PD).

NOCE - National Opticianry Competency Examination Practice Test

NOCE - National Opticianry Competency Examination Practice Test

NOCE Dispensing Instrumentation Questions and Answers