NOCE Dispensing Instrumentation Questions and Answers — 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?
- +0.50 -2.00 x 090
- +0.50 -2.00 x 180 (Correct answer)
- -1.50 +2.00 x 090
- -1.50 -2.00 x 180
Correct answer: +0.50 -2.00 x 180
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?
- +3.50 -1.50 x 135
- +2.00 +1.50 x 045 (Correct answer)
- +2.00 -1.50 x 135
- +3.50 +1.50 x 045
Correct answer: +2.00 +1.50 x 045
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?
- Nose pad adjusting pliers
- Lens thickness calipers
- Wide jaw angling pliers (Correct answer)
- Chassis punch
Correct answer: Wide jaw angling pliers
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?
- Distometer
- Pupillometer
- Lens Clock (Spherometer) (Correct answer)
- Polariscope
Correct answer: Lens Clock (Spherometer)
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?
- The occluder should be used for monocular readings only.
- The forehead bar should be removed.
- The measurement dial should be set to 40 cm.
- The vertex distance should be set to zero. (Correct answer)
Correct answer: The vertex distance should be set to zero.
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).
Question 6: To make a plastic frame more pliable for an adjustment, an optician would use a frame warmer. What is the primary material used as the heating medium in most common optical frame warmers?
- Hot water
- Infrared light
- Salt or glass beads
- Forced hot air (Correct answer)
Correct answer: Forced hot air
The most common type of frame warmer in a dispensing office is a forced hot air blower. This device allows for controlled, concentrated heat to be applied to a specific area of a plastic frame, making it pliable enough for adjustments without damaging the material.
NOCE Dispensing Instrumentation Questions and Answers
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?