Dispensing Procedures and Instrumentation Flashcards
6 cards from real NOCE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Dispensing Procedures and Instrumentation flashcards as text
A patient wearing progressive addition lenses complains that they have to tilt their head down to see distant objects clearly. Which of the following is the MOST likely cause of this issue?
Answer: The fitting height is too high.
If the fitting height of a progressive lens is set too high, the patient's pupils will be positioned too far up in the lens corridor. This forces them to tilt their head downward to look through the distance portion of the lens, which is located at the top.
When using a manual lensometer to verify a prescription containing prism, the reticle target is displaced from the center. What is the correct initial procedure to measure the amount and direction of the prism?
Answer: Use the prism compensating device to bring the target to the center of the reticle.
A manual lensometer is equipped with a prism compensating device specifically designed to measure prism. By adjusting this device, the dispenser can move the reticle target back to the center, and the amount and direction of the prism can be read directly from the prism scale.
Which instrument is considered the gold standard for accurately measuring a patient's interpupillary distance (PD)?
Answer: A pupilometer
A pupilometer is a specialized instrument that measures the distance between the pupils with high accuracy by using a corneal reflection system. While a millimeter ruler can be used, it is more prone to parallax and other human errors, making the pupilometer the most precise and reliable tool for this measurement.
A patient selects a frame that, when adjusted, will sit 16 mm from their cornea. The original refraction was performed at a vertex distance of 11 mm. The prescription is -9.50 D sphere. What dispensing procedure is critical to ensure the patient experiences the correct lens power?
Answer: Order the lenses with a compensated power calculation.
When the vertex distance at which a patient wears their glasses differs significantly from the refraction vertex distance, especially with higher prescriptions (generally over +/- 7.00 D), the effective power of the lens changes. Moving a minus lens further from the eye makes it effectively stronger (more minus). A compensated power calculation must be performed to adjust the ordered lens power so the patient perceives the intended refractive correction.
During the final fitting of a pair of metal-framed spectacles, the dispenser notices the bottom of the frame front is angled too far away from the patient's cheeks. Which adjustment should be made?
Answer: Increase the pantoscopic tilt.
Increasing the pantoscopic tilt involves angling the bottom of the frame front closer to the patient's cheeks. This adjustment is typically made by carefully bending the temples downwards at the hinge or endpiece. This ensures the lens is properly positioned for optimal optics, especially for multifocal lenses.
Which of the following instruments is used to measure the curvature of the front or back surface of a spectacle lens?
Answer: Lens Clock (Geneva Gauge)
A lens clock, also known as a Geneva Gauge or spherometer, is a mechanical instrument used to measure the surface power of a lens. It has three prongs; the central one moves to measure the sagitta (depth of the curve), which is then converted to diopters on the device's dial. It can measure both the front (base) and back curves.