NOCE Optical Instrumentation Usage Questions and Answers — Questions and Answers
Question 1: An optician is using a manual keratometer to measure the corneal curvature of a patient. The horizontal meridian reading is 44.50 D and the vertical meridian reading is 42.75 D. What does this finding indicate?
- Against-the-rule astigmatism (Correct answer)
- With-the-rule astigmatism
- Oblique astigmatism
- A spherical cornea
Correct answer: Against-the-rule astigmatism
Against-the-rule astigmatism is present when the horizontal meridian of the cornea is steeper (has a higher dioptric power) than the vertical meridian. In this case, the horizontal reading of 44.50 D is steeper than the vertical reading of 42.75 D.
Question 2: When using a digital pupillometer to take a monocular pupillary distance (PD) measurement for progressive lenses, the optician should instruct the patient to fixate on:
- A distant object directly in front of them
- The optician's occluded eye
- The light source within the instrument (Correct answer)
- A near object held at 40 cm
Correct answer: The light source within the instrument
A digital pupillometer has an internal fixation target, often a small light or dot, for the patient to look at. This ensures the patient's eyes are in the primary position, allowing for an accurate measurement of the distance from the center of the bridge of the nose to the center of each pupil for a precise monocular PD.
Question 3: While verifying a prescription with a manual lensometer, the optician finds that the sphere lines come into focus at -1.50 D. After turning the power drum further, the cylinder lines come into focus at -3.00 D. To correctly identify the axis of the cylinder, what must be done?
- Rotate the power drum back and forth until both sets of lines are equally blurry.
- Note the axis wheel reading when the sphere lines are in focus.
- Adjust the axis wheel until the three parallel cylinder lines appear straight and unbroken. (Correct answer)
- Center the target reticle using the prism compensation device.
Correct answer: Adjust the axis wheel until the three parallel cylinder lines appear straight and unbroken.
In manual lensometry for a spherocylindrical lens, after focusing the sphere lines, the next step is to focus the cylinder lines. If the cylinder lines (the triple lines) appear broken or skewed, the axis wheel must be rotated until they are continuous and straight. The reading on the axis wheel at this point indicates the correct cylinder axis.
Question 4: A patient is being evaluated for a soft contact lens fitting. Which slit lamp illumination technique is most effective for assessing the overall fit, including lens movement and centration, without causing excessive tearing?
- Sclerotic scatter
- Specular reflection
- Diffuse illumination with low to medium magnification (Correct answer)
- Direct focal illumination with a narrow beam
Correct answer: Diffuse illumination with low to medium magnification
Diffuse illumination provides a broad, even light that allows for a general overview of the anterior eye and the contact lens. Using low to medium magnification (6x to 16x) is ideal for observing the lens's position, coverage, and movement upon blinking, providing a comprehensive assessment of the fit without the intensity of other techniques that might cause reflex tearing and alter the natural fit.
Question 5: Which of the following is the first and most critical step an optician must perform before using a manual lensometer to ensure accurate readings for any patient's glasses?
- Placing the glasses with the temples facing away from the operator.
- Setting the power drum to the approximate sphere power of the lens.
- Turning the power drum to +10.00 to fog the target.
- Focusing the eyepiece for their own eye. (Correct answer)
Correct answer: Focusing the eyepiece for their own eye.
Before any measurements are taken, the eyepiece of the lensometer must be focused for the individual operator's eye. This is done by turning the eyepiece to the most plus setting, then slowly turning it back until the reticle (crosshairs) is in sharp focus. Failure to do so will introduce error into all subsequent power readings.
Question 6: An optician is neutralizing a lens and finds that the target mires cannot be centered in the reticle, even with the lens stage centered. The intersection of the mires is displaced 2 units up and 3 units to the left (toward the nose for a right lens). What instrument should be used to quantify this finding?
- Geneva lens clock
- Distometer
- Prism compensating device (Correct answer)
- Pupilometer
Correct answer: Prism compensating device
When the mires in a lensometer cannot be centered on the reticle, it indicates the presence of ground-in prism. If the amount of prism is greater than what can be measured by the reticle's concentric rings (typically up to 5 prism diopters), the prism compensating device is used to dial in prism until the target is centered, thereby measuring the amount and direction of the prescribed prism.
NOCE Optical Instrumentation Usage Questions and Answers
An optician is using a manual keratometer to measure the corneal curvature of a patient.
The horizontal meridian reading is 44.50 D and the vertical meridian reading is 42.75 D.
What does this finding indicate?