ABO NOCE Basic Opticianry Optical Instrumentation Use Questions and Answers 5 — Questions and Answers
Question 1: A lens clock reading on the front surface of a lens shows +6.00 D and the back surface shows –2.00 D. Using a simplified calculation (n=1.53), the approximate lens power is:
- +4.00 D (Correct answer)
- +8.00 D
- +6.00 D
- +2.00 D
Correct answer: +4.00 D
Using the lensmaker's equation simplified, the approximate power is the sum of the front and back surface powers: +6.00 + (–2.00) = +4.00 D.
Question 2: What is the purpose of the 'nose piece' or 'lens stop' on a lensometer?
- It holds the patient's nose during measurement
- It supports and positions the lens being measured at the correct distance (Correct answer)
- It adjusts the eyepiece magnification
- It controls the illumination intensity
Correct answer: It supports and positions the lens being measured at the correct distance
The lens stop holds the spectacle lens at the precise focal distance from the lensometer's collimating lens for accurate power measurement.
Question 3: Which type of lensometer reticle pattern uses a bullseye (circle with cross) target?
- American Standard (ANSI) pattern (Correct answer)
- European pattern with cross-hair only
- Progressive lens pattern
- Prism verification pattern
Correct answer: American Standard (ANSI) pattern
The American Standard lensometer uses a bullseye target with concentric circles and crossed lines to allow simultaneous sphere, cylinder, and prism measurement.
Question 4: During lensometer verification, a lens shows 2 prism diopters base-out in the right lens. On the lensometer, this means the target is displaced:
- 2 rings toward the nose side of the reticle
- 2 rings toward the temporal side of the reticle (Correct answer)
- Vertically upward by 2 rings
- Vertically downward by 2 rings
Correct answer: 2 rings toward the temporal side of the reticle
Base-out prism displaces the target toward the temporal (outer) side of the reticle because prism bends light toward its base.
Question 5: A PD ruler is being used to measure a patient's binocular distance PD. The ruler should be aligned:
- From the outer edge of one iris to the outer edge of the other iris
- From the center of one pupil to the center of the other pupil (Correct answer)
- From the inner edge of one iris to the outer edge of the other iris
- From the outer edge of one cornea to the inner edge of the other cornea
Correct answer: From the center of one pupil to the center of the other pupil
PD is the distance between the centers of the two pupils and must be measured center-to-center for accurate optical alignment.
Question 6: An infrared (IR) thermometer is sometimes used in optical dispensing to:
- Measure the refractive index of lens materials
- Verify the temperature of a frame warmer to prevent overheating frames (Correct answer)
- Test the UV blocking ability of lenses
- Measure the patient's body temperature
Correct answer: Verify the temperature of a frame warmer to prevent overheating frames
IR thermometers help opticians monitor frame heater temperatures so plastic frames are not overheated, which can cause warping, discoloration, or bubbling.
Question 7: When verifying a finished pair of spectacles, the lensometer is used to check all of the following EXCEPT:
- Sphere power of each lens
- Cylinder power and axis of each lens
- Optical center placement and prism
- The frame's pantoscopic tilt angle (Correct answer)
Correct answer: The frame's pantoscopic tilt angle
Pantoscopic tilt is a physical frame adjustment measured with a protractor or by visual assessment, not by the lensometer.
ABO NOCE Basic Opticianry Optical Instrumentation Use Questions and Answers 5
A lens clock reading on the front surface of a lens shows +6.00 D and the back surface shows –2.00 D.
Using a simplified calculation (n=1.53), the approximate lens power is: