COT Spectacle Dispensing and Frame Fitting — Questions and Answers
Question 1: When measuring monocular pupillary distances (PDs) for a progressive addition lens prescription, the technician measures the distance from the center of each pupil to:
- The outer canthus of the same eye
- The center of the bridge of the frame
- The center of the nose bridge (midline) (Correct answer)
- The inner canthus of the opposite eye
Correct answer: The center of the nose bridge (midline)
Monocular PD is measured from the center of each pupil to the midline (center of the nose). This gives a right PD and a left PD separately, which is critical for progressive lenses where optical centers must be precisely aligned to each pupil independently.
Question 2: Pantoscopic tilt of a spectacle frame refers to:
- The inward angle of the temples wrapping around the head
- The horizontal rotation of the frame front on the face
- The vertical forward tilt of the lens plane, with the bottom of the lenses closer to the cheeks than the top (Correct answer)
- The curvature of the frame front in the horizontal plane (face-form wrap)
Correct answer: The vertical forward tilt of the lens plane, with the bottom of the lenses closer to the cheeks than the top
Pantoscopic tilt is the vertical angle of the spectacle lens plane relative to the face — ideally 8–12° — with the lower edge of the lenses tilted toward the cheeks. This aligns the optical axis of the lens with the natural downward gaze direction used for reading.
Question 3: Vertex distance becomes clinically significant when a patient's spectacle prescription exceeds approximately:
- ±1.00 D
- ±2.00 D
- ±4.00 D (Correct answer)
- ±8.00 D
Correct answer: ±4.00 D
Vertex distance (the distance from the back surface of the spectacle lens to the front of the cornea) must be accounted for in prescriptions of approximately ±4.00 D or greater. At higher powers, even a few millimeters of difference in vertex distance changes the effective power of the lens reaching the eye.
Question 4: A patient's new glasses sit too close to the eyelashes, causing discomfort. The correct adjustment to increase the distance between the lenses and the eyes is to:
- Increase the pantoscopic tilt by angling the bottom of the frame outward
- Open the nose pads outward to push the frame away from the face (Correct answer)
- Tighten both temples to pull the frame back on the head
- Replace the frame with one that has a longer bridge
Correct answer: Open the nose pads outward to push the frame away from the face
Adjusting the nose pads outward (increasing the pad spread) raises the frame higher and pushes it away from the face, increasing vertex distance and reducing contact with the eyelashes. This is the appropriate frame adjustment for glasses sitting too close to the eyes.
Question 5: When fitting a patient for spectacles, the correct temple length provides support by:
- Resting the temple tip on the top of the ear with no contact behind the ear
- Bending at the ear level and resting on the mastoid bone behind the ear (Correct answer)
- Crossing directly behind the skull above both ears
- Curving tightly over the ear and pressing on the side of the head
Correct answer: Bending at the ear level and resting on the mastoid bone behind the ear
A properly fitted temple should bend at approximately the level of the top of the ear and rest along the side of the head, with the temple tip resting behind and below the ear on the mastoid area. This distributes weight properly and prevents the frame from sliding down.
Question 6: A patient complains of eyestrain and distorted vision with new progressive addition lenses, despite having worn progressives before. The FIRST verification step should be to:
- Reduce the near addition power by 0.25 D
- Verify the optical center height and monocular PD against the patient's measurements (Correct answer)
- Replace the lenses with flat-top bifocals
- Add antireflective coating to reduce glare
Correct answer: Verify the optical center height and monocular PD against the patient's measurements
Complaints of distortion and eyestrain with progressive lenses most commonly result from incorrect fitting parameters, particularly the optical center height or monocular PD being off. The first step is always to verify that the lenses were made to the correct measurements before considering prescription changes or alternative lens designs.
COT Spectacle Dispensing and Frame Fitting
When measuring monocular pupillary distances (PDs) for a progressive addition lens prescription, the technician measures the distance from the center of each pupil to: