Dispensing and Fitting Procedures Flashcards

When measuring the segment height for a patient being fitted with lined trifocal lenses, what is the correct anatomical reference point to use as the starting position for the measurement?

Answer: The lower margin of the pupil

The standard fitting practice for lined trifocal lenses is to measure from the lower margin of the patient's pupil down to the deepest part of the lens eyewire. This placement ensures that the intermediate segment is positioned correctly for the patient's line of sight when they look down slightly for tasks like computer use, while also allowing access to the near segment below it.

A patient returns to the dispensary complaining that with their new glasses, straight lines and rectangular objects, like door frames, appear bowed or curved. The prescription and PDs have been verified as correct. Which of the following is the most likely cause of this specific distortion?

Answer: A significant change in base curve from the previous lenses

A significant change in the base curve of the lenses from what the patient was previously accustomed to can induce peripheral distortions. This can cause a 'barrel' distortion in minus lenses or 'pincushion' distortion in plus lenses, making straight lines appear curved. While other factors can cause adaptation issues, the perception of bowed lines is a classic symptom of base curve-induced distortion.

An optician needs to increase the face form (wrap) on a patient's metal frame to provide a closer fit and reduce peripheral distortion. Which of the following adjustments should be made?

Answer: Bend the endpieces inward, toward the face

Increasing face form, or wrap, involves creating more of a curve in the frame front to match the contour of the patient's face. For metal frames, this is achieved by carefully bending the endpieces inward, which brings the temples closer to the head and wraps the lenses around the face.

During the final fitting of a new pair of glasses, the optician observes that the bottom edge of the frame front is angled significantly away from the patient's cheeks. To correct this and add proper pantoscopic tilt, what adjustment is required?

Answer: Angle the temples downward from the endpiece

Increasing pantoscopic tilt involves angling the bottom of the frame front closer to the patient's cheeks. This is accomplished by bending the temples downward at the hinge or endpiece. This adjustment ensures the optical axis of the lens is properly aligned with the visual axis, especially when the patient is reading.

A patient has a prescription in their right eye of -2.00 DS with 3Δ of Base Down prism prescribed. When verifying this lens in a manual lensometer, where should the target's mires be located relative to the reticle's center crosshairs?

Answer: Centered on the third ring directly above the center

In a manual lensometer, the target is displaced in the direction of the prism's base. Therefore, for a Base Down prism, the target mires will be displaced downward. However, to bring the target back to the center of the reticle for measurement, the lens itself must be moved upward. Thus, when the lens is centered where the prism is to be verified, the mires appear displaced upward, toward the base. For 3Δ of Base Down prism, the mires will be centered on the third ring above the central crosshairs.

A first-time progressive lens wearer is dispensed their new glasses. The frame has been fully adjusted for pantoscopic tilt, face form, and vertex distance. What is the most crucial instruction an optician should give the patient to aid in adaptation?

Answer: "Point your nose at what you want to look at, especially when reading."

The key to successfully adapting to progressive addition lenses is learning to use the correct portion of the lens for the intended viewing distance. Because the sides of the lens contain peripheral distortion, wearers must be taught to turn their head and point their nose directly at the object of regard, rather than just moving their eyes. This aligns the visual axis with the clear central corridor of the lens.