The process for fitting the temporary prisms is straightforward, and has been determined from clinical trials. Until you are experienced with fitting the prisms, do not vary from the process outlined below. Varying from the standard process reduces the success rates dramatically. The concept of peripheral prisms is quite simple, but varying the fitting can have unexpected consequences. If you have a non-traditional case that you feel requires a change to the standard fitting protocol, please contact us to discuss potential variations.
ITEMS NEEDED FOR FITTING
1. Preparing for Fitting
Observe patient’s normal head posture and walking stance when greeting patient.
Clean patient’s glasses. Put glasses on patient and apply template on front side of the lens on hemi side. Center red template dot over patient’s pupil. If black patches on template overlap frame rim, re-adjust frame and re-apply template to reduce or eliminate overlap. If you are considering a frame for the permanent prisms, be aware of the red FRAME CLEARANCE lines around the outside of the template. These need to be inside the frame rim if you’re to order the permanent Peli Lens™
Prisms are fit monocularly on the side of the hemianopsia:
• Right side for right hemi
• Left side for left hemi
Add occluder to the other lens. If necessary, use small tabs of scotch tape to temporarily secure template to lenses.
4. Positioning Template
Have patient walk naturally back and forth in front of you.
Observe head posture while comparing to earlier stance and position observation. Ask patient if black template portions are obstructing vision at the top or the bottom. Re-adjust
template if necessary and repeat observation, making adjustments as needed.
• On rear surface of lens, place one clean Peli press-on prism, pointed-end toward temporal, directly over one of the black portions of the template.
• Repeat with second Peli press-on and press both firmly in place. Verify separation of 12 mm and base direction (out)
• If prisms overlap the edge of the frame, the excess should be trimmed
6. Verifying Placement
Put the glasses on the patient to re-verify placement. Remove occluder, template, and markings while leaving the prisms in place.
Training is imperative to success with the Peli Lens. In addition to the basic training below, in-office vision therapy sessions have been shown to increase the patient’s ability to differentiate what’s in the prism and what is not. It is highly recommended to incorporate some vision therapy into the Peli Lens fitting.
Overview of Prism Use
Instruct patient not to look into the prisms. Peli Prisms expand the peripheral vision which enables the patient to detect objects in the blind field. The patient should be taught that looking into the prisms will cause double vision. They should always look through the prism-free central portion of the lens.
Demonstrating Field Expansion
Demonstrate the prism effect by conducting confrontation field. On the second administration demonstrate the expansion to the patient by asking him to look at the hand position through the center of the lens using head and eye movements. Demonstrate to the patient the double vision that occurs when looking into the prism. Tell the patient to avoid double vision by not looking directly into the prisms.
Reach and Touch Training:
While the patient is fixating on your nose reach your hand into the patient blind side and have patient grab at your hand as he detects it through the prism(s). It may take 3 tries before he/she succeeds. This “game” should be practiced at home.
This is similar to patient adaptation to wearing bifocals for the first time. Again, observe patient’s head posture to detect possible need for adjustment of frames or prism placement. Lead patient from uncluttered areas such as a hallway to progressively cluttered areas such as a waiting room filled with chairs as potential obstacles. Constantly ask patient to report his/her observations.
Sending Patient Home:
Record final fitting positions (patients like to experiment and may move them) and make sure prisms are securely attached to the rear of the lens. For best prism adhesion, follow 3M Press-On™ Prism Application Instructions. Instruct patient to wear only in familiar settings or when walking with a companion in unfamiliar settings for a one month trial period. Provide cleaning and care instructions.
Make a follow-up appointment for after the trial period to assure adaptation and to determine if the press-ons should be replaced with the permanent Peli Lens™.