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. You can also download our complete fitting guide for more detail and different fitting options.
ITEMS NEEDED FOR FITTING
1. Preparing for Fitting
- Observe patient’s normal head posture and walking stance.
2. Placing Template
- Place the template on the eye with the temporal field defect
- (left hemi = left eye, right hemi = right eye).
- Place an occluder on the opposite eye. If you do not
- have an occluder, you can use the yellow cling provided with the fitting kit.
- Position the red dot in the center of the template directly over the patient’s pupil. If black part of the template overlaps the frame rim, adjust the frame and re-apply template to reduce or eliminate overlap.
- Have the patient walk around again to ensure the template has not changed their gait. If patient’s gait changed because of template, adjust placement of template accordingly.
3. Placing Prisms
- On the rear surface of the lens, firmly place the Peli press-on prisms, with pointed end towards temple, directly over the black portions of the template.
- Verify that there is 12mm of separation between the prisms.
- If prisms overlap the edge of the frame, trim off the excess.
- Remove template
4. Final Fitting
- Remove the marks, occluder and press any air bubbles out of the temporary prisms.
- Record the final fitting positions and return glasses to the patient.
Y – X = Z or X + Z = Y
_______:X = Lower Height (measurement from the top of
the bottom prism to the bottom of the lens)
_______:Y = Upper Height (measurement from the bottom
of the top prism to the tom of the lens)
_______:Z = Separation (measurement from bottom of top
prism to the top of the bottom prism)
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 them 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.
Importance of Training & Recommended Exercises
When first worn, peripheral prisms create a certain level of visual confusion. The patient tries to distinguish what information is in their blind field, and what information is in their seeing field. The goal of training is to minimize this confusion. A pilot study done at Schepens Eye Research Institute showed patients to be 95% accurate in distinguishing the confusing images after just six one-hour training sessions in their driving simulator.
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 they detect it through the prism. This should be practiced at home with a loved one, or by one’s self.
In a vision therapy or occupational therapy setting, many doctors or therapists will set up a reach and touch program on a Sanet Vision Integrator or similar reach/touch device.
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:
Before you send your patient on their way, make sure you give them the patient take home brochure. The brochure covers the at home continued training, cleaning instructions, and benefits and permanent prism options.
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™.