Measuring line, or segmented, tri-focals manually, isn’t that much different from the measuring of segmented bifocals. The only difference is where the segment is positioned in the pair of eyewear, or eyeglasses. Opticians must know how to do this manually.
- Seat the patient directly in front of you
- Place the adjusted frame onto the patient’s face and ask patient to adjust to how they will more than likely wear them if necessary.
- Instruct patient to look into the distance, at least twenty feet away.
- You, the Optician, adjust your seat so that you are seated at the same height as the patient.
- Use a permanent marker (Sharpie), draw a line on the lens directly beneath (1mm-2mm) the pupil of patient. Do this to both eyes. This is where the laboratory technicians will position the top segment.
- Remove the eyewear.
- Measure the segment height with a PD stick.
- Document this for the laboratory.
In a tri-focal lens, there are three fields of vision – distance, intermediate and near. There will be a two segments, but only the top segment is used for fitting a patient properly for eyeglasses.