Fitting BiOptic Telescopes: Determining Location and Mounting Angle with BiOptic Fitting Apertures

1. Fitting BiOptic Telescopes: Determining Location and Mounting Angle with BiOptic Fitting Apertures Robert B. Greer, O.D., F.A.A.O. University of California, Berkeley School of Optometry

2. BiOptic fitting apertures • Opaque black rings • Varying outside diameters • Outside diameter noted in the corner of the aperture • 14, 16, 19, 22, 24, 27 and 33mm • Central 3mm clear zone • Static cling vinyl • Easily positioned on the lens

3. BiOptic fitting apertures - benefits • Confirmation of vertical and horizontal placement of BiOptic telescopes • Direct measurement of the telescope mounting angle • Allows patient and doctor to see where the telescope will be located • Shows how much of the lens will be occupied by the telescope • Enables the patient/doctor to see what head movement is needed to access the telescope

4. BiOptic fitting apertures Outside diameter, in mm, is noted in the upper left corner of each aperture

5. Vertical placement • For distance, the BiOptic telescope is usually mounted centrally or high in the lens • Usually as high in the lens as possible, especially for driving or if near tasks will also be performed while wearing a distance BiOptic • 3mm between the edge of the telescope and frame must remain for lens structural strength • For near, the BiOptic telescope is mounted centrally or low in the lens • Central location may work best for computer use

6. Vertical placement Aperture high on the lens for distance use Aperture low on the lens for near use

7. Horizontal placement - distance • For distance the telescope is placed at the monocular distance inter-pupillary distance (IPD) • The IPD is often measured using traditional techniques such as rulers or corneal reflection pupillometers

8. Horizontal placement - near • For near the telescope is placed at the monocular near PD appropriate for that working distance • Ian Bailey created a “rule of thumb” for calculating the near IPD: • Near IPD = Distance IPD - 1.5(working distance) • The working distance is expressed in diopters • Example • A patient with a 65 mm distance IPD wants to work at 25 cm which is a working distance of 4 diopters • Near IPD = 65 - 1.5 (4) = 59 mm

9. Mounting angle • The telescope must be angled so that its viewing axis points towards the eye’s center of rotation • BiOptic fitting apertures allow for a direct measurement of the mounting angle • Mounting angle is referenced to the frame front • A telescope mounted perpendicular to the frame would have a mounting angle of zero degrees

10. Mounting angle • Measurement of the mounting angle requires a simple protractor with a plumb line • The plumb line may be a straightened paper clip or any other straight piece of metal

11. Telescope viewing axis Mounting angle Primary gaze - horizontal Distance mounting angle Patient tilts head forward and sights a target at eye level through the aperture Telescope viewing axis - horizontal Telescope mounting angle = Frame angle Protractor measures frame angle

12. Distance mounting angle

13. Near mounting angle Primary gaze - horizontal Mounting angle Telescope viewing axis Patient tilts head backwards and sights a target at eye level through the aperture Telescope viewing axis - horizontal Telescope mounting angle = Frame angle Protractor measures frame angle

14. Near mounting angle

15. References • Bailey IL. Centering high-addition spectacle lenses. Optometric Monthly. July 1979;95-100. • This presentation was downloaded from www.BiOpticDriving.org