Fitting BiOptic Telescopes: Fitting BiOptic Telescopes: Determining Location and Determining Location and

Mounting Angle with BiOptic Mounting Angle with BiOptic Fitting AperturesFitting Apertures

Fitting BiOptic Telescopes: Fitting BiOptic Telescopes: Determining Location and Determining Location and

Mounting Angle with BiOptic Mounting Angle with BiOptic Fitting AperturesFitting Apertures

Robert B. Greer, O.D., F.A.A.O.

University of California, Berkeley

School of Optometry

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BiOptic fitting aperturesBiOptic fitting apertures

Opaque black ringsVarying outside diameters– Outside diameter noted in the corner of the

aperture– 14, 16, 19, 22, 24, 27 and 33mm

Central 3mm clear zoneStatic cling vinyl

Easily positioned on the lens

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BiOptic fitting apertures - benefitsBiOptic 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

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BiOptic fitting aperturesBiOptic fitting apertures

Outside diameter, in mm, is noted in the upper left corner of each aperture

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Vertical placementVertical placement For distance, the BiOptic telescope is usually

mounted centrally or high in the lensUsually as high in the lens as possible, especially for driving or if near tasks will also be performed while wearing a distance BiOptic3mm 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

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Vertical placementVertical placement

Aperture high on the lens for distance use

Aperture low on the lens for near use

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Horizontal placement - distanceHorizontal 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

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Horizontal placement - nearHorizontal 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

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Mounting angleMounting 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

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Mounting angleMounting 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

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Primary gaze - horizontal

Telescope viewing axis

Mounting angle

Distance mounting angleDistance mounting angle

Patient tilts head forward and sights a target at eye level through the aperture

Telescope viewing axis - horizontal

Telescope mounting angle = Frame angleTelescope mounting angle = Frame angle

Protractor measures frame angle

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Distance mounting angleDistance mounting angle

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Primary gaze - horizontal

Telescope viewing axis

Mounting angle

Patient tilts head backwards and sights a target at eye level through the aperture

Telescope viewing axis - horizontal

Protractor measures frame angle

Telescope mounting angle = Frame angleTelescope mounting angle = Frame angle

Near mounting angleNear mounting angle

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Near mounting angleNear mounting angle

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ReferencesReferences

Bailey IL. Centering high-addition spectacle lenses. Optometric Monthly. July 1979;95-100.

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