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172 Ophthalmic Lenses

Fig. 11.57: Marking vertical lines on the layout

Fitting Height

The fitting cross on progressive addition lens must coincide with the pupil
centre of the wearers in their natural posture. The position of the pupil
centre relative to the correctly adjusted frame is the fitting height, and is
specified as the distance above the deepest point of the inner frame rim to
the nearest 1mm. Occasionally some practitioners prefer to specify the fitting
height as mm above datum, which is the line halfway between the
uppermost and lowermost rims of the frame.

The following procedure is used to measure the fitting height:
• Place your self opposite and at the same height as the wearer.
• Ask the wearer to adopt a comfortable posture and look straight ahead.
• Ask the wearer to look at your LE.
• Hold a pen torch just below your LE.

Fig. 11.58: Fitting height measurement