Page 206 - PowerPoint 演示文稿

196 Ophthalmic Lenses

Fig. 14.4

Fig. 14.5: Change of dioptric power in ratio changing horizontal inclination

some deviation in axis and unwanted prismatic effect. There will always
be some decent ration required as seen in the Figure 14.5.

Measuring Horizontal Inclination

While measuring the horizontal inclination, the frame must be on the head
of the athlete because the spreading of the sides as the frame passes over
the temples tends to decrease the horizontal inclination and the
measurements must be made in this situation. It is not sufficient to take
these measurements on the frame on its own. The following step has to be
followed to take the measurement of horizontal inclination:
1. Determine the Geometric centre: Mark the geometric centre on the demo
lens with vertical line using boxed lens system. The boxing system is based
upon the idea of drawing an imaginary box around a lens shape with the
box’s sides tangent to the outer most edges of the shape. The system uses
the sides of the boxes as reference points for the standard system of
measurements (Fig. 14.6).