Page 204 - PowerPoint 演示文稿

194 Ophthalmic Lenses

eyes. So protection is an important factor while dispensing lenses to the
player. Each sport requires some sort of protection from high speed
projectiles to play safely and comfortably. Besides protection, enhancing
vision for superior performance is also very critical in sports.
The big advantage of an optical appliance is that they allow the eyes to
be protected. A well designed sports specific frame is usually wrapping
around the face following the facial anatomy, protecting against light,
particles and insects from the sides and above and also shielding the eyes
from pollen and wind, in contrast to everyday frame which are fairly flat
across the front.

Fig. 14.1: Everyday frame

Fig. 14.2: Sports frame

With the right choice of lens, complete UV protection can be given and
by removing blue and UV light, contrast enhancement can be achieved
which is directly related to increased sporting performance. However, use
of wrap around frames for prescription means that standard calculations
are no longer valid because of the way in which the frames wraps around
the eyes and cause:
1. Change in dioptric power
2. Unwanted prismatic effects
3. Oblique astigmatism.
The lens tilt also leads to induced decent ration. In addition, the high base
curve lens leads to impaired optical properties in the periphery and one of
the essentials of a sports spectacle is to enhance peripheral vision.