Page 95 - PowerPoint 演示文稿

Anti-reflection Coated Lens 85

2. Backward Reflection: Backward reflections occur when some of the
light behind the patient is reflected from the back surface of the lens
into his eyes as shown in Figure 8.1A. This can be annoying at times
when reduced lighting conditions are encountered such as at dusk or
while driving at night.
3. Internal Reflection: Internal reflection is caused by light being reflected
between the two lens surfaces as shown in Figure 8.1C. The amount of
reflection caused in this manner depends upon the power and position
of the lens in front of the eyes.

4. Corneal Reflection: Corneal reflection is caused by light being reflected
from the corneal surface and then interacting with the lens surfaces as
shown in Figures 8.1D and E.

Fig. 8.1
A. Light reflected from the rear lens surface into the eye
B. Light reflected from the front lens surface into the eye
C. Light entering the eye after double reflection within lens
D. Light reflected by cornea to rear lens surface and back into the eye
E. Light reflected by cornea to front lens surface and back into the eye
While frontal reflections would appear only to be a cosmetic problem
they do reduce the amount of light transmitted through to the eyes.
Backward, internal and corneal reflections all cause ghost imaging that
in turn can lead to reduce visual acuity due to blurring and reduced
contrast, which overall reduces the effectiveness of the prescription lens
and thereby reduces its efficiency.

PRINCIPLE OF ANTI-REFLECTION COATING
Anti-reflection coating is applied on the lens surface to reduce the loss of
light due to reflection and increase the light transmittance through the lens
to the eyes. To understand how it is achieved, we need to remember
“Quantum theory” that tells that the light travels in waves similar to those
in the ocean.