Dispensing Optics

1. LENS REFLECTIONS AND
ANTIREFLECTIVE
COATINGS

2. REFLECTIONS
Troublesome to the wearers
because
2) Produce ghost image
3) Falsification of image position
4) Haze and loss of contrast
5) Produce veiling glare

3. Reflected image is troublesome if
2) It’s located near a fixated object
3) It’s sufficiently intense to stand out
from its background
4) It is in focus

4. TYPES OF THE SURFACE REFLECTION
(1)
• Most intense
• 4.3 % of the total reflection

5. (2)
Intensity of the image is 3.94%

6. (3)
Most troublesome though intensity is only
0.17 %

7. (4)
Intensity of the image is 0.09 %

8. (5)
Intensity is 0.08 % of the incident light

9. METHODS TO CONTROL
1) Base curve selection
2) Alteration of pantoscopic tilt
3) Changing the vertex distance
4) Selection of small lens sizes
5) Patient education and counseling
6) ANTIREFLECTIVE COATINGS

10. ANTIREFLECTIVE COATING

11. Optical principle of ARC
• Works on the principle of
INTERFERENCE
• Conditions should be satisfied for good
ARC are
1) Amplitude condition
2) Path condition

12. How does it work?
A B
M N
Air (Na) Cancellation
P O
X X’
Coating (nc)
¼ wavelength Reinforcement
K L
Y Y’
Glass (Ng) Q R

13. PRODUCTION OF ARC
GLASS
 Clean the lens thoroughly
 Place in the vacuum chamber and remove all
the air
 Heat to about 300 C for hardness
 MgF2 pellets are heated to about 2500 C
for vaporization which deposits on the lens
 Thickness can be confirmed by
1) Observing the color of the light reflected
from lens surface
2) Photoelectric cell

14. PLASTIC
 CR-39 lenses are heated to less than 100 C
( Excessive heating may lead to loss of stability
and optical characteristic )
 lenses are boiled for 2 hours to remove water
vapor and volatile organic compounds
 Process carried out with electron beam
evaporation sources and micro processor
controlled monitoring technique
 Thin coat of NaO2 ( Quartz ) is applied for
hardness on which the ARC is given

15. Hydrophobic coat
• hydrophobic top coat
• any number of anti-
reflection vacuum
layers (metal oxides)
• hard coating layer
• adhesion layer
• lens substrate
less than 1/300th
the thickness of a
human hair

16. Advantages of ARC

17. • Better cosmesis
• Better vision
–increased transmission
–reduced secondary reflections
(night driving)
–reduced side glare
–reduced eyeball reflections

18. DRAWBACK OF ARC
• Historical reasons, education
• “Durability”
• “Difficult to clean”

19. .........are ARC lenses