Topics: Absorptive lens

1. Transmission and
Absorptive Lens
Mohammad Arman Bin Aziz
Optometry Faculty
ICO, CU
May 11, 2014

2. Absorption & Transmission
• Light may be defined as a form of electromagnetic radiant energy that is
capable of stimulating our retinal photoreceptors and causing the
sensation of vision.
• When light strikes a lens, it results -
• Reflection
• Absorption
• Transmission
• Light transmission through a lens is determined by calculating
• percentage of light lost by reflection-front surface
• percentage of light lost by absorption
• percentage of light lost by reflection-back surface

3. Reflection
•Amount of light reflected by a lens
surface
IR = ( I )
(n' – n)2
(n' + n)2

4. Absorption
•Lambert’s law of absorption
•For an absorptive material, layers of equal
thickness absorb equal quantities
(percentages) of light regardless of the
intensity of the light
•Transmittance factor (q)

5. •If light passes through a number of lenses, one
after another, the ultimate opacity is found by
multiplying the separate opacities of each of
the lenses.
OU=(O1)(O2)(O3)…
Absorption

6. •If light passes through a number of lenses, one
after another, the ultimate transmission is found
by multiplying the separate transmission of each
of the lenses.
TU=(T1)(T2)(T3)…
Absorption

7. • Additional terms used in connection with absorption are
• Opacity = reciprocal of transmission
• Density = stated for a given thickness
Absorption
O =
1
T
density = - log T

8. EM Spectrum

9. The optical spectrum
•We are regularly exposed to some UV radiation, the
visible spectrum, and the IR portion of the electro-
magnetic spectrum.
•Although exposure to radiation bordering on the
visible spectrum does not cause the sensation of
vision, these bands of radiation can exert harmful
effects on the eyes.

10. •UV radiation extends approximately from 100 to
380 nm.
•The certain bands of UV radiation are associated
with particular biological effects, the UV spectrum
is arbitrarily subdivided into three bands:
•UV-A extends from 380 to 320 nm.
•UV-B extends from 320-290 nm.
•UV-C extends from 290-200 nm.

11. The visible spectrum
• The visible spectrum, extending from approximately 380 to
760 nm.
• The range varies with the level of illumination, the clarity of
the crystalline lens of the eye, and other factors relative to
the observer.
• Within the specified boundaries, radiation reaching the
retina acts as a physical stimulus to produced electrical
impulses that are conducted via the optic nerve to the
occipital cortex of the brain, which provides the sensation of
vision.

12. The IR spectrum
•The IR spectrum extends from 760 to 106
nm.
•It is divided into three portions:
•IR-A extends from 760-1400nm.
•IR-B extends from 1400-3000nm.
•IR-C extends from 3000 nm – 1 mm.

13. Classification of radiation effects
• Draper’s law states that for radiation to have an effect on a
substance through which it travels, it must be absorbed by the
substance.
• Radiation has no effect (beneficial or deleterious) on a
substance through which is completely transmitted or by which
it is completely reflected.
• Radiation in the region of the visible spectrum causes the
sensation of vision because it is absorbed by the
phpotopigments of the retina.
• Ionizing radiation
• Non-ionizing radiation

14. Ionizing radiation
• Most ionizing radiation pass through the eye, but small
amount is absorbed.
• The damage depends on the exposure time, concentration,
and the type of radiation.
• Ionizing radiation may have direct or indirect effect on
ocular tissue.
• A direct effect may produce cellular anomalies or death.
• Indirect effect can result in damage to the blood vessels
and thus restrict the blood supply to the tissue.

15. • Ionizing radiation can affect nearly all ocular tissue. Of the
ocular tissue, the conjunctiva, cornea, and lens are the most
vulnerable.
• At low level, the conjunctiva vessels become engorged and
the cornea loses its normal luster.
• Heavier doses result in exfoliation of the epithelium cells,
cornea ulcer, and keratitis.
• The most common effect of ionizing radiation is the formation
of cataract.
• High level of ionizing radiation can result in retinal damage
and degeneration; extremely high levels can result is sudden
blindness.

16. Nonionizing radiation
•When radiation is absorbed by an ocular tissue,
various effects are produced by the transfer of
radiant energy to the molecules and atoms of the
absorbing tissue.
•The absorbed energy can affect the visual apparatus
in the following ways:
• The thermal effect
• The photochemical effect
• Photoluminescence (fluorescence)

17. Nonionizing radiation
• The thermal effect
• Heating effect
• Solar retinopathy, cause by looking directly at a solar eclipse.
• The photochemical effect
• In the visible spectrum, produces a chemical reaction in the retina
initiating the sensation of vision.
• Harmful photochemical effects can occur with other ocular tissues, such
as photokeratitis produced by excessive absorption of UV radiation by the
cornea.
• Photoluminescence (fluorescence)
• The lens is capable of visible fluorescence when illuminated by UV light.

18. •As radiant energy passes through the eye, it is
attenuated in a number of ways:
•Absorption by the ocular media
•Scattering within the eye
•Reflection by the various optical interfaces
•Loss caused by the aberrations of the eye’s optical
system
Concentration of radiant energy by the eye

19. •The concentration of radiant energy within the eye
also depends on the size of the pupil and the angular
extent of the source.
•For a point source of high intensity, refraction by the
eye’s optical system concentrates the energy of the
retina (A) and cause tissue damage, but has little
effect on the cornea and the lens.
•Solar retinopathy: occur after exposure to a solar
eclipse.

20. A small source of low-intensity radiation is usually harmless to the
retina, an extended source of the same intensity may provide a
dangerous concentration of radiant energy in the lens.
A
B
Concentration of energy in the eye. A, point source; B. extended source.

21. Absorption of radiation by the ocular
tissue
• The tear layer absorbs only a small amount of radiation.
• absorbs below 290 nm and IR radiation above about 3000 nm.
• transmits radiation from approximately 290 to 3000 nm.
• The cornea absorbs UV radiation.
• absorbs below 290 nm and IR radiation above about 3000 nm.
• transmits for UV in the range 290 to 315 nm and for IR in the range of
1000 to 3000 nm.
• High transmission in the range extending from 315 to 1000 nm, which
includes the long UV wavelengths, all the visible spectrum, and the
shorter IR wavelengths.
• The transmission of the cornea particularly for the shorter wavelengths
decreases markedly with age.

22. •The aqueous humor absorbs very little radiation, with
the result that any radiation that is transmitted by the
cornea is also transmitted by the aqueous humor, and
passes to the iris and the lens.
•In the iris, the uveal pigment absorbs radiation and
converts in the heat.
• This conversion can be accompanied by a marked
contraction of the pupil, probably because of the release of
histamine.

23. •The lens, like the cornea, has variable absorption
properties, depending on age.
• The child absorbs UV radiation below about 310 nm and IR
radiation beyond 2500 nm, and thus transmits UV radiation
between 310 – 380 nm.
• Old adult absorbs almost all radiation below about 375 nm
and therefore transmits very little UV radiation.
• There is no change in the absorption of IR radiation with
increasing age.

24. •The vitreous mainly absorbs radiation below 290 nm
and above 1600 nm and therefore transmits to the
retina radiation in the range from 290 to 1600 nm.
• As the lens absorbs more UV radiation with increasing
age, the amount of UV radiation available to the vitreous
gradually decreases.

25. •The radiation received by the retina is the
radiation transmitted by vitreous.
•Although UV radiation received by the retina
decreases in amount with age, IR radiation does not
decrease in amount -94% of IR radiation of 770 nm
reaches the retina, then falls to 90% at 900 nm to a
very low level beyond 1500 nm.

26. Transmission of radiation by the ocular
media
Ultraviolet (nm) Visible (nm) Infrared (nm)
Tear layer 290 -380 380-760 760-3000
Cornea 290-380 380-760 760-3000
Aqueous 290-380 380-760 760-3000
Lens (child) 310-380 380-760 760-2500
Lens (older adult) 375-380 380-760 760-2500
Vitreous 290-380 380-760 760-1600

27. 1. RADIATION CAN DAMAGE EYES
1. Short Term
• Excessive blinking, swelling or difficulty looking at strong light.
• Exposure also causes acute photokeratopathy (Sunburn of the
cornea)
1. Long Term
• cataracts (cloudiness of the lens)
• Pterygium (an overgrowth of the conjunctiva on to the cornea)
• Solar keratopathy (cloudiness of the cornea)
• Cancer of the conjunctiva
• Skin cancer of the eyelids and around the eyes

28. How sunglasses protect the eyes
• Sunglasses reduce
• The amount UV/ Infrared radiation that reaches the eyes.
• Close fitting, wrap around styles prevent UV rays from entering through the
sides and top of sunglasses.

29. 2. Illumination??? Brightness
• High levels of illumination can cause discomfort
• Comfortable level of illumination is 400 ftL (summer day under a shade
tree)
• Uncomfortable level of illumination (sunny Texas day in July--10,000
ftL)

30. 3. Glare
•Defined as one or more areas in the field of vision that
are of sufficient brightness to cause
• an unpleasant sensation
• a temporary blurring of vision
• a feeling of ocular fatigue
• Remember ? Types
• Disability glare
• Discomfort glare
• Specular reflection glare

31. Reduces the amount of transmitted light or radiant energy
Acts as a filter
May be uniform or neutral, absorbing light of all wavelengths
equally
May be selective, absorbing light of certain wavelengths more
than others
1. Absorptive Lenses

32. Major forms of absorptive lenses
1. Tinted solid glass lenses
2. Glass lenses with surface coatings
3. Tinted plastic lenses
4. Photochromatic lenses
5. Polarizing lenses

33. 1. Tinted solid glass lenses
 Introduction of metals or metallic oxides during
manufacturing by mixing it in the batch
 Spectral transmission characteristics are
controlled by the quantities of metals used
 Color imparted is of no significance other than
cosmetic

34. 34
Tinted solid glass lenses
• Elements used and the colors they produce are
 Manganese – pink
 Cobalt – blue
 Cerium – pinkish brown
 Nickel – brown
 Uranium – yellow
 Chromium – green
 Gold – red
 Silver – yellow
 Didynium – pink
 Vanadium – pale green

35. 2. Glass lenses with surface coatings
• Thin metallic oxide is deposited on the surface of
the lens
• Requires high temperatures
• AR coated lenses
• Ray diagram ? Principle???????
nC = √nG

36. 3. Tinted plastic lenses
Tinted by dipping into a dye
Dye penetrates the lens surface to a uniform
depth;
 therefore, no change in density with changes in lens
thickness from lens center to edge
Over-tinting a lens can be reversed by dipping the
lens into a bleaching solution

37. 4. Photochromic Lenses (Glass)
• Developed by Corning in 1964
• Glass contains silver halide crystals ? Plastic
• Lenses darken when exposed to long-wavelength UV
radiation
• UV transforms silver halide crystals into silver and
halogen atoms
• Darkening rate is temperature dependent

38. •“In-Mass” technology
Corning SunSensors
Rodenstock
•Imbibed technology
Transitions
Photochromic Lenses Plastic

39. •In-Mass
•Molecules never “wear out”
or fatigue
•Darkens up to 50%
•Scratches do not affect
performance
•Exterior 1.5 mm of lens
activated preventing
uneven darkening

40. •Imbibed
Darkens consistently across
across the lens, regardless
of prescription
Available in wide range of
materials and designs
Photochromic Lenses Plastic

41. Photochromic Lenses Glass

42. Photochromic Lenses Plastic
Corning SunSensors

43. Photochromatic Lenses Plastic
Imbibed
In-mass

44.  Splitz (Sola)– changeable fashion tint
 Blue lenses darken to green
 Rose lenses darken to purple
 Yellow lenses darken to orange
 Solera (Invicta) – darken into a darker fashion tint outdoors
 Yellow, orange, rose, violet, blue & teal
Photochromatic Lenses Plastic
Fashion Tints

45. 5. Polarizing Lenses
• Invented in 1929 by Dr. Edwin C. Land, founder of the Polaroid
Corporation.
• Originally manufactured with 2 sheets of glass laminated with adhesive
to either side of the polarized film—over time, delaminating became a
problem.
• In 1990’s, manufacturing changed to suspending the polarized film
within the lens mold and casting the lens with the film in place.

46. • Eliminates specularly reflected horizontally polarized light
• Improves visual acuity and restores the natural balance of light
intensities.
• Helpful for -
• fisherman by reducing glare from the water;
• motorists for reducing glare from the road;
• skiers for reducing glare from snow.

47. • Materials that best polarize light by reflectance are generally
nonconductors, called dielectrics: such as glass, pavement,
sand and snow.
• Light reflected from a dielectric is completely polarized at a
specific angle of incidence (Brewster’s Angle).

48. Sunlight
Light reflected off a
horizontal surface is
mostly horizontally
polarized

49. • Brewster’s Angle occurs when the angle between the
associated refracted and reflected rays at the surface is 90°.
• Brewster’s Angle
tan i = n
Here,
n = index of the medium to
which the light is incident,
i = angle of incidence

50. Specular Reflecting Glare With polarized lenses
Polaroid lenses admit only the
vertically vibrating light wavesReflected horizontally
polarized light

51. Categories of absorptive lenses
oLenses for general wear
o Absorbs spectrum evenly and little more UV radiation ,visible light and IR
radiation than clear ophthalmic crown glass
oSelectively absorb UV radiation and transmit visible spectrum evenly
oOutdoor use
oSelectively absorb portions of the visible spectrum in non-uniform
manner
oWhose absorption characteristics vary with level and type of
illumination (photochromic)
oMiscellaneous
oOccupational use

52. Specification of transmission
• Transmission properties
• Spectral transmission curve.
• Shows percentage of transmission for all visible spectrum and
portion of UV and IR radiations.
• Depicts the amount of radiant energy transmitted as a percentage of
the radiant energy entering the lens as a function of wavelength.
• Manufacturers transmission data based on lens thickness of 2mm.

53. General wear lenses absorbing spectrum evenly
• Lightly tinted
• Absorbs little or no more UV, visible or IR radiation than OCG
• Indoor/cosmetic tints
• Cerium oxide
• Useful
• Lightly pigmented individuals
• High refractive errors
• Not in good general health
• Poorly designed artificial illumination

54. Lenses selectively absorb UV radiation but
transmit visible radiation evenly
• CR-39 lenses
• UV absorbers
• UV- 380(optical radiation group)
• Absorb all radiation below 400nm
• NoIR lenses, absorbs all radiation below 400nm
• Glass lenses
• Transmit < 5% of UV radiation below 400nm
• American optical hazelmaster ,Vision ease yellow
• Shooting and night driving lenses

55. •Spectra shield human II
•Unique glass lens
• 28 layers of dielectric material on the concave surface.
• Reflect all UV radiation below 400nm and IR >700nm.
•Corning photochromic lenses.

56. Lens that selectively absorb portion of visible spectrum
• Not common.
• Yellow, blue and bluish green.
• Absorb all illumination below 500nm
and greatly reduce scattering of light
• Blue light most scattered
• Hunting and shooting purposes.
• Blue for cosmetic.

57. Lenses for occupational useLenses for occupational use
Glass blowers lens
Filters out the yellow band of the spectrum
Clearly see what is happening to the glass than the flame
Didymium filter lens
Rose color in incandescent lightning
Aqua –fluorescent lightning
Welding lens
Same as above
Luminance transmission –shade number

58. Standards for absorptive lenses
• ANSI Z 80.3-1995 ophthalmic non prescription sunglasses and
fashion wear
• 1. General purpose:
• 8-40% of transmission in the visible range
• UVA: not greater than transmittance of visible range
• UVB: not greater than one half of the transmittance of visible spectrum
or 5%
• 2. Cosmetic use;
• More than 40% transmittance in visible spectrum
• UVA: not greater than transmittance of visible range
• UVB: not greater than one half of the transmittance of visible spectrum
or 30%

59. Standards for absorptive lenses
•Special purpose;
•Minimal transmittance for visible spectrum 3%
•UVA one half of the amount of visible spectrum
•UVB not greater than 1%