1. Vision:
Stimulus & the Eye
© Wesner, M. F.

2. Physical Characteristics of Light
The basis of all vision is the presence of physical light.
NOTE: An object is NOT a visual stimulus, rather the light emanating from a light source or reflected from the object’s surface is the stimulus.

3. Two ways to think about light:
1. Light as particles of energy (e)
{ Isaac Newton (1687). Principia Mathematica. Publication included his theories on gravity, calculus and his observations from his Experimentum Crucis. }
2. Light as a waveform.
{ Christiaan Huygens (1690). Treatise on Light }
Light as particles of energy (e).
Light as a waveform.
NOTE: Both are appropriate depending on the application.

8. l1 1 second Light speed is constant: c = 3 X 108 m/sec
n1=2.0 cycles/sec l2
n2=4.0 cycles/sec
Light speed is constant: c = 3 X 108 m/sec

9. e µ n n “nu” = c/l “lambda” ; l µ 1/n
NOTE: Planck-Einstein relation: e = hn;
where e “epsilon” is the energy state of a photon (or energy contained in a quantum packet), h is Planck’s constant (6.624x10-27 erg-sec) & n is frequency (cycles/sec).
Because the speed of light c is constant..
n “nu” = c/l “lambda” ;
where n (cycles/sec), c (m/sec), and l (m [or cm, or nm]/cycle)
l µ 1/n
e µ n
thus..

12. I Color Percepts linear units
The measurement of the number of repeating units of a propagating wave (the number of times a wave passes per unit of space of the same phase).

13. Going from long to short l, the perceptual interpretations are as follows :
“red”
“orange”
“yellow”
“green”
“blue”
“indigo”
“violet” R
O Y G B I V
ROY G. BIV

14. Sources of photons..
luminescent - electrical e is used to excite the electrons of an atom.
Visible phosphor
Hg+ gas
Common fluorescent lamp:
incandescent - thermal e is used to agitate molecules (e.g., high temperature of a tungsten coated filament will release visible photons).
UV quanta e-
Incandescent sources can give off a limited or broad range of frequencies depending on temperature and/or type of heated material(s).

15. Color Temperature -where higher temperatures produce higher frequency photons (shorter wavelengths).
Black Body Radiator - an enclosure that has perfect “black walls” that absorb all electromagnetic radiation.
(Note: hypothetical. Bureau of Standards has something that comes close)
Possible to measure spectral output of incandescent source based on °Kelvin.

16. (total radiated power per unit area).

18. 20000 K
5000 K
20000 K
5000 K

19. Correlated Color Temperature is used when measuring the chromaticity (l properties) of any light source (including luminescent sources). This assumes the spectral distribution of the source can be approximated to one produced by a black body radiator (i.e., usually used when measuring broad-band light sources).

20. Spectral Distributions
Narrow band - few wavelengths. Can be defined by half-bandwidth.
Broad band - source composed of many photons (remember: the e contained in a photon identifies its spectral wavelength).
monochromatic (hypothetical)
Total e
(# of
Photons)
l (in nm)
400
700
550
Equal e “white” (hypothetical)

21. Spectral Distributions
Can have “near monochromatic” light (e.g., lasers and light passing through interference filters.
Total e
(# of
Photons)
l (in nm)
400
700
550
monochromatic (hypothetical)
half-bandwidth of ±12 nm

22. Spectral Distributions
NOTE: Psychologically, you can perceive narrow- and broad-band lights as equal ! Two stimuli that appear perceptually equal are known as metamers.
bipartite
Total e
(# of
Photons)
440
+550
+660 + +
Equal e “white”
440
550
660
l (in nm)

23. Light as a wave..

24. Divergence

25. 6 meters or >
Parallel or
Collimated light

26. Can also have Convergence..

27. Two Ways Light Rays Can Change Directions (Bend)
Refraction - bending of light rays from one refractive media into another.
h term used to indicate refractive index
hvacuum = hglass =
hair = hwater =
hdiamond = 1.6 +

28. Refraction hair sin i = sin q hglass hglass hair
NOTE: Going from rarified to dense medium ( hair< hglass ) refracting ray bends TOWARDS the normal. Because hglass> hair, refracting ray bends AWAY from the normal. q’ i’ q i
hglass
hair
Willebrord Snel van Royen, or Snellius (1621)
hair
sin i = sin q
hglass
Snell’s Law:

29. Refraction hglass hair
Increase angle of incidence (i) get a proportional increase (Snell’s Law) in the angle of refraction (q) .
Increase angle of incidence enough, you reach a critical angle. i’
hair
hglass q

30. Surpass the critical angle, & you get reflection.
hair
hglass q

32. hv

33. Image formation by lenses
TTop: Light emanates from a point source in all directions. When some portion of the rays passes through a lens, refraction causes the rays to converge back to a point. An image of the point is created on an appropriately positioned imaging surface. Bottom: An extended object can be considered as a spatially distributed collection of points. The lens produces a spatially distributed image of the object on the imaging surface.

34. Properties of Lenses Two base-in glass prisms:
hglass
hair
hglass
This makes a positive (+) lens.

35. Properties of Lenses Two base-out (apex-in) glass prisms:
hglass
hair
hglass
This makes a negative (-) lens.

36. Power of a Lens - Diopter (D)
Diopter (D) = hair / focal length (fl)
1 / fl
real image fl
virtual image
- fl

37. Focal Position of an Extended Object
real image fl
virtual image
Chief ray
- fl

38. It is this special case fl that is used to define the power (D of a lens).
1/fl = 1/do + 1/di

39. Diopter (D) = hair / fl ~ 1.0 / fl in meters
0.5 D = 1.0 / 2 m D = 1.0 / -2 m
0.33 D = 1.0 / 3 m D = 1.0 / -3 m
23.0 D = m (or 4.3 cm)
Cornea: Diopters
Lens relaxed: Diopters
Total eye: Diopters
Typical myopic correction: D

40. Chromatic Aberration “white” hn
hglass
“white” hn
Ended 11/09/05
Paraxial ray shows no chromatic aberration

41. Two Ways Light Rays Can Change Directions (Bend)
Refraction - bending of light rays from one refractive media into another.
Reflection (scatter) - light rays change direction at the surface of two different refractive media with the light coming back to original media (i.e., no penetration into other media (angle of incidence is > critical angle)

46. - intraocular fluids
Aqueous humor-synthesized and secreted from ciliary epithelial cells lining the ciliary processes.
Vitreous gel
Canal of Schlemm-found in angle between cornea and iris. Meets with trabecular meshwork that passes metabolically “used” aqueous through to a venous portal system.

47. Closed-angle glaucoma - a build up of pressure in the anterior chamber due to a blockage in the canal of Schlemm.
Open-angle glaucoma - a slowly developing glaucoma due to a noncongestive build up of pressure in the anterior chamber. Sometimes due to excess inflow (oversecretion) or lack of appropriate outflow due to metabolic problems.

48. The Lens & Accommodation:

53. Lens capsule pulled tight – low refractive power.
Lens capsule slackens. Crystalline lens thickens yielding greater refractive power.

55. Due to Rayleigh Scatter..
Note: Trying to focus on objects or lights sources composed of only short wavelengths are usually less distinct (more blurry).
Due to Rayleigh Scatter..
“white” hn
hglass

56. Rayleigh Scatter..
retina
“white” hn
hglass
& why the sky is blue..

57. Lenticular (lens & cornea) & axial length.. Is there a miscorrelation?

58. The axial ammetropias - refractive errors due to a miscorrelation of lenticular refractive power and axial size of the eye (as opposed to emmetropia or normal-sightedness).

59. Normal sighted (i.e., correlated) (emmetropia)
AXIAL LENGTH TOO SHORT
(hypermetropia or hyperopia)
AXIAL LENGTH TOO LONG
(myopia)

61. Focal Position of an Extended Object
real image fl
virtual image
Chief ray
- fl

63. Environmental Myopia?

66. Astigmatism is a cylindrical aberration

68. Cataracts..

69. ordered array of crystallins protein array folds and collapses
entangled mass not unlike neurofibrillary tau protein entanglements in Alzheimer’s brain
ordered array of crystallins
protein array folds and collapses

70. Short wavelength light and cataracts?
Rayleigh scatter suggests that higher frequency photons (shorter wavelengths) are more susceptible to refraction and reflection (e.g., chromatic aberration). Therefore, the preretinal lenticular elements may be susceptible to these scattering wavelengths, particularly UV photons. The energy from these quanta could disrupt the protein elements in the lens ultimately leading to opacification.

72. Claude Monet (1899)

80. Cone Mosaic
Color added

81. F
OD fixate

82. F
OD fixate

84. Retinal duplicity
Photopic

88. 11/16/05

89. Centrally fixated field
Log mmL

92. Normalized curves

101. Peripheral Cones
FIG. 1. Spectral sensitivities (l/threshold) of dark- adapted foveal cones, peripheral rods, and peripheral cones (broken line). All sensitivities are expressed relative to the maximum sensitivity of the fovea. The relative positions of these functions on the ordinates are therefore those observed in the eye.

103. Figure 9.20
Figure 9.20
Scotopic and photopic spectral sensitivity curves are shifted with respect to each other.
Vertical difference at any given wavelength is known as photochromatic interval.
Horizontal shift of peak sensitivity is known as Purkinje shift.
Scotopic system is more sensitive at all wavelengths except beyond 650 nm.

105. X = Vl Total e (# of Photons) l (in nm) 400 550 700 Radiometric
Sensitivity
l (in nm)
400
550
700 Vl X
Intensity
l (in nm)
400
550
700
Photometric =

106. steradian