19. Optics of the eye19. Optics of the eye19. Optics of the eye
황반
각막
수정체
망막
시신경
조리개
Human Eye, RelaxedHuman Eye, Relaxed
3.6 mm
7.2 mm
20 mm
n’ = 1.33
15 mm
F F’H H’
P = n’/f2 = 1.334/20mm = 66.7 Diopter (1/m)
n = 1.45
Accommodation (수정체원근조정)Accommodation (수정체원근조정)
• Refers to changes undergone by lens to enable imaging of closer objects
• Power of lens must increase• There is a limit to such accommodation however and objects
inside one’s “near point” cannot be imaged clearly
• Near point of normal eye = 25 cm
• Fully accommodated eye P = 70.7 for s = 25 cm, s’ = 2 cm
•• Relaxed power of eye Relaxed power of eye P = 66.7 for s = infinite, s’ = 2 cm
Myopia: Near Sightedness (근시)Myopia: Near Sightedness (근시)
Eyeball too large ( or power of lens too large)
BlurredvisionDistant object (∞∞)
Myopia – Near SightednessMyopia – Near SightednessFar point of the eye is much less than Far point of the eye is much less than ∞∞, e.g. , e.g. llff
Must move object closer to eye to obtain a clear imageMust move object closer to eye to obtain a clear image
MyopicMyopic
F.P.F.P.
Normal N.P.Normal N.P.
MyopicMyopic
N.P.N.P.
If
MyopiaMyopia
e.g. le.g. lff = 2m= 2m
fsn
l f
1''1
1/2 + 1.334/0.02 = 0.5 + 66.7 = 67.2 D1/2 + 1.334/0.02 = 0.5 + 66.7 = 67.2 D
67.2 D is the67.2 D is the relaxed power of eye relaxed power of eye much larger than 66.7 D!much larger than 66.7 D!
To move far point to To move far point to ∞∞, must decrease power to 66.7, must decrease power to 66.7
Use negative lens with P = Use negative lens with P = -- 0.5 D0.5 D
Laser Eye surgeryLaser Eye surgeryRadial Keratotomy(Radial Keratotomy(각막절개각막절개) ) –– Introduce radial cuts to the Introduce radial cuts to the cornea of the elongated, myopic eyeballcornea of the elongated, myopic eyeball
Usually use lasersUsually use lasers of a COof a CO22(10.6 (10.6 µµm) , YAG (532nm), m) , YAG (532nm), ExcimerExcimer(<300nm) for almost 100% absorption by the corneal tissue(<300nm) for almost 100% absorption by the corneal tissue
Front viewFront viewFlatteningFlattening
Distinct Distinct visionvision
LASIK: Laser Associated Stromal Insitu Keratomileusis LASIK: Laser Associated Stromal Insitu Keratomileusis
http://medcity.com/lasik/
LASIK(각막상피+각막실질)의 Flap & Laser
LASEK각막상피 Flap & Laser
PRK각막상피제거후 Laser
Hyperopia – Far Sightedness (원시)Hyperopia – Far Sightedness (원시)
Eyeball too small Eyeball too small –– or lens of eye canor lens of eye can’’t fully accommodatet fully accommodate
Image of close objects formed behind retinaImage of close objects formed behind retina
Hyperopia – Far SightednessHyperopia – Far Sightedness
Suppose near point = 1mSuppose near point = 1m
Dsn 7.677.661''
11
Recall that for a near point of 25 cm, we need 70.7DRecall that for a near point of 25 cm, we need 70.7D
Use a positive lens with +3 D power to correct this Use a positive lens with +3 D power to correct this personperson’’s vision (e.g. to enable them to read)s vision (e.g. to enable them to read)Usually means they can no longer see distant Usually means they can no longer see distant objects objects -- Need bifocals!Need bifocals!
Correction lenses for myopia and hyperopiaCorrection lenses for myopia and hyperopia
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/Vision.html
Bifocal lens
Multifocal (progressive) lens
• Radiometry : measurement of EM radiation
• Photometry : psycho-physical (human response)measurement of radiation
Photometry
Photometric unit = 685 x V() x radiometric unit
Luminous efficiency V()
radiometry photometry
watt (W)W/m2
W/srW/(sr.m2)
lumen (lm) lux (lx)candela (cd)Cd/m2
Radiant flux :Irradiance :
Radiant intensity :Radiance :
: Luminous flux: illuminance : luminous intensity: luminance
Radiometry and PhotometryTable 19-1
555 nm Radiant flux of 1 Watt at 555 nm
is the luminous fluxof 685 lm (lumen)
Radiant flux of 1 Watt at 610 nm
is the luminous flux
of 342.5 lm (lumen)
Photometric unit=
685 x V() x radiometric unit
610 nm
Luminous efficiency V()
CIE (International Commission on Illumination)Luminous Efficiency curve
2
22
photometric unit 685 radiometric unit
lumens (lm) = Watts
lux (lx) =
candela (cd) =
luminance (cd / )=
V
Wm
Wsr
Wmm sr
Photometric Units
Brightness (luminance)
Wien displacement law
Planck’s blackbody radiation
Color temperature of light source ?
: the blackbody temperature with the closest spectral energy distribution
-> the sun has a color temperature rangeof 5000 K ~ 6000 K
Color temperature