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