Introduction to the Eye and AO in Vision Science€¦ · Introduction to the Eye and AO in Vision Science Stacey S. Choi O.D., Ph.D. Department of Ophthalmology & Vision Science University

Introduction to the Eye and AO in Vision Science

Stacey S. Choi O.D., Ph.D.

Department of Ophthalmology & Vision ScienceUniversity of California, Davis

2008 CfAO Summer School, August 4 - 8

Outline

• Principle of AO in Vision Science

• AO in Retinal Imaging (UC Davis) • Clinical Application of AO (UC Davis)• Ongoing Work/Future Applications

• AO in Vision Testing (UC Davis)

• Basics on the eye

Structure of the Eye• Basic components: Cornea, iris (pupil), lens, retina

Cornea

Pupil

Lens

Iris

Optic Nerve

Retina

Fovea

Refractive indicesCornea = 1.376Humors = 1.336Lens = 1.41-1.38

Radii of CurvatureAnterior cornea = 7.7 mm ⇒ +49DPosterior cornea = 6.8 mm ⇒ -6DAnterior lens = 10.0 mm ⇒ +6DPosterior lens = -6.0 mm ⇒ +11D

Total = 60D

Eye length = 24 mmPupil diameter = 2-8 mmCorneal thickness ~ 0.5-0.7mmLens thickness = 4 mm, φ = 9 mm

Vision• Emmetropia

Light focuses on the retina

Vision• Emmetropia

– Sharp vision– No correction required– Vision: 20/20 or better (2/15)

Refractive Error• Myopia (= nearsightedness)

Light focuses in front of the retina

Refractive Error• Myopia (= nearsightedness)

– Too powerful optics before the retina– Long eyeball– Vision: poorer than 20/20, e.g. 20/30,

20/40 …20/200 etc. (20/200 = seeing details that a normal eye

can see at 200 feet away at 20 feet)– Negative spherical lens to correct

Refractive Error• Hypermetropia (= farsightedness or hyperopia)

Light focuses behind the retina

Refractive Error

• Hypermetropia (= farsightedness)

– Too weak optics before the retina– Short eyeball– Vision: poorer than 20/20, e.g. 20/30,

20/40 …20/200 etc. – Positive spherical lens to correct

Refractive Error• Astigmatism

Light focuses at different planes along vertical and horizontal meridians

– Rugby ball or American football shaped cornea

Refractive Error• Astigmatism

and/or

– Lens position, e.g. tilted (lenticularastig.)

– Cylinder lens to correct– Can occur in conjunction with myopia

and hyperopia

Spherical Cornea = no astigmatism

Presbyopia– Reduction in the focusing power of the eye

with age (i.e. loss of accommodation)– Hardening of lens inside the eye– Requires reading glasses

Layers of the Retina• Light must travel through all of the blood vessels and

neural cells before being absorbed by the rods and cones.

RodsCones

Horizontal Cells

Bipolar CellsAmacrine Cells

Ganglion Cells

Pigment Epithelium

> 200 µm

light

Blood Vessels

Outline





Photo Courtesy of R. Wainscoat

Adaptive optics allows telescopes to see through the turbulent atmosphere

Without AO With AO

Weather on Neptune Resolved With AO

Courtesy of Bruce Macintosh, LLNL

Wavefront Error

SPATIAL Cornea ⇒ anterior surface⇒ posterior surface

Crystalline lens

Cornea (Anterior > Posterior) > LensΔn = 0.376 Δn = 0.05

TEMPORAL Accommodation, Tear film qualityEye / Head movements

Perfect Eye

Planar wavefront

Spherical wavefront

Aberrated Eye

Aberrated wavefront

Wavefront Errors of the Eye:

Aberrations in Lens and Cornea Distort Wavefront

Deformable MirrorCorrects Wavefront

Sharp ImageThis correction, which can typically be completed in less than half a second, provides substantial improvements in visual performance and the quality of retinal images.

How Adaptive Optics works:

Adaptive optics can correct the eye’s higher order aberrations

Aberration Map Point of Light Image

6.8 mm pupil

Before adaptive optics:

After adaptive optics: 1 deg

Adaptive Optics for Vision Science

Without AO With AO

Improving qualityof the retinal images

Without AO With AO

Improvinghuman vision

Upcoming presentations…….

• Robert Zawadzki– AO Instrumentation Vision Science

(9am, 8/7, Thurs.)

• Austin Roorda– AO-Psychophysics (9am, 8/8, Fri.)

• Don Miller– AO System Design Vision Science

(2pm, 8/7, Thurs.)

AO systems at UC Davis

AO-Flood Illuminated Fundus Camera AO-OCT

Outline





Spatial frequency [c/deg]

Correcting higher order aberrations as well asdefocus and astigmatism increases contrast

sensitivity about 2 fold in white light

1 10 100

GYY

Con

trast

sen

sitiv

ity

1

10

100

Higher order aberrations also corrected with AO

Defocus and astigmatism onlycorrected

YY

1 10 100

x 2.4 x 1.8

6 mm pupil57 td

Courtesy of GY Yoon

Aging effect on CSF

Elliot, Choi, Doble, Hardy, Evans, Werner (2008)

Average CSF

Young Subjects

Old Subjects

Without AO

With AO

With AO

Without AO

Without AO With AO

Reducing Higher Order AberrationsReduces Haloes and Sharpens Edges

Next Generation PhoropterCurrent Phoropter

Requires lengthy subjective procedure

Computes refraction automaticallyfrom wave aberration

Simulation of Visual Benefit

Bausch & Lomb AO Zywave

M. Venkiteshwar et al. – Accepted for ARVO 2008

Clinical Application of Correcting Higher Order Aberrations

• Customized Laser Refractive Surgery

– Wavefront-guided LASIK (Laser-Assisted In-Situ Keratomileusis)

– LASEK (Laser epithelial keratomileusis)

• Customized Contact Lenses

• Customized Intraocular Lenses

• Microkeratome to cut a thin flap of cornea

• Apply the excimer laser to remove tissue from within the cornea

• Became the most popular and trusted technique for correcting vision, exceeding one million cases per year

LASIK Procedure:

LASEK: similar to LASIK with much thinner flap

• The excimer laser uses wavefront information to change the shape of the cornea by ablating tissue.

• “CustomCornea” (Alcon LADARVision laser), “CustomVue” (Visx S4 laser), and “Zyoptix” (Bausch & Lomb Technolas 217z laser) have the ability to create an ablation customized from an individual patient's wavefront evaluation.

Wavefront LASIK / LASEK

Customized Contact Lenses

Phase Plate

Yoon’s laboratory, Center for Visual Science, U of Rochester

Cataracts

Normal Cataract

Intraocular Lens (IOL)

Outline





Current Camera for Taking Images of the Retina

Conventional Adaptive Optics Fundus Camera

Fourier-domain OCT

AO-OCT

∆x ~ 2.5 µm; 7 mm pupil

∆x ~ 15 µm, ∆z ~ 3.5 - 6 µm; 36 fps, 6.7 mm pupil

∆x ~ 3 µm, ∆z ~ 6 µm; 36 fps, 6.7 mm pupil

Imaging Modalities

DM

WFSSC

EYESLD

UC Davis AO Flood Illuminated Fundus Camera

AO - OCT system

AO images of cones in normal retina

200 μm

AO-OCT

AO-FundusCamera

Outline





Retinal Dystrophy

• 33 year-old female

• VA 20/25

• Color Vision: within

normal limits

Rod-Cone Dystrophy

0 2 4 6 8 10 12 14nV/deg^2

Field View

45°

0 2 4 6 8 10 12 14nV/deg^2

Field View

45°

49%

57% 61% 74%

96%

AO en face Images

200μm

100μm8° NR4° NR 2° TR

100μm 100μm 100μm

1000 A-scans; Δ x = 6 mm; δx ~ 15 μm; δz ~ 3 μm; τ = 100 μs; T = 0.1 s

1000 A-scans; Δ x =1 mm; δx ~ 3.5 μm; δz ~ 6 μm; τ = 50 μs; T = 0.05 s; 18 frames/s

Contrast Sensitivity Function (CSF)

Choi et al., “In vivo Imaging of the Photoreceptor Mosaic in Retinal Dystrophies and correlations with Visual Function”, IOVS, 2006, 47, No. 5, 2080-2092.

AMD

0 2 4 6 8 10 12 14nV/deg^2

Field View

45°

0 2 4 6 8 10 12 14nV/deg^2

Field View

45°

• 80 year-old male

• VA 20/20

• Color Vision: within normal limits

• Humphrey Visual Field: within

normal limits

Non-Exudative AMD

1000 A-scans; Δ x = 6 mm; δx ~ 15 μm; δz ~ 4.5 μm; τ = 100 μs; T = 0.1 s

100μm

200 μm

100μm

FD-OCT Image

1000 A-scans; 1x1 mm; 3D Volume / 100 B-scans, τ = 50 μs; 18 Frames/s; 5.6 s / Volume

Optic Neuropathy

NAION• 57 year old male

• Diagnosis: Bilateral non-arteritic anterior ischemic optic neuropathy (NAION)

• Year of Diagnosis: OS 1994 OD 1996

• VA: OD 20/60+2OS 20/20-2

• Color vision: OD abnormalOS borderline

Right eye – AO en face Images

Right eye - AO-OCT

(a)

12

(b)

2

RPE

31

Choi et al., “Changes in Cellular Structures revealed by Ultra-high Resolution Retinal Imaging in Optic Neuropathies ”, IOVS, 2008, 49, 2103-2119.

Outline





Ongoing Work / Future Applications:• Improvement of current systems (e.g. better DMs)

• Track photoreceptor loss in retinal degenerative diseases

• Try to image more cell types in the retina

• Monitor the health of retinal vasculature without fluorescein angiography (i.e. leakages)

• Perform retinal surgeries with AO precision e.g. more localized and precise laser surgery for retinal vascular diseases

Documents

Introduction to the Eye and AO in Vision Science€¦ · Introduction to the Eye and AO in Vision Science Stacey S. Choi O.D., Ph.D. Department of Ophthalmology & Vision Science University