Marilyn ZúñigaAdvisor: Dr. Roorda

Supervisor: Dr. GrieveSite: University of California-Berkeley

Imaging Intrinsic Signals in the Retina Using Different Powers of Red Light as a

Stimulus

Outline• Background

– Anatomy of Eye– References

• Experiment– Adaptive Optics Scanning Laser

Ophthalmoscope (AOSLO)– Methods: Dual Frame Imaging

• Results– Systematic Trend Observed with Higher

Energies– Limitations– Future Experiments

Background: The Retina

Fovea

Motivation

• In brain imaging, brain function is assessed by looking for changes in scattered light in response to a stimulus

• Researchers have recently observed similar reflectance changes in the retina in response to a visible light stimulus

• We want to look for these intrinsic signals in the retina using AOSLO

Previous Research

Detected IR Changes On Subjects After Stimulus Exposure

AuthorImaging Method Subject

Flash Type Flash Duration

Flash Power IR Change

Tsunoda Fundus Macaque White 1 ms41.9 cd-s/m2 Decrease

Abramoff Fundus Human Green 3 sec 10 cd/m2 Decrease

Grinvald Fundus Cat Green 1 sec N/A

Increase dim stimulus; decrease bright stimulus

Bizheva OCTRabbit in vitro White 200 ms

2300 photons/rod/flash Increase

Srinivasan OCT Rat in vivo White 1.3 s1400 cd/m2 Increase

Roorda and Grieve AOSLO Human Red 0.5-5 s Various  

Horizontal Scanner

Wavefront Correction

Vertical Scanner

Eye

Laser

ConfocalPinhole

PMTWavefront

Sensing

LightDetection

LightDelivery

Raster Scanning

DeformableMirror

Experimental Methods: The AOSLO

red on

red on

1.2 degrees (~ 360 microns)

Method: Dual Frame Imaging

Frame 1: Red Laser Frame 2: Infrared Laser

red on

IR on

red on

IR on

Procedure: Intrinsic Imaging of Retina

Frame 1: Red Laser Frame 2: Infrared Laser

Dual Imaging

Sets of 5 Randomized Trials (30 seconds)

Constant infrared light

(840 nm)

Control (no red flash

stimulus)

Flashes of Red Light (658 nm;

0.5-5 s)

Image Analysis 1

1) Compensation for Eye Movements

– Signals may be detected from different parts of the retina as the eye moves

• Solution– Stabilization of

movies to better extract the signal

Image Analysis 22) Compensation for Eye Blinking

- Intensity changes due to blinking are larger than the desired signal

• Solution- Compare stimulated vs. unstimulated region of the

retina (ratio of upper to lower half of IR image)

Frame 1: Red Laser Frame 2: Infrared Laser

Intensity Ratio of Stimulated to Unstimulated Retinal Areas

0 5 10 15 20 25 30

Preliminary Testing

Standard Deviation

Mean of 5 Trials

Legend

Inte

nsit

y R

ati

o

Time (seconds)

0.92

0.96

1.00

1.04

1.08

Two Second Red Flash

Energy: 2.00E-05 Joules

Visible Light Stimulus

Experiment One:

Half Second Red Flash

with Designated

Powers

Time (seconds)

Energy (Joules)

1.00E-08

2.14E-08 2.04E-06

9.55E-07

4.47E-07

2.09E-07

9.77E-08

4.57E-08

Control

9.33E-06

4.37E-06

Inte

nsi

ty R

atio

0 5 10 15 20 25 30

0.92

0.96

1.00

1.04

1.08

0 5 10 15 20 25 30

Standard Deviation

Mean of 5 Trials

Legend

Energy (Joules)

1.02E-05

3.12E-05 8.40E-05

7.26E-05

5.16E-05 Control

Experiment Two:

Three Second Red Flash with Designated

Powers

Time (seconds)

Inte

nsi

ty R

atio

0.92

0.96

1.00

1.04

1.08

5 10 15 20 25 300 5 10 15 20 25 300

Standard Deviation

Mean of 5 Trials

Legend

Image of Retina Before Stimulation

Image of Retina After Stimulation

Summary/Conclusion

• Systematic change (increase in scattered lR light in response to stimulation) observed with higher flash energies and a longer flash duration

Future Plans

• More testing with different stimuli and possibly patients with retinal disease

Acknowledgements• Austin Roorda; Advisor• Kate Grieve; Supervisor• Kaccie Li• Ethan Rossi• Pavan Tiruveedhula• Pinky Weiser• Yuhua Zhang• Funding Provided by NSF

and the Center for Adaptive Optics Grant No. AST-9876783

Thank you!

Questions?