Adaptive Optics for the Human Eye
 

The main factor limiting high resolution imaging of the living human retina is blur caused by aberrations in the eye's optics. Adaptive optical techniques work well to correct the aberrations. There are two main components to the adaptive-optics retinal imaging apparatus. The first is the Hartmann Shack wavefront sensor used to measure the aberration of the eye. The second is the optical compensation of the aberrations with a deformable mirror. These aspects of the adaptive optics system are well-described by Liang et al (1994), Liang & Williams (1997) and Liang, Williams & Miller (1997). The following pair of images shows the improvement offered by adaptive optics:
 

  Before and After Comparison           

Several figures in Liang, Williams and Miller (1997) did not reproduce well so they are available here for preview:

 figure 10 figure 11a  figure 11b figure 12

New Results
(by Austin Roorda)

Single frame images are excellent and virtually every cone can be resolved.

Averaging multiple frames makes it easier to localize the cones and allows fine photometric measurements. This is a registered sum of 61 frames taken from five separate days. The retinal location is 1 degree nasal from the foveola (located to the right). The size of the image is 0.47 degrees square. All images were taken with incoherent light at 550 nm. There is no post processing of this image except for the subtraction of a dc component to enhance contrast.

The dark line down the center of the above image is the shadow of a capillary. The capillary lies about 100 microns anterior to the photoreceptor layer and when in focus is about 6 microns in diameter. The following images show the same region of retina viewed in different focal planes. Both images are 425 pixels across spanning a 1 degree retinal patch.
Capillaries  Photoreceptor layer (100 microns posterior to the capillaries)

Capillaries can be made more salient by inverting the images. The following images show capillaries at about 3 degrees eccentricity in two different subjects.
The capillaries transmitted most of the 630 nm light used for this image but the sides of the smallest capillaries are clearly visible.
Two single frame images are joined together to show capillaries branching from a larger blood vessel (550 nm light)
 

For more links about vision in general check out the Vision Science Page.

Read a recent online review article published by Science News.

Stay tuned for more......
 

References:

J. Liang, B. Grimm, S. Goelz and J.F. Bille, "Objective measurement of wave aberrations of the human eye with use of a Hartmann-Shack wave-front sensor," J. Opt. Soc. Am. A 11, 1949-1957 (1994).
J. Liang and D.R. Williams, "Aberrations and retinal image quality of the normal human eye," J. Opt. Soc. Am. A 14, 2873-2883 (1997).
J. Liang, D.R. Williams and D. Miller, "Supernormal vision and high-resolution retinal imaging through adaptive optics," J. Opt. Soc. Am. A 14, 2884-2892 (1997).
D. Miller, D.R. Williams, G.M. Morris and J. Liang, "Images of cone photoreceptors in the living human eye," Vision Res. 36, 1067-1079 (1996).
 

this page was updated last on May 25, 1999