Measuring the eye

Our eyes are like windows, I’ve been told. We use them to look out at the world, and doctors use them to look into our body; a non-invasive health check. But our window is not really top-quality, which blurs the seeing in both directions. Glasses and contact lenses have long been used to better see the world. They correct low order errors, like defocus and astigmatism, and give improved vision.

Of course, some glasses just serve as inexpensive identity props, 

 more funky ones let you see wrackspurts.

For doctors to look into our eyes, we turn to imaging systems that compensate these aberrations and image the retina, blood vessels and other features in the eye. The efficiency of correction both ways depends much on how accurately the aberrations are measured.

In 1961 Mikhail Smirnov developed a subjective technique to measure the aberrations of the eye. The individual would look at two incoming beams of light, use the on-axis beam as reference and change the position/angle of the off-axis beam to try and fuse the two beams at the retina. This gave the slope of the wavefront and allowed step-by-step measurement of the eye’s aberrations.

Imaging Rods In-vivo

Rods are the retinal cells that we use to see in dim light conditions. They are much smaller than cones which are used to see during the day and in bright light settings. The Williams lab at the University of Rochester pioneered the use of Adaptive Optics to image and resolve cone photoreceptors, blood vessels, retinal pigment epithelial cells and ganglion cells. They have shown much work in the areas of color vision, light sensitivity and disease detection. But rods were hard to image, and when then were seen there was much jubilance.

Recent work by the Rochester team shows repeatable imaging of rods in the human retina! How did they do it? Better design! Alf Dubra’s design has reduced astigmatism in both the pupil and image planes for better adaptive optics wavefront correction and improved imaging performance. They have two papers (here and here). The first shows a lot of good imaging results. The second one is super for system details.

Ref: OSA News

The Williams Lab is where I did much of my PhD research. So any fun stuff from there is always interesting to me! And an actual online video with interview and all!!! Now that I simply have to put on my blog! :)