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.