Wednesday, June 13, 2012

opticks at first hand (sight)

Over the last 12 months, my eyesight got steadily worse in one eye, by 6 diopters. This was diagnosed as a cataract, which initially just changes the refractive index of the liquid in the lens of the eye (before eventually crystallizing and becoming opaque). The amount of light getting through slowly decreases too, but focus is the obvious thing that goes first. So yesterday I had the operation to replace the natural lens with an artificial implant. Because I spend a lot of time reading (paper and on screen) I asked for the fixed focus lens to be a bit nearer than the horizon - this means I have slightly fuzzy vision at "infinity" but can read a book at 30-100cm which is better than I ever had before this! What is interesting about this technically is that its an opportunity to observe optics in action "at close up" - when they remove the natural lens (with ultrasound piezo-electric crystals), you basically get a very fuzzy (un-focussd) image - during the operation, under local anaesthetic, you can see some things (I think they try to knock out the eyesight with the strong anaesthetic injected into the eye, but I have a lot of resistance to painkillers (as I discovered when I had 6 shots of diamorphin after a 70km bike collision gave me an open fracture (now repaired with titanium bits in my leg)). Anyhow, so aside from seeing these huge needles poking into my eye, I then got to see this guy slipping in the new lens. Then they put a patch on overnight, so all was opaque, til this morning when I took it off and voila - the bright new fixed focus world! As good as the surgeon's (a Mr Brazier) word, I now have perfect focus at decent reading distance in the left eye, and accommodating vision from there to infinity in the right eye. Newton stuck pins in his own eyes when working on optics - but it sure is interesting to see all this from inside one's own head. Two things are interestng - one that nature just does evolve stuff like cameras; and second, that physics inside one's own biology doesn't work any different from in the lab:)