Notes about eyeglasses #

These are my barely-organized notes about my need for eyeglasses to correct my nearsightedness. It is likely that I have some of this wrong because I don't fully understand it.


When an optometrist measures your "prescription" they're measuring the 0th and 1st order zernicke polynomials. The 0th order is "sphere" and is a single number, rounded to the closest 0.25. The 1st order is "cylinder" (astigmatism) and has two numbers: a direction axis and an amount. There are higher order aberrations too but the optometrist doesn't measure these. These higher order aberrations can cause halos and other effects; see this example image that shows a "coma" (point smeared out like a comet), "spherical aberration" (starbursts and halos), and "quadrefoil" (point spreads out multiple directions). Laser surgery can often correct these but sometimes the healing process generates new ones.