This comes via Bright Eyes News (where I get almost all my vision-related news): an online vision acuity simulator – you can enter a prescription and see a simulation of what a vision chart would look like to someone with that prescription who isn’t wearing glasses. [Updated 3/1/2009: As Annie notes in the comments, the simulator will only show prescriptions between -5 and +5, any worse and you’ll get a note that it’s beyond simulation range.] As anyone who’s read this blog for a while knows, I’m fascinated by learning more about what Zoe sees. But nearly as interesting as the simulation were the following disclaimers:
- The magnitude of the optical aberration (how blurry the image gets) depends on the width of the eye’s pupil, which changes all the time.
- The brain and vision-related neurons make a lot correction work in creating an illusion of a sharp image with clear edges.
- A positive spherical diopter [farsightedness] in prescription can be cancelled by the eye’s own lens, but with a constant load on the ciliary muscle.
Basically, this means that what the simulation shows for Zoe is not necessarily what she perceives when she isn’t wearing her glasses. For one, her brain is correcting some of the image, but more importantly, because of her accomodative esotropia, she can cross her eyes to compensate for some of the blurriness, it just means that if she does that, she’ll see double, and eventually her brain will turn off the input from one eye leading to amblyopia. (Many thanks to Dr. Bonilla-Warford of Bright Eyes news for helping me make sense of this).