Date: Sun, 30 Oct 2011 10:33:46

Author: --- Steve Wonnell

Subject: Re: Optical Trick - can someone explain?


Seems to me that the water droplets on your glasses would have a focusing effect on the light from infinity, so that the light passing through the floaters in your eye casts a much stronger-than-normal shadow, relative to the overall light intensity, and thus calling your brain's attention to the shadows?

On Oct 29, 2011, at 11:25 PM, Paul Nord wrote:

> Yes Chuck. But why does a drop of water and a distant point source make them so visible?
> On Oct 29, 2011, at 10:13 PM, chuck britton wrote:
>> I have been amused/entertained my my floaters at least since the first grade. (Extremely near sighted if that makes a difference.)
>> My understanding has always been that they are 'loose' cells floating in the vitreous humor just in front of the retina, casting a shadow thereon. Sometimes form strings of cells.
>> .
>> At 10:20 AM -0500 10/29/11, Paul Nord wrote:
>>> The other evening my kids discovered a curious thing. If you look through a drop of water on your glasses at a distant light source you will see an array of curious objects floating around. I tried it myself and discovered that you always get the same set of floaters - different drop, different spot on the glasses, same floaters. It would seem that the floaters must be inside the eye, or possibly on the surface of the eye.
>>> Can anyone have a good quick explanation of the optics involved here?
>>> Paul

Steven K. Wonnell, Ph.D.
Manager, Physics Instructional Resources
Department of Physics and Astronomy
The Johns Hopkins University
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