The College of Optometrists

how do we tell the difference!? whats all this talk of reversed illumination?

use retro. microcysts appear as dents (i.e. visible from the back) due to high refractive index.

vacuoles are larger and more round, and more difficult to see in retro.

My understanding is that a microcyst exhibits "reversed illumination".

This means that if you have a slit beam at the left hand edge of your round lesion, the left half of the lesion will be dark and the right half will be illuminated i.e. the illumination has been reversed.

A vacuole with the slit beam alomg the left hand edge of the lesion will show the left half of the lesion illuminated and the right half dark i.e the illumination is not reversed.

There's an excellent picture illustrating this on the CLRU grading poster.

I've never really understood why this occurs. My logic tells me that any 'filled' lesion such as a cyst would be illuminated where the light first hits it, whereas with the vacuole being devoid of substance would be illuminated to its opposite edge since you can't see light unless it hits something. Don't like to know things without understanding why. Can you explain?