I was thinking, as I so often do, about some random things (heh, link with site name there, nice) and my thoughts turned to the opticians.
Why I wondered to myself is the eye exam always carried out in a darkened room?

Then sudden inspiration stuck, if the room is well lit, or even bright, then the pupils will contract, making the apature to the eye smaller, thus increasing the eyes Depth of field. This will in turn slightly fudge or hide any sight defects that the person being tested may have.
Ultimately resulting in an incorrect perscription, assuming that corrective lenses are needed.

This I though was quite a neat theory and wanted to check it out to see if I was correct.

Unfortunately as yet I have not been able to find any information on the subject of why sight tests are usually done in a darkened room… so I don’t know if I’m right.

If anyone knows for defiante or has any other ideas, well thats what the comments are for 🙂