Eyesight

[Lasercookie]

My optometrist said that it's measured in dioptres - which is basically an inverse metre.

Summarising what he said was along the lines of 2.00 dioptre prescription = 1/2 = 0.5m is where your focus point is, after that everything blurs out. I can't remember my exact prescription, but I remember testing it out and it was approximately the inverse of my prescription where stuff starts to blur out (though I tend to not notice how blurry what I see with my eyes are unless I've just put on/taken off my glasses).

http://en.wikipedia.org/wiki/Dioptre

within the international system of units this unit for optical power would need to be specified explicitly as the inverse metre (m−1)

http://en.wikipedia.org/wiki/Eyeglass_prescription

This will relate to some of the lens stuff you did in Unit 2 Physics:
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/eyedef.html#c2
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/foclen.html