APPLE INSIDER
Apple’s forthcoming “Apple Glass” could feature systems that register dilated pupils, and so alter brightness to provide a comfortable viewing experience and monitor the user’s attention.

One of the issues said to be delaying “Apple Glass” is the fact that they’ll have to be comfortable to wear for protracted periods. Alongside lightweight frames, though, Apple is also looking at how this — or any Apple AR headset — can adjust what you see based on how you’re reacting. A pair of recently revealed patent applications propose simply altering the brightness, or actually changing what’s shown on the headset depending on the wearer’s interest.
Source: APPLE INSIDER