Did you know that there are 6 muscles that control your eye, these are known as the extraocular muscles and on average they move close to 100,000 times a day! Four of them enable your eye to look up, down, side to side, whilst the others counteract the natural movements of the head.
Apparently this is the equivalent of your leg muscles walking 50 miles a day, so it’s no wonder your poor eyes just want to shut at the end of the day! A tell tale sign that your eyes may be getting tired is the characteristic ‘eye twitch’ known as Blepharospasm, this is when your eye muscles are saying ‘time to chill out now, I've had quite enough for one day’!
Eye Doctor Guide, (2013). Eye Twitching Causes, Symptoms and Treatment. Retrieved 8th November, 2013, from http://www.eyedoctorguide.com/eye_problems/eye-twitching.html