Since one year I have noticed that my right pupil dilates more than the left one when dimming the light. Eg. left and right are both 3 mm in the light, and 4.5 and 5.75 mm when dimmer. Sometimes it is worse than on other times. The first time I noticed it was when I felt my eye straining (like muscle cramp) in front of a computer screen. Several times i noticed it when checking as i felt a kind of an eye cramp, and it disappeared shortly after. In daylight you do not see a difference, so small is it (just happened to be checked by a GP for suspected concussion). This is not anisocordia. Can this really be just an eye strain caused by past computer screen usage, or a stress symptom? Because of this strain which i feel now and then, i hope this is a muscle, not my nerve or brain.