I used to notice the same thing about my pupils, and I still do at times. And for a while, it really worried me. That is, until I sought the proper medical attention and had testing done which came back negative.
It's actually very common for one pupil to be slightly larger than the other, especially as you age.
The vast majority of the time, this is due to your pupils responding to the amount of light being absorbed. And, depending on the angle of the light source, one pupil may be absorbing more light than the other.
On rare occasions, a difference in pupil size may be due to a serious neurological condition, which may be symptomless (other than the different pupil sizes).
If possible, I recommend you go see a neurologist for some peace of mind.
P.S. - Different pupil sizes can also be due to an eye injury which has resulted in the injured eye's pupil having to dilate itself more than the other in order to absorb the same amount of light.
Hey ro4eva,
Actually, the pupils should be constricting the same, even if one eye is absorbing more light than the other. This is because signals arising from both retina of the eyes converge to the pretectal area of the midbrain, which then activates both Edinger-Westphal nuclei equally. Each Edinger-Westphal nucleus then sends signals down the oculomotor nerve to the ciliary ganglion to constrict the pupil.
So the problem is likely to be altered transmission in one of the oculomotor nerve, rather than a differential absorption of light between the two eyes. Even if one eye is blind and cannot absorb any light, if light is shone into the other eye, BOTH pupils will constrict equally because of the above mechanism. This is why the pupillary light reflex is known as a consensual reflex.
Hope all is going well with you buddy.