I've Been Using Botox for Four Years Now and As I Look at my Eyes, They Seem to Look Smaller and Smaller. Why is This?

Hi TO.  There is more than one explanation, but without photos it's difficult to say what is happening.  

One answer is that this is just part of the natural aging process.  As we age, gravity pulls our facial features downward.  This may be happening naturally with your brow, which puts more downward pressure on the lids, which can make the eye appear smaller - less of it is visible.  As we age, the skin on the upper eyelid becomes less elastic.  This excess tissue can also make your eyes appear smaller.

Alternatively, the ongoing Botox injections, because they can relax the forehead muscles, may have contributed to the facial structure being slightly lower.  This can have the same affect as the natural again process described above.  

Finally , if your injector is using too much Botox in the forehead, he could be dropping your brow with each injection.  Again, before and after pictures would help.  

It may be time to consider a Botox browlift, surgical browlift and/or blepharoplasty (eye surgery) as another option.

The frontalis muscle is the main elevator of the eyebrows.  BOTOX treatment in the forehead weakens this muscle.  This means the forehead relaxed and the eyebrow fall.  The upper eyelid fold gets heavier as this muscle relaxed.