I looked up some medical articles considering Lexapro. Sleepiness and insomnia are among the often occurring side-effects. They both can cause his eyes to look different. When you are tired your eyes become harder to hold open, and dull. I don't know whether your husband eyes are looking similar to (really) tired ones.
The advice they give in the articles is to continue taking Lexapro, but visit a doctor as well. I agree, since the doctor can tell you best what is going on.
I hope this helps!
Acceptance is the key
Existential depression and Insecurity
Try to keep smiling! :)