Hi, I can help you with your question today.
The first thing you need to do is rinse his eyes thoroughly.
If you have a saline eyewash (OTC human eye rinse), that would be best.
If not, just use fresh water and rinse for 5 minutes.
After that, I recommend having him evaluated by your local vet.
It is likely that the flea treatment will cause conjunctivitis and corneal ulceration.
I would start with a physical exam and a fluorescein stain of the eye.
This will reveal any ulcers.
If we find ulceration, Mac will need topical antibiotics.
He may also benefit from oral or topical pain medications if he is very uncomfortable.
Please let me know if you have further questions. I am happy to continue until I provide the service that you seek.