Can be a couple of things...
Eyes get red from the squeezing pressure of being pushed through the birth canal. Usually resolves ok without intervention, but ask the vet about eye intment.... could be a scratched cornea... you don't want to mess with that, call the vet and see about antibiotic eye ointment.
Could be that the eye lashes turn in a bit...as the foal gets a few meals, fills out a bit, the eye lashes turn the right direction.
BUT...... one of the VERY FIRST symptoms of sepsis is blood shot eyes.Could be your foal may need to see the vet ASAP, and start on a bunch of medicines, antibiotics,probiotics, IV fluids, etc.
Robin