Hello,
It's a sub conjunctival hemorrhage. Happens spontaneously. Most common reason being high blood pressure. Other reasons like lifting heavy weights, coughing, sneezing, vomitting etc.
Next Steps
it will resolve on its own in a few days. Rule out high blood pressure. if it's high,he needs medications to control bp.
Health Tips
start him on moxiflox eyedrop four times a day , to prevent any infection.