2 yr old cousin, last night i noticed the corner of his eye really red. he hasn't said anything about it, but its really red just the corner.

Angular conjunctivit: It is a bacterial infection , please go to an ophthalmologist for treatment.

Check if still prese: Likely nothing more serious than allergy or non specific irritation . If there is a yellow discharge it could be an infection like pink eye conjunctivitis, however with the history of knee pain he should be checked for a rheumatoid arthritis which could damage the eye due to an assoc inflammation.

See a doctor: A red eye just in the corner could be from various causes such as trauma, an infection or an allergy. It is a good idea for it to be checked out. Sometimes a blood vessel ruptures from coughing or vomiting. A two year old could have injured the eye with a toy or another object.