The pediatrician referred my son to the opthalmologist because he has no red eye(like in pictures) when light is shined in his right eye. what causes?

Wide range of probs: Lack of a red reflex (red eye look that you sometimes see in flash photos) indicates something blocking the reflection of the light inside the eye. The causes range from eye misalignment, cataracts, refractive error, and rarely, tumor inside the eye. Your child should definitely get it checked out.

Poor red reflex: Loss of red reflex in one or both eyes can be secondary to numerous issues. The most common causes are related to eye misalignment, cataract or other media opacty, or normal eye with abnormal reflex. Other more serious conditions can rarely cause this issue so i strongly recommend keeping the followup appointment with the ophthalmologist for a complete evaluation.