Many people have trouble with red eye in images.
Although red eye can easily be corrected with image editing software, it’s a great idea to know how to prevent it from occurring. Red eye tends to occur in light eyed people when the camera flash hits their retina. To prevent it, many cameras have an automatic red eye reduction mode, which is when the camera does two flashes - one closes your pupils and the second one will atually catch the image.
Or you can get your subject to look away from the camera to avoid the reflection. Also allow maximum light in so the subject pupils shrink first.