Normally, the pineal gland governs a person' s sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye  Nonetheless, many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle
So the neural pathway by which the pineal gland receives information from the eye probably does not pass through the visual cortex
Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern