For what its worth the so called 'third eye' that some meditation practitioners aim to open may or may not have biological roots. I can't find a definitive answer about humans, but some claim the pineal gland, the gland that apparently produces the DMT (spirit molecule) and is not separated by the blood brain barrier, has actual photoreceptors (rods and cones) like a primitive eye. It also apparently gets calcified early on. (I'm not arguing that since it exists it's a given that it's ok to mess with it.
Here's how wikipedia puts it.
The results of various scientific research in evolutionary biology, comparative neuroanatomy and neurophysiology have explained the evolutionary history (
phylogeny) of the pineal gland in different vertebrate species. From the point of view of biological evolution, the pineal gland represents a kind of atrophied
photoreceptor. In the epithalamus of some species of amphibians and reptiles, it is linked to a light-sensing organ, known as the
parietal eye, which is also called the pineal eye or
third eye.[8]