 As green iguanas have only a few rod cells, they have poor vision in low-light conditions.At the same time, they have cells called “double cone cells” that give them sharp color vision and enable them to see ultraviolet wavelengths.This ability is highly useful when basking so the animal can ensure that it absorbs enough sunlight in the forms of UVA and UVB to produce vitamin D.

Green iguanas have a white photosensory organ on the top of their heads called the parietal eye (also called the third eye, pineal eye or pineal gland), in contrast to most other lizards that have lost this primitive feature.