I find something fascinating about eyes, it is suggested that the first organisms with a modification resembling an eye lived around 550 million years ago, and over time they have progressively evolved to the complex structures we know as our eyes today. The early ‘eyes' were simple photo-receptor proteins which were sensitive to light, they could see shapes or color but could not tell if it was light or dark. Because these organisms used photosynthesis to create food for themselves, being able to determine where the most light was coming from was a huge advantage.
The image below is a HDR image of my Daughters eyes, this was captured with a Nikon D610 and Sigma 150mm macro. Settings were 150mm, f/5.6, 1/250 seconds, ISO 1600. Image is a three shot HDR stack which was edited in Aurora HDR, before being finished off in Luminar 4 (AI Structure, AI Enhance).