Fergus Gill / 2020VISION / Yellowhammer (Emberiza citrinella) perched on snowy branch. Perthshire, Scotland, February. Did you know? Beethoven's pupil claimed that the famous 'fate motif' of his 5th Symphony was inspired by the...

Stephen Dalton / Close up of eye of Common green iguana (Iguana iguana)

Kim Taylor / Tokay gecko {Gecko gecko} eye showing pupil partially closed. Captive occurs Asia.

Chris Newbert / Blue Parrotfish (Scarus coeruleus) eye, Belize

Martin Dohrn / Lioness head portrait in moonlight Serengeti NP, Tanzania, East Africa. Note dilated pupils. Image taken using 'Starlight Camera' technology without artificial lighting.

Ingo Arndt / Red-eyed Tree Frog (Agalychnis callidryas) eye closed with semi-transparent eyelid that allows it to see its surroundings even while resting, Costa Rica

Ingo Arndt / Red-eyed Tree Frog (Agalychnis callidryas) eye, Costa Rica

Ingo Arndt / Red-eyed Tree Frog (Agalychnis callidryas) semi-transparent eyelid that allows it to see its surroundings even while resting, Costa Rica

Dr. Axel Gebauer / Red panda (Ailurus fulgens), close up of eye detail, captive

ZSSD / Fiji Banded Iguana (Brachylophus fasciatus) eye, native to Fiji

Chien Lee / Tokay Gecko (Gecko gecko) juvenile showing vertical pupil, Uthai Thani, Thailand

James Christensen / Ecuadorian Toad-headed Pit-viper (Bothrocophias campbelli) eye and pit sensory organ, Mindo, western slope of Andes, Ecuador