Geckos are lizards belonging to the infraorder Gekkota, found in warm climates throughout the world. They range from 1.6 to 60 cm (0.64 to 24 inches). Most geckos cannot blink, but they often lick their eyes to keep them clean and moist.
They have a fixed lens within each iris that enlarges in darkness to let in more light.
Carp's barking gecko licking its cornea to clear it of dust
Geckos are unique among lizards in their vocalizations, which differ from species to species. They use chirping or clicking sounds in their social interactions, and sometimes when alarmed. They are the most species-rich group of lizards, with about 1,500 different species worldwide. The New Latin GEKKO and English "gecko" stem from the Indonesian TOKEK, Malay GEKOQ, which is imitative of sounds that some species make.
All GECKOS except species in the family Eublepharidae lack eyelids; instead, the outer surface of the eyeball has a transparent membrane, the cornea. Species without eyelids generally lick their own corneas when they need to clear them of dust and dirt.
Nocturnal species have excellent night vision; their color vision in low light is 350 times more sensitive than human color vision. The nocturnal geckos evolved from diurnal species, which had lost the eye rods. The GECKO eye, therefore, modified its cones that increased in size into different types, both single and double. Three different photopigments have been retained and are sensitive to UV, blue, and green. They also use a multifocal optical system that allows them to generate a sharp image for at least two different depths.
Most gecko species can lose their tails in defense, a process called autotomy.
Recourses from: https://en.wikipedia.org/wiki/Gecko