Further refinements would include a colored ring, called the iris, that controls the amount  of light entering the eye, a tough white outer layer, known as the sclera, to maintain its structure, and tear glands that secrete  a protective film.
Ajustamentos posteriores incluíram o anel colorido — a íris — que controla a quantidade de luz  que entra no olho; uma forte camada branca externa — a esclera — que mantém a estrutura ocular; e as glândulas lacrimais que segregam o filme protector.