By 1837, Lear's deteriorating health and eyesight made it impossible for him to continue his work for Lord Stanley. His eyesight had never been good; he wore thick-lensed glasses, and remembered with horror his "ante-spectacled" early childhood. The finely detailed work of illustration grew increasingly difficult for him. In 1836, Lear complained in a letter to John Gould, "my eyes are so sadly worse, that no bird under an Ostrich shall I soon be able to see to do." Moreover, his asthma and bronchitis were exacerbated by the damp climate of northern England. In 1837, he became dangerously ill. Lord Stanley, together with his nephew Robert Hornby, offered to send Lear to Rome to recover his health, and to study painting.

Lear was just 25. He never worked as a natural history illustrator again.