Cancer eye, technically known as squamous Cell Carcinoma, is a common locally invasive tumor of the eyes and eyelids of older cattle. Like pinkeye, its occurrence is associated with exposure to sunlight and is more common in cattle with white eyelids and conjunctiva. As a result, cancer eye is very common in Colorado dairy cattle. The third eyelid appears to be the most common site of cancer eye in dairy cows, followed in frequency by the lower lid and then by the limbus (junction of the clear cornea with the sclera or colored portion of the eye). Cancer eye may exist in a "premalignant" form as a flat white plaque or as a wart-like growth on the lower lid. The malignant form is not well-circumscribed, and its surface is ulcerated. Malignant squamous cell carcinoma will grow steadily and will invade adjacent tissues including the eyeball itself, conjunctiva, and eventually the bony orbit. Once the eyeball is invaded, blindness in the affected eye will soon follow. Metastasis to distant sites is uncommon; the tumor is more likely to extend to local lymph nodes such as those below the ear and behind the mandible.