Researchers are keeping an eye on this extremely rare cancer.

A Chinese woman has been diagnosed with ocular melanoma after initially believing she had something caught in her right eye.

The 47-year-old — who hails from the city of Xian — visited her local doctor last August after itching her eye for two weeks.

She was left stunned to learn that she actually had a small, malignant lesion growing on the inside of her eyelid, which doctors determined was a malignant melanoma — a serious type of skin cancer.

The woman’s story was published Thursday in the New England Journal of Medicine, with researchers noting that ocular melanoma is so uncommon that it only affects one in every five million people.

The woman’s cancer was even rarer than that, as the malignant lesions rarely grow on the inside of an eyelid.

Doctors found the “pigmented lesion” by performing an eyelid eversion — whereby a person’s eyelid flap is pulled up as they look downwards, exposing what is concealed inside the top of the eye.

Medics noted that the legion was “large,” with a biopsy confirming it was cancerous.

The woman was offered surgery to remove the lesion, but — given the delicate place in which it was positioned — the procedure was not without risks.

She declined and instead chose to be treated with pembrolizumab — an antibody drug used to treat other forms of skin cancer.

The legion has not grown any bigger in the seven months since she has been diagnosed, and the woman’s vision has not been affected.

Early signs of ocular melanoma include blurred vision or flashes in the eye. Around 80 percent of those diagnosed with the cancer are still alive five years after their initial diagnosis.