There are several reasons for pigmentation changes in the whites of the eyes. And the most common is a freckle or mole. These pigmented cells can occur anywhere of our body, of course, include the eyes. But there is rare to develop to some serious form of cancer. To be safe, you are required a physical examination by his personal physician, and you can get some useful advices from them after eye exam.
The dark spots on the white of the eyes are usually caused by melatonin which can also cause freckles and moles on the skin. Once you have dark spots on white of eyes, they do not fade or disappear. So you should take measures to prevent more dark spots on your eyes appearing. When you go outdoors, you'd better wear a wide-brimmed hat or sunglasses to protect the eyes from the harmful UV rays.
In general, if there are dark spots on the whites of your eyes, from a professional point of view, it may be pigmentary patches or pigmented nevus of sclera or bulbar conjunctiva, and it is same with freckle or mole on peopleâ€™s body. In a medical point of view, it does not matter, and do not need treatment. If this spot grows quickly, you need to go to hospital for examination or treatment.