The inability to focus on things that are near (nearsighted) is a well-known mercury symptom. This has to do with an increase in intraocular (within-the-eye) fluid pressure which changes the shape (focal-length) of the eye. In about 5% of mercury toxic people, it works the opposite way: This pressure decreases and makes them farsighted.

I've also read about "lazy eye" conditions being cause by a weaking of the muscles of the eye.

Dizzyness and loss of equilibrium is also well-known as mercury symptoms. Mercury alters some pressure mechanism in the inner ear that alters your sense of balance. I've read about this but not enough to fully understand it at this time.

Mercury also interferes with the heart beat making it weak which can cause loss of balance when standing up or performing physical activity. It can cause low blood pressure as well.