This video shows a person with left lateral rectus palsy. On asking him to look to the left side, he can not move the left eyeball completely, and it stops in the middle. However, on asking him to look to the right side, both eyeballs move normally.
Lateral rectus muscle is supplied by the abducens nerve (also known as abducent or sixth cranial nerve) and is responsible for abduction (or outward movement) of the eyeball.
There are many causes of sixth cranial nerve (lateral rectus) palsy. In this case, it was due to diabetic cranial mononeuropathy. It can also be caused by orbital apex syndrome or cavernous sinus thrombosis. It can be a false localising sign in patients with raised intracranial pressure.