Fourth Cranial Nerve (Trochlear Nerve) Palsy: This is a common cause of diplopia, especially if it is acquired, due to the nerve's long intracranial course making it susceptible to injury from various causes such as trauma, stroke, or aneurysms.

Third Cranial Nerve (Oculomotor Nerve) Palsy: This can cause diplopia due to the nerve's control over several extraocular muscles. It can be caused by aneurysms, diabetes, or trauma.
Sixth Cranial Nerve (Abducens Nerve) Palsy: Similar to the third and fourth nerves, palsy of the sixth nerve can lead to diplopia due to its role in controlling the lateral rectus muscle, often caused by increased intracranial pressure, stroke, or diabetes.
Strabismus: A misalignment of the eyes that can cause diplopia, often due to issues with the extraocular muscles or nerves controlling them.
Myasthenia Gravis: An autoimmune disease that can cause fluctuating muscle weakness, including the muscles controlling eye movements, leading to diplopia.

Aneurysm (especially Posterior Communicating Artery Aneurysm): Although less common, an aneurysm pressing on the third cranial nerve can cause diplopia and is a medical emergency if it ruptures.
Stroke or Cerebral Vasculitis: Conditions affecting the brain's blood supply can lead to diplopia among other symptoms and require immediate medical attention.
Multiple Sclerosis: An autoimmune disease that can affect the brain and spinal cord, leading to a wide range of symptoms including diplopia, due to its potential to affect any part of the central nervous system.
Thyroid Ophthalmopathy (Graves' Disease): Can cause diplopia due to inflammation and swelling of the tissues around the eye, including the extraocular muscles.

Wernicke's Encephalopathy: A condition caused by thiamine deficiency, often seen in alcoholics, which can lead to ophthalmoplegia (paralysis of one or more extraocular muscles) and consequently diplopia.
Tolosa-Hunt Syndrome: A rare disorder characterized by headache, pain around the eye, and ophthalmoplegia, including diplopia, due to inflammation of the cavernous sinus or superior orbital fissure.
Congenital Cranial Dysinnervation Disorders: Rare conditions present at birth that affect the control of eye movements, leading to diplopia and other ocular motility issues.