Devics' Disease is also called Neuromyelitis Optica or NMO. It is an autoimmune demyelinating disease of the brain affecting the brain and spinal cord. Devics' disease is basically a combination of multiple sclerosis and optic neuritis.

Internuclear ophthalmoplegia (INO) is a disorder of eye movements caused by defective neuronal connections in the MLF (medial longitudinal fasciculus). Patients have difficulty performing conjugate gaze. This is because the cranial nerves VI and III are affected in diseases such as multiple sclerosis. 

Lhermitte's sign or Lhermitte's phenomenon is a shock-like sensation felt when a person flexes his or her neck. The pain radiates from the neck to the spine, legs, arms, and sometimes the trunk.

Lhermite's sign is also called the barber chair sign.

One-and-a-half syndrome is a disorder of eye movements in the horizontal direction. 

Patients have a combination of two defects:

• Ipsilateral conjugate horizontal gaze palsy (one) and
• Ipsilateral internuclear ophthalmoplegia (INO) (a half).

Uhthoff phenomenon occurs in patients with multiple sclerosis. It is a temporary worsening of the pre-existing neurological signs after the patient is exposed to increased temperatures such as after a hot shower.

This phenomenon usually lasts less than 24 hours. It is also called the Uhthoff sign or Uhthoff syndrome.

The mechanism of Uhthoff's phenomenon has not been clearly explained, however, the hot temperature reduces the transmission of neuronal signals and there is a reduction in the speed of action potentials in the brain. Heat is thought to increase the time voltage-gated channels are in the inactive state.