Binocular diplopia Binocular diplopia is when both eyes look at an object as two images, and the diplopia disappears when one eye is covered. Related eye diseases Diplopia suggests disease of the extraocular muscles themselves, most commonly thyroid-related ophthalmopathy, which is often accompanied by protruding eyes and receding upper lids, and thyroid function tests, which are abnormal in most people. The next is a disease of the neuromuscular junction, such as myasthenia gravis. In addition to the traction of the corresponding eye muscles (e.g., the external rectus muscle pulls the eye outward), the movement of the eye muscles is controlled by the central cranial nerve, which is the “superior” of the eye muscles. In addition to problems with the eye muscles themselves, such as edema or traumatic compression or rupture, and the effects of these diseases, it is also possible that the “superior” cranial nerve has a problem and is “out of tune”. In the patient population, the most affected cranial nerves are the abducens nerve, followed by the oculomotor nerve and the trochlear nerve; therefore, the symptoms can be as diverse as those described above, such as painful ocular muscle paralysis and diabetic peripheral neuropathy, which can lead to paralysis of the oculomotor, trochlear and abducens nerves, which govern eye movements, and therefore cannot command the corresponding extraocular muscles to perform joint eye movements. There are many linking fibers between the various cranial nerve nuclei located in the midbrain and between the nuclei and the brain to complete the transmission of information, and if there is a problem with the cranial nerve nuclei and these connecting fibers, they also cannot complete binocular monocular vision. Cerebral infarction and intracranial tumors are common causes that affect the function of the cranial nuclei and destroy these connecting fibers. Our eyes are able to move in unison under the unified command of the brain, which includes a complex neural regulation of the six muscles of each eye under the command of three pairs of cranial nerves, as well as the cerebral cortex and nucleus accumbens. The six muscles of each eye work closely with each other to make the eye turn freely up and down, left and right in a coordinated manner. When we usually move our brains, the eye will turn in a slithering manner; when we are distracted, the eye will turn aimlessly. The inner activity of a person can also be shown by the rotation of the eyeballs. When the eyes are turning in all directions, there is always more than one muscle playing the main role and several other muscles playing a coordinating role. The action of both eyes must be consistent, and when the eyes are gazing to the right, the right external rectus and the left internal rectus must contract equally at the same time, otherwise they will not be able to obtain monocular vision. But when one or more of the six muscles that govern the rotation of the eye have a problem, the muscles of both eyes do not act in concert, and the rotation of the eye is limited, or the eye is tilted to one side, forming a strabismus, when seeing things will be blurred; or an object can be seen as two, causing double vision, that is, diplopia. Thus it seems that diseases from the eyes to the brain can cause diplopia, which is often a precursor of some systemic diseases.