Double vision is the appearance of two shadows, commonly known as “double vision” or “superimposed shadow”. Some people with astigmatism who do not wear glasses also have these symptoms, but there are several types of diplopia that cannot be ignored because they can be life-threatening if left unattended. For example, a patient once came to me for two weeks because of diplopia and was diagnosed with nasopharyngeal carcinoma, which was later confirmed by biopsy and CT, and the patient was transferred to radiotherapy in time. So, how can we eliminate those deadly “diplopia”, we need to start from the following questions. 1, monocular diplopia or binocular diplopia? Generally speaking, binocular diplopia is a more serious problem. So how can we count binocular diplopia? You can do a little test, first cover any eye (left eye and right eye covered once), there should be no diplopia, but, open both eyes, diplopia appears. At this time, it is binocular diplopia, be careful. 2.Horizontal diplopia or vertical diplopia? Generally speaking, the problem of vertical diplopia is more serious. Sometimes there is both vertical diplopia and horizontal diplopia, so we will classify this mixed diplopia as vertical diplopia. 3. Is there any aggravation of diplopia in each eye position? The symptoms of diplopia need to be evaluated in multiple eye positions, so patients need to look at themselves up and down, left and right, to see if they find any aggravation or reduction of diplopia in a certain direction. Often, many patients do not pay attention to this point and lose some of the information about their symptoms at home. 4. That is, whether the symptoms of diplopia will be light in the morning and heavy in the afternoon, and whether the symptoms will be aggravated after a day of exertion. If these symptoms are present, we need to focus on ruling out myasthenia gravis, because this disease can involve the respiratory muscles in severe cases, causing breathing difficulties. 5. What is the condition of the upper eyelids? Some people have receding eyelids that appear large, but this is not good because it may be related to thyroid eye disease. Some people have droopy upper eyelids, which is not good information because it may be related to paralysis of the brain nerve. 6. Can the eyes turn freely? Some people cannot turn their eyes freely, or they just cannot turn in a certain position, which indicates a problem with innervation, because there are six muscles that govern eye movements, and three brain nerves are innervated respectively. In the case of the nasopharyngeal carcinoma patient mentioned earlier, the sixth pair of nerves (abducens) was invaded, causing horizontal diplopia in both eyes and the inability to turn one eye outward. If middle-aged patients have such a condition, they should be excluded. 7. Is there any dilation or narrowing of the pupils? Abnormal pupil dilation and narrowing is not good information, but it is necessary to check for horner’s syndrome and aneurysm in the brain if the pupils are narrowed. ”The diagnosis of diplopia is based on the diagnosis of the cause of the disease and the need to find the cause of diplopia. The above points are provided for patients to know, hoping to help you monitor your condition and provide enough information for the doctor’s consultation, so as to better help the doctor to get the correct diagnosis and overcome the disease together!