Sight without sight is, as the name implies, eyes that see but pretend not to see. In fact, we encounter such a category of patients in our outpatient clinics who may feel that he/she cannot see, cannot recognize things that are commonly used, and cannot even see objects around him/her. While the patient is busy wearing glasses or after an outpatient eye examination, he/she is found to have normal vision and no ophthalmic problems. At this point, it is time to be alert to the possibility of a specific type of dementia (scientific name: Alzheimer’s disease) called posterior cortical atrophy. Posterior cortical atrophy (PCA) is a chronic progressive neurodegenerative disease with visual symptoms as the first cause. The visual symptoms are not actually a loss of visual acuity or damage to the optic nerve, but rather a visual atrophy of the parietal lobe associated with visual space and the occipital lobe associated with visual cognition in the posterior part of the brain. It is due to abnormal integration of the higher visual centers of the brain and lack of spatial perception of objects, which is why the symptoms of visual but not visible occur. Approximately 85% of patients have the visual variant of Alzheimer’s disease, with an early age of onset, mostly between 50 and 65 years of age. Because of the atypical presentation, diagnosis and treatment are often delayed. And patients almost always go to the eye clinic first for examination without finding abnormalities. It is only when the disease worsens and affects memory and other cognitive functions that patients visit neurology, by which time the best time for treatment may have been missed. Patients with posterior cortical atrophy often complain that they tend to bump into the rearview mirror when driving and parking becomes difficult. They do not know the depth of stairs and cannot find the next section of the newspaper. This is because patients lose the ability to recognize the spatial location of objects and the spatial relationships between objects. Because of the lack of spatial perception, the patient is unable to fully “understand” the relative position and size of objects, for example, when writing, the patient is unable to arrange the space according to the existing strokes, so all “paintings” have no sense of space. All of the “drawings” have no sense of space, and all of the parts of the drawing are not less than one, but cannot be effectively integrated into a normal figure. Some patients, despite their complaints of not being able to see, can see parts of a picture, but cannot recognize the whole picture, similar to “seeing the trees but not the forest”. Some patients even tell the doctor, “The faces of people in front of me look the same, and I can’t even recognize common things like key chains, apples, or hot water bottles on the table, but I can recognize them with my sense of touch or hearing”. This may be due to a loss of visual perception, which includes loss of face recognition, the inability to distinguish between men and women, and the inability to recognize oneself from several faces in the mirror. It also includes loss of object recognition, where the patient is unable to classify multiple objects according to their form, material, color, and purpose when placed together. Later, when the doctor shook the keychain, “jingle, jingle”, he blurted out “keychain”. Some patients are unable to distinguish colors that they used to be able to distinguish correctly, which is a kind of color loss. Difficulty in writing or clumsy writing, difficulty in calculation, and difficulty in distinguishing left from right are also common symptoms of the disease. We have performed visual-related tests such as drawing, reading, and naming by looking at pictures, and the results suggest severe impairment, while other cognitive functions such as language, memory, attention, and executive functions perform normally. If the patient does not receive reasonable treatment during this period, the symptoms may gradually worsen over 2-3 years. For example, memory loss, repetitive questioning, and forgetting appointments occur. Some patients also experience lack of fluent speech expression, difficulty finding words, etc. Later in the disease, full-blown dementia is manifested, and it becomes difficult to distinguish this period from typical Alzheimer’s disease. The current treatment for posterior cortical atrophy is also a comprehensive and holistic approach that includes pharmacological treatment of its underlying causes, compensatory approaches, cognitive rehabilitation, and treatment of its complications. Pharmacological interventions in the early stages of the disease can relieve symptoms and improve the quality of life of patients. At the same time, we can help patients with rehabilitation training, such as identifying commonly used, essential items with specific functions through repeated practice; providing non-verbal motor-sensory instruction: for example, identifying a comb by combing the hair; having patients draw clocks, houses, and indicate the route home on a map; encouraging patients to use more tactile and auditory senses in their lives; and labeling objects. If you experience any of the above symptoms and your eye examination is normal, please visit the memory clinic of neurology promptly. Memory scales, blood tests and imaging tests can help with early diagnosis and treatment.