Low vision is traditionally defined as a visual dysfunction that cannot be improved by surgery, medication, or general optometry, and mainly includes decreased visual acuity and reduced visual field. The clinical manifestations of patients with low vision are: 1, vision: vision is significantly lower than normal, but some patients with vision loss, especially when the macula and central recess function loss, the retina close to the macula will often occur compensatory effect or can be trained to compensate for macular function so that less or no impact on visual function. 2.Visual field: It shows as central or peripheral visual field damage. 3, contrast sensitivity: contrast sensitivity thresholds are significantly impaired in patients with low vision. 4.Dark adaptation: Poor dark adaptation. Due to damaged rod cells, patients with night blindness have better vision in brightly lit daytime, but have difficulty seeing in dark or dimly lit conditions. 5. Color vision impairment: Patients with low vision recognize colors only by the lightness or darkness of different colors, and thus often misidentify colors. Optic neuritis, cone cell degeneration can be manifested as red-green color vision disorder; retinal edema, subretinal fluid and glaucoma can be manifested as blue-yellow color vision disorder. 6, binocular vision: binocular visual insufficiency, general strabismus or congenital ophthalmoplegia patients do not have the ability to fuse. The manifestation of visual dysfunction is also affected by age, systemic diseases and psychological disorders.