Myopia of 800 degrees belongs to high myopia, it is possible to donate blood, but it is usually not recommended to do so, because highly myopic people donating blood may cause blurred vision, retinal detachment, dry fissure macular hemorrhage and so on. 1. Blurred vision: When donating blood, the blood supply to the eye is insufficient due to the reduction of blood in the fundus, which may cause the symptom of blurred vision. 2. Retinal detachment: Since the retina of highly myopic patients may have lesions, blood donation may lead to a sudden change in the blood perfusion of the choroid, and the retinal blood vessels will be pulled and thinned, which will in turn cause retinal detachment. 3. Dry lacunar macular hemorrhage: Highly myopic people have metabolic disorders due to the large size of the eyeball and the normal relationship between the retina and the choroidal tissue at the bottom of the eye. After blood donation, the small blood vessels in the macular area may rupture due to pulling factors, causing macular hemorrhage and affecting vision. In general, it is best not to donate blood if you have 800 degrees of myopia, but if you are in a special situation, you can decide whether to donate blood after being evaluated by a doctor.