Hello It seems from the history that your uncle who is a known diabetic is having diminution of vision. The causes for loss of vision in diabetics are mainly by posterior segment problems like diabetic retinopathy leading to vitreous hemorrhage, macular edema, proliferative diabetic retinopathy, diabetic papillopathy... He needs to consult retinal specialist for further evaluation by tests like indirect ophthalmoscopy, B scan, fundus fluorescein angiography, ocular coherence tomography... to find out the underlying cause and treatment accordingly. Thank you