Keep seeing 'tadpole' shapes?!

Hi guys. My aunt told me she could see shape of tadpole in the middle of the vision whenever she looks outside; when there is sun light. Afternoon's bright sun light would cause the vision of the 'tadpole' to be stronger and darker. However, she won't have such problem when she is looking on to something that is not bright, for example. if she is reading a book or anything that do not have a bright light source, ie, the sunlight, in the background.

she told me she could see shape of a tadpole and its black in the middle, and have zig-zag lines in the middle of the 'tadpole' image.

please help me by giving me accurate information as she is afraid she would turn blind and she has visited a doctor about the problem but the doctor couldn't diagnose her problem properly.