There is no requirement for a vision test in radiology or any other medical specialty AFAIK, but most medical boards require you indicate if you have any medical condition which could interfere with your ability to practice your specialty. Medical ethics and licensing bodies mandate that you not perform any medical task in which a medical condition makes you unsafe.
To the OP, you have a challenging situation. It is very likely that you could practice all or most areas of radiology safely at the present, however in my opinion you will always be second guessing yourself as to whether your vision impairement might be degrading your performance. You asked about resolution: Most X-sectional imaging studies (CT, MR) is on the order of mm resolution. Nukes is in the range of 2-5 mm resolution. (however the images are displayed in a small format, so 1 mm on the screen or film will correspond to perhaps 5-10 mm on the patient) Radiography and mammography is sub mm (fine breast calcs in the range of 0.1-0.5 mm), and mammo probably the most demanding in that the morphology of those small calcifications determines their risk of malignancy.
The situation will be similar for pathology and surgical specialties. It goes without saying that if your condition were to become known during a malpractice lawsuit etc, it would be highly damaging.
For these reasons, althought you could probably do it, I think you will be able to rest easier in a non-imaging, nonsurgical (medical) specialty. Since you like radiology, something like neurology where you see a lot of patients and their scans (but are not responsible to interpret the scans) may be ideal. Good luck.
Addendum: There are ways to measure your visual system's spatial and contrast resolution. These tests can be performed by your opthalmologist. THis may also help you decide.