Wet AMD is diagnosed by an optometrist or ophthalmologist in the exam room, by using the microscope with some lenses so we can see the retina. That is done in combination with some pictures that we take, the most important of which is called OCT or optical coherence tomography. That picture gives us a cross-section right through the macula in a very highly magnified view, and we can see fine details such as if there's fluid in the retina or fluid under the retina.
Sometimes, less so nowadays, but very frequently in the past, we would use dye-based techniques, one of the most important of which was called fluorescein angiography. For these techniques, we put dye in the patient's vein that goes to the eye. Depending on how the dye can leak out of these abnormal blood vessels, that will tell us if the macular degeneration has become wet.