Optical Coherence Tomography (OCT)

This produces photographic 'slices' of transparent and semi-transparent tissues, such as the retina at the back of the eye. 

With OCT, it is possible to see the the different layers of the retina, as well as the  retinal pigment epithelium under the retina and the choroid. 

OCT also demonstrates abnormal fluid collections (edema) within and underneath the retina. 

It also provides clues to the diagnosis of some intraocular tumors, such as metastases, which tend to have a 'lumpy, bumpy' surface.