What is a "split-body" RCT? I am reading the RCT Wikipedia page, in particular the classification by study design.
There are described four types of RCT: (i) parallel groups (ii) crossover (iii) cluster (iv) factorial.
Then there is written:

An analysis of the 616 RCTs indexed in PubMed during December 2006 found that 78% were parallel-group trials, 16% were crossover, 2% were split-body, 2% were cluster, and 2% were factorial

What is a "split-body" RCT?
It is not described in the paragraph before.

It's a trial whether the two interventions are applied to different parts of the same person.  One setting is ophthalmology, with different treatments applied to each eye, but this is an example with different patches of skin
