On 2015 Nov 18, David Keller commented:

An interesting & important discovery, using a powerful new technique, but further study is required

This retrospective observational study demonstrated powerful and convincing associations between the use of levodopa (L-dopa) and reduced incidence, and delayed onset, of age-related macular degeneration (AMD). Bravo to these investigators, who correctly note: "Our data indicates prospective clinical trials to determine whether L-DOPA can prevent AMD are warranted". Prospective randomized trials of levodopa are indeed now required, in order to prove a cause and effect relationship between taking levodopa and the diminished and/or delayed risk of AMD. The reason is that retrospective, non-randomized studies can only demonstrate associations, not causality. Thus, the statement "exogenous L-dopa was protective against AMD" must be understood to mean that taking L-dopa was associated with lower risk of AMD, not necessarily that taking L-dopa caused a lower risk of AMD. This distinction is frequently lost when results from studies such as this are presented in the popular press, and even in the medical literature.

On 2015 Nov 18, David Keller commented:

An interesting & important discovery, using a powerful new technique, but further study is required

This retrospective observational study demonstrated powerful and convincing associations between the use of levodopa (L-dopa) and reduced incidence, and delayed onset, of age-related macular degeneration (AMD). Bravo to these investigators, who correctly note: "Our data indicates prospective clinical trials to determine whether L-DOPA can prevent AMD are warranted". Prospective randomized trials of levodopa are indeed now required, in order to prove a cause and effect relationship between taking levodopa and the diminished and/or delayed risk of AMD. The reason is that retrospective, non-randomized studies can only demonstrate associations, not causality. Thus, the statement "exogenous L-dopa was protective against AMD" must be understood to mean that taking L-dopa was associated with lower risk of AMD, not necessarily that taking L-dopa caused a lower risk of AMD. This distinction is frequently lost when results from studies such as this are presented in the popular press, and even in the medical literature.