6afb5300_usation___HealthNewsReview_org__Study_design
A 40% reduction of incident early age-related maculopathy was associated with fish consumption at least once a week. Eating fish may help preserve eyesight in older people. [Problem] Preserve and help are both active and causal; may help sounds like a caveat designed to convey uncertainty, but causality is still implied. [Suggested language] People who ate fish at least once a week were observed to have fewer cases of a certain type of eye problem. However, a true experimental randomized trial would be required in order to attribute this to their fish consumption, rather than to some other factor in their lives. This was an observational study  not a trial. [Study design] 
Prospective cohort study of dietary fat and age-related maculopathy (observational)
Observational Studies - Does The Language Fit The Evidence? - Association Versus Causation - HealthNewsReview.org
Study design