Population / problem examples: astigmatism, myopia, cataracts, eye tracking, children, adults, aged
Intervention examples: corrective lens, surgery
Comparison interventions are optional
Outcome examples: improved vision
Use "OR" when combining terms within the same PICO frame.
Use "AND" when combining terms from different PICO frames.
The "NOT" operator is a very blunt instrument; avoid it most of the time.