Measurement Methods

Appearance alone is not the basis for assessing internal biological status. The Likert scale was the most commonly used satisfaction measurement instrument across included studies. Measurement inconsistency limited meta-analysis to isolation precautions. Different reporting formats were used even for the same satisfaction instrument. HCAHPS was used in eight studies, mostly from the United States. Best-corrected visual acuity is measured in each eye using a logMAR ETDRS tumbling E chart at 4 metres. Fundus photography uses 45-degree macula-centred imaging with a Canon CR-2 digital retinal camera. Skin carotenoids are measured using the Veggie Meter with white LED light and reflection spectroscopy. Blood testing includes a complete blood count and biochemistry panel from non-fasting peripheral venous blood. Optical coherence tomography uses the Heidelberg Spectralis HRA+OCT with macular volume and high-resolution cross scans. The protocol combines multiple data streams to assess internal biological status.