A retinal scanner was a device which was used to perform a retinal scan, a scan of the retina.
The assay office aboard Deep Space 9 used Cardassian MK-12 scanners with L-90 enhanced resolution filters to secure the properties of their customers. (DS9: "Q-Less")
In 2369, the Kobliad Security officer Ty Kajada asked Doctor Julian Bashir if he had performed a retinal imaging scan to confirm that there was no residual activity in Rao Vantika's visual cortex. At the same time she did such a scan with a retinal scanner. (DS9: "The Passenger")