Business Segments - Schedule of Revenue Information by Product (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues	$ 10,664	$ 11,320	$ 31,685	$ 31,133
G6
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues	2,962	2,860	9,419	8,715
Retina
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues	5,788	6,672	16,635	17,160
Other
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues	$ 1,914	$ 1,788	$ 5,631	$ 5,258