Business Segments - Schedule of Revenue Information by Product (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues		$ 8,803	$ 10,664	$ 24,043	$ 31,685
Cyclo G6
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues		2,776	2,962	7,812	9,419
Retina
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues		4,429	5,788	11,171	16,635
Other
Entity Wide Information Revenue From External Customer [Line Items]
Total revenues	[1]	$ 1,598	$ 1,914	$ 5,060	$ 5,631

[1] Includes service contract revenues of $302 and $437 and $929 and $1,041 recognized during the three and nine months ended September 26, 2020 and September 28, 2019, respectively. Other also includes revenues from paid service, royalty, freight and legacy G probes.