Operations and Basis of Presentation - Additional Information (Detail) $ in Thousands, Surgery in Millions	1 Months Ended		6 Months Ended		12 Months Ended
	Apr. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Product _People Case	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) Surgery	Jan. 01, 2019 USD ($)
Operations [Line Items]
Number of products approved | Product			2
Proceeds from Issuance of Common Stock		$ 28,900	$ 18,343	$ 34,471
Accrued Development Milestone Current	$ 15,000				$ 15,000
Cash and cash equivalents			44,161		45,261
Operating Lease, Liability			3,590
Operating Lease, Right-of-Use Asset			$ 3,291		$ 0
Accounting Standards Update 2018-11 [Member]
Operations [Line Items]
Operating Lease, Liability						$ 3,700
Operating Lease, Right-of-Use Asset						$ 3,500
Senior Secured Term Loan [Member]
Operations [Line Items]
Proceeds from Issuance of Common Stock	18,300
Additional borrowing amount	$ 15,000
YUTIQ [Member]
Operations [Line Items]
Number of new cases of blindness every year | Case			30,000
YUTIQ [Member] | Minimum [Member]
Operations [Line Items]
Number of people affected by posterior segment of eye in U.S. each year | _People			55,000
YUTIQ [Member] | Maximum [Member]
Operations [Line Items]
Number of people affected by posterior segment of eye in U.S. each year | _People			120,000
DEXYCU [Member]
Operations [Line Items]
Number of cataract surgeries performed in U.S. | Surgery					4.8
Estimated annual growth rate of cataract surgeries performed in U.S.			8.00%