The reconciliation of intangible assets for the years ended December 31, 2022 and 2021 was as follows (in thousands):


	Year Ended			Year Ended
	December 31,			December 31,
	2022			2021
Patented technologies
Gross carrying amount at beginning of period	$	68,322		$	68,322
Impairment of acquired intangible assets		(20,699	)		—
Gross carrying amount at end of period		47,623			68,322
Accumulated amortization at beginning of period		(45,573	)		(43,113	)
Amortization expense		(2,050	)		(2,460	)
Accumulated amortization at end of period		(47,623	)		(45,573	)
Net book value at end of period	$	—		$	22,749

The net book value of the Company’s intangible assets at December 31, 2022 and 2021 is summarized as follows (in thousands):


					Estimated
					Remaining
					Useful Life at
	December 31,		December 31,		December 31,
	2022		2021		2022
					(Years)
Patented technologies
DEXYCU / Verisome	$	—	$	22,749		—
Total intangible assets, net	$	—	$	22,749

On November 1, 2022, the CMS published in the Federal Register the Calendar Year (CY) 2023 Medicare Hospital Outpatient Prospective Payment System and ASC Payment System Final Rule (Final Rule). The Final Rule terminated the pass-through related separate payment for DEXYCU, which was no longer separately reimbursed by Medicare as of January 1, 2023, when furnished in hospital outpatient departments and ASC settings. The Final Rule will reduce the amount of Medicare reimbursement provided to the Company’s DEXYCU customers and is expected to result in a significant reduction in the Company’s DEXYCU product revenues (see Note 3). The Final Rule and a reduced revenue forecast of the DEXYCU asset group were determined to be the impairment indicator of the Company’s finite-lived intangible assets related to DEXYCU with carrying value of $20.7 million.

The Company performed an impairment test based on the projected future cash flows. As of November 1, 2022, the forecasted probability-weighted undiscounted cash flows for the intangible assets were not expected to recover the intangible assets related to DEXYCU. To assess the recoverability of the intangible assets, the Company used income-based valuation methodologies. Under the income-based approach, the forecasted cash flows expected for the intangible assets were discounted using after-tax cost of capital rates taking into account Company-specific risks. Based on the above analyses, the Company recorded an impairment charge of $20.7 million in the fourth quarter of fiscal 2022, related to the acquired technology in connection with the acquisition of DEXYCU, and was included in impairment of acquired intangible assets in the Company’s statement of comprehensive loss. The aggregate amount of the intangible assets related to DEXYCU was zero as of December 31, 2022.

The Company amortizes its intangible assets with finite lives on a straight-line basis over their respective estimated useful lives. Amortization expense for intangible assets totaled $2.1 million and $2.5 million for the years ended December 31, 2022 and 2021, respectively. Amortization expense was reported as a component of cost of sales for the years ended December 31, 2022 and 2021, respectively.