Revenue from Contracts with Customers	12 Months Ended
Dec. 31, 2018
Revenue from Contract with Customers
Revenue from Contracts with Customers	Note 6. Revenue from Contracts with Customers The Company’s net sales are generated primarily from sales of iStent products to customers. Customers are primarily comprised of ambulatory surgery centers and hospitals, with distributors being used in certain international locations where the Company currently does not have a direct commercial presence. Disaggregation of revenue The Company’s disaggregation of revenue is consistent with its operating segments disclosed in Note 11, Business Segment Information, and all of the Company’s net sales are considered revenue from contracts with customers. Contract balances Amounts are recorded as accounts receivable when the Company’s right to consideration becomes unconditional. As payment terms on invoiced amounts are typically 30 days, the Company does not consider any significant financing components in customer contracts given the expected time between transfer of the promised products and the payment of the associated consideration is less than one year. As of December 31, 2018 and December 31, 2017, all amounts included in accounts receivable, net on the consolidated balance sheets are related to contracts with customers. The Company does not have any contract assets given that the Company does not have any unbilled receivables and sales commissions are expensed within selling, general and administrative expenses within the consolidated statement of operations when incurred as any incremental cost of obtaining contracts with customers would have an amortization period of less than one year. Contract liabilities reflect consideration received from customers’ purchases allocated to the Company’s performance obligation to issue a rebate to customers who may be eligible for a rebate at the conclusion of their contract term. This performance obligation is transferred over time and the Company’s method of measuring progress is the output method, whereby the progress is measured by the estimated rebate earned to date over the total rebate estimated to be earned over the contract period. The Company’s rebate allowance is included in accrued liabilities in the consolidated balance sheets and estimated rebates accrued were not material during the periods presented. During the year ended December 31, 2018, the Company did not recognize any revenue related to changes in transaction prices regarding its contracts with customers and did not recognize any material changes in revenue related to amounts included in contract liabilities at the beginning of the period.

Note 6. Revenue from Contracts with Customers

The Company’s net sales are generated primarily from sales of iStent products to customers. Customers are primarily comprised of ambulatory surgery centers and hospitals, with distributors being used in certain international locations where the Company currently does not have a direct commercial presence.

Disaggregation of revenue

The Company’s disaggregation of revenue is consistent with its operating segments disclosed in Note 11, Business Segment Information, and all of the Company’s net sales are considered revenue from contracts with customers.

Contract balances

Amounts are recorded as accounts receivable when the Company’s right to consideration becomes unconditional. As payment terms on invoiced amounts are typically 30 days, the Company does not consider any significant financing components in customer contracts given the expected time between transfer of the promised products and the payment of the associated consideration is less than one year. As of December 31, 2018 and December 31, 2017, all amounts included in accounts receivable, net on the consolidated balance sheets are related to contracts with customers.

The Company does not have any contract assets given that the Company does not have any unbilled receivables and sales commissions are expensed within selling, general and administrative expenses within the consolidated statement of operations when incurred as any incremental cost of obtaining contracts with customers would have an amortization period of less than one year.

Contract liabilities reflect consideration received from customers’ purchases allocated to the Company’s performance obligation to issue a rebate to customers who may be eligible for a rebate at the conclusion of their contract term. This performance obligation is transferred over time and the Company’s method of measuring progress is the output method, whereby the progress is measured by the estimated rebate earned to date over the total rebate estimated to be earned over the contract period. The Company’s rebate allowance is included in accrued liabilities in the consolidated balance sheets and estimated rebates accrued were not material during the periods presented.

During the year ended December 31, 2018, the Company did not recognize any revenue related to changes in transaction prices regarding its contracts with customers and did not recognize any material changes in revenue related to amounts included in contract liabilities at the beginning of the period.