Glaukos (GKOS) experienced a sharp pre-market decline of 13.82%, driven by investor concerns over weaker-than-expected sequential revenue growth for its iDose product in Q4 2025.

The medtech firm reported preliminary Q4 iDose sales of approximately $45 million, representing a 13% sequential increase from Q3. This growth fell short of some analysts' expectations, overshadowing the company's reaffirmed 2026 net sales guidance of $600 million to $620 million. Analysts noted that seasonal factors and a strong Q3 distorted the sequential growth trend, but the market reacted negatively to the slowdown.

Despite Glaukos maintaining its 2026 revenue outlook and reporting strong preliminary Q4 net sales of $143 million (up 36% YoY), the focus remained on the iDose performance, leading to the stock's pre-market plunge.