Thursday was another down day for the stock market, which reacted negatively as earnings season began in earnest. Investors weren't pleased with the performance that major bank stocks had during the first quarter, and ongoing nervousness about the way the U.S. is handling its international relations slipped into market sentiment as well. Adding to the downward pressure today were poor showings from several individual stocks, and Apogee Enterprises (NASDAQ:APOG), Embraer (NYSE:ERJ), and Glaukos (NYSE:GKOS) were among the worst performers on the day. Below, we'll look more closely at these stocks to tell you why they did so poorly.

Apogee gives a cloudy outlook

Shares Apogee Enterprises dropped 13% after the company reported its fiscal fourth-quarter financial results. Apogee said that revenue climbed 20% to $314.1 million, but operating margin contracted significantly, leaving it with just a 3% rise in operating income. Yet the architectural glass specialist's guidance for the coming fiscal year didn't live up to investor expectations, with anticipated 10% revenue growth falling well short of the consensus among those following the stock for 15% top-line gains. Earnings of $3.35 to $3.55 per share would also be at the low end of what investors wanted to see. Given the strength of the commercial construction industry, one would have hoped that Apogee could produce better results.

Window products from Apogee.

Image source: Apogee Enterprises.

Embraer announces delivery numbers

Embraer stock declined 6% in the wake of its announcement of delivery figures for the first quarter of 2017. The regional jet specialist said that it delivered 18 commercial aircraft during the quarter, including 16 E175 aircraft and two of the newer E195 models. At the same time, Embraer had executive deliveries of 15 jets, including 11 light jet aircraft and four large jets. The aircraft manufacturer celebrated the rollout of the new E190-E2, which it claims is the most efficient aircraft in the single-aisle jet market. With airlines lining up to purchase the new lines and the executive jet market's Phenom entries performing well, Embraer appears to be doing things right during a strong time for the aerospace industry.

Glaukos deals with a possible pay cut

Finally, shares of Glaukos closed down 8%. The medical device maker had to deal with the potential for a revenue-cutting move from an administrator connected to the Medicare program. A ruling from the Medicare administrator suggested that one of Glaukos' glaucoma stent products should be priced at between $200 and $300 rather than the current $800 to $900 reimbursement rate. The rate won't go into effect until mid-May, giving Glaukos time to seek review and reversal of the decision. Nevertheless, the episode highlights the pressure on pharmaceutical and medical device companies right now in the current government environment, in which any sign of a profit that might be too large causes alarms to go off and risks attracting the ire of lawmakers and regulators looking for potential cost savings.

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