The S&P 500 was down 0.5% in midday trading to 2,136.15.
The Dow Jones Industrial Average was down 0.6% to 18,115.92.
The NASDAQ was down 0.4% to 5,236.90.
The yield on a 10-year Treasury bond was down 0.4% to 1.70%.
The price of gold was down 0.4% to $1,312.
Irvine-based Aerie Pharmaceuticals Inc. was up 13% to $34.58 and a $965 million market cap. The clinical-stage pharmaceutical company reported positive results in Phase 3 testing for Roclatan, a drug to lower internal eye pressure.
Irvine-based Impac Mortgage Holdings Inc. fell 10% to $13.13 and a $162 million market cap on 20 times its average trading volume. The mortgage lender priced an offering of 3 million common shares at $13. The number of shares it plans to sell is 20% higher than the 2.5 million it previously said it would sell.