The S&P 500 was flat in midday trading at 2,260.20.
The Dow Jones Industrial Average was down 0.1% to 19,908.63.
The NASDAQ was up 0.1% to 5,450.22.
The yield on a 10-year Treasury bond fell 0.6% to 2.54%.
The price of gold rose 0.3% to $1,134.
Irvine-based Aerie Pharmaceuticals Inc. was up 2.6% to $38.17 and a $1.3 billion market cap on moderate volume. The clinical-stage pharmaceutical company is developing eye drop treatments to lower intraocular pressure in patients with glaucoma or ocular hypertension.