Aerie Pharmaceuticals Inc., which specializes in eye treatments, reported a larger-than-expected second quarter loss due to higher expenses, but sales of its key drug were strong.

The Durham-based company reported a net loss of $44.7 million, or $1.14 per share, compared to a net loss of $21.8 million, or 63 cents per share, in the same quarter a year ago. Analysts were estimating a net loss of 88 cents per share.

Revenues for the quarter were $2.4 million, less than the $6.1 million estimated by Wall Street. The company did not have any revenues in the second quarter of 2017.

“We remain very well-financed, including the flexibility of having our $100 million undrawn credit facility, as we continue with our preclinical retina program and global expansion activities,” said Chief Executive Officer Vicente Anido in a statement.

Aerie’s shares fell $1, to $63.75, in Thursday afternoon trading.

Sales of its Rhopressa eye treatment started on April 30 and totaled $2.4 million in the quarter. The company expects to produce sales of the eye drop between $20 million and $30 million for the year.

Rhopressa reduces eye pressure for patients with glaucoma or ocular hypertension.

Selling, general and administrative expenses more than doubled in the quarter to $39.9 million, up from $17.1 million in the second quarter a year ago.

Research and development expenses rose to $18.1 million in the quarter from $10.6 million in the second quarter a year ago.