Aerie Pharmaceuticals, a biotech firm focused on ophthalmology and calls itself the “glaucoma company,’ is raising another round of financing.

The RTP-based firm reported in a regulatory filing that it is seeking to raise $15 million.

So far Aerie has closed on $3 million from five investors who were not identified.

The financing is a mix of debt, options and warrants.

No other transaction, such as a merger or acquisition, is involved in the fund raising, Aerie said.

In March 2011 the firm raised $30 million.

The company also secured three new investors in its “Series B round of institutional backing: Clarus Ventures and Sofinnova Ventures, who led the round, as well as Osage University Partners.

Existing investors Alta Partners and TPG Biotech also participated.

In 2005, Aerie reported raising $21 million.

According the firm’s website, it has raised a total of $61 million from investors Alta Partners, Clarus Ventures, Osage University Partners, Sofinnova Ventures, and TPG Biotech.