EX-5.1

Exhibit 5.1

Hogan Lovells US LLP

1735 Market Street, Floor 23

Philadelphia, PA 19103

T +1 267 675 4600

F +1 267 675 4601

www.hoganlovells.com

January 18, 2019

Board of Directors

EyePoint Pharmaceuticals, Inc.

480 Pleasant Street

Watertown, MA 02472

Ladies and Gentlemen:

We are acting as counsel to EyePoint Pharmaceuticals, Inc., a Delaware corporation (the “Company”), in connection with the Company’s issuance of up to $20,000,000 of shares of the Company’s common stock, par value $0.001 per share (the “Shares”), from time to time and at various prices in an “at-the-market” offering pursuant to that certain At Market Issuance Sales Agreement, dated January 18, 2019 (the “Agreement”), by and between the Company and B. Riley FBR, Inc. (“Placement Agent”). The Shares have been registered under the Securities Act of 1933, as amended (the “Act”), pursuant to the Company’s registration statement on Form S-3 (File No. 333-228581), filed with the Securities and Exchange Commission (the “Commission”) on November 28, 2018 (the “Registration Statement”), a base prospectus dated December 11, 2018 (the “Base Prospectus”), and a final prospectus supplement dated January 18, 2019, (together with the Base Prospectus, the “Prospectus”). This opinion letter is furnished to you at your request to enable you to fulfill the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration Statement.

For purposes of this opinion letter, we have examined copies of such agreements, instruments and documents as we have deemed an appropriate basis on which to render the opinions hereinafter expressed. In our examination of the aforesaid documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to us, the authenticity of all original documents, and the conformity to authentic original documents of all documents submitted to us as copies (including pdfs). As to all matters of fact, we have relied on the representations and statements of fact made in the documents so reviewed, and we have not independently established the facts so relied on. This opinion letter is given, and all statements herein are made, in the context of the foregoing.

This opinion letter is based as to matters of law solely on the Delaware General Corporation Law, as amended. We express no opinion herein as to any other statutes, rules or regulations.

Based upon, subject to and limited by the foregoing, we are of the opinion that following (i) execution and delivery by the Company of the Agreement, (ii) issuance of the Shares pursuant to the terms of the Agreement, and (iii) receipt by the Company of the consideration for the Shares specified in the resolutions of the Board of Directors, the Shares will be validly issued, fully paid, and nonassessable.

Hogan Lovells US LLP is a limited liability partnership registered in the District of Columbia. “Hogan Lovells” is an international legal practice that includes Hogan Lovells US LLP and Hogan Lovells International LLP, with offices in: Alicante Amsterdam Baltimore Beijing Berlin Brussels Caracas Colorado Springs Denver Dubai Dusseldorf Frankfurt Hamburg Hanoi Ho Chi Minh City Hong Kong Houston London Los Angeles Madrid Miami Milan Moscow Munich New York Northern Virginia Paris Philadelphia Prague Rome San Francisco Shanghai Silicon Valley Singapore Tokyo Ulaanbaatar Warsaw Washington DC Associated offices: Budapest Jakarta Jeddah Riyadh Zagreb. For more information see www.hoganlovells.com