UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

Check the appropriate box:

☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material under § 240.14a-12

Clearside Biomedical, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement if Other Than the Registrant)

Payment of Filing Fee (Check all boxes that apply)

☒ No fee required

☐ Fee paid previously with preliminary materials

☐ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11

P.O. BOX 8016, CARY, NC 27512-9903 Scan QR for digital voting Meeting Materials: Notice of Meeting and Proxy Statement & Annual Report or Form 10-K Important Notice Regarding the Availability of Proxy Materials for the Stockholders Meeting To Be Held On June 20, 2024 For Clearside Biomedical, Inc. Stockholders of record as of April 22, 2024 Annual Meeting of Stockholders To order materials for this and/or future stockholder meetings, use one of the Thursday, June 20, 2024 8:00 AM, Eastern Time 900 North Point Parkway, Suite 200 Alpharetta, GA 30005 following methods. Internet: For a convenient way to view proxy materials, VOTE, and obtain www.investorelections.com/CLSD directions to attend the meeting go to www.proxydocs.com/CLSD To vote your proxy while visiting this site, you will need the 12 digit control number in the box below. Call: 1-866-648-8133 This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. This is not a ballot. You cannot use this notice to vote your shares. We encourage you to access and review all of the important information contained in the proxy materials before voting. Email: paper@investorelections.com Under United States Securities and Exchange Commission rules, proxy materials do not have to be delivered in paper. Proxy materials can be distributed by making them available on the * If requesting material by e-mail, please send a blank e-mail with the internet. 12 digit control number (located below) in the subject line. No other requests, instructions OR other inquiries should be included with your If you want to receive a paper or e-mail copy of the proxy material, you must request one. e-mail requesting material. There is no charge to you for requesting a copy. In order to receive a paper package in time for this year’s meeting, you must make this request on or before June 10, 2024. Your control number Have the 12 digit control number located in the box above available when you access the website and follow the instructions. SEE REVERSE FOR FULL AGENDA Copyright © 2024 BetaNXT, Inc. or its affiliates. All Rights Reserved

Clearside Biomedical, Inc. Annual Meeting of Stockholders THE BOARD OF DIRECTORS RECOMMENDS A VOTE: FOR ON PROPOSALS 1, 2 AND 3 PROPOSAL 1. Election of Directors 1.01 Richard Croarkin 1.02 William D. Humphries 1.03 Nancy J. Hutson 2. Approval on an advisory basis, the compensation of the Company’s named executive officers, as disclosed in the proxy statement. 3. Ratification of the selection of Ernst & Young LLP as independent auditors for the fiscal year ending December 31, 2024. NOTE: In their discretion, the proxies are authorized to vote upon such other business as may properly come before the meeting, including any adjoumment or postponement thereof.