UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

OF THE SECURITIES EXCHANGE ACT OF 1934

For the month of October 2025

Commission File No. 001-39621

OPTHEA LIMITED

(Translation of registrant’s name into English)

Level 4

650 Chapel Street

South Yarra, Victoria, 3141

Australia

(Address of registrant’s principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F.

Form 20-F ☒ Form 40-F ☐

EXHIBIT INDEX

Exhibit		Description
99.1		~~Press Release -~~ Opthea ~~Received~~Notice ~~A$10.8~~of ~~million~~Annual ~~R&D~~General ~~Tax Incentive~~Meeting

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereto duly authorized.

OPTHEA LIMITED (Registrant) By: /s/ Jeremy Levin Name: Jeremy Levin Title: Executive ~~Officer~~Chair

Date: 10/0610/2025

Filing Compare · Opthea Ltd