The results prompted an analyst to call the treatment "a game changer."
Shares of the Alpharetta, Ga., company at last check were up 46% to $4.41.
Clearside said the initial lowest planned dose of 0.03 mg CLS-AX was well tolerated with no serious adverse events and no drug-related treatment-emergent adverse events observed throughout the study.
The company said the improvements after receiving an injection of CLS-AX for wet AMD were reflected in the BCVA score, or best corrected visual acuity, with five of six patients each gaining four or more letters.
Roth Capital analyst Zegbeh Jallah reiterated a buy rating and a $9 price target on the company after Clearside unveiled the early safety and efficacy data.
CLS-AX was safe and well-tolerated with no inflammation, allowing for enrollment into Cohort 2, Jallah said in a research note, according to the Fly.
Even "more impressive" were the early efficacy data showing that a single dose of CLS-AX led to best corrected visual acuity improvements, beyond that achieved with "gold standard" Eylea, the analyst said. That makes the Clearside drug a "game changer," Jallah said.
Regeneron Pharmaceuticals (REGN) - Get Report, which makes Eylea, did not immediately respond to a request for comment. Eylea is Regeneron's first approved drug in 2011 and remains the company's top seller.
In February, Regeneron said Eylea's fourth-quarter U.S. net sales increased 10% to $1.34 billion over the year-earlier total. In May, the company said first-quarter sales of Eylea increased 15% to $1.35 billion.
In April, Regeneron said its Regen-Cov antibody cocktail may work well at treating people who have been exposed to COVID-19 but are not showing symptoms. The company unveiled positive results for Regen-Cov in March.