An experimental eye drug from Genentech Inc. and Novartis AG, when used in combination with an established drug, helped forestall blindness in an early-stage study, but showed an increased risk of a serious side effect, Genentech said on Tuesday.

Researchers studied Lucentis, an injectable treatment for wet age-related macular degeneration, in combination with Visudyne, an established drug by QLT Inc. and Swiss drugmaker Novartis.

Genentech said about 90 percent of patients maintained or improved vision when treated by the combination of Lucentis and Visudyne after one year, when compared with about 68 percent of those treated with Visudyne alone.

But a preliminary analysis of the data showed an increased risk of serious uveitis in patients treated with the combination therapy versus those treated only with the older drug Visudyne. Full results of the phase I/II study won’t be released until mid-July.

Uveitis is an inflammation in the pigmented inside lining of the eye, the uvea, that can rapidly damage the eye and produce long-term vision threatening complications.

Wet form age-related macular degeneration, a leading cause of blindness, is a condition in which leaking blood vessels form in the eye and eventually block vision.

Merrill Lynch analyst Eric Ende, in a research note, said the safety profile of the two drugs used in combination “may temper use.”

Earlier in May, Genentech and Novartis released preliminary results from a large-scale study of Lucentis that showed about 95 percent of patients maintained or improved their vision after a year.

Ende said he does not expect the latest results of Lucentis in combination with Visudyne to pose a serious risk to the commercialization of Lucentis. But he said more safety and efficacy data may be required to drive sales of Lucentis when used in combination with Visudyne.

Novartis has secured marketing rights to Lucentis outside the United States. Genentech, which developed Lucentis, has retained U.S. marketing rights.

In a recent interview, a Novartis executive said the company expects the total market for drugs like Lucentis could eventually top $1 billion a year.

Genentech and Novartis expect to file for regulatory approval to market Lucentis with regulators in Europe and the United States early in 2006.

Shares of Genentech rose 12 cents to $79.38 on the New York Stock Exchange early Tuesday afternoon.