Spark Therapeutics, which makes the therapy, today announced the whopping price tag. Called Luxturna, it was approved by the FDA in December, but Spark didn’t disclose the price at the time.

Now it has. And it’s a lot.

In a class of its own. The only approved gene therapy for an inherited type of blindness will cost $425,000 per eye—the most expensive single dose of a drug in the U.S. At $850,000 for both eyes, that would be more than 10 times the median net worth of an American family.

Who will benefit? The therapy is meant to restore eyesight in people who have a specific genetic mutation that causes degeneration of the retina. Spark hasn’t said how many people that is, but by our own estimates, it may be fewer than 30 patients a year.

Is it worth it? While the therapy does stop patients’ eyesight from getting worse and even restores some sight, it’s not a cure, and no one is sure how long the effects last. By contrast, a gene therapy on the market in Europe, called Strimvelis, effectively cures patients with a rare type of immune deficiency for the low, low price of $714,000.