A first-of-its kind genetic treatment for blindness will cost $US850,000 ($A1.2 million) per patient, making it one of the most expensive medicines in the world and raising questions about the affordability of a coming wave of similar gene-targeting therapies.
The injectable treatment from Spark Therapeutics can improve the eyesight of patients with a rare genetic mutation that affects just a few thousand people in the US.
Previously there has been no treatment for the condition, which causes complete blindness by adulthood.
Pricing questions have swirled around the treatment due to a number of unusual factors - it is intended to be a one-time treatment, it treats a very small number of patients and represents a medical breakthrough.
Previously, Spark suggested its therapy, Luxturna, could be worth more than $US1 million ($A1.4 million).
But the company said on Wednesday it decided on the lower price after hearing concerns from health insurers about affordability.
Consternation over skyrocketing drug prices, especially in the US, has led to intense scrutiny from patients, politicians, insurers and hospitals.
Approved last month, Luxturna, is the nation's first gene therapy for an inherited disease.
It requires a 45-minute operation in which a tiny needle delivers a replacement gene to the retina, tissue at the back of the eye that converts light into electric signals that produce vision.
The treatment is part of an emerging field of medicine that could produce dozens of new gene-targeting medications in the next few years.
Like Luxturna, these therapies are generally intended to be taken once, a fact which drug developers argue sets them apart from traditional drugs taken for months or years.