Gene Therapy for Inherited Retinal Disease: How Voretigene Neparvovec Works and What Other Conditions Have Trials Underway

Research-informed explainer — last updated April 12, 2026

Voretigene neparvovec (Luxturna) became the first FDA-approved gene therapy for an inherited retinal disease in 2017, delivering a working copy of the RPE65 gene directly into the retinal cells of patients who had been losing vision since childhood — and the pivotal phase 3 trial showed meaningful functional improvements in a population for whom no other treatment had previously existed. Beyond RPE65-mediated disease, clinical trials are now underway for X-linked retinitis pigmentosa, Leber hereditary optic neuropathy, Stargardt disease, and other inherited retinal conditions, making this a rapidly expanding therapeutic landscape for patients who were previously told nothing could be done.

This article draws on research from five specialist physicians with direct contributions to inherited retinal disease genetics and gene therapy science. Dina Gewaily, MD, Ophthalmology Specialist at Lancaster General Hospital, participated in the pivotal phase 3 Luxturna trial published in The Lancet (1,829 citations) — the definitive safety and efficacy study that led to FDA approval. Eric Pierce, MD, PhD, William F. Chatlos Professor of Ophthalmology and Director of the Ocular Genomics Institute at Massachusetts General Hospital and Mass Eye and Ear, published the phase 1 dose-escalation RPE65 gene therapy trial (852 citations), the contralateral-eye safety study (450 citations), and the AAV2 readministration trial in three adults with congenital blindness (387 citations). Byron Lam, MD, Professor of Ophthalmology at Bascom Palmer Eye Institute, published first-in-human X-linked retinitis pigmentosa gene therapy results in Nature Medicine (347 citations) and two studies on gene therapy for Leber hereditary optic neuropathy (226 and 200 citations). Elias Traboulsi, MD, at the Cleveland Clinic, contributed to the identification of surviving photoreceptors in blind RPE65-mutant eyes (280 citations) and the discovery of NMNAT1 as a cause of Leber congenital amaurosis (201 citations) — foundational work explaining why gene therapy can restore vision only if the photoreceptors themselves are still viable. Shizuo Mukai, M.D., at Massachusetts General Hospital, published the rhodopsin Pro23His transgenic mouse model for autosomal dominant retinitis pigmentosa (457 citations), the preclinical system used to develop gene therapies for the most common form of RP.

What is an inherited retinal disease?

Inherited retinal diseases (IRDs) are a group of more than 260 genetic disorders caused by mutations in genes responsible for photoreceptor function or survival. The most commonly known include:

• Leber congenital amaurosis (LCA): Severe vision loss present from birth or early infancy, often caused by mutations in RPE65, CEP290, or GUCY2D among others.
• Retinitis pigmentosa (RP): Progressive loss of peripheral vision beginning in adolescence or early adulthood, eventually affecting central vision; caused by mutations in over 80 genes, most commonly RPGR (X-linked form), RHO, and USH2A.
• Stargardt disease: Juvenile-onset macular dystrophy caused by mutations in ABCA4, affecting central vision in the first or second decade of life.
• Leber hereditary optic neuropathy (LHON): Mitochondrial DNA mutations causing acute or subacute central vision loss, predominantly in young men.

Together, IRDs affect approximately 1 in 2,000 people worldwide and are the leading cause of legal blindness in working-age adults in high-income countries.

How the RPE65 gene causes blindness

The retinal pigment epithelium (RPE) is a single layer of cells behind the photoreceptors that is essential for recycling visual pigment. The RPE65 protein converts all-trans retinyl esters back into 11-cis retinal — the chromophore that photoreceptors need to respond to light. Without a functional RPE65, the visual cycle cannot complete. Photoreceptors are present but cannot signal; patients see only in very bright light, if at all.

A critical discovery by Dr. Traboulsi and colleagues was that photoreceptors in RPE65-mutant eyes, while non-functional, remain structurally present for years after the onset of blindness. This was the prerequisite insight for gene therapy: if you can restore the missing enzyme while the photoreceptors are still alive, vision can recover.

What voretigene neparvovec does

Voretigene neparvovec (Luxturna) uses an adeno-associated virus serotype 2 (AAV2) vector as a molecular delivery vehicle. AAV2 is a non-replicating virus that has been engineered to carry the working human RPE65 gene. The vector is injected subretinally — under the retina, directly adjacent to the RPE cells — during a brief outpatient surgical procedure.

Once delivered, the AAV2 vector infects RPE cells and the RPE65 gene becomes expressed persistently without integrating into the cell's chromosomes. The RPE cells begin producing functional RPE65 protein, the visual cycle resumes, and photoreceptors regain the ability to respond to light.

What the phase 3 trial showed

The pivotal phase 3 trial, in which Dr. Gewaily participated, enrolled 31 patients with confirmed biallelic RPE65 mutations and residual retinal function. The primary outcome was a full-field light sensitivity threshold (FST) test — a standardized measure of the dimmest light a patient can detect.

At one year, patients in the treatment group showed a mean improvement of 1.8 log units in FST compared with essentially no change in controls — equivalent to detecting light 63 times dimmer than at baseline. Tested with a mobility maze (navigating a course under varying light conditions), 88% of treated patients improved by at least one lux level compared with 11% of controls.

Critically, both eyes are treated — typically two to seven days apart — because the natural history of untreated RPE65 disease is bilateral progression to near-complete blindness. Dr. Pierce's contralateral-eye safety study provided the safety data that made bilateral treatment standard practice.

Why timing matters: photoreceptor survival

Dr. Pierce's phase 1 dose-escalation trial demonstrated an important and sobering finding: younger patients responded better than older ones. The likely explanation is progressive photoreceptor degeneration over time — even though photoreceptors survive for years in RPE65 disease, they do eventually die. Once they are gone, restoring RPE65 cannot recover vision.

This creates a critical window for treatment. Current guidelines recommend evaluating patients for gene therapy as soon as biallelic RPE65 mutations are confirmed, rather than waiting until vision is severely compromised. The earlier the treatment, the more photoreceptors remain viable, and the greater the potential for functional improvement.

The pipeline beyond RPE65

RPE65-mediated LCA is rare — affecting an estimated 1,000–2,000 patients in the United States. But the success of Luxturna has accelerated trials for far more common IRDs:

X-linked retinitis pigmentosa (RPGR mutations): Dr. Lam and colleagues published first-in-human results in Nature Medicine in 2020, treating six patients with RPGR-associated XLRP. The trial demonstrated dose-dependent improvements in retinal sensitivity with an acceptable safety profile. This is significant because RPGR mutations account for roughly 70% of X-linked RP and 10–15% of all RP cases.

Leber hereditary optic neuropathy (LHON): Dr. Lam published two studies evaluating intravitreal AAV injection carrying the ND4 gene for the most common LHON mutation (m.11778G>A). Phase 3 data suggest improved visual acuity in treated versus untreated fellow eyes, though outcomes have been more variable than RPE65 therapy.

Stargardt disease / ABCA4 mutations: Phase 1/2 trials are underway using both AAV and non-viral delivery approaches. ABCA4 is among the largest genes that can be packaged in AAV vectors, creating delivery challenges that researchers are addressing with novel dual-vector strategies.

CEP290-associated LCA: An antisense oligonucleotide (sepofarsen) rather than gene replacement therapy — a RNA-targeted approach designed to correct the most common intronic mutation in CEP290.

What to expect from the procedure

Subretinal injection is performed under general or local anesthesia in an operating room. A vitrectomy (removal of the vitreous gel) precedes the injection. Recovery typically takes one to two weeks; heavy lifting and strenuous activity are restricted. Transient subretinal fluid, inflammatory reactions, and small macular holes have been reported but are uncommon. The procedure is performed at specialized retinal centers with experience in subretinal surgery.

Luxturna is currently priced at approximately $425,000 per eye, making it one of the most expensive medications ever approved. Spark Therapeutics and major insurance carriers have negotiated outcomes-based contracts. Patient assistance programs and Medicaid coverage exist, but access remains a significant barrier for many families.

Questions to ask your doctor

• Has genetic testing confirmed which gene is mutated and whether I or my child has biallelic (both copies affected) mutations in a gene with an available treatment?
• What is my current level of residual retinal function, and how does that affect candidacy for gene therapy?
• Is there a clinical trial for my specific genetic mutation that I should be evaluated for?
• What centers have experience performing subretinal injections, and how many cases have they done?
• Are both eyes eligible for treatment, and what is the timing between eyes?
• If photoreceptors continue to degenerate after treatment, can the therapy be repeated?

The bottom line

Voretigene neparvovec represents a proof of concept that delivering a working gene directly to retinal cells can restore vision that has been absent for years — but it works only as long as the target cells remain alive. For patients with RPE65-mediated disease, early evaluation and treatment while photoreceptors are still present is essential. For the broader inherited retinal disease community, the pipeline of trials targeting RPGR, CEP290, ABCA4, and other genes offers genuine reasons for optimism in conditions that were, until very recently, considered completely untreatable.