Gene Therapy for Inherited Retinal Disease: A Single Injection, A Single Gene

The eye was always going to be where gene therapy proved itself first. It is small, enclosed, partly immune-privileged, and every part of it can be watched directly through an ophthalmoscope.

In 2017, that promise became a licensed product: a single subretinal injection, for a single gene, in a single inherited retinal disease.

Gene therapy for inherited retinal disease is no longer experimental for at least one condition, and dozens more are now in active clinical trials.

What it offers is fundamentally different from every other treatment on this site – a one-time intervention aimed at the genetic cause, not lifelong management of its downstream effects.

What it cannot yet offer, for most patients, is treatment at all – eligibility remains tightly restricted to specific mutations with viable remaining retinal tissue.

What Is Gene Therapy for Retinal Disease?

Gene therapy delivers genetic material into retinal cells to correct or compensate for a disease-causing mutation, most commonly using an adeno-associated virus (AAV) vector injected into the subretinal space.

Current and investigational approaches fall into distinct strategies:

Gene augmentation – delivering a functional copy of a gene to compensate for a loss-of-function mutation, the approach behind the only currently licensed retinal gene therapy
Gene editing – using CRISPR-based tools to correct the mutation directly within the patient’s own genome, still investigational for retinal disease
Optogenetic therapy – introducing light-sensitive proteins into surviving retinal cells to restore some light perception in advanced, photoreceptor-depleted disease
RNA-based approaches, including antisense oligonucleotides, targeting specific mutations at the RNA level rather than the DNA level

Gene augmentation is the only strategy with a licensed product so far, and it is the one this article focuses on.

Voretigene Neparvovec: The First Approved Retinal Gene Therapy

Voretigene neparvovec is an AAV2 vector delivering a functional copy of the RPE65 gene, for biallelic RPE65 mutation-associated retinal dystrophy – a spectrum including Leber congenital amaurosis and some forms of retinitis pigmentosa
RPE65 encodes an enzyme essential to the visual cycle in the retinal pigment epithelium; without it, photoreceptors cannot regenerate the visual pigment needed to respond to light
The pivotal trial demonstrated meaningful improvement in functional vision, measured using a multi-luminance mobility test navigating an obstacle course under varying light levels, alongside improvements in visual field and light sensitivity
Treatment is a single subretinal injection per eye, typically performed as two separate procedures, and is approved for patients with sufficient viable retinal cells at the time of treatment

The mobility test outcome measure is worth understanding specifically, because it captures something visual acuity charts do not – functional vision in the low-light conditions that mattered most to these patients’ daily lives.

Patient Selection

Confirmed biallelic RPE65 mutations on genetic testing – this is a molecularly defined indication, not a clinical diagnosis alone
Sufficient viable retinal cells, generally assessed by residual retinal thickness on OCT and functional visual field, since the therapy rescues surviving cells rather than regenerating lost ones
Treatment is generally more effective the earlier it is given in the disease course, before extensive photoreceptor loss has occurred
Genetic counselling is an essential part of the pathway, both for diagnosis confirmation and for family implications

This is the central limitation of the entire field so far: gene therapy can rescue retina that is still alive, but it cannot restore retina that has already degenerated.

Surgical Delivery

Procedure

Delivery requires pars plana vitrectomy to access the subretinal space
A fine cannula creates a localised retinal detachment (a “bleb”) to deliver the vector precisely beneath the retina at the treatment site
Careful surgical technique is required to avoid foveal trauma while still achieving adequate posterior pole coverage

Perioperative Considerations

Perioperative corticosteroids are typically used to reduce the immune response to the viral vector
Careful patient positioning postoperatively supports even distribution of the therapeutic bleb and reabsorption of subretinal fluid

The delivery procedure is, in effect, borrowed directly from vitreoretinal surgery – the therapeutic innovation is entirely in the vector and the gene, not in a new surgical technique.

Gene Therapy in Clinical Development

X-linked retinitis pigmentosa, targeting RPGR mutations, is in advanced clinical trials
Choroideremia, targeting CHM mutations, has shown encouraging early trial results
Achromatopsia and other cone-specific disorders are being investigated with gene augmentation approaches
Optogenetic therapy has shown proof-of-concept partial visual restoration in advanced retinitis pigmentosa with essentially no surviving photoreceptors, a fundamentally different and more ambitious target than gene augmentation
Gene editing approaches for dominant conditions, where simply adding a normal gene copy is insufficient because the mutant copy remains active, are in earlier-stage development

The field is moving from “replace a missing gene” toward “edit the gene in place,” which is the harder problem but the one that will eventually be needed for dominant inherited retinal disease.

Safety Considerations

Surgical risks common to any vitrectomy and subretinal injection – retinal tear, detachment, endophthalmitis and cataract
Intraocular inflammation related to the viral vector, generally managed with perioperative corticosteroids
Transient intraocular pressure elevation
Chorioretinal atrophy has been reported at or near the injection site in some cases, a specific complication under active study
Long-term durability of effect is still being characterised as real-world follow-up data accumulate beyond the original trial period

Durability is the open question hanging over the entire field – a treatment framed as one-time only holds up if its effect does not fade, and that evidence is still maturing.

Prognosis

Gene therapy has proven the concept for inherited retinal disease, but its reach remains narrow.

Patients treated with voretigene neparvovec have shown sustained functional visual improvement over the published follow-up period to date
Only a small minority of inherited retinal disease is currently treatable, since eligibility depends on a specific, molecularly confirmed mutation with a licensed or trial-available therapy
The pipeline of gene-specific trials is expanding steadily, and genetic testing for inherited retinal disease is increasingly relevant even where no treatment yet exists, since it determines trial eligibility
The single biggest practical barrier for most patients remains access to genetic testing and diagnosis in the first place, not the therapy itself

The most useful thing this technology has changed, for now, is the value of an accurate genetic diagnosis – even in inherited retinal disease without a licensed treatment, knowing the gene is what keeps a patient’s options open as the field expands.

References

Russell S, Bennett J, Wellman JA, et al. Efficacy and safety of voretigene neparvovec for RPE65-mediated inherited retinal dystrophy. The Lancet. 2017.
Maguire AM, Russell S, Wellman JA, et al. Efficacy, safety, and durability of voretigene neparvovec: results up to 4 years. Ophthalmology. 2019.
Sahel JA, Boulanger-Scemama E, Pagot C, et al. Partial recovery of visual function in a blind patient after optogenetic therapy. Nature Medicine. 2021.
Gene Therapy for Inherited Retinal Disease. EyeWiki, American Academy of Ophthalmology.
Retinitis Pigmentosa and Gene Therapy. StatPearls, NCBI Bookshelf.