New treatments developed for inherited retinal diseases

At least 40 new treatments for inherited retinal diseases are being developed, but only two are currently commercially available, according to the authors of a new review.

“Most of the health technologies identified are still at an early stage of development and it is difficult to estimate when treatments might be available,” write Joanna Smith of the NIHR Horizon Scanning Centre at the University of Birmingham in Birmingham, United Kingdom, and her colleagues from two other UK centres.

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The authors scanned medical databases, and spoke to patients, clinical experts and commercial developers to identify those technologies on the horizon. They published their findings on 26 June in the journal Eye.

New treatments could help a lot of people in the United Kingdom, according to the authors. There are more than 100 inherited retinal diseases, all of them incurable. In England and Wales they are the leading cause of visual impairment registration in the working-age population, the authors report. Healthcare providers currently manage the diseases with genetic counselling and education. They try to improve the patients’ residual vision with low vision aides, computer software, orientation and mobility training. Some people in the United Kingdom, however, don’t have access to these services, Dr Smith and her colleagues found.

The researchers counted 29 new technologies whose developers claim to have the potential to slow or stop the diseases in the relatively near term, and another 11 relevant technologies in earlier phases of development. Of these, the ARGUS II and the Alpha IMS are commercially available and CE marked.

Next: Breaking down the new technologies

Most of the new technologies in development are implants that sit on or underneath the retina. Some, such as the ARGUS II, link to an external camera on a spectacle frame. Others incorporate light-sensitive photodiodes. These devices rely on intact nerve fibres of the retina that can respond to stimulation and transmit information to the visual cortex. To interpret this information, users need training and support. Clinical experts interviewed by the authors pointed out that healthcare providers will have to take this into consideration.

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The devices will not work well in people with severe infantile-onset retinal dystrophies who have never had sight. And it’s not clear yet how long the devices will remain biocompatible. For example, they might cause conjunctival erosion, retinal detachments, increased intraocular pressure or decreased retinal perfusion. It also remains to be seen what long-term effects this nerve fibre stimulation will produce.

Patients interviewed pointed out that developers must take aesthetics into consideration. Some said they would not want to wear a device that is too conspicuous, even if it helped them see. For example, some expressed doubt over the PRIMA device because it requires gaming-style goggles to be worn.

Out of five drugs in phase II or III development, three are in development for retinitis pigmentosa. The authors found that the drug farthest along in commercial development is isopropyl unoprostone, which is administered as eye drops. The drug is currently in a phase II clinical trial. Multiple drugs for slowing or halting the progression of Stargardt macular dystrophy are in pre-clinical or phase I development, they write.

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Patients and clinical experts told the authors that the technologies most likely to succeed are gene therapies. The retina offers good surgical access through either intravitreal injection or subretinal injection, the authors pointed out. The blood–retina barrier reduces the risk of damage from the immune system by separating the subretinal space from the blood supply, and a single-administration of a vector could be more much effective than repeated drug treatments. Currently, researchers are working to optimise the adeno-associated virus delivery vector to enhance gene expression and allow larger genes to be delivered. They hope this will increase chances of the treatment successfully targeting either the retinal pigment epithelium or photoreceptor cells. Other researchers are developing lentiviral vectors to target retinitis pigmentosa associated with Usher syndrome type 1B and Stargardt macular dystrophy.

Next: Five regenerative and cell therapies examined

As an alternative, retinal pigment epithelium cells could be replaced through transplantation. This approach appears to work in animal models, the clinical experts said. Some studies suggest that stem cells can regenerate lost photoreceptors, restoring vision. Since the immune system may destroy donor cells, researchers are working on treating cells extracted from the patient to correct the genetic error, then re-implanting them. This approach could also avoid ethical concerns related to the use of embryonic cells.

The authors identified five regenerative and cell therapies. Renexus has proceeded farthest in clinical trials. This technology consists of encapsulated human cells genetically modified to secrete cliliary neurotrophic factor, which stimulates and protects neural cells. But preliminary results in achromatopsia and retinitis pigmentosa have been disappointing, the authors said.

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Interviews with patients revealed some broader concerns about the new technologies. Patients pointed out that many people with inherited retinal diseases have been discharged from National Health Service care because their conditions are incurable. As a result, these people may have trouble accessing new treatments as they become available. Patients wanted better dissemination of information about emerging treatments in the hope that this could improve access. They called for outreach to a more diverse representation of ethnic groups, particularly since some conditions are concentrated in specific ethnic groups. Patients interviewed expressed concern that more expensive treatments would be reserved for young patients. They also worried that news media reports could raise unfounded hopes. Most of these concerns are still hypothetical, however, as the authors point out that most new treatments are a long way from clinical practice.