Inherited disorders of the retina are one of the leading causes of
childhood blindness and for the most part there are no effective
treatments. Loss of vision is caused by the gradual death of the
light-sensitive cells in the retina. We are investigating several
different approaches to developing effective treatments.
We are at
the beginning of an exciting new era where
untreatable blinding genetic eye disease will be
amenable to treatment.
Gene therapy for childhood blindness
A group led by Professor Robin Ali are trying
to improve the function of the light-sensitive cells and
prevent their death using gene therapy – the
introduction of a normal copy of the gene into the
retina to replace the faulty gene. This new human
gene is inserted into a harmless virus which then
transports the gene into the retinal cells, where the
gene is able to function normally. In 2008 we
performed the first gene therapy clinical trial for
retinal disease in man, treating a rare form of
infantile onset retinal disease. We have shown that
the treatment is effective in improving sight and we
are currently investigating the optimal dose to use
and the optimal age for treatment to be given.
Artificial retina
Artificial retina is an approach to replace the retinal cells
that have died. This requires a source of healthy
retinal cells but this is currently not available. We
have a team of scientists working towards developing
retinal cells from human stem cells. This is a complex
process, but we have made major advances over the
last few years and this form of treatment is a realistic
possibility within the next five years.
When the light-sensitive cells in the retina have
died completely, the retina fails to function and
the patient is blind, even though the nerves that
transmit information from the eye to the visual part
of the brain still work. This has led to the idea of
developing an artificial retina that will stimulate the
nerves within the eye directly and convey visual
information to the brain. Moorfields is one of a few
centres internationally involved in a multicentre
clinical trial of one form of retinal implant, the Argus
II retinal implant. Since 2008 our surgeons, led by
Mr Lyndon da Cruz, have carried out seven
successful operations to insert the Argus II retinal
implant into the eyes of seven blind patients
suffering from severe retinitis pigmentosa.
The Argus II system uses a spectacle-mounted
camera to feed visual information to electrodes in the
eye. The electrical pulses emitted induce responses in
the retina that travel to the brain via the optic nerve.
The brain is then able to perceive patterns of light
and dark spots corresponding to the electrodes
stimulated, and the implants generate consistent
visual perceptions for the patients. The early results
of the trial are very promising. As the technology
improves, the next generation of these retinal
implants will revolutionise the treatment of
patients who are blind due to retinal disease.
Genetics of human retinal disease
Another aspect of research within the theme is to
identify the specific genetic changes causing retinal
disease within families, and then to carry out detailed
investigation of retinal function using electrophysiology
and psychophysics and correlate this with the structure
of the retina. We have access to state-of-the-art
imaging, so it is now possible to image the different
layers of the retina and even the light-sensitive cells
themselves. We use the same approach to study the
effects of novel therapies such as gene therapy.
The testing and imaging of young children is
especially challenging. Young patients cannot
follow instructions or sit patiently through long
testing sessions, so we need to use specially
developed child-friendly methods to measure their
vision accurately. We have recently recruited a new
research group, led by Dr Marko Nardini, who have
expertise in measuring vision in infants and young
children. They are developing novel methods of
testing using state-of-the-art ‘eye tracking’
equipment that records where on a screen the child is
looking. By displaying specially designed patterns
and measuring the child’s eye movements towards
them, we can test how well children can see. These
methods work even with very young infants.