Some 150 years ago, the first images of the living human retina were obtained. Since then, clinicians and scientists alike have relied on the continued development of new and improved ways to visualise the back of the eye. This has been greatly aided by advances in optics and photonics, electronics and computer technology.
Unlike the imaging of everyday objects, achieving a high resolution image of the back of the eye can be limited due to what is known in the imaging world as optical imperfections or aberrations. Optical imperfections of the cornea, lens and tear film result in optical aberrations that degrade the images doctors obtain of the retina. However, with learning’s from the astronomy world we are now welcoming a new generation of imaging technologies that can compensate for these optical imperfections. This includes Adaptive Optics (AO).
Adaptive Optics was originally developed for ground-based telescopes to compensate for the aberrations caused by turbulence in the earth’s atmosphere. When applied to ophthalmology, AO can compensate for the eye’s aberrations, thereby allowing for the non-invasive visualisation of some of the smallest human structures in the living retina such as single rod and cone photoreceptors or retinal pigment epithelium (RPE) cells. AO by itself does not provide a retinal image, rather an AO subsystem must be incorporated into an existing imaging device. In recent years, AO has been successfully integrated with the three primary ophthalmic imaging devices (conventional fundus camera;Fundus photography involves photographing the rear of an eye so that the central and peripheral retina, optic disc and macula can be visualized, Scanning laser ophthalmoscope (SLO); uses horizontal and vertical scanning mirrors to scan a specific region of the retina, and Optical Coherence Tomography (OCT);An imaging process whereby a cross-section picture of your retina is taken and allows your eye doctor to study each layer of the retina in more detail), with each offering different benefits.
Uses and Applications
While AO retinal imaging started with vision science applications, these have translated into clinical applications that are rapidly expanding. By themselves, adaptive optics images are just high-quality pictures of light sensitive rod and cone cells. However, when you couple this with genetic information such as the specific mutation causing a condition, a greater context is gained that enables more insightful interpretation of the features in the images. In fact, AO is literally changing the way scientists and ophthalmologists (eye doctors) see the retina.
With AO, we can now study the detailed structure and function of single rod and cone photoreceptor cells. It also allows us to study the function of cone cells, for example, in areas that are not usually visible when using other imaging techniques. We can even image and study the exact same area in the retina over a period of years. As such, AO is proving incredibly useful for tracking and monitoring disease progression, which is an important element of Natural History studies.
As novel treatments to slow disease progression in inherited retinal degenerations are developed, it will be critical to evaluate the effect treatments have on individual photoreceptor cells. Given the non-invasive nature and high-resolution of AO imaging, it is an ideal tool to evaluate response of individual photoreceptor cells to potential treatments that may provide a suitable outcome measure to assess experimental treatments in clinical trials.
Future of Adaptive Optics
Ultimately, AO will help clarify our understanding of eye disease and improve detection, diagnosis and management of conditions like inherited retinal degenerations but also other conditions such as albinism or colour blindness. Moreover, AO also allows researchers to purposefully control aberrations of the eye in vision simulators of major benefit for intraocular lens design and pre-surgery vision evaluations.
In 2017, Fighting Blindness invested in a piece of technology that will serve to assist in developing critical clinical and research adaptive optics in Ireland, making us just a small handful of countries in the world with this technology. Prof Brian Vohnsen (Retina 2017 Speaker) is the Principal Investigator for the Advanced Optical Imaging Group (AOI Group) at University College Dublin. Together with his clinical colleagues at the Mater Misericordiae University Hospital, they aim to embed AO into future research efforts and clinical management of people living with IRDs.
We also aim to build capacity and expertise amongst the retinal community in Ireland and each year we endeavour to coordinate training programmes with centres of expertise in the USA.
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