Advanced OCT and Adaptive Optics Imaging in Retinal Disease (The ACAD Study)

Diseases affecting the vitreous, retina and choroid are among the commonest causes of sight-loss and vision impairment in England and Wales.

These diseases may display a wide range of pathological features including vitreous, retinal and subretinal haemorrhage; macular fluid; choroidal inflammation and choroidal masses.

The retina is a 'window to the brain' and there is increasing evidence that neurodegenerative disorders such as Multiple Sclerosis, Parkinsons Disease and Alzheimers Disease have retinal manifestations which may have prognostic implications, afford earlier diagnosis, and potentially act as surrogate endpoints for treatment trials.

In 2012, a further advance in OCT technology was brought to market with the arrival of the first commercial available swept-source OCT (SS-OCT) device (the Topcon DRI OCT). SS-OCT technology uses a tuneable laser light source with a longer wavelength of light (typically 1040-1050 nm central wavelength) than the light sources seen in more conventional SD-OCT devices. This leads to greater tissue penetration with less backscatter from the RPE, producing images of the choroid with greater resolution with fast image acquisition speeds (100,000 A scans/s) and longer line scan lengths. The ability to take rapid scans with the only commercially available SS-OCT device (the DRI, Tocon Inc. Paramus, NY, USA) also enhances image quality by line scan averaging capability.

The high axial resolution of OCT allows discrimination of the distinct retinal layers that are affected differentially in different diseases. More direct visualisation of the photoreceptor layer is afforded by use of an Adaptive Optics Scanning Light Ophthalmoscope (AOSLO), which provides excellent lateral resolution and allows direct visualisation of the cone and rod photoreceptor mosaics in vivo by correcting for ocular aberrations and resulting in a lateral comparable with histopathological sections.

In this study AO images will be correlated with SD- and SS-OCT and used to comprehensively assess the integrity of the photoreceptor mosaic. Furthermore AO and OCT will be used to measure nerve fibre layer loss and optic disc changes if relevant to the disease.

The imaging modalities used in this study will be spectral domain optical coherence topography (SD-OCT), swept source optical coherence tomography (SS-OCT), and adaptive optics scanning light ophthalmoscope (AOSLO)

The study will examine 300 patients (up to 600 eyes) in a single visit with a further Adaptive Optics (AO) imaging taken in a subset of patients (up to 200).

Patients in whom AO imaging was possible from a technical perspective will be invited back for further imaging after 6-12 months (at a standard NHS follow up visit) to probe longitudinal changes.

An examiner will scan the participants study eye(s) on the same day on each of the 3 imaging modalities SD-OCT, SS-OCT and AOSLO.

Finally a questionnaire will be used to explore whether participants preferred one OCT imaging modality over the other (SS-OCT vs SD-OCT).