Our Research

Visual Optics and Retinal Imaging

Over the last few years, adaptive optics (AO) has enabled imaging at the cellular level in the living eye. This literally provides a window into the state of people's health, as well as opening up the possibility of earlier detection of retinal disease. AO-assisted imaging is able to monitor changes in retinal microstructure at a pre-clinical stage of disease, opening up the possibility of new diagnostic and treatment protocols to preserve the normal functioning of the retina. AO-assisted retinal imaging systems are available for use in the clinic, but they have not been widely adopted due to the lack of automatic tools to process the high-resolution images and to detect and track features of interest. In this project, we are collaborating with a team of ophthalmologists in Rome to develop these tools. As an example, many retinal conditions affect the photoreceptor cone mosaic. We have developed techniques (some based on astronomical image processing) to accurately identify cone photoreceptors and to track them among images taken at different times. We are investigating parameters of the photoreceptor mosaic (cone density, regularity, nearest-neighbour distance) and how they change over different stages of retinal diseases. Figure 1 shows an example of a high-resolution retinal image (on the right-hand side), with automatic identification of the cones (green dots) and automatic segmentation of the shadows of retinal blood vessels. The purpose of an ophthalmic adaptive optics system is to compensate for wavefront aberrations caused by a distorting ocular medium, which blurs the retinal field. AO systems are comprised of three main elements: a wavefront sensor that measures distortion as the light scatters off the retina and exits the eye, a wavefront corrector (adaptive mirror) that compensates for this distortion, and a control system to measure the distortion from the sensor and adjust the mirror shape for optimal correction.

Once the image of the retinal field is corrected by the AO system, the image processing is applied to enhance the level of detail visible for diagnostic of patient's health and early detection of retinal abnormality. Knowing the limitations of AO correction, it is vital to develop image processing techniques that allow obtaining useful biometric data from the image and use it in a clinical setting.

Adaptive Optics Vision Simulators

Enterprise Ireland has funded (0.3 M Euro International Research Grant) under a Eureka program the "For Your Eyes only" project, which aims at developing a customised surgical procedure and personally optimised intra-ocular lens design for cataract patients.The aging eye is usually affected by cataract when the crystalline lens becomes cloudy and needs to be replaced by an artificial (intra-ocular) lens that is transparent and has correct optical power to focus light exactly onto the retina. Figure 2 shows an aberrated eye with natural crystalline lens and the eye after cataract surgery with an implanted intra-ocular lens (IOL). A customised IOL design allows bringing most of light in one focus.

Optimising surgical outcomes is the main goal of the project; we modelled the corrected visionby mimicking the optical effect of the intra-ocular lens after implantation into the eye. The vision simulator system offers such possibility thanks to adaptive optics. The deformable mirror (DM)is the key component that can act as an intra-ocular lens with the patient specific shape or could negate the effect of the natural crystalline lens. For example to estimate spherical aberration (SA) of the crystalline lens, the subject's corneal topography and wavefront aberrations have to be measured and modelled with exact ray-tracing. Figure 3 shows the vision simulator system. The patient looks through the system at a target on the OLED microdisplay. This new method allows one to evaluate different optical designs of intraocular lenses subjectively for the patient prior to implantation surgery. Three types of single-piece IOL such as equi-spherical monofocal, aspheric monofocal, and diffractive bifocal were assembled into a model eye and evaluated using AO system. Comparative analysis of these IOL designs reveals the one that is optimal for the patient.