The evaluation and development of a retinal imaging densitometer

The research described in this thesis presents the development and evaluation of a prototype multispectral, imaging densitometer. Ultimately, the aim was to develop a method of simultaneously isolating the contributions from the three main photoreceptors, across the retina. Thus, providing the clinician with a viable tool for assessing outer retinal function both efficiently and directly. The construction and use of the prototype multispectral imaging densitometer was described in detail. Healthy participants were recruited and imaged to evaluate the baseline capability of the device. The results were validated through comparison to published values for optical density, regeneration rates and photopigment distribution as obtained through in vivo, in vitro and in situ techniques. A novel ocular reflection model was developed to characterise and mathematically remove the pre-receptoral stray light from the images. Whilst the preliminary investigation returned regeneration rates in line with values from the literature, a ‘red shift’ of approximately 30nm was highlighted in the experimental absorption spectra of the visual pigments, hindering their isolation. Investigation into this phenomenon suggested that the cause was pre-receptoral stray light, with both the crystalline lens and the inner retinal layers contributing to the effect. Attempts to remove the crystalline lens component showed a partial reduction of the ‘red shift’. Greater success was achieved through the modelling of the experimental ocular reflection data to simultaneously characterise the contribution from both components. This research has shown that mapping of visual pigment optical density across the retina is possible with the retinal densitometer described. With further development, the technique is likely to become a useful tool in the diagnosis and monitoring of outer retinal disease