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Optics used in ophthalmology and the medicine industry


By Optitec

Use of measurement of light reflection for detection of eye pathologies and qualification of drug efficacy

The cornea is a transparent tissue, due to the unique architecture of collagen (fibrils, fibres and lamellae), fibril size (less than the wavelength of visible light), regular spacing between collagen fibrils (due to proteoglycans), absence of vascularisation, low numbers of keratocytes and delicate regulation of hydratation. Any alteration in the structure of one or more of the tissue’s layers can bring about loss of transparency. From a physical point of view, the main cause of opacity in cases of oedema is a significant increase in the tissue’s diffusion of visible light. Although the cornea’s transparency is yet to be fully explained, theories do exist. Thanks to the experience acquired by the Fresnel Institute with regard to modelling and characterisation of heterogeneous environments, we can now set ourselves ambitious objectives. The aim of the project is to utilise high-performance electromagnetic models to measure and analyse physical properties representing the corneal tissue’s diffusion of light – i.e. the quantity of light re-emitted in all directions when the tissue is exposed to light. This phenomenon, which is due to inhomogeneities in tissue surface or volume, should enable characterisation of such heterogeneities’ signatures, and of the tissue’s pathological state. The method does not involve any contact with the tissue (distance measurement of light diffused), and is non-destructive (no preparation or colouration of the sample) and non-ionising (source of visible light). It will enable development of new diagnosis protocols to be used in qualification of drug efficacy. The project therefore bears upon detection of even the slightest modification in tissue structure causing changes in angular diffusion, and consequent early detection of pathologies and assessment of the effectiveness of medical treatments.

A preliminary study has enabled explanation of the increased levels of diffusion that come with increased cornea’s thickness (stage of oedema), through confrontation of measurements of diffusion, three-dimensional imaging of tissue structure (by OCT) and electromagnetic modelling. The origin of such diffusion was identified and modelisations correlated with measurements. We hope to use this as a basis for further research into corneal pathologies. The presence of localised defects (scarring following trauma or surgery, keratitis, hyperhydration deposits in cases of oedema, etc.) and non-uniform development of tissue organisation (such as occurs in cases of keratoconus) also modify light diffusion. Similarly, drug treatments act to reduce or eliminate the effects of target pathologies, so bringing about modifications in the tissue’s heterogeneity and a consequent signature in analysis of the signal diffused, this time as diseased tissue returns to a structure approaching that of healthy tissue. Detection and interpretation of such diffusion signal modification will provide an effective diagnostic tool.

Contact for any precision: Ms Carole Deumié, Professor, ECM, Fresnel Institute – UMR 7249, Marseille.