MODELING AND SIMULATION OF ILLUMINATION EFFECTS FOR EVALUATION OF MICROVESSELS OF THE CONJUNCTIVA

We present the development of a comprehensive model that was undertake n to determine the relationships between the components of an image an d the light intensity values present in the image of the microvessels of translucent tissues such as the bulbar conjunctiva. Experiments wer e conducted during the modeling process by use of a cylindrical microv essel embedded in a diffuse medium (phantom) on a reflecting backgroun d to affirm model components and simulations. The three-dimensional mo del was reduced to a single illumination plane with four regions of in terest and modeled as Lambertian radiators and surfaces. The modeling showed that the top of the cylinder and its immediate vicinity are dif fuse reflectors of light from the source plus light reflected from the background. The limbus of the cylinder is a diffuse reflector of the source and background illumination and a specular reflector of backgro und reflections that achieve a high grazing angle with the cylinder. T he immediate vicinity of the cylinder receives direct illumination fro m the source, but the light is partially obscured by the cylinder. The region beyond the shadow of the cylinder is a diffuse reflector of th e overhead light. The diffuse medium additionally reflects the source and also attenuates the illumination reaching the other components of the scene. The direct-and reflected illumination at each region of the model was calculated by use of specific geometric relationships. To v erify those calculations, we analyzed a video simulation for the effec ts of different illumination conditions and their contributing element s. Intensity values were calculated from the relative reflectivity dat a determined from the video signals. The illumination values at the po ints along the line at the meridian of the cylinder were due to its re flectivity and also that-of the medium. Similarly, the values of point s distant from the shadow of the cylinder were due to the reflectivity of the background and the medium. The excellent agreement between the model and the phantom provides a foundation for the detection and pre cise measurement of microvessel dimensions within a diffuse medium. Th e additional ability to compute relative depth, from a single view, al so permits discrimination between neighboring microvessels in complex images.