Design and optimization of a retinal exposure detector

The design and optimization of a retinal exposure detector for measuring the total amount of light entering the human eye and falling on the retina is presented. The retinal exposure device was designed by first determining the spatial efficiency function of the human eye system. This is accomplished by combining the spatial response function of the average human eye with a standard facial cutoff function. The eye's spatial efficiency function is ascertained through ray trace analysis with optical modeling software of published theoretical and biometric wide-angle eye models. All major factors affecting light propagation, such as volume attenuation, the gradient index of the lens, aspheric surface curvatures, partial reflection, and vignetting are included in the simulation. A practical metering device that mimics the calculated total eye system spatial response function was designed and optimized by again employing optical simulation software. The final design consisted of baffles, a lens system, a decentered aperture, an optical diffuser, optical filters, and a silicon photodiode. The response of the prototype retinal exposure detector device design was shown to match that of the theoretical eye response to within three percent.