Imaging and confocal systems for in vivo measurements of human-iris spectral reflectance

Two experimental configurations, an imaging system and a confocal system, are constructed to measure the spectral reflectance of human irises in vivo. The light from a white light-emitting diode (LED) is focused on the iris and the reflected light is measured by a spectrometer. A flat plate coated with barium sulphate Ba₂ SO₄ with reflectance 0.99 for visible light is used as a reference to calibrate the system. Samples of gray-blue and black-brown eyes are measured to compare the performance of the two systems. The differences between the reflectance spectra of the two systems show that Fresnel reflection from the interface between air and cornea is the dominating effect. The spatial filtering characteristic of the confocal system provides a nice capability in eliminating the contribution of cornea reflectance.