Spectral reflectance of the normal and abnormal human fundus oculi
Cullen, Anthony Peter
Studies of the fundus oculi with light of restricted spectrum are not new. The object of this investigation is to evaluate the usefulness of monochromatic light in differentiating between various structures, both normal and abnormal, in the human fundus oculi. Previous work is reviewed and the basic principles involved are presented. Transmittance of the eye and light losses in the eye are considered and known absorption of reflection curves of fundal structures are given since differences in these are responsible for their varied appearance. The initial studies were carried out using a monochromator and fundus camera system; these were unsuccessful because of inadequate illumination. Ultra-fast film gave results but these were so grainy and lacking in contrast that they were rejected. Later studies utilized narrow pass band interference filters incorporated into the Zeiss Fundus Camera and the results were recorded on fine grain panchromatic film. These were more successful. Colour film offered no advantages since the results were inevitably monochromatic. Visual observation was not used other than to focus the equipment because of the low sensitivity of the human eye at either end of its spectral range. Because of cost photography was chosen in preference to a television system. The results confirm the hypothesis that the appearance of a fundal structure depends upon its spectral characteristics. Monochromatism in itself is not clinically useful and blue light and red light are of only limited value. Monochromatic light between 500 nm and 600 mn produces considerable contrast in the fundus picture and offers information additional to the observed in polychromatic light.