Differential imaging in scanning laser ophthalmoscopy.

Differential imaging may be useful for understanding pathologies of the choroid. We use a prototype scanning laser ophthalmoscope capable of simultaneous multiple wavelength imaging to record fundus images. The advantages of simultaneous acquisition compared to serial acquisition are, reduced image capture times, and image registration is not required. The system is run under non-confocal conditions in using slit apertures with a width of up to 600 microm. The laser lines launched into the SLO were the 633 nm line of a HeNe- laser, and the 815 nm line from a tunable (740 nm to 840 nm) cw Ti:Sapphire-laser. The difference in absorption at these two wavelengths is used to produce a differential image. We compare conventional imaging with differential spectral imaging for viewing the choroidal vessels. Qualitative results show the contrast of choroidal vessels in differential imaging is improved compared with normal imaging in the region of the optic disk and for the level of pigmentation in the subjects examined.