Abstract

We investigated how near infrared light improves the noninvasive in vivo imaging of features beneath several layers of retinal tissue in the human eye. Decreasing absorption with increasing wavelength by melanin and hemoglobin allows infrared light to image deep layers. We performed two experiments with a scanning laser ophthalmoscope, which produces real-time monochromatic images focused at the test wavelength. First, we studied light scattering in patients and normal observers with 10-50 μW of 830-nm light (Liconix diode laser) with a series of apertures conjugate to the retinal plane. Second, we investigated wavelength effects (790-890 nm) in four subjects with a tunable Ti:sapphire laser (Titan-cw,SEO) that had a Gaussian beam profile and low electronic noise. This laser, when pumped by a 5-W argon laser, emitted 600 mW and 800 nm. Only 10 μW was needed to produce high quality images. With both lasers, many structures were well-visualized at wavelengths longer than 820 nm: the choroidal vessels, subretinal deposits in normal and patient eyes, and macular edema. Features beneath a hemorrhage were readily seen, while features beneath a scar could not be visualized in any conditions with these low-light levels. In some types of pathology, the lateral distribution of scattered light was much wider than normal.

© 1991 Optical Society of America