Electronic ophthalmoscopy functional 4-D imaging of the retina.

摘要

The development of the electronic ophthalmoscope is reviewed from a historical perspective. Since a flying-spot scanning principle for such an ophthalmoscope was first disclosed in 1950, enabling milestones have included the introduction of the laser, inversion of the usual Gullstrand's configuration of optical pupils in 1977, and the application of the optical principle of confocality by means of double or de-scanning in 1983. High resolution and high contrast confocal 790 nm infra-red scanning laser ophthalmoscopy (SLO), in real-time at video rate, is a very non-invasive imaging technique when compared to purely optical techniques of fundus examination. A lateralized dark-field imaging of the retina is obtained when using asymmetrically placed confocal apertures. Diode pumped solid state (DPSS) or He-Ne lasers emitting from 532 nm to 660 nm are used for red and red-free fundus imaging. The diode 790 nm and DPSS 490 nm lasers are also used for fluorescence excitation.;This confocal-gated scanning laser ophthalmoscopy provides a relatively large depth of focus to the image because of the focusing characteristics of Gaussian beams. For optical sectioning of the retina, interference-gated fast spectral domain optical coherence tomography (SD-OCT), also in the infra-red, provides the necessary small depth of focus. When synchronizing SLO and OCT imaging, the SLO video provides the necessary two-dimensional fiducial landmarks in real-time for precise sectional viewing of the retina with OCT over time in the same place, independent of fixational eye movements.;In microperimetry, graphics are created in the laser raster with a fast 80 MHz - 25 ns sub-pixel rise-time or better acousto-optic modulator, Bragg angle optimized for 532 nm to 660 nm wavelengths over a 40 dB attenuation range. The software kernel comprises 4 alternative forced choice (4AFC), parameter estimation by sequential testing (PEST) algorithms, and manual or automated tracking algorithms based on two-dimensional normalized gray-scale correlation. They enable fast and accurate registration of fixation patterns, precise measurements of potential acuities and retinal sensitivity using a wide range of background illumination levels. Opto-electronic characteristics of physiologic significance are discussed. Clinical examples are given in the field of low vision rehabilitation and laser treatment for age-related maculopathy.