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A. Unterhuber, B. Povaay, E. J. Fernandez, B. Hermann, B. Hofer, H. Sattmann, W. Drexler; Ophthalmic Ultrahigh Resolution Optical Coherence Tomography: Eliminating Chromatic Aberration of the Human Eye. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4249.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate improvements in axial resolution and signal to noise for ultrahigh resolution frequency domain optical coherence tomography (UHR-FD-OCT) using spectral bandwidths exceeding 150 nm.
A high speed (up to 25k depth-scans/s) UHR-FD-OCT system has been designed to support 240 nm of spectral bandwidth centred at 800 nm. For illumination a special ultra-broadband Titanium:Sapphire laser based on all chirped specialty mirrors has been set up, emitting 300 nm bandwidth at full width half maximum (FWHM). Chromatic aberrations of the human eye at this wavelength range usually prohibit improvement of axial resolution to levels below 3 µm, which already can be achieved with ~120 nm wide spectral bandwidths. A specially designed optical element has been introduced into the scanning beam path to exactly compensate the chromatic effects of the human eye. The device has been tested in normal human subjects.
Measurements on healthy retinas reveal for the first time that effective axial resolutions better than 3 µm can be achieved in vivo. Although chromatic aberrations are the main limitation for axial resolution improvement precise compensation of high order dispersion had to be performed. Results achieved with the broadband three-dimensional UHR-FD-OCT system depict an effective axial resolution of ~1 µm giving access to finer morphological detail in addition to sensitivity improvements.
Chromatic aberration corrected UHR-OCT employing spectral bandwidths larger than 150 nm does not only improve transversal resolution, but also the effective axial resolution and signal to noise. Correct compensation of these effects leads to tomograms with unprecedented microstructural tissue information. Furthermore employing extremely broad bandwidth might allow the extraction of depth resolved spectroscopic information due to the overlap of absorption features of clinically interesting chromophores (i.e. haemoglobin).
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