Three-dimensional optical coherence tomography at 1050 nm versus 800 nm in retinal pathologies: enhanced performance and choroidal penetration in cataract patients

Abstract

In recent years, frequency domain optical coherence tomography (FD-OCT),^{1, 2, 3, 4, 5, 6} also referred to as spectral or Fourier domain OCT, has proven to combine high speed and ultrahigh resolution imaging.^{7, 8, 9} High-speed, frequency-domain-based optical coherence tomography ophthalmic imaging systems are commonly designed to operate around $800\mathrm{nm}$ , which allows for several thousand depth scans per second for three-dimensional (3-D) in vivo imaging of the human retina with retinal pathologies.^{10, 11} In FD-OCT, the interference pattern in the optical frequency spectrum is analyzed to provide both high-sensitivity and high-speed, depth-resolved measurements of the human retina. Time domain (TD) standard^{12, 13, 14} and ultrahigh resolution OCT^{15, 16, 17} have already demonstrated their clinical value as a noncontact diagnostic tool for the evaluation of retinal diseases by providing virtual sections of the retina at high axial resolution. While these techniques have achieved notable successes, they are limited by relatively low signal-to-noise ratios (SNR) and therefore long data acquisition times that make them unsuitable for 3-D retinal imaging. By contrast, high-speed FD-OCT, either in its time-encoded form with high-speed spectrally swept sources and a single detector,^{4, 6} or spatially encoded using broadband sources and a spectrometer, is widely expected to revolutionize clinical OCT-based retinal imaging. At present, standard resolution ophthalmic OCT sources commonly operate using $800\mathrm{nm}$ light sources with up to $30\mathrm{nm}$ bandwidth and $\sim 10\mu \mathrm{m}$ axial resolution.^{12, 13, 14} Ultrahigh resolution ophthalmic OCT systems operate in the $650\text{to}950\mathrm{nm}$ wavelength range, which falls almost completely outside the sensitivity profile of the human eye to visible light but within the transparency region below the $970\mathrm{nm}$ water absorption peak or due to limited availability of appropriate light sources. Although $800\mathrm{nm}$ OCT systems can resolve all major retinal layers, image quality can be severely degraded by abnormal opaque, scattering intraocular media like corneal haze or cataracts. In clinical OCT imaging, cataracts present a significant barrier to the derivation of high-resolution images of the retina. Cataracts degrade the transparency of the lens and remain a major cause of vision loss in both the developed and developing world.¹⁸ Most cataracts are age related, but secondary lens opacities can arise as result of other ocular diseases.