Three-Dimensional High Speed OCT at 1050 nm vs. 800 nm: Enhanced Penetration Into Choroidal Tissue and Through Cataracts

Abstract

Purpose:: To determine the advantages of 1050 nm radiation compared with 800 nm ultrahigh resolution optical coherence tomography (OCT) in retinal imaging for eyes with highly scattering eye media such as cataracts.

Methods:: Two high speed (~10 k depth scans/second) 3D-OCT systems were built around broadband light sources operating at central wavelengths of 800 and 1050 nm. Both systems employed the spectrometer based frequency domain (FD) design to support the full bandwidth of the sources (~160 nm and ~70 nm), resulting in effective axial resolutions of ~3 and ~7 µm respectively and comparable sensitivity in normal subjects. Volumetric tomograms of normals and patients with different stages of cataract were taken consecutively with the same protocol by both FD-OCT systems. Image data was post processed and rendered with the same procedures for both systems.

Results:: Results achieved with 3D OCT at 1050 nm reveal for the first time decisive improvements in image quality for patients with clinically significant cataract (i.e. +12 dB improvement at LOCS III: NO1.5 NC1.5 C2.2 P3.0). Furthermore, greater optical penetration was possible using the longer wavelength system, enabling volumetric imaging of the choroidal vasculature in both normal and cataractous eyes. We noted that this deeper level of imaging was also possible in eyes with pathological retinal thickening.

Conclusions:: The lower scattering at 1050 nm significantly improved the imaging performance in cataract patients; thereby widening the clinical applicability of ophthalmic OCT. Additionally the lower susceptibility to scattering at 1050 nm allowed deeper penetration into tissue compared with the conventionally used 800 nm radiation. The use of longer imaging wavelengths should increase the usability of OCT in the early diagnosis of diabetic retinopathy and age related macular degeneration.

Keywords: laser • imaging/image analysis: clinical • cataract