Enhanced visualization of choroidal vessels using ultrahigh resolution ophthalmic OCT at 1050 nm

Abstract

In this article the ability of ultrahigh resolution ophthalmic optical coherence tomography (OCT) to image small choroidal blood vessels below the highly reflective and absorbing retinal pigment epithelium is demonstrated for the first time. A new light source (lambdac= 1050 nm, Deltalambda = 165 nm, Pout= 10 mW), based on a photonic crystal fiber pumped by a compact, self-starting Ti:Al2O3 laser has therefore been developed. Ex-vivo ultrahigh resolution OCT images of freshly excised pig retinas acquired with this light source demonstrate enhanced penetration into the choroid and better visualization of choroidal vessels as compared to tomograms acquired with a state-of-the art Ti:Al2O3 laser (Femtolasers Compact Pro, lc= 780 nm, Deltalambda= 160 nm, Pout= 400 mW), normally used in clinical studies for in vivo ultrahigh resolution ophthalmic OCT imaging. These results were also compared with retinal tomograms acquired with a novel, spectrally broadened fiber laser (MenloSystems, lambdac= 1350 nm, Deltalambda= 470 nm, Pout = 4 mW) permitting even greater penetration in the choroid. Due to high water absorption at longer wavelengths retinal OCT imaging at ~1300 nm may find applications in animal ophthalmic studies. Detection and follow-up of choroidal neovascularization improves early diagnosis of many retinal pathologies, e.g. age-related macular degeneration or diabetic retinopathy and can aid development of novel therapy approaches.

Optical coherence tomography today: speed, contrast, and multimodality

“…Those wavelengths experience less scattering than the ones at 800 nm, allowing, therefore, for better contrast in deeper tissue layers. 144,145 In ophthalmology, it is of increasing interest to achieve better contrast for choroidal structures that lie below the strongly scattering pigment epithelium [ Fig. 4(d)].…”

Optical coherence tomography—current technology and applications in clinical and biomedical research

“…However, these long wavelengths are not suited for probing the posterior eye segment in vivo due to strong signal attenuation in the vitreous which mainly consists of water. Hence, the 800 nm range exhibiting very low water absorption is commonly used for retinal imaging [52]. For deep penetration into the subretinal layers, the 1050 nm band provides the best trade-off between these factors [52], while at the same time featuring minimal chromatic dispersion in water [53].…”

“…For this special purpose, the 1050 nm band is interesting, since it exhibits a local minimum of absorption and vanishing chromatic dispersion in water. Since Považay et al demonstrated the potential for deep penetration into the choroid in 2003 [52], a growing number of studies makes use of the 1050 nm range [171,172]. Depending on the diagnostic value of choroid images, 1050 nm OCT may become an additional standard tool for ophthalmology.…”

Cellular Level Imaging of the Retina Using Optical Coherence Tomography

“…This wavelength regime is of interest since the absorption of melanin in RPE decreases with wavelength, therefore imaging with wavelengths greater than 800 nm should allow for better imaging of the choroid below the RPE layer. In a study by Povazay et al, (2003) a Ti:Sapph laser was launched into a PCF generating a supercontinuum source from 400 to 1200 nm which was then passed through long pass filter, resulting in a spectrum with a 165 nm bandwidth centered around 1050 nm . OCT images of ex-vivo pig retina were acquired and also compared with OCT images using a 165 nm bandwidth Ti:Sapph laser at 800 nm .…”