Date Published: April 9, 2019
Publisher: Public Library of Science
Author(s): Marco Pellegrini, Mariano Cozzi, Giovanni Staurenghi, Federico Corvi, Demetrios G. Vavvas.
To compare swept source OCTA device, with and without the extended field imaging (EFI) technique, to standard fluorescein angiography (FA) in the clinical practice.
Consecutive patients with vascular disorder patients underwent FA with 55-degree lens (Spectralis Heidelberg Engineering, Heidelberg, Germany) and OCTA with the prototype PlexElite (Carl Zeiss Meditec, Dublin, CA) using a 12 mm x 12 mm volume scan pattern centered on the fovea and a prototype of + 20.00-diopter designed specifically by Zeiss. The imaging methods were compared for visible field of view, extension of non-perfused areas, presence and number of neovessels, vessel density (VD) and fractal dimension (FD).
Forty-three eyes of 27 patients were included. The mean extension ratio of EFI SS-OCTA compared to SS-OCTA without EFI and FA were 1.97 ± 0.02 and 0.85 ± 0.01. The mean extension of non-perfused areas with EFI SS-OCTA (34.22 ± 33.4 mm2) was significantly higher than SS-OCTA without EFI (20.46 ± 18.70 mm2), and with FA (27.55 ± 4.4 mm2). The mean VD and FD of EFI SS-OCTA were significantly different compared to SS-OCT without EFI.
EFI SS-OCTA captured larger areas than SS-OCTA without EFI and FA. OCTA in a single shot is able to obtain more information of the retina without the use of montage techniques. Despite the determination of retinal ischemia seems to be easier and more accurate using EFI SS-OCTA, FA offers more details of the perfusion status of the retina.
In clinical practice the gold standard for the evaluation of retinal perfusion and neovascularization is fluorescein angiography (FA) . It is based on the intravenous injection of fluorescein dye followed by images acquisition. However, FA has several limitations including possible side effects ranging from nausea, vomiting, yellow pigmentation to severe anaphylactoid reactions . Moreover, it produces only two-dimensional images in which fluorescence signals of the superficial and deep capillary networks overlap and are difficult to distinguish, even more when the dye leaks [1,3].
This study was approved by the Luigi Sacco Hospital Ethics Committee in Milan. A written informed consent was obtained from all subjects. The study followed the tenets of the Declaration of Helsinki for research involving human subjects. Consecutive patients with vascular disorder presenting to the Eye Clinic, Department of Biomedical and Clinical Sciences, Luigi Sacco Hospital, University of Milan from September 15th 2017 to March 15th 2018 were prospectively included. Inclusion criteria were age ≥ 18 years old and the presence of either retinal or choroidal vascular disorders. Subjects with significant media opacities and poor cooperation were excluded from the study. All subjects underwent a complete ophthalmic examination, including a detailed medical history, refraction, intraocular pressure measurement, anterior segment and dilated fundus examination and FA performed using the 55-degree lens (Spectralis Heidelberg Engineering, Heidelberg, Germany). The same day, OCTA imaging was performed using the PlexElite (Version 126.96.36.19930, Carl Zeiss Meditec, Dublin, CA). An expert operator (MC) performed all the examinations using a 12 mm x 12 mm volume scan pattern centered on the fovea and using a + 20.00-diopter add-on prototype lens designed specifically by Zeiss to perform EFI examination and to avoid the positional instability of the lens. Following each examination, images were deemed acceptable if the retinal vessels were clearly visible and distinguishable.
A total of 43 eyes of 27 patients (age, 61.3±14.4 years; 17 male and 10 female) were included in this study; 5 eyes of 4 patients were excluded due to image artefacts related to poor fixation. Thirty-two eyes (74%) were affected by diabetic retinopathy, 8 (19%) by retinal vein occlusion, 2 (5%) by retinal vein occlusion secondary to radiation retinopathy and 1 (2%) by Coat’s disease. Twenty-five eyes (58%) were treatment naïve whereas 18 (42%) underwent previous treatments including laser photocoagulation or with anti-vascular endothelial growth factor (VEGF) injections in the previous 6 months. The mean BCVA was 20/40 (range, 20/200 to 20/20) (Table 1) (S1 File).
OCTA is a recent imaging technique that allows qualitative and quantitative assessment of retinal and choroidal vessels in a limited area using computer-generated algorithms to determine blood flow [4,5]. One of the main deficiencies of this imaging technique is related to its limited field of view suggesting a primary application to disorders affecting the macular region. However, previous reports have documented the possibility of using additional convex lenses to increase the examination field of view (EFI technique) .