OCT Angiography of Retinal Pathologies Using Ultrahigh Speed Swept Source Optical Coherence Tomography

Abstract

 

Purpose

 

We investigate dye-free angiography of the retinal capillary network and choriocapillaris in retinal pathologies using ultrahigh speed swept source OCT (SSOCT).

 

Methods

 

Measurements were performed with an ultrahigh speed SSOCT prototype instrument at 1µm wavelengths with an A-scan rate of 400kHz. Three age-related macular degeneration (AMD) patients without geographic atrophy (GA) and four nonproliferative/proliferative diabetic retinopathy (NPDR/PDR) patients with or without macular edema (DME) were imaged. OCT angiograms were generated by calculating speckle decorrelation between B-scans acquired from the same location. OCT retinal angiograms were generated by projecting all blood vessels above the Bruch’s membrane (BM). OCT choriocapillaris angiograms were generated by extracting an en face plane below the BM.

 

Results

 

Compared to a normal subject (Fig.1(A)), patients with mild NPDR and PDR (Figs.1(B,C)) exhibit capillary dropouts near the foveal avascular zone. The PDR patient also exhibits capillary loops and a sparser capillary density than both the normal and NPDR. Choriocapillaris angiograms require careful interpretation because there is a structural variation dependent on fundus positions (Fig.2(A-C)) as well as between subjects (Fig.2(D,E)). In AMD, there is no obvious correlation between choriocapillaris losses and drusen (Figs.2(F,G)). However, the drusen can be classified according to the cross sectional morphology and RPE integrity. Some drusen show increased light penetration into the RPE, suggesting that the RPE is locally compromised (Fig.2(H,J)). A subset of drusen with increased light penetration also exhibit focal loss of choriocapillaris (Fig.2(I,K)).

 

Conclusions

 

Although more extensive studies are required to definitively identify trends, these pilot investigations demonstrate that OCT angiography using ultrahigh speed SSOCT can reveal additional information on retinal pathologies that is not visible using conventional structural OCT.

 

 

OCT retinal angiograms of (A) a normal subject and (B,C) NPDR and PDR patients. 3mm×3mm field of view.

 

 

OCT choriocapillaris angiograms of (A-C) a normal subject at different fundus locations, (D,E) two normal subjects at the central fovea, and (F) an AMD patient. (G) Intensity fundus projection of the AMD patient in (F). (H,J) Intensity cross-sections and (I,K) angiographic cross-sections extracted from (G) and (F). Scale bars: 500µm.

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 412 age-related macular degeneration • 499 diabetic retinopathy