Commentary: Double-layer sign" on spectral domain optical coherence tomography in pachychoroid spectrum disease.

Sir,

We would like to congratulate Sheth et al for their work on “Double-layer sign” on spectral domain optical coherence tomography in pachychoroid spectrum disease.[1] Double-layer sign (DLS) is an optical coherence tomography (OCT) finding, which is produced due to the shallow irregular pigment epithelial detachment. The upper hyper reflective band of the double layer is of the retinal pigment epithelium (RPE) and the bottom band is of the Bruch's membrane (BM). This finding was first reported in eyes with polypoidal choroidal vasculopathy (PCV) and later in eyes with age-related macular degeneration, central serous chorioretinopathy (CSCR), and high myopia.

On cross-sectional OCT, the space within the DLS could be hypo- or hyperreflective. DLS with internal hyporeflectivity are usually avascular. The DLS with internal hyperreflectivity may harbour early type 1 choroidal neovascularisation (CNV).[2] However, not all low-lying Pigment Epithelial Detachments (PEDs) with internal hyperreflectivity contain type 1 CNV. Differentiating such vascularized and nonvascularized low-lying PEDs becomes difficult on conventional imaging. OCT angiography has been found to be a more sensitive tool in identifying the internal vascularity of these shallow PEDs [Fig. 1] when compared with conventional angiography.[3] Correct segmentation using RPE fit, between RPE and BM, is required for the complete visualisation of the network.

Figure 1

(a) Optical coherence tomography of right eye of a patient with chronic central serous chorioretinopathy demonstrating a double layer sign with internal hyperreflectivity. (b) Optical coherence tomography angiogram at the level of outer retina delineating the vascularity within the double-layer sign. (c) The fellow eye of the same patient of central serous chorioretinopathy with hyporeflectant double layer. (d) Optical coherence tomography angiogram does not show any vascularity within the double layer

Eyes with chronic CSCR tend to have flat irregular PEDs. With the advent of OCT angiography, the detection of CNV in such eyes has increased significantly (up to 35%) compared with previous imaging modalities. The presence of neovascularisation may warrant additional anti-VEGF therapy.

Pachychoroid neovasculopathy (PNV)[4] is an entity that comprises of choroidal neovascularisation when associated with thick choroid along with relative absence of drusen. This is considered as a part of the “pachychoroid spectrum,” which also includes pachychoroid pigment epitheliopathy, CSCR and PCV. Chronic CSCR may secondarily develop type 1 neovascularisation, in which case they may be re-labelled as PNV. Presence of hyperreflective DLS is a must in PNV; however, occurrence of hyperreflective DLS on OCT in chronic CSCR is not uncommon.