Maanasi Mahalingam, M.Optometry
Elite School of Optometry, Units of Medical Research Foundation, India.
Rapid progress in retinal and choroidal imaging techniques has led to visualize the retinal and choroidal microvascular structures in depth both quantitatively and qualitatively. The advent of Enhanced depth imaging (EDI-OCT) and Swept Source Optical Coherence Tomography Angiography (SSOCTA) has enabled a better appreciation of choroidal structures and retinal disorders. One such choroidal finding is pachychoroid. Choroid is composed of three different layers between the Bruch’s membrane and Choroidal-scleral junction. Choriocapillaris, which is the innermost layer and Sattler’s and Haller’s layer, which is composed of small and large blood vessels respectively.(1)
Figure 1 shows the multimodal imaging in a case of pachychoroid pigment epitheliopathy. (a) Colour fundus photo (b) Macular OCT showing focal RPE and choriocapillaris attenuation (black arrows) and pachy vessels (white arrows). (c) FAF (Fundus Autofluorescence) (d) FFA (Fundus Fluorescein Angiography) (e) ICGA.
[Pic Courtesy – Kumawat D. Pachychoroid Spectrum Disorders: A Review of Clinical Features and Management. Delhi J Ophthalmol 2019;30(1)]
Pachychoroid spectrum is a group of diseases with thickened choroid (more than 300 microns) and share a similar pathological mechanism. These diseases manifest as the dilatation of Haller’s layer in the choroid, thereby compressing the overlying Choriocapillaris and Sattler’s layer. (1–3) The clinical manifestations of the spectrum vary considerably among the diseases, but they share the similar morphological features. The entities in the spectrum are pachychoroid pigment epitheliopathy (PPE), central serous chorioretinopathy (CSC), pachychoroid neovasculopathy (PNV) and polypoidal choroidal vasculopathy (PCV).
PPE is the forme fruste of CSC and has RPE (Retinal Pigmented Endothelium) alterations, but without sub retinal fluid. CSC is associated with serous macular detachment, with or without pigment epithelial detachment (PED). PNV is the late complication of CSC and PPE and share common features with CSC and PPE. Along with the common features, PNV eyes show type 1 vascularization below the RPE. PCV is characterized by aneurysmal dilatations seen as orangish red nodules beneath the RPE, along with sub retinal fluid, peaked PED, sub retinal haemorrhage and lipid exudation.(1,4)
There are certain common features in multimodal imaging such as Optical Coherence –
Tomography (OCT), Indocyanine green angiography (ICGA) and Optical Coherence Tomography Angiography (OCTA). In OCT, focal or diffuse choroidal thickening with dilated choroidal vessels is seen. Any choroidal thickness more than 300 microns is pachychoroid.4 In ICGA, pachy vessels, choroidal filling defects suggestive of choroidal ischemia along with choroidal hyperpermeability is seen in all the entities. Early phase of ICGA shows delayed arterial filling and late phase shows choroidal vascular hyperpermeability (CVH), which occurs due to leakage from the dysfunctional outer choroidal vessels or choriocapillaris.
|Name of the entity||Clinical features||OCT||ICGA||OCTA|
|1.PPE||Focal foveal/ extrafoveal areas of RPE mottling along with decreased fundus tessellation||Focal RPE alterations with pachy vessels and choriocapillaris attenuation and no SRF.||CVH in the areas of RPE mottling.||No evidence of choroidal NV.|
|2.CSC||Round or oval detachment at the macula with the presence of subretinal fluid||Well defined serous retinal detachment, pigment epithelial detachment and outer retinal atrophy||CVH||No evidence of choroidal NV.|
|3.PNV||Features of PPE and CSC, along with type 1 NV.||Type 1 neovascularization with pachychoroid and shallow irregular RPE detachment.||CVH||Type 1 NV is represented as a tangled network.|
|4.PCV||Orangish red nodules beneath the RPE with multiple recurrent serosanguineous retinal and RPE detachments.||Type 1 NV with aneurysmal dilatations, thumb shaped PED and double layer sign.||CVH with branched vascular network and aneurysmal dilatations||BVN corresponding to double layer sign and polypoidal lesions.|
Table 1: Multimodal imaging of pachychoroid spectrum.(5,6)
PPE – Pachychoroid Pigment Epitheliopathy, CSC – Central Serous Chorioretinopathy, PNV- Pachychoroid Neovasculopathy, PCV – Polypoidal choroidal Vasculopathy, CVH – Choroidal Vascular Hyperpermeability, NV – Neovascularization, BVN – Branched Vascular Network.
Since most of the disease in this spectrum share similarities, they also have unique features associated with them. Multimodal imaging plays a mandatory role in diagnosing and differentiating the unique features of each disease. Thus, earlier recognition of the disease in this spectrum is important, as they mimic other diagnosis in the natural course and treatment.
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