Commentary: Pachydrusen: A tell-tale sign of pachychoroid phenotype.

The pachychoroid phenotype encompasses changes in morphology of choroid which are physiological as well as pathological. The clinical characteristics of pachychoroid phenotype are reduced choroidal vascular markings in fundus, drusenoid retinal pigment epithelium (RPE) changes, and small pigment epithelium detachments.[1] These eyes have increased thickness of choroid on optical coherence tomography (OCT) and choroidal hyperpermeability on indocyanine green angiography.[1] Identifying such eyes is utmost important because they are prone to develop central serous chorioretinopathy (CSC), polypoidal choroidal vasculopathy, and sub-RPE neovascularization.[12] Initially, a thick (pachy) choroid was considered as the cornerstone of pachychoroid phenotype which was defined as subfoveal choroidal thickness of >300 micron or extrafoveal focus of thick choroid exceeding subfoveal choroidal thickness by 50 micron or more.[3] With the evolution of our knowledge about pachychoroid, it is now believed that the total thickness of choroid was not the sole criterion to define pachychoroid phenotype and eyes with choroidal thickness less than 300 micron too could manifest pathological changes of diseases associated with pachychoroid. Cheung CMG et al. described that eyes with increased thickness of choroidal Haller's layer (pachy-vessel) and compression of overlying Sattler's layer and choriocapillaris develop changes in the RPE and were to be considered as pachychoroid phenotype.[4]

The understanding about pachychoroid spectrum of disorders is still evolving. It is obvious that swept-source OCT or spectral domain OCT with enhanced depth imaging was a prerequisite to identify these eyes. However, there are subtle clinical fundus findings, which help clinicians to think about the possibility of dealing with an eye with pachychoroid. Diffuse, focal or multifocal reddish-orange hue of the fundus, reduced choroidal vascular markings, and drusenoid RPE changes on posterior pole on indirect ophthalmoscopy are such signs suggesting a thicker choroid and probably pachychoroid phenotype.[1] Richard Spaide further elucidated the nature of these drusenoid RPE changes and explained them as drusen, which were different from those found in age-related macular degeneration.[5] He coined the term “pachydrusen” to describe drusen in pachychoroid eyes that were large (>125 micron) and were distributed over entire posterior pole, even around the optic disc. Unlike large soft drusen, pachydrusen had well defined and complex margins and could be found in isolation or clusters. Identifying pachydrusen on fundus should be a hint or tell-tale sign of underlying pachychoroid phenotype.

The authors in the published study (citation to be updated) report the prevalence of pachydrusen in CSC as 6.82% which is lower than the previous report from Japan.[67] This variation could be due to demographic and ethnic differences of the study populations. This study carries it value for being the first from India to report the prevalence of pachydrusen in CSC. It is intriguing to note that the authors did not find any significant difference in subfoveal choroidal thickness among CSC eyes with and without pachydrusen because CSC can be seen in eyes with normal choroidal thickness as well. Further they did not find higher choroidal thickness at the site of pachydrusen compared to subfoveal choroidal thickness, which has recently been reported by Baek J et al.[8] In the present study, these findings have been obtained from small number of eyes with pachydrusen (nine out of 132 eyes). However, these findings still point toward a possible role of demographic variation in the choroidal morphology. The present study also reports pachydrusen as a feature of chronic, persistent or resolved CSC and not of acute CSC. It will be interesting to note pachydrusen in eyes with uncomplicated pachychoroid or pachychoroid pigment epitheliopathy which have not developed CSC. Similarly, a longitudinal study of pachydrusen in CSC will be able to shed light on their natural history, their influence on spontaneous resolution of CSC, as well as on the response to treatment.