OSLI Retina

April 2020

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206 Ophthalmic Surgery, Lasers & Imaging Retina | Healio.com/OSLIRetina Practical Retina Incorporating current trials and technology into clinical practice Pachychoroid Disease by K. Bailey Freund, MD The Greek root word παχύ, or "pachy," means "thick," so the pachychoroid spectrum of dis- eases share a com- mon feature: a thickened choroid. A number of con- ditions have been categorized under the pachychoroid spectrum, includ- ing uncomplicated pachychoroid, cen- tral serous chorio- retinopathy, pachychoroid pigment epitheliopathy, pachychoroid neovas- cularization, aneurysmal type 1 neo- vascularization / polypoidal choroidal vasculopathy, focal choroidal excava- tion, and peripapillary pachychoroid syndrome. However, as our under- standing of this group of conditions has deepened, the focus has shifted to- ward elucidating what may represent a common etiopathogenesis. Improvements in retinal imaging technology over the last decade, par- ticularly in optical coherence tomog- raphy, have allowed greater resolu- tion, quantitation, and understanding of the choroid in both healthy and diseased states. Many factors affect choroidal thickness, including age and axial length; therefore, diagnosis of a pachychoroid spectrum condition often relies more now on identifying large pachyvessels in Haller's layer than the numerical choroidal thick- ness, as well as other clinical findings such as reduced fundus tessellation and visibly dilated choroidal vessels. This installment of Practical Retina benefits from the expertise of K. Bai- ley Freund, MD, from Vitreous Retina Macula Consultants of New York in Manhattan, who has been one of the pioneers in describing this group of conditions and postulating mecha- nisms for a shared etiology. Dr. Freund updates the retina community on the current understanding of the pachy- choroid spectrum of diseases. In 2013, the term "pachychoroid" was introduced by Warrow et al. in a description of patients manifesting retinal pigment epithelium (RPE) disturbances over areas of choroidal thickening in eyes lacking objective findings indicative of prior episodes of subretinal fluid (Figure 1). 1 The authors suggested that pachychoroid pigment epitheliopathy (PPE) might be a forme fruste of central serous chorioretinopathy (CSC). They noted that the findings of PPE resembled those often found in the fellow eyes of patients with unilateral CSC, which included dilated choroidal veins and choroidal vascular hyperpermeability (CVH) seen with indocyanine green angiography (ICGA). 1,2 The majority of eyes had "drusenoid RPE lesions," which, unlike soft drusen seen in typical AMD, had irregular shapes and were usually found as isolated lesions over large choroidal vessels. Although most of their patients had minimal or no visual symptoms and had findings remaining stable over extended follow-up intervals, they often carried more ominous diagnoses such as age-related macular degeneration (AMD), adult-onset pattern dystrophy, punctate inner choroidopathy, and retinal pigment epitheliitis. Warrow et al. suggested that PPE was likely part of a broader spectrum of pachychoroid-related entities and predicted that PPE eyes might subsequently develop type 1 (sub-RPE) macular neo- vascularization (MNV), which could then produce aneurysmal changes commonly known as "polyps." 1 The authors proposed the term "pachychoroid neovascularization" (PNV) to describe type 1 MNV evolving from PPE. They noted that distinguishing PNV from MNV secondary to prior CSC could be challenging. Subse- quent evidence that PNV might evolve from PPE was provided by Pang and Freund. 2 In the intervening years since the original description of PPE, interest in a pachychoroid disease spectrum has grown quickly. A PubMed search using the term "pachychoroid" showed 144 cita- tions, of which 56 were from 2019. Much of the work in refining this disease mechanism has occurred in Asia, where patients with neovascular AMD often lack the soft drusen defining typical AMD but instead have pigmentary abnormalities and choroidal features that are indistinguishable from those of PPE and PNV. 3-8 Recogni- tion that the branching vascular network (BVN) giving rise to the aneurysmal lesions of poypoidal choroidal vasculopathy (PCV) is histologically a form of type 1 MNV led Dansingani et al. to propose the term "aneurysmal type 1 MNV" to describe these neovessels (Figures 2 and 3). 9-11 An obvious conclusion is that many cases of PCV presenting in eyes with pachychoroid disease features evolve from PNV. Given this presumed association, this author currently uses the term "aneurysmal PNV" to describe these findings while using the more generic term "aneurysmal type 1 MNV" to describe K. Bailey Freund doi: 10.3928/23258160-20200326-01 Howard F. Fine Practical Retina Co-Editor

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