The advances in imaging technology, such as enhanced-depth imaging OCT and swept-source OCT, has allowed us to study the choroid in more detail. In recent years, a group of disorders was found to have the common characteristics of thickened choroid. In these disorders, dilatation of Haller’s layer with compression of adjacent Sattler’s layer and choriocapillaris were observed. This group of disorders was named the pachychoroid disease spectrum. The disease entities within the pachychoroid spectrum all exhibit the characteristic choroidal alternations and are believed to share similar pathogenesis pathways. The major entities described in pachychoroid disease spectrum include central serous chorioretinopathy (CSC), pachychoroid pigment epitheliopathy (PPE), pachychoroid neovasculopathy (PNV), and polypoidal choroidal vasculopathy (PCV). Focal choroidal excavation and peripapillary pachychoroid syndrome were also found to have features of pachychoroid. It is now believed that pachychoroid disease spectrum is a continuum of diseases, where PPE is a forme fruste of CSC and PCV is an aneurysmal dilatation of type 1 choroidal neovascularization standing at the end of the spectrum.

Despite growing interest and research in pachychoroid disease in recent years, many questions remain unsolved. For example, the evolution of disorders in the spectrum, exact pathogenesis, associated risk factors, and mechanism for disease progression are unknown. There is a lack of consensus on the therapeutic approach and treatment modalities (anti-VEGF treatments, photodynamic therapy, subthreshold laser) for different stages of the disease. Therefore, it is important to understand the pathogenesis and natural course of disease in order to guide treatment strategy.

The aim of this Special Issue is to attract research to improve understanding of the development of pachychoroid, further reveal the characteristics, associated conditions, natural course, and connections among different pachychoroid disorders, and determine the most effective treatment for different conditions. Review articles summarizing the latest understanding of the disease and therapeutic strategy with up-to-date evidence are also welcome.

Potential topics include but are not limited to the following:

• Spectrum of clinical entities classified under pachychoroid disease
• Advanced diagnostic methods and techniques
• Characteristics in imaging (e.g. OCT, OCT angiography, fluorescein angiography, indocyanine green angiography, fundus autofluorescence, wide-field images, etc.)
• Microperimetry and electrodiagnostics in different pachychoroid disorders
• Epidemiology among different populations
• Genetics and risk factors for pachychoroid development
• Causes and pathogenesis for pachychoroid development
• Natural history and prognosis of disease
• Therapeutic approaches and outcomes (e.g. anti-VEGF treatment, subthreshold laser treatment, photodynamic therapy etc.)
• Risk factors and mechanism for formation of polypoidal choroidal vasculopathy
• Risk factors and mechanism for development of choroidal neovascularization in central serous chorioretinopathy