A recent study published in Diagnostics identifies multimodal imaging traits to distinguish primary inflammatory choriocapillaropathies, such as multiple evanescent white dot syndrome and idiopathic multifocal choroiditis, from primary photoreceptoritis.
Inflammatory disorders affect the outer retina through various processes. Some of them are caused by the primary involvement of the outer retina, as in the case of acute zonal outer occult retinopathy. Others indirectly influence the photoreceptors due to the inflammatory involvement of choriocapillaris. Multiple evanescent white dot syndrome and idiopathic multifocal choroiditis destroy the photoreceptors due to the ensuing ischemia. Multimodal imaging makes it possible to distinguish between these two types of outer retinal disorders.
Vulnerability of the Outer Retina
The choriocapillaris is the primary source of oxygen and nutrients for the watershed region of the outer retina. Hypoxemia can readily harm structures such as photoreceptors because these cells have active metabolic processes. Loss of the outer segments of photoreceptors can result from an oxygen shortage, such as that experienced in inflammatory choriocapillaris non-perfusion.
Main Mechanisms of Inflammatory Diseases Damaging the Outer Retina
Inflammatory choriocapillaris non-perfusion (choriocapillaritis), which results in ischemia on the RPE-photoreceptor complex, is one factor that can cause secondary damage to photoreceptors. Indocyanine green angiography is the gold standard for identifying primary inflammatory choriocapillaropathies and detecting even the slightest choriocapillaris non-perfusion. From one choriocapillaritis to another, the degree of damage can differ significantly. Multiple evanescent white dot syndrome and idiopathic multifocal choroiditis are choriocapillaritis entities that share a relatively severe involvement of the choriocapillaris.
In contrast to idiopathic multifocal choroiditis, where the vessel closure is more proximal and the choriocapillary non-perfusion areas are slightly larger, resulting in chorioretinal scars due to RPE damage, multiple evanescent white dot syndrome produces less ischemia which allows photoreceptors to recover more quickly.
Due to the high variability and wide range of severity other choriocapillaritis entities, such as acute posterior multifocal placoid pigment epitheliopathy/acute multifocal choriocapillaritis are less suitable for determining the nature of the lesion processes by multimodal imaging.
One disease that results in primary photoreceptoritis is acute zonal outer occult retinopathy (AZOOR). Given that corticosteroids are effective in treatment, inflammatory variables undoubtedly play a part. Anti-retinal antibodies have been found in some patients, leading to the degenerative theory. Classed choriocapillaritis and primary photoreceptoritis are challenging to identify. Multimodal imaging has made it possible to separate the mechanisms involved in outer retinal disorders.
Investigation of Inflammatory Disorders to the Outer Retina by Multimodal Imaging
Inflammatory disorders to the outer retina have been misunderstood in the past. These diseases have been subjected to an in-depth investigation by developing multimodal imaging. The choriocapillaritis entities have been characterized, although there are still some opposing perspectives regarding multiple evanescent white dot syndrome. Depending on the size of the choriocapillaris arteries engaged in the process, these ailments are caused by choriocapillaris non-perfusion of varying severity and extension.
Multiple evanescent white dot syndrome involves small end-capillary low-flow capillaries that OCT-A cannot detect. Idiopathic multifocal manifests similarly, but the lesions are longer, resulting in smaller chorioretinal scars. The first period of idiopathic multifocal resembles multiple evanescent white dot syndrome. The sequence of events and the role of ischaemia have been thoroughly investigated experimentally by Papasavvas et al.
Impaired glucose uptake in photoreceptors owing to ischaemia or other factors hinders the outer segment's renewal and rod photoreceptors' survival. On the other hand, primary photoreceptoritis is caused by inflammatory factors. The photoreceptor is directly affronted as part of the procedure. A typical symptom of AZOOR is primary photoreceptoritis.
Patients and Methods Examined in this Research
In this retrospective investigation, patients with inflammatory outer retinal pathology, including multiple evanescent white dot syndrome, idiopathic multifocal choroiditis and acute zonal outer occult retinopathy were examined by multimodal imaging and had been examined in the Centre for Ophthalmic Specialized care from 2012 to 2018 were included. Patients with poor image quality or incomplete multimodal imaging were disqualified. Fundus photography, fluorescein angiography (FA), indocyanine green angiography (ICGA), and spectral domain optical coherence tomography were all used in the imaging study (SD-OCT). Investigations did not include information on the course of treatment or progression, they primarily focused on multimodal imaging results.
ICGA capable of detecting choriocapillary non-perfusion is no longer used in many multimodal imaging investigations. As a result, it is impossible to distinguish between choriocapillaritis and photoreceptoritis. This is also the cause of the incorrect classification of multiple evanescent white dot syndrome as photoreceptoritis. Multimodal imagindistinguisheshs the pathophysiology of disorders affecting the outer retina more precisely. ICGA is the distinguishing imaging technique that differentiates photoreceptoritis and choriocapillaritis.
Papasavvas, I., Mantovani, A., & Herbort, C. P. (2022). Diagnosis, Mechanisms, and Differentiation of Inflammatory Diseases of the Outer Retina: Photoreceptoritis versus Choriocapillaritis; A Multimodal Imaging Perspective. Diagnostics, 12(9), 2179. https://www.mdpi.com/2075-4418/12/9/2179/htm