Swept-source optical coherence tomography angiography features of sub-retinal fibrosis in neovascular age-related macular degeneration

Subretinal fibrosis secondary to neovascular age-related macular degeneration: mechanisms and potential therapeutic targets

Subretinal fibrosis is the end-stage sequelae of neovascular age-related macular degeneration. It causes local damage to photoreceptors, retinal pigment epithelium, and choroidal vessels, which leads to permanent central vision loss of patients with neovascular age-related macular degeneration. The pathogenesis of subretinal fibrosis is complex, and the underlying mechanisms are largely unknown. Therefore, there are no effective treatment options. A thorough understanding of the pathogenesis of subretinal fibrosis and its related mechanisms is important to elucidate its complications and explore potential treatments. The current article reviews several aspects of subretinal fibrosis, including the current understanding on the relationship between neovascular age-related macular degeneration and subretinal fibrosis; multimodal imaging techniques for subretinal fibrosis; animal models for studying subretinal fibrosis; cellular and non-cellular constituents of subretinal fibrosis; pathophysiological mechanisms involved in subretinal fibrosis, such as aging, infiltration of macrophages, different sources of mesenchymal transition to myofibroblast, and activation of complement system and immune cells; and several key molecules and signaling pathways participating in the pathogenesis of subretinal fibrosis, such as vascular endothelial growth factor, connective tissue growth factor, fibroblast growth factor 2, platelet-derived growth factor and platelet-derived growth factor receptor-β, transforming growth factor-β signaling pathway, Wnt signaling pathway, and the axis of heat shock protein 70-Toll-like receptors 2/4-interleukin-10. This review will improve the understanding of the pathogenesis of subretinal fibrosis, allow the discovery of molecular targets, and explore potential treatments for the management of subretinal fibrosis.

Subretinal hyperreflective material in regions of atrophy and fibrosis in eyes with neovascular age-related macular degeneration

BACKGROUND

Subretinal hyperreflective material (SHRM) is a significant biomarker for poor visual outcomes in neovascular age-related macular degeneration (nAMD); however, its relationship with fibrosis and atrophy is not well understood. This study aims to evaluate the relationship between SHRM, atrophy, and fibrosis in eyes receiving antivascular endothelial growth factor therapy for nAMD.

METHODS

Post-hoc analysis of the 65 patients enrolled in the SEVEN-UP study, a multicenter cross-sectional study of patients originally enrolled in the ANCHOR and MARINA trials of ranibizumab. Color fundus photographs (CFP) were reviewed and manually segmented to define regions of atrophy and fibrosis. SHRM borders on OCT volume scans were manually delineated, and thickness measurements were computed and compared in corresponding regions of atrophy and fibrosis on the CFPs.

RESULTS

Of the 65 subjects, 51 eyes showed atrophy and/or fibrosis on CFP and were included in the final analysis. Both atrophy and fibrosis regions exhibited SHRM on OCT. The mean SHRM thickness on OCT was significantly greater in CFP-fibrosis regions (44.19 ± 46.95 μm) compared with CFP-atrophy regions (14.28 ± 13.35 μm; p < 0.001). Additionally, the average maximum height of SHRM in fibrotic regions (268.04 ± 130.05 μm) was significantly thicker than in atrophic regions (121.95 ± 51.17 μm; p < 0.001).

CONCLUSIONS

Although atrophy and fibrosis are thought to be different end-stage outcomes in eyes with nAMD, they both demonstrate SHRM on OCT; the main distinction being thickness. Given these similarities, these regions of nAMD-associated atrophy may be better-termed "atrosis" to distinguish these lesions from typical atrophy in the absence of neovascular disease.

Fibrosis in neovascular age-related macular degeneration: A review of definitions based on clinical imaging

Despite the success of antiangiogenic therapy in controlling exudation in neovascular age-related macular degeneration (nAMD), the involvement of the outer retina in fibrosis results in gradual vision loss over time. The development of drugs that prevent or ameliorate fibrosis in nAMD requires that it is accurately detected and quantified with reliable endpoints and identification of robust biomarkers. Achievement of such an aim is currently challenging due to the lack of a consensus definition of fibrosis in nAMD. As a first step towards the establishment of a clear definition of fibrosis, we provide an extensive overview of the imaging modalities and criteria used to characterize fibrosis in nAMD. We observed variety in the selection of individual and combinations of imaging modalities, and criteria for detection. We also observed heterogeneity in classification systems and severity scales for fibrosis. The most commonly used imaging modalities were color fundus photography, fluorescein angiography and optical coherence tomography (OCT). A multimodal approach was frequently utilized. Our review suggests that OCT offers a more detailed, objective and sensitive characterization than color fundus photography/fluorescein angiography. Thus, we recommend it as a primary modality for fibrosis evaluation. This review provides a basis for future discussions to reach a consensus definition using standardized terms based on a detailed characterization of fibrosis, its presence and evolution, and taking into consideration impact on visual function. Achieving this goal is of paramount importance for the development of antifibrotic therapies.

Molecular mechanisms of TGFβ-mediated EMT of retinal pigment epithelium in subretinal fibrosis of age-related macular degeneration

Age-related macular degeneration (AMD) is one of the leading causes of blindness in the elderly, affecting the macula of the retina and resulting in vision loss. There are two types of AMD, wet and dry, both of which cause visual impairment. Wet AMD is called neovascular AMD (nAMD) and is characterized by the formation of choroidal neovascular vessels (CNVs) in the macula. nAMD can be treated with intravitreal injections of vascular endothelial growth factor (VEGF) inhibitors, which help improve vision. However, approximately half the patients do not achieve satisfactory results. Subretinal fibrosis often develops late in nAMD, leading to irreversible photoreceptor degeneration and contributing to visual loss. Currently, no treatment exists for subretinal fibrosis, and the molecular mechanisms of fibrous tissue formation following neovascular lesions remain unclear. In this review, we describe the clinical features and molecular mechanisms of macular fibrosis secondary to nAMD. Myofibroblasts play an essential role in the development of fibrosis. This review summarizes the latest findings on the clinical features and cellular and molecular mechanisms of the pathogenesis of subretinal fibrosis in nAMD and discusses the potential therapeutic strategies to control subretinal fibrosis in the future.

Review of Fibrosis in Neovascular Age-Related Macular Degeneration

PURPOSE

To report the diagnosis and definitions, epidemiology, risk factors, and visual outcomes of fibrosis in neovascular age-related macular degeneration (nAMD).

DESIGN

Systematic review and meta-analysis.

METHODS

The review was performed using the Cochrane Handbook and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Observational studies and randomized controlled trials were included.

RESULTS

Identification of fibrosis is challenging. Optical coherence tomography angiography and polarization-sensitive optical coherence tomography represent novel options in multimodal imaging. The prevalence of fibrosis at baseline, 12, 24, and 60 months was 13%, 32%, 36%, and 56%, respectively. Approximately 60% of the fibrosis burden in nAMD at 5 years was present in the first year of treatment. Fibrosis development was highest in the first 12 months and slowed down over time. The risk factors of fibrosis included classic choroidal neovascularization (CNV), intra-retinal fluid, hemorrhage, hyperreflective material, CNV lesion size, and retinal thickness. Sub-retinal fluid and pigment epithelial detachment may be protective. Treatment-associated factors included disease activity and time to diagnosis. At baseline, the best corrected visual acuity in eyes with fibrosis was poorer than in eyes without fibrosis (-18.50 letters); this difference became larger at 12 months despite treatment (-26.86 letters).

CONCLUSIONS

There is a need to identify effective treatment strategies for fibrosis and to closely monitor at-risk patients. More studies involving multimodal imaging are required to clarify the definitions and grading criteria for fibrosis.

Towards a better understanding of non-exudative choroidal and macular neovascularization

Non-exudative macular and choroidal neovascularization (MNV and CNV) usually refers to the entity of treatment-naïve type 1 neovascularization in the absence of associated signs of exudation. Histopathological studies, dating back in the early 70s, identified the presence of non-exudative MNV, but the first clinical report of this finding was in the late 90s using indocyanine green angiography in eyes with age-related macular degeneration (AMD). With more advanced retinal imaging, there has been an ever increasing appreciation of non-exudative MNV associated with AMD and CNV with other macular disorders. However, consensus regarding the exact definition and the clinical management of this entity is lacking. Furthermore, there may be variation in the imaging features and clinical course suggesting that a spectrum of disease may exist. Herein, we review the large body of published work that has provided a better understanding of non-exudative MNV and CNV in the last decade. The prevalence, multimodal imaging features, clinical course, and response to treatment are discussed to elucidate further key insights about this entity. Based on these observations, this review also proposes a new theory about the origin and course of different sub-types of non-exudative MNV/CNV which can have different etiologies and pathways according to the clinical context of disease.

Optical Coherence Tomography Angiography in Intermediate and Late Age-Related Macular Degeneration: Review of Current Technical Aspects and Applications

Optical coherence tomography angiography (OCTA) is a non-invasive diagnostic instrument that has become indispensable for the management of age-related macular degeneration (AMD). OCTA allows quickly visualizing retinal and choroidal microvasculature, and in the last years, its use has increased in clinical practice as well as for research into the pathophysiology of AMD. This review provides a discussion of new technology and application of OCTA in intermediate and late AMD.