Age-related macular degeneration (AMD) is the most common cause of severe and irreversible vision loss in the elderly population in industrialized countries.
1–5 The neovascular form of AMD (nAMD) is characterized by the development of marked degrees of retinal edema, sub- or intraretinal fluid, hemorrhage, and/ or fibrous scarring, if left untreated.
6 Since the introduction of anti-VEGF agents, the visual prognosis of patients with nAMD has improved drastically.
7–10 The pivotal phase III studies testing the efficacy of intravitreal ranibizumab as treatment for nAMD have shown that monthly injections over the course of 2 years can halt disease progression in most patients.
10–12 Nevertheless, morphologic changes are also noted under therapy, and visual function demonstrates a huge variability between patients. In addition, simply due to the large number of patients, monthly injections appear to be difficult to implement in clinical practice for both logistical as well as economical reasons. Even though intravitreal injections are a safe procedure, every injection bears the risk of endophthalmitis; moreover, monthly administration of anti-VEGF agents is cost-intensive and was found to be associated with progressive geographic atrophy.
13,14 Flexible regimens rely on specified retreatment criteria, including changes in best corrected visual acuity (BCVA), as well as leakage in fluorescein angiography (FA), morphologic findings in optical coherence tomography (OCT), and/or in ophthalmologic fundus examination.
15 Recently, OCT has become a valuable, if not the most valuable tool in the diagnosis and monitoring of patients with nAMD.
8,16,17 The role of morphological OCT parameters for visual function is currently being discussed very controversially.
In various pharmaceutical studies, as well as in clinical practice, a reduction in central retinal thickness (CRT) was considered a therapeutic success even though it has been shown that a decrease in retinal thickness is not necessarily related to superior retinal function. The dissociation between CRT and BCVA highlights the need for OCT parameters, which better indicate the functional success of therapy.
9,18,19 Some authors have identified structural changes relevant for visual function based on the analysis of time-domain OCT (TD-OCT) scans.
13,20–22 Since spectral-domain OCT (SD-OCT) has largely replaced TD-OCT due to better image quality and faster imaging speed, a more detailed analysis of the retinal microstructure has become available.
23–26 Despite an abundant offer of morphologic features in the clinical management of patients, however, the diagnostic “view” of the treating ophthalmologist alone is rather inconsistent and substantial inconsistencies were noted even between retina experts.
27 Solid and quantitative automated algorithms and procedures are more promising to provide fast and reliable insights into structure-function correlations.
In this prospective study, the influence of ranibizumab therapy on the foveal microstructure has been investigated using a quantitative analysis of SD-OCT scans through the entire fovea of treated individuals over a continuous 2-year follow-up period. The foveal center was analyzed systematically in this study for two reasons: first, the foveal center is the most important retinal area for distance visual acuity and, second, an automated algorithm for an evaluation of the retinal microstructure is more likely to be technically feasible and clinically implementable in a smaller section of the central retina.
28,29 Attention has been directed to lesions of the external limiting membrane (ELM) and the ellipsoid zone (EZ) (formerly known as the boundary between the inner and the outer segments)
30 of the photoreceptors, as both of these lines have been shown to reflect photoreceptor function and may explain distinct recovery patterns of visual acuity.
31–36 Other OCT features typical of nAMD, like the presence of subretinal fluid (SRF), retinal pigment epithelium detachment (PED), drusen, intraretinal cysts, subretinal mass, and subretinal pigment epithelium mass were also evaluated in this study.