Age-related macular degeneration eyes presenting with cuticular drusen and reticular pseudodrusen

Lysolipids are prominent in subretinal drusenoid deposits, a high-risk phenotype in age-related macular degeneration

Introduction

Age related macular degeneration (AMD) causes legal blindness worldwide, with few therapeutic targets in early disease and no treatments for 80% of cases. Extracellular deposits, including drusen and subretinal drusenoid deposits (SDD; also called reticular pseudodrusen), disrupt cone and rod photoreceptor functions and strongly confer risk for advanced disease. Due to the differential cholesterol composition of drusen and SDD, lipid transfer and cycling between photoreceptors and support cells are candidate dysregulated pathways leading to deposit formation. The current study explores this hypothesis through a comprehensive lipid compositional analysis of SDD.

Methods

Histology and transmission electron microscopy were used to characterize the morphology of SDD. Highly sensitive tools of imaging mass spectrometry (IMS) and nano liquid chromatography tandem mass spectrometry (nLC-MS/MS) in positive and negative ion modes were used to spatially map and identify SDD lipids, respectively. An interpretable supervised machine learning approach was utilized to compare the lipid composition of SDD to regions of uninvolved retina across 1873 IMS features and to automatically discern candidate markers for SDD. Immunohistochemistry (IHC) was used to localize secretory phospholipase A2 group 5 (PLA2G5).

Results

Among the 1873 detected features in IMS data, three lipid classes, including lysophosphatidylcholine (LysoPC), lysophosphatidylethanolamine (LysoPE) and lysophosphatidic acid (LysoPA) were observed nearly exclusively in SDD while presumed precursors, including phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidic acid (PA) lipids were detected in SDD and adjacent photoreceptor outer segments. Molecular signals specific to SDD were found in central retina and elsewhere. IHC results indicated abundant PLA2G5 in photoreceptors and retinal pigment epithelium (RPE).

Discussion

The abundance of lysolipids in SDD implicates lipid remodeling or degradation in deposit formation, consistent with ultrastructural evidence of electron dense lipid-containing structures distinct from photoreceptor outer segment disks and immunolocalization of secretory PLA2G5 in photoreceptors and RPE. Further studies are required to understand the role of lipid signals observed in and around SDD.

Differentiating drusen and drusenoid deposits subtypes on multimodal imaging and risk of advanced age-related macular degeneration

Drusen are extracellular material considered a precursor lesion to advanced age-related macular degeneration (AMD), located either on the retinal pigment epithelium (RPE) or the sub-RPE; they contain various proteins associated with inflammation and lipids. Previous studies suggest that the lifecycle of drusen varies depending on drusen type and size. In general, conventional drusen grow and aggregate/coalesce in the first stage, and in the second stage, they regress with or without showing RPE atrophy. The risk of advanced AMD also varies depending on the drusen and drusenoid deposit types' along with their size and RPE abnormalities. In eyes with macular neovascularization (MNV), specific drusen/drusenoid deposits are closely associated with the MNV subtype. Recently, pachychoroid-associated drusen (pachydrusen) were proposed and clinical findings regarding this entity have been accumulating, as more attention is focused on drusen as well as pachychoroid diseases. With the advance in imaging modalities, various modalities can show specific characteristics depending on drusen types. To assess the risk of advanced AMD, it is essential for physicians to have accurate clinical knowledge about each druse/drusenoid lesion and correctly evaluate its imaging characteristics using multimodal imaging. This review summarizes the latest clinical knowledge about each druse/drusenoid lesions and documents their imaging characteristics on multimodal imaging, allowing clinicians to better manage patients and stratify the risk of developing advanced AMD. The most representative cases are illustrated, which can be helpful in the differential diagnosis of drusen and drusenoid deposits.

Fluorescence Lifetime and Spectral Characteristics of Subretinal Drusenoid Deposits and Their Predictive Value for Progression of Age-Related Macular Degeneration

Purpose

To measure fundus autofluorescence (FAF) lifetimes and peak emission wavelengths (PEW) of subretinal drusenoid deposits (SDD) in age-related macular degeneration (AMD) and their development over time.

Methods

Fluorescence lifetime imaging ophthalmoscopy (FLIO) was performed in 30 eyes with optical coherence tomography (OCT)-confirmed early or intermediate AMD and SDD. Contrasts of mean lifetimes in short- (SSC) and long-wavelength channels (LSC), PEW, and relative fluorescence intensity were determined as differences of the respective measures at individual SDD and their environment. Measurements were made at baseline and at follow-up intervals 1 (13-36 months) and 2 (37-72 months), respectively.

Results

Of 423 SDD found at baseline, 259, 47, and 117 were hypoautofluorescent, isoautofluorescent, and hyperautofluorescent, respectively. FAF lifetimes of SDD were significantly longer than those of their environment by 14.5 ps (SSC, 95% confidence interval [CI], 13.3-15.7 ps) and 3.9 ps (LSC, 3.1-4.7 ps). PEW was shorter by 1.53 nm (1.07-1.98 nm, all contrasts P < 0.001) with higher contrasts for hyperfluorescent SDD. Over follow-up, SDD tended to hyperautofluorescence (relative intensities increased by 3.4% [95% CI, 2.9%-4.1%; P < 0.001] in follow-up 2). Hyperautofluorescence was associated with disruption of the ellipsoid zone on OCT. Disease progression to late-stage AMD was associated with higher lifetime contrast in SSC (15.9ps [14.2-17.6 ps] vs. 11.7 ps [9.9-13.5 ps], P < 0.001) at baseline.

Conclusions

SDD show longer FAF lifetimes and shorter PEW than their environments. A high lifetime contrast of SDD in SSC might predict disease progression to late-stage AMD.

Enhanced Detection of Reticular Pseudodrusen on Color Fundus Photos by Image Embossing

PURPOSE

To evaluate whether processing a color fundus photo (CFP) using an image embossing technique can improve the detection of reticular pseudodrusen (RPD).

METHODS

This post-hoc analysis included the eyes of subjects enrolled in the Amish Eye Study with early or intermediate age-related macular degeneration and evidence of RPD. All patients underwent CFP, near-infrared reflectance (NIR), and fundus autofluorescence (FAF) imaging. The ground-truth presence of RPD was established with a combination of NIR and FAF imaging. An embossing processed (EP) image was created by replacing each pixel of the CFP image with a highlight or a shadow representing light and dark boundaries in the original CFP image. The presence of RPD in CFP and EP images was assessed by two graders in a masked fashion and the sensitivity of CFP and EP for detection of RPD was evaluated. Cohen's kappa (k) was used to test inter-grader agreement for CFP and EP.

RESULTS

A total of 106 eyes from 62 patients with RPDs were analyzed. The sensitivity for detection of RPD on CFP and EP was 63.2% (95%CI: 52.0%-74.4%) and 91.5% (95%CI: 85.0%-98.0%), respectively. The inter-rater reliabilities of CFP and EP for RPD detection were 0.81 and 0.84, respectively.

CONCLUSIONS

Embossing of CFP can improve the sensitivity for detection of RPD. The embossing technique can be a useful tool for better assessment of the true frequency of RPD in datasets where only CFP images are available.