Retromode Imaging in Age-Related Macular Degeneration

Abstract

Background and Objectives: Retromode is a relatively new retinal-imaging technique that is based on the transillumination principle and is obtained with a scanning laser ophthalmoscope that uses light in the infrared spectrum. The laser light penetrates into the deep retinal layers and the choroid. Retromode images are captured with a laterally displaced aperture, and the detector captures only the scattered light. The result is a high-contrast pseudo-three-dimensional image. Age-related macular degeneration (AMD) is a disabling retinal disease. AMD is characterized in its early stage by small and intermediate drusen formation, while the signs of intermediate AMD are large drusen and/or pigmentary abnormalities. Late AMD has two forms, geographic atrophy, which is the advanced form of dry AMD, and wet AMD. Most of the lesions of AMD are located in the outer layers of the retina. This new imaging method can provide a glimpse of the deep retinal layers' topographic changes in a non-invasive, fast, and effective way that can match the other imaging tools available. Materials and Methods: The literature review was performed by searching the PubMed database using the following combination of keywords: retromode imaging and age-related macular degeneration. Relevant images similar to the ones in the literature were identified and used as models. Results: The purpose of this article is to highlight the utility of incorporating retromode imaging into the multimodal evaluation of the retina in patients with AMD and to gather and integrate these findings into a brief but comprehensive paper. Conclusions: Retromode imaging is a good screening, diagnosis, and monitoring tool for patients with AMD.

Keywords: age-related macular degeneration; multimodal imaging; pseudo-three-dimensional; retromode imaging; scanning laser ophthalmoscope.

Figure 1

Scanning laser ophthalmoscope: three different aperture types: (A) confocal (with a central aperture). (B) retromode (with a laterally deviated aperture to the left or to the right), and, respectively, (C) the ring aperture.

Figure 2

Early AMD. Multimodal imaging of small and medium drusen. (A) Color scanning laser ophthalmoscope photography shows multiple small drusenoid round, yellow deposits. (B) On the fundus autofluorescence, drusen hardly cause any effect. (C) Retromode deviated to right and (D) retromode deviated to left display drusen as small elevations or depressions, respectively. Drusen number and extension are obviously more easily visualized on the retromode images than on the cSLO image. (E) SD-OCT section, which shows drusen as small elevations of the RPE.

Figure 3

Intermediate AMD. (A) Multiple medium and large drusen can be seen on the cSLO image. (B) On green FAF, large drusen appear as hyper-autofluorescent patches. (C) Retromode deviated right depicting elevated, large drusen. (D) Retromode deviated left shows a “moon surface” appearance (zoomed image in the red square). (E,G) En-face OCT showing the location of the section in (F,H) SD-OCT showing multiple small, medium, and large drusen.

Figure 4

(A) On the retromode image DR dot SDDs are round, hyporeflective lesions, and ribbon SDDs are difficult to see. (B) Retromode image DL shows each dot SDD as “hyporeflective core” with a “hyperreflective halo” [24], while the ribbon SDDs tend to have a reticular structure. (C) SD-OCT shows dot SDD (red arrow), ribbon SDDs (yellow arrows), and also a hyper-reflective layer on the retinal surface.

Figure 5

Drusen and dot subretinal drusenoid deposits (SDD) in a patient with co-existent angioid streaks: (A) cSLO showing multiple drusen and SDDs, with peripapillary radiating irregular lines. (B) In green FAF, temporal to the fovea, drusen are seen as hypo- and hyper-autofluorescent round lesions. (C) In retromode deviated right, elevated lesions can be seen, and in (D) retromode deviated left, small, depressed lesions are detected. (E) En face OCT of (F) SD-OCT shows multiple small, medium, large drusen and also dot SDD (red arrow).

Figure 6

Geographic atrophy. (A) cSLO image showing round patches of GA where the choroidal vessels are visible, surrounded by large and medium drusen. (B) Green FAF showing confluent hypo-autofluorescent areas. (C) DR and (D) DL retromode images of GA seen as round patches with homogenous reflectivity where the underlying choroidal vessels are visible. (E) SD-OCT showing RPE and outer retinal atrophy temporal to the fovea (red arrows) with foveal sparing (yellow short arrow). (F) SD-OCT showing large area of RPE and outer retinal atrophy (red arrows).

Figure 6

Geographic atrophy. (A) cSLO image showing round patches of GA where the choroidal vessels are visible, surrounded by large and medium drusen. (B) Green FAF showing confluent hypo-autofluorescent areas. (C) DR and (D) DL retromode images of GA seen as round patches with homogenous reflectivity where the underlying choroidal vessels are visible. (E) SD-OCT showing RPE and outer retinal atrophy temporal to the fovea (red arrows) with foveal sparing (yellow short arrow). (F) SD-OCT showing large area of RPE and outer retinal atrophy (red arrows).

Figure 7

(A) The cSLO shows subfoveal fibrosis surrounded by exudates. (B) Mottled, irregular autofluorescence pattern with a central hypo-autofluorescent core. (C) Retromode DR and (D) Retromode DL images showing large, oval, concave, and, respectively, convex cystoid spaces. (E) Large intraretinal cystoid spaces seen over an area of subretinal fibrosis on SD-OCT.

Figure 8

Multimodal imaging of a full-thickness macular hole (FTMH). (A) cSLO image showing a red central round area. (B) Green FAF showing central hyper-autofluorescence. (C,D) Retromode DR and DR showing a “single round excavation” [55] and the cystoid spaces around it. (E) SD-OCT where the large FTMH is visible.

Figure 9

Epiretinal membrane (ERM). (A) cSLO image showing ERM folds on the retinal surface. (B,C) Retromode DR and DL images represent a characteristic “fingerprint” aspect [56]. (D) SD-OCT showing the irregular hyper-reflective layer on the retinal surface.