Fig. 7.1
SS-OCT B-scan of a patient with early age-related macular degeneration. Hard drusen are extracellular deposits located in the space between the elevated RPE and Bruch’s membrane. The protrusions of the RPE into the retina on SS-OCT appear as well-defined and usually smaller than a retinal vein’s width (<63 μm). The contents are sometimes moderately reflective (a). Longer-wavelength, SS-OCT allow for higher tissue penetration with image-quality loss, which allows us to see below the RPE. In the image, clearly defined Bruch’s membrane (red arrow) (b)
Fig. 7.2
SS-OCT B-scan of a patient with intermediate age-related macular degeneration. Soft drusen contents are sometimes moderately reflective and sometimes barely reflective at all (a). Margins are more difficult to identify than in the case of hard drusen (b), and separation between RPE and Bruch’s membrane becomes clearer
7.2.1 Basal Laminar Drusen (Cuticular Drusen)
Basal laminar drusen appear as multiple small yellow lesions in the macular area, growing from the Bruch’s membrane showing a continuous nodular display. They tend to appear in relatively young adults. Pseudovitelliform macular detachments have been related to this type of drusen. On OCT B-scans they show a particular pattern that Leng et al. described as sawtooth pattern [24]. These authors also state the RPE overlying these lesions may suffer modifications leading to attenuation or increase of the OCT signal of the tissues below, depending on the damage or thickening of the RPE (see Fig. 7.3) [24].
Fig. 7.3
Cuticular drusen. As is the case with typical drusen, these drusen are located beneath the RPE. Cuticular drusen are thought to damage the RPE cells as a result of steep protrusion of drusen into it. These damaged sites exhibit window defects. In typical cases, small, steep protrusions in the RPE known, as “sawtooth,” are visible on SS-OCT
7.2.2 Reticular Pseudodrusen
Reticular pseudodrusen (RPD), easier to identify at first using blue light [25, 26], were described by Arnold and colleagues as a yellowish interlacing network of oval-shaped or roundish lesions, with a diameter of 125–250 mm, which were seen in red-free fundus photography and infrared scanning-laser ophthalmoscopy [27]. RPD have been associated with a higher likelihood of developing neovascular AMD and GA [28, 29]. RPD have been associated with choroidal vascular abnormalities such as the loss of the inner and middle layers of the choroid, subsequently leading to fibrous replacement of choroidal stroma [30]. On SS-OCT they are seen as subretinal accumulation of material typically forming sharp peaks or broader, rounder elevations (see Fig. 7.4) [31].
Fig. 7.4
SS-OCT B-scan of a patient showing reticular pseudodrusen (RPD). RPD are seen as triangular highly reflective deposits on the apical side of RPE, which differs from typical drusen location. RPD are a risk factor of progression to late AMD and for the development of retinal angiomatous proliferation
7.2.3 Pigment Epithelium Detachment (PED)
Pigment epithelium detachment (PED) may appear in the absence of clinically or angiographically detectable CNV. They can be well-defined and contain only serous material. OCT imaging shows a clear detachment between Bruch’s membrane and the RPE, creating an optically empty space. It may also reveal neurosensory retinal detachments that do not necessarily mean there is a CNV present (see Fig. 7.5) [32]. On the other hand, patients may show PED of reflective contents as soft drusen coalesce and grow, forming drusenoid PED. Type I CNV typically grow below the RPE and can lead to a clear detachment between RPE and Bruch’s membrane of irregular hyperreflective content representing fibrovascular tissue (see Fig. 7.6). RPE tears can develop between detached and attached RPE if tangential forces are strong enough. They may appear spontaneously or after laser photocoagulation, photodynamic therapy, or anti-VEGF (vascular endothelial growth factor) intravitreal injections. Age and size of the PED are risk factors for presenting a RPE tear (see Fig. 7.7).
Fig. 7.5
Serous pigment epithelium detachment. The contents of the PED are optically empty and no CNV reflectivity is appreciated. The presence of subretinal fluid (blue arrows) is not necessarily linked to the existence of choroidal neovascularization
Fig. 7.6
SS-OCT B-scan of a patient showing a massive fibrovascular PED. Bruch’s membrane can be clearly seen (red arrows). Migrating RPE cells are seen within the sensory retina (yellow arrow) (a). Subretinal fluid is a frequent finding in the context of fibrovascular PED (blue arrow) (b)
Fig. 7.7
When tangential forces are strong enough, the RPE can suffer a tear (red arrows), leading to a neovascular growth over it and under the neurosensory retina, and visual acuity loss. RPE tear and subretinal fluid (green arrow) (a). RPE tear with intraretinal fluid (blue circle) (b)
7.3 Late AMD
7.3.1 Neovascular AMD
Neovascular AMD is defined by the presence of a choroid neovascularization leading to hemorrhagic or serous complications for patients suffering from this disease. It was classically subcategorized based on fluorescein angiography findings in the original classification by Donald Gass [33], but the advent of new technologies like spectral domain OCT (SD-OCT) led Freund and colleagues to propose a new classification of neovascular AMD based on the location of the CNV in relation to the RPE [34]. The subtype of CNV and its nature are key factors to therapeutic decisions, response, and visual prognosis [22, 34].
7.3.1.1 Type 1
In Type 1, CNV are located underneath the RPE without infiltration of the subretinal space. This kind of CNV was previously classified as occult under Gass’ system (see Fig. 7.8). Theories state its pathogenesis is based on a compensatory response to the hypoxia suffered by the external neurosensory retina, inducing pathological modifications and increasing the size of choroidal vessels [35]. If this is true, destroying theses CNV complexes could be potentially harmful to an already compromised retina leading to RPE atrophies and VA loss. Type 1 CNV shows better visual prognosis than other types of CNV. Maduration of choroid vessels forming the CNV may lead to the appearance of polypoidal dilations leading to polypoidal choroidal vasculopathy (PCV) (see Fig. 7.9) [36].
Fig. 7.8
SS-OCT of the left eye of a patient suffering from type 1 choroidal neovascularization. CNV is confined to the space between RPE and Bruch’s membrane and B-scans reveal an RPE elevation showing hyperreflectivity of the subretinal space due to exudation and hemorrhage, along with intraretinal cysts (green circles). Thanks to its deeper penetration, this device allows a clear visualization of Bruch’s membrane (a straight, highly reflective line indicated by red arrow) despite the high density of the CNV tissue (a). B-scan of left eye of another patient showing a type 1 CNV that exhibits moderate reflectivity and is located below the RPE (b)
Fig. 7.9
SS-OCT B-scan of the left eye of a patient diagnosed of polypoidal choroidal vasculopathy. Note the polypoidal lesion nasally to the fovea (red circle), detaching RPE and Bruch’s membrane. A double layer sign describes the parallel appearance of the detached RPE line and this bold line derived from the complex. These kinds of lesions induce the appearance of neurosensory retinal detachments due to the accumulation of subretinal fluid (blue arrow) (a). Moderately reflective contents suggest the presence of fibrovascular tissue (orange circle) (b)
7.3.1.2 Type 2
In Type 2, the CNV complex is located above the RPE in the subretinal space. It matches the previously classified classic CNVs (see Fig. 7.10). Type 2 CNV damages the RPE and alters the ellipsoid line, so the loss of the external blood-retinal barrier leads to much more frequent recurrence. On the other hand, they show better response to treatment. It is the most common type of CNV in patients with fewer diffuse lesions of the RPE and more focused on the macula like pathological myopia, lacquer cracks, and inner punctate choroidopathy. SS-OCT images may show spirals or tubulations of the external retina (see Fig. 7.11). Tubulations are structures encircled by a moderately reflective ring first described by Freund et al. in adjacent areas to atrophic retina, between the CNV and outer plexiform layer.
Fig. 7.10
SS-OCT B-scan of a type 2 CNV. These lesions are located between the RPE and the neurosensory retina (red arrow). Intraretinal cysts (green circle), subretinal fluid (blue arrow) and fibrovascular RPE detachments (orange arrow) are also shown. Another case of type 2 CNV, above the RPE (red arrow) (b). SS-OCT horizontal scan of the right eye: CME accompanied by a large foveal cystoid space (asterisk) exists over the entire macular area. The RPE line is seen over almost the entire length and appears flat on this scan. There are highly reflective clumps above the RPE, which are due to CNV and fibrin
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