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Serous PED
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Retinal pigment epithelial detachment (PED) is part of
age-related macular degeneration (AMD) clinical spec-
trum. Different types of PED have been reported in
the literature, related or not with AMD. Serous PED is
defined as an area of sharply demarcated, dome-shaped
serous elevation of the retinal pigment epithelium. In
AMD, serous PED is frequently associated with cho-
roidal neovascularisation (CNV). The presence of this
lesion worsens the prognosis of the disease, preluding to
the formation of a large disciform scar that ends with a
poor visual outcome. Even though no clear therapeutic
indications are so far set for its treatment, the early detec-
tion of a serous PED is therefore important for the prog-
nosis and the management of these patients.
The histopathology of a serous PED is consistent with
the detachment of the RPE basement membrane along
with the overlying retinal pigment epithelium from the
remaining Bruch’s membrane by the accumulation of
fluid
(1)
.
Retinal pigment epithelium (RPE) monolayer is ana-
tomically located between the external retinal layer, the
outer segments apex, and the Bruch’s membrane. RPE
functions, fundamental for the photoreceptors metabo-
lism, include the outer blood-retinal barrier formation
and the fluid exchange balance, that physiologically
flows from the vitreous into the choroid. In normal
conditions, RPE basement membrane is attached to the
inner collagenous layer of Bruch’s membrane. Although
the correct pathology of the serous PED formation is
not completely known, there are some evidences con-
cerning AMD aspects that can at least partially explain
it. In AMD, there are degenerative changes in Bruch’s
membrane that are likely implicated in the adhesion
loss between these two layers and can explain the patho-
genesis of the serous PED. Aging thickening of Bruch’s
membrane, more evident in AMD, has been shown to
be secondary to accumulation of debris and lipids, most
of them phospholipids that greatly decrease its hydraulic
conductivity
(2,3,4)
. Moreover, the localized accumulation
of basal linear deposits between the RPE basement mem-
brane and the outer collagen layer of Bruch’s membrane,
increases the pathologic damage through the drusen for-
mation
(5)
. These two facts significantly combine to bring
about an hydrophobic barrier that prevent the fluid out-
flow towards the choroid, that causes liquid accumula-
tion in the subretinal pigment epithelium space
(6-9)
.
In
AMD, serous PED can be either associated or not with
CNV, although the vascularised sort is by far the most
observed. The formation of soft drusen predispose the
progression to advanced AMD, with the development
of CNV. Various theories concerning the relationship
between serous PED and CNV have been proposed. To
explain its pathogenesis, firstly Gass theorized the growth
of newvessels from the choroid inside the Bruch’s mem-
brane thickness, that actively leak increasing the hydro-
static pressure causing RPE detachment among the less
adherent layers
(10)
.This concept has been later sustained
by the evidence that the development of CNV comes
with inflammatory mechanisms that add more damage
to Bruch’s membrane, supporting RPE separation from
the inner collagenous layer
(11,12,13)
. When the growth of
newvessels arises from the inner retina, more recently
described as retino-choroidal anastomoses (RCA) or
retinal angiomatous proliferation (RAP), it has been
hypothesized that the serous PED formation, very fre-
quently associated, can be reconducted to a RPE inva-
sion by the neovascular complex
(14-16)
. On the contrary,
other authors observed that the presence of a PED can
represent a pre-existing condition that can promote the
CNV’s growth through a further Bruch’s membrane
damage, expression of the same disease ongoing
(2,17)
.
1. Serous PED in AMD
Author:
Ugo Introini, MD, PhD
Department of Ophthalmology University Vita-Salute
Scientific Institute San Raffaele
Milano, Italy
