The abnormalities can be seen, particularly when the

The principal clinical manifestations secondary to PCV
are seen in the posterior segment. Polypoidal choroidal vascularization is
characterized by the presence of dilated, choroidal vascular channels ending in
orange, bulging, polyp-like dilations in the peripapillary and macular area.
Variably sized serous and serosanguineous detachments of the neurosensory retina
and pigment epithelium around the optic nerve or in the central macula are the
most frequent presentation. In areas where the retina is flat, the silhouette
of the abnormal vascular abnormalities can be seen, particularly when the
vascular components are large and the overlying pigment epithelium is atrophic.
The typical presentations for a patient who is symptomatic for less than three
months is extensive subretinal exudation and bleeding with minimal cystic
change in the retina and a surprisingly good visual acuity (VA). This disparity
between the severity of the serosanguineous detachments and good vision is best
explained by the minimal intraretinal changes. For patients with symptoms
longer than 3 months, there are considerable lipid depositions from proteineous
leakage from active aneurysmal elements in the polypoidal vascular
abnormalities.

The polypoidal lesions range from being very small,
detectable only with angiography, to medium or large, and the perfusing,
branching inner choroidal vessels have a similar degree of variability. PED is often
associated with polypoidal structures. Microrips of RPE and RPE tears may occur
at the margin of the serosanguineous PED.(56,57) Polypoidal lesions are also usually located at the margin of the
PED, and they may create a notch in the accompanying PED visible on
angiography. Associated features are recurrent subretinal hemorrhage and
vitreous hemorrhage, relatively minimal fibrous scarring, absence of retinal
vascular disease, pathologic myopia, and signs of intraocular inflammation.

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Multiple or independent vascular abnormalities may
appear in the same eye, and there is a marked tendency toward bilaterality. As
a rule, the presence of PCV in one eye generally means that the fellow eye is
at high risk of similar clinical changes. Sometimes the vascular abnormality is
only evident on angiography or high-resolution optical coherence tomography
(OCT) imaging.

Drusen may also be seen in patients with PCV,
generally in white patients. Among Japanese patients with PCV, 23% showed soft
drusen in the central macula in conjunction with the polypoidal vascular
abnormality.(58)

PCV may also be seen in eyes with other macular
abnormalities such as sickle cell retinopathy(59), central serous chorioretinopathy(7), typical neovascular (type 1 or 2) age-related macular
degeneration(60), melanocytoma of the optic nerve(61), circumscribed choroidal hemangioma(62), the tilted disk syndrome and pathological myopia(63), and choroidal osteoma.(64) Retinal microangiopathy may occur in a chronic
macular detachment secondary to polypoidal choroidal vasculopathy.(65)  Retinochoroidal
anastomosis may coexist with PCV.(59) Although type 2 neovascularization has been described
in eyes with independent polypoidal abnormalities, some retinal specialists
believe that this is more likely to be a very localized, proliferating, and
masquerading PCV abnormality.(60)

Natural course

The natural history of PCV depends on factors
including location (peripapillary vs. macular), size of the lesion, and
associated bleeding and exudation— which may resolve or progress, sometimes to
extensive subretinal fibrosis. The history is probably heavily influenced by
the racial background and individual genetic makeup and modified by systemic
factors such as hypertension.(66) Hirami et al found 36 of 85 patients (42%)
with PCV (mean age 72 years) had hypertension.(67) In Japanese patients, PCV is a chronic disease with a
variable course. For polypoidal lesions in the macula, 50% of patients in one
study had a favourable course with follow-up of 39.9 months. In the
remaining half the disorder persisted, occasionally with recurrent bleeding and
leakage, resulting in macular degeneration and visual loss.(68) Polypoidal structures may also involute spontaneously.(69) Soft drusen can coexist either in eyes with polypoidal lesions
or unaffected eyes.(58) There appears to be a difference in the clinical features
between early and late stage PCV: ”the longer the disease period, the larger
the lesion.” Microrips of RPE at the margin of the pigment epithelial
detachment are not uncommon in PCV; however, they often disappear
spontaneously.(56) Ueta et al investigated the development of PCV in
fellow eyes of exudative AMD in a Japanese population.(33) The cumulative incidence of involvement was 3.2% in 1
year, 11.1% in 3 years, and 11.1% after 5 years. RPE atrophy was a common finding
in fellow eyes that developed PCV.

Investigations

FFA

Fundus fluorescein angiographic (FFA) features of PCV are
similar to that of occult CNV.(70,71) A diffuse stippled hyper
fluorescence is noted in the area of lesion with no evidence of a classic
component. Rarely, the polyps are also visible. The shorter wavelength in FFA
as compared to ICG cannot pass effectively through the RPE and thus fails to
highlight the choroidal abnormalities. Also fluorescein has a lower affinity to
plasma protein as compared to ICG and leaks profusely through the
choriocapillaris. This may mask the underlying polypoidal lesions and branch
vascular network.

ICGA

ICG dye is 98%
protein bound, has poor permeability and fluoresces in the near infrared range
(790-805 nm). The retention of ICG in the choroidal circulation makes it ideal
for imaging choroidal circulation. As the operating wavelength is longer it can
fluoresce better through
pigment, fluid, lipid and haemorrhage than fluorescein dye.

ICGA is indicated when sero-sanguineous maculopathy is associated with one or
more of the following features: massive submacular haemorrhage, presence of
subretinal orange nodule, no response to anti-VEGF, notched PED, double layer
sign on SS-OCT, as these may have a pachychoroid pathology like PCV.(72) If only FFA is carried out, these may be misdiagnosed
as occult or minimally classic CNV. Hence it is important to carry out ICGA in
all such cases. Moreover, PCV primariy involves inner choroidal vasculature
hence ICGA is necessary for the diagnosis of PCV.(5)

Polyps appear
as early hyper fluorescence with nodular appearance with a halo of hypoflurorescence
around the nodule. The presence of orange-red sub- retinal nodules with
corresponding ICG hyper fluorescence is considered pathognomonic of PCV.(73) Majority of the polyps appear within the first minute
of ICGA(74), although the EVEREST study recommended a time window
of 5 minutes in which the polyps of PCV appear after injection of ICG dye.(75)

The late phase of angiogram may be associated with a
reversal of the pattern of fluorescence observed previously. The area
surrounding the lesion becomes hyper-fluorescent and the center of the lesion
demonstrates hypo-fluorescence.(75) This helps in determining the activity of polyps. The
polyps may be solitary or multiple. Different morphological patterns have been
described: a ring (or ‘whorl’ pattern) or
cluster (or ‘bunch of grapes’), latter carrying a worse prognosis. Although
majority of polyps are macular, polyps can also be classified based on location
as(11,76)

·        
peripapillary
(within one disk diameter of the optic disk),

·        
subfoveal

·        
juxtafoveal(within
200 microns of fovea)

·        
extrafoveal

On dynamic ICGA, abnormal vessels corresponding
to the branching vascular network can be seen in about 70% cases(77). Based on this, Spaide et al classified PCV into 2
types(78): Type 1 (polypoidal CNV): polyps with well defined
branching vascular network (BVN, both feeder and draining vessels); Type 2
(typical PCV): polyp with absent BVN (neither feeder not draining vessels). Also
pulsatile fill of polyps on dynamic ICGA is a characteristic feature of PCV.

The Everest study, has further described the imaging
standards and grading protocol of PCV.(75) PCV was diagnosed based on early sub-retinal ICGA
hyper-fluorescence (appearing within the first 5 min of ICG dye injection) and
at least one of the following diagnostic criteria:

·        
Nodular
appearance of the polyp on stereoscopic viewing

·        
Hypo-fluorescent
halo around the nodule

·        
Abnormal vascular
channel(s)supplying the polyps

·        
Pulsatile filling
of polyps

·        
Orange
sub-retinal nodules corresponding to the 
hyper-fluorescent area on ICGA

·        
Massive-submacular
haemorrhage

Sub-macular haemorrhage occurs as a
frequent complication off PCV. As stated previously ICG has the ability to
fluoresce through haemorrhage and thus becomes indispensable in diagnosis of
PCV especially when other modalities of diagnosis cannot be used in presence of
haemorrhage. Hence, ICGA is the gold standard for diagnosis of PCV.

ICGA can detect polyps in all the cases.
BVN and pulsatile hyper-fluorescence have not been reported in all cases on
ICGA and require dynamic imaging, although when present are characteristic of
PCV. It has been seen that OCT-A is a better modality for characterisation of
BVN.(79) As ICGA is an invasive procedure it cannot be used at
every visit to the clinic for which non-invasive modalities like OCT-A is
preferable. It has to be used with caution in patients with liver disorders as
ICG is primarily metabolised in the liver.

OCTA

OCTA is a novel non invasive imaging modality that helps in vivo
visualization of retinal vasculature. This modality helps in distinguishing
flow within the vessels from motionless tissues by utilizing several protocols
like SSAD (Split spectrum Amplitude decorrelation), phase variance and speckle variance
etc.(1) OCTA guides in the better axial localization of the pathology, unlike
FFA and ICG. (2)

OCTA helps in better visualization of BVN. The BVN are constantly
visualized as hyper flow structure (55 to 100% detection rate) due to the
linear blood flow within these vessels. (3) These high flow vessels are
recognized at the level of Bruch’s membrane as supported by the
histopathological studies. The BVN complex flow is detected at an average of
28.6 microns below the RPE reference plane as proposed by a recent OCTA guided
study by Chi et al. (4) Different patterns like seafan, tangled and medusahead
have been described based on the morphological appearance of the BVN.(5)

 The polyp detection rate is
comparatively lesser (50 – 75%) though higher detection rates up to 93% have
been reported.(6) The polyp is mostly identified as a hypo-flow round structure
or as a hyper-flow lesion with a surrounding hypo-intense halo. It is suspected
that the low flow status doesn’t indicate the absence of circulation rather
points to the fact that the level of flow is not within the detectable range of
OCTA. It is hypothesized that the circulation within the polyp can be too
turbulent to be sensed. The non-uniform flow is further explained by
histo-pathological reports that have demonstrated partial obstruction of
polypoidal lumen because of the combination of vessel hyalinization, thrombus,
basement membrane thickening and neutrophil adhesion to the vessel wall. The
flow in the polypoidal lesion is noticed at an average of 45.3 microns above
the RPE reference plane. The active flow is mostly localized in the saccular
structures lying beneath the roof of a pigment epithelial detachment. Various
polyp morphological flow patterns like cluster, nodules, ring and dot have been
described.(7,8)

    OCTA guides in understanding
the anatomy and pathophysiology of PCV. Recently Chi et al have reported the
existence of a choroidal stalk connecting the entire PCV complex with the
underlying larger choroidal vessels. Pathological larger choroidal vessels
called the pachy vessels in the outer Haller’s layer have also been described.
(4)

    OCTA also plays a role in
managing the disease. Teo et al have reported that longitudinal OCTA shows a
more significant reduction in lesion flow and pachy vessel size with
combination therapy than monotherapy in PCV. The reduction in flow rates on
OCTA shows up early as compared to the reduction in the sub-retinal fluid on
OCT. Similarly, the residual linear flow in BVN is detectable even after
therapy though OCT showed no fluid, alerting the ophthalmologist to expect
recurrences in future.(9)

    Though OCTA assists in
studying the anatomy and pathophysiology of PCV there are potential
disadvantages. Visualization of pathology becomes difficult when there is an
overlying hemorrhage or fluid. Further polyp detection rates are comparatively
lesser as explained before. OCTA hence provides complementary information and
must not be considered as a substitute for the gold standard ICGA in detecting
and managing PCV.