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EXTENDED REPORT
Immunopathology of intraocular silicone oil: enucleated eyes
Louisa Wickham, Riaz H Asaria, Robert Alexander, Phil Luthert, David G Charteris
...................................................................................................................................
See end of article for
authors’ affiliations
........................
Correspondence to:
L Wickham, Moorfields Eye
Hospital, City Road, London
EC1V 2PD, UK; louisa.
wickham@moorfields.nhs.uk
Accepted
14 September 2006
Published Online First
27 September 2006
........................
Br J Ophthalmol 2007;91:253–257. doi: 10.1136/bjo.2006.103564
Aims: To characterise the distribution of silicone oil in ocular tissues in globes enucleated after complicated
retinal detachment, and to document the distribution and nature of any associated inflammatory response.
Method: 9 enucleated globes that had previously undergone retinal detachment surgery with silicone oil and
7 control globes that had undergone enucleation after retinal detachment surgery (n = 2) or ocular trauma
(n = 5) were studied. Sections were histologically examined using light microscopy to document the
distribution of silicone oil in ocular tissues. Immunohistochemical analysis was carried out using the ABC
technique and a panel of monoclonal and polyclonal antibodies. Electron microscopy was undertaken to
observe the penetration of silicone oil in the trabecular meshwork of the anterior chamber drainage angle.
Results: Silicone oil was distributed throughout the globes—notably in the iris, ciliary body, retina, trabecular
meshwork and epiretinal membranes. Focal areas of intraretinal silicone were associated with disorganised
retinal architecture, retinectomy sites or subretinal oil. The distribution of macrophages was closely related to
the distribution of silicone oil. T and B lymphocytes were not associated with silicone oil unless additional
pathology was also present—for example, cyclitic membrane or uveitis. One of the nine eyes had silicone oil
present in the optic nerve. In the control globes, the inflammatory response was mediated primarily by
macrophages and T lymphocytes, and was less marked than that observed in the silicone oil globes.
Conclusion: This study shows that silicone oil may be sequestered in varied ocular tissues and is associated
with localised inflammation mediated by macrophages.
S
ilicone oil is often used as a tamponade agent in the
treatment of complicated retinal detachments. However,
its benefits must be weighed against the risk of the
complications associated with its use—cataract, band kerato-
pathy, secondary glaucoma and potentially reduced visual
acuity.
1–5
The toxic effects of silicone oil are thought to be due
to the migration and subsequent sequestration of silicone oil
within ocular tissues as shown by several histopathological
and clinical case series.
6–14
Silicone oil has been observed in
varied intraocular structures from the cornea to the retina, and
also with progression through the optic nerve to the optic
chiasm and brain.
6812
The presence of an associated inflam-
matory response in ocular tissue has also been documented,
characteristically showing macrophages and giant cells laden
with lipid vacuoles.
13–18
In eyes that have undergone enucleation
for advanced pathology, a degree of inflammation can be
expected and it can be difficult to distinguish the inflammation
due to the underlying pathology from that attributable to
silicone oil. The nature and distribution of the inflammatory
response associated specifically with silicone oil has yet to be
characterised.
14
This study was undertaken to analyse the distribution of
silicone oil and its associated immunopathology in silicone-oil-
filled globes, and to compare it with that seen in enucleated
globes from patients with no history of silicone oil exposure. In
addition, transmission electron microscopy was carried out on
four of the silicone-oil-filled globes and on three of the control
globes to determine the nature of silicone oil migration in the
trabecular meshwork of the drainage angle.
METHODS
This study was granted ethics approval by the Moorfields local
research ethics committee (CHAD 1009).
Nine silicone-oil-filled eyes and seven control eyes enucleated
after retinal reattachment surgery were analysed. Wherever
possible, clinical case details were obtained from the referring
hospital.
Processing/staining
Formaldehyde-fixed specimens were embedded into paraffin
wax using xylene as the ante-medium. Tissue sections were
stained by the haematoxylin and eosin sequence to assess
general morphology. The immunohistochemical distribution of
CD45RO (UCHL1) and CD45 (leucocyte common antigen) for T
lymphocytes, CD20 (L26) for B lymphocytes, Mac 387 and
CD68 (PGM1) for macrophages, Cam 5.2 for retinal pigment
epithelium cells and glial fibrillary acidic protein (GFAP) for
glial tissue was studied using a conventional alkaline phos-
phatase avidin-biotin complex method. The antigens were
visualised as the red final reaction product of Vector red (Vector
Laboratories, Peterborough, UK). Appropriate negative (using
non-immune serum from the same species as the primary
antibody and at the same protein concentration) and positive
(using tissues known to express the antigen) controls were
analysed. Table 1 outlines the primary antibodies used and the
antigen retrieval information.
A semiquantitative analysis of the cellular response and
degree of silicone infiltration in intraocular tissues was under-
taken. Grade + was used to indicate the presence of silicone oil
or the presence of inflammatory cells. If silicone oil was
observed in ocular tissues in .5 high-powered fields, grade ++
was recorded. The diameter of one high-powered field was
0.5 mm. Similarly, the presence of macrophages in .5 high-
powered fields was denoted as ++.
Transmission electron microscopy
Specimens originally prepared for routine wax embedding were
dewaxed overnight in xylene, and then rehydrated to 10-min
rinses in 36100% and 1690%, 70% and 50% ethanol. After
2610-min changes of distilled water, blocks were fixed for 2 h
in 1% osmium tetroxide, dehydrated to absolute alcohol by
reversing the above process, passed through 2620-min changes
of epoxy propane and left overnight in a 1:1 mixture of epoxy
Abbreviations: GFAP, glial fibrillary acidic protein
253
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propane:araldite resin. After 12 h, the specimens were placed in
100% resin for 6 h with rotation, and then embedded and cured
overnight in an oven at 60
˚
C.
Semi-thin (1 mm) sections for light microscopy and ultra-
thin (70 nm) sections for transmission electron microscopy
were cut using a Leica Ultracut S microtome fitted with a
diamond knife. Semi-thin sections were stained with alcoholic
toluidine blue. Ultra-thin sections were contrasted by sequen-
tial staining with saturated uranyl acetate in 50% ethanol
followed by lead citrate, and viewed and photographed in a
JEOL 1010 transmission electron microscope (JEOL Ltd, Tokyo,
Japan) operating at 80 kV.
RESULTS
Silicone oil globes
Clinical details
The silicone-oil-filled group consisted of six males and three
females. The average age at the time of enucleation was
40.4 years (range 11–86 years). The cause of initial presenta-
tion was rhegmatogenous retinal detachment (n = 3), pene-
trating eye injury (n = 4) and blunt trauma (n = 2). Silicone oil
was present in all nine eyes at the time of enucleation. It was
possible to document the duration of silicone oil tamponade in
six of the nine cases: the average duration was 5 years (range
7 months–14 years).
Globes
Macroscopically, seven of the nine patients were aphakic at the
time of enucleation and two patients were pseudophakic. A
total retinal detachment was observed in two globes and a
funnel retinal detachment in another two. In addition, a
suprachoroidal haemorrhage was also noted in one globe.
In the silicone-oil-filled globes, macrophage distribution was
closely related to the distribution of silicone oil (table 2). The
number of macrophages per high-powered field generally
reflected the degree of silicone oil distribution in the tissue.
When this was not the case, there was a history of secondary
pathology—for example, in one eye, an increased macrophage
response in the anterior chamber was secondary to a perforated
corneal ulcer and associated hypopyon. Similarly, one patient
(number 4) had a membrane occluding the anterior chamber
drainage angle with an associated macrophage and T lympho-
cyte infiltrate. Silicone oil was present in epiretinal membranes
on the retinal surface in all nine globes, and in seven this was
associated with a macrophage response. Giant cells were
observed in epiretinal membranes in three globes. In four eyes
silicone oil was found in the retina, with focal areas of retinal
infiltration by macrophages occurring at retinectomy sites
(either in the anterior frill of residual retina or at the posterior
margin of the retinectomy), in grossly disorganised retina, or
associated with the presence of subretinal silicone oil (fig 1).
Silicone oil sequestered in the drainage angle, iris, ciliary body,
retina and in epiretinal membrane was notable by the presence
of small eccentric pigment granules in and adjacent to
microglobules of oil. In lipid-laden macrophages, these pigment
granules were also observed in and surrounding the phago-
cytosed silicone microglobule (fig 1). These pigment granules
were not observed in silicone oil found in the optic nerve (fig 2).
Silicone oil, in association with macrophages, was present in
the optic nerve in one patient who had a history of prolonged
raised intraocular pressure due to secondary glaucoma 3 years
after his initial surgery (fig 2). In this eye, silicone oil was
observed in an epiretinal membrane but was not found
elsewhere in the globe.
T lymphocytes were seen in five of the nine specimens. When
present, T lymphocytes were found in cyclitic membranes
(n = 1), proliferative vitreoretinopathy epiretinal membranes
(n = 1), in membranes occluding the anterior chamber drai-
nage angle (n = 2) and perivascularly in areas of inflammation
(n = 4; fig 3). Perivascular populations of T lymphocytes were
also found in the choroid and sclera (n = 4). T lymphocytes
were not distributed in association with silicone oil. B
lymphocytes were found in three of the nine specimens.
When present, B lymphocyte populations were found together
with T lymphocytes.
The distribution of retinal GFAP was increased in all nine
globes, being observed in all retinal layers. This did not differ
from the control globes, where GFAP distribution was also
increased in all seven eyes.
Transmission electron microscopy of the globes showed
silicone oil in the trabecular meshwork in three of the four
patients analysed (fig 4). Silicone oil was seen as discrete
Table 1 Antigens studied
Antigen Target Antibody source Antigen retrieval* Antibody dilution
CD45RO T lymphocytes Dako Heat mediated 1:800
CD45 T lymphocytes Dako Heat mediated 1:800
CD20cy B lymphocytes Dako Heat mediated 1:600
Mac 387 Macrophages Dako Trypsin 1:100
CD68 Macrophages Dako Trypsin 1:100
Cam 5.2 RPE cells BD Biosciences Trypsin 1:50
GFAP Glial tissue Dako Trypsin 1:2000
GPAF, glial fibrillary acidic protein; RPE, retinal pigment epithelium.
Dako, Ely, UK; BD Biosciences, California, USA.
*Tissue sections were treated either by heat mediation, performed in an 800-W microwave oven by heating 50 g/l urea
in 50 mM TRIS-HCl buffer, pH 9.5, for 10 min, followed by cooling for a further 25 min; or by trypsination, performed in
a37
˚
C incubator by exposure to 1 g/l trypsin in 100 mM TRIS-HCl buffer, pH 7.8, for 15 min.
Figure 1 Immunochemistry of the anterior edge of a retinectomy site in an
enucleated globe after treatment with silicone oil. Intraretinal macrophages
(CD68 antibody (red), haematoxylin counterstain) containing
phagocytosed silicone oil (arrow) and eccentric pigment granules
(arrowhead) are shown. Original magnification 6400.
254 Wickham, Asaria, Alexander, et al
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microglobules with small eccentric pigment granules (fig 5) on
light microscopy.
Control globes
Clinical details
In the control group, five cases were male and two cases female.
The average age at the time of enucleation was 45.7 years
(range 23–71 years). The presenting pathologies were rhegma-
togenous retinal detachment (n = 2), penetrating eye injury
(n = 4) and blunt trauma (n = 1).
Globes
Macroscopically, one patient was aphakic and six patients were
phakic. A total retinal detachment was noted in three globes
and a funnel retinal detachment in one. A staphyloma and
encirclement band was also observed in one globe.
In the control population, T lymphocytes were present in five
of the seven globes. As in the case of the globes containing
silicone oil, T lymphocytes were found in epiretinal proliferative
vitreoretinopathy membranes (n = 2), cyclitic membranes
(n = 2) and perivascularly (n = 3). B lymphocytes were found
in association with T lymphocytes in two eyes. Macrophage
infiltration was much less marked than that seen in the
silicone-oil-filled eyes, and their distribution mirrored that of T
lymphocytes. A scanty distribution of macrophages was also
seen in areas of chronically detached retina and subretinal fluid
(fig 6). In this group, optically empty spaces similar to those
found in the silicone-oil-filled group were noted (fig 6)
distributed in the retinal architecture and choroid. These spaces
were not found in any other ocular structure, and could be
distinguished from those found in the silicone-oil-filled globes
by the absence of localised inflammatory cells and pigment
granules.
Staining for GFAP was observed throughout the retinal layers
in all seven control globes. Comparison of the silicone oil globes
and the controls showed no differences in the distribution of
GFAP.
DISCUSSION
This study shows widespread infiltration of ocular tissue by
silicone oil, in agreement with the findings of several previous
reports.
5–14
In addition, by immunohistochemical analysis we
have shown that the intraocular inflammatory response
associated with sequestered silicone oil differs from that seen
in eyes with similar pathologies but without silicone oil.
Examination of nine globes exposed to silicone oil found that
the oil was closely associated with localised inflammation,
suggesting that the inflammatory response was at least partly
attributable to the presence of silicone oil rather than coexisting
ocular pathology. Further evidence of this is the absence of an
intense localised macrophage response in control eyes.
Macrophages often contained phagocytosed silicone oil and
seemed to remain viable despite large volumes of silicone oil in
the cell, a finding that has been noted in other studies.
17 19
Inflammatory responses mediated by T and B lymphocytes
were not found in regions of silicone sequestration unless
associated with other pathology—for example, cyclitic mem-
branes, which suggests that these cells do not have a major role
in the response to the presence of silicone oil. This was also
supported by similar findings in the control globes where T and
B lymphocyte infiltration was observed at sites of intraocular
Figure 2 Light photomicrograph (haematoxylin and eosin) showing the
presence of silicone oil in the cupped optic nerve head. Original
magnification 6100.
Table 2 Distribution of silicone oil in intraocular tissues of the silicone oil globes
Patient
ERM Retina Optic nerve Ciliary body Iris Angle/TM Cornea Conjunctiva
Oil M Oil M Oil M Oil M Oil M Oil M Oil M Oil M
1 ++ ++ + –––++ ++ + ++ ++ ++ ––++
2 ++ ++ + + NA NA ++++––––NANA
3 ++ ––+ ––+++– + ––––––
4 ++ ++ –––––––––++ ––++
5 ++ ++ + + –––+ ––––––––
6 + –––––––+++ + ––––
7 ++ ++ –––––––+ ––––––
8 ++ ++ + + ––+++++++– ++
9 ++––++ + ––––––––––
ERM, epiretinal membrane; M, macrophage distribution; TM, trabecular meshwork; NA = specimen did not contain this structure; +, presence of silicone oil or
inflammatory cells; ++, silicone oil was observed in ocular tissues in .5 high-powered fields; –, absent.
Figure 3 Immunohistochemistry of a control globe showing perivascular T
lymphocytes (arrow: CD45 antibody (red), haematoxylin counterstain).
Original magnification 6200.
Immunopathology of intraocular silicone oil 255
www.bjophthalmol.com
inflammation (epiretinal and cyclitic membranes and perivas-
cularly) and in the subretinal fluid of chronic detachments.
Our study also supports the findings of two previous studies
which observed that tissue infiltrated with silicone oil is usually
confined to the retinal surface.
20 21
In the silicone-oil-filled
globes, intraretinal silicone oil was observed only when the
retinal architecture was considerably disorganised—for exam-
ple, at retinectomy sites or in areas where subretinal oil was
noted. A similar finding was reported by Kirchhof et al
22
in a
case series of eight eyes in which intraretinal silicone oil was
absent unless accompanied by subretinal oil. In addition, it has
been hypothesised that the integrity of the outer limiting
membrane may impede further silicone oil migration.
23
Silicone oil was observed in the optic nerve of one globe in a
patient with a history of raised intraocular pressure after oil
injection. In a previously reported series of 74 globes, silicone
oil was present in the optic nerve in 14 cases (24%), and in 10 of
the 14 eyes with silicone oil in the optic nerve, there was a
history of raised intraocular pressure after silicone oil injection,
6
a finding that has also been documented in other case
reports.
924
Migration of silicone oil into the optic nerve may
be responsible for cases of unexplained visual loss before and
after silicone oil removal, which have recently been
reported.
25 26
Our study also showed ultrastructural evidence of silicone in
the trabecular meshwork in four patients, and immunohisto-
chemically we found a macrophage response associated with oil
in the meshwork. A previous study failed to show evidence of
silicone oil or macrophages in the drainage angle in two
patients with secondary glaucoma attributed to silicone oil.
27
The differences between these studies and the drainage angle
findings may be related to sampling artefacts depending on
which part of the angle is studied. Overall, our results suggest
trabecular infiltration by silicone oil and an associated
trabeculitis. These changes are likely to persist even after oil
removal, and may well account for the chronically raised
intraocular pressure seen in eyes that have previously had
intraocular silicone oil.
It should be noted, however, that the globes studied have in
general advanced intraocular pathology (as is the case in
previous similar series), and the infiltration of silicone oil we
have found may not reflect its distribution in eyes with less
advanced pathology and shorter durations of silicone oil
exposure. We have noted in a series of retinectomy specimens
(where pathological changes are less advanced) that silicone
infiltration into the retina was uncommon and generally
confined to regions of disorganised and gliotic retina (data
submitted). Nevertheless, the widespread distribution of
silicone oil suggests its potential (given appropriate intraocular
conditions such as retinal scarring) to cause ongoing pathology.
The difficulty of having complete certainty in detecting
silicone oil in intraocular tissue deserves emphasis. Silicone oil
is removed during the routine processing of tissue for
histological analysis, and therefore its presence appears as
optically empty spaces in tissue sections. Similar findings are
also found in tissues that have not been exposed to silicone
oil,
21–23
and may be due to tissue oedema, gliosis or processing
artefacts. In long-standing retinal detachment or other
advanced retinal pathology, areas of retinal oedema may be
seen as rounded, optically empty spaces, and can be very
difficult to distinguish from silicone oil. In the current study,
the presence of silicone oil was closely related to an
inflammatory response that can suggest the presence of foreign
material. We observed that optically empty spaces due to
silicone oil were also associated with small eccentric granules of
Figure 4 Transmission electron micrograph showing the presence of
silicone oil in the trabecular meshwork of the anterior chamber in a globe
treated with silicone oil (arrow). Original magnification 62000.
Figure 5 Transmission electron micrograph of a microglobule of silicone
oil in the trabecular meshwork with eccentric pigment granules (arrow).
Magnification 65000.
Figure 6 Immunochemistry showing optically empty spaces (arrow heads)
seen in the retina of a control globe. A single macrophage (CD68 antibody
(red), haematoxylin counterstain) is also shown (arrow). Original
magnification 6200.
256 Wickham, Asaria, Alexander, et al
www.bjophthalmol.com
pigment both within and surrounding the oil globule,
apparently related to the macrophage-mediated inflammatory
response as shown in fig 1. This finding was not seen in
optically empty spaces in the control specimens (fig 6).
In conclusion, this study has shown that silicone oil may be
sequestered in varied ocular tissues—notably iris, ciliary body,
trabecular meshwork, retina and epiretinal membranes. In
globes with advanced pathology, silicone oil seems to initiate a
localised inflammatory response mediated by macrophages,
whereas other associated ocular pathology is characterised by
a marked T lymphocyte infiltrate, with some involvement of
B lymphocytes and macrophages. Our findings suggest that
intraretinal oil usually occurs as a result of persistent retinal
detachment or retinal injury; however, sequestration of silicone
oil in other tissues, notably the drainage angle, ciliary body and
optic nerve, may occur despite retinal reattachment surgery.
Removal of silicone oil may not reverse the inflammatory cycle
initiated by its injection, and explains the ability of silicone oil
to cause multiple long-term sequelae.
Authors’ affiliations
.......................
Louisa Wickham, David G Charteris, Moorfields Eye Hospital, London, UK
Riaz H Asaria, Royal Free Hospital, London, UK
Robert Alexander, Phil Luthert, Institute of Ophthalmology, London, UK
Competing interests: None declared.
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