To compare, through
a randomized, multicenter surgical trial, the postoperative tamponade effectiveness
of intraocular silicone oil with that of an intraocular long-acting gas
(initially sulfur hexafluoride [SF6], later perfluoropropane [C3F8]) for
the management of retinal detachment complicated by proliferative vitreoretinopathy
(PVR), using vitrectomy and associated techniques.
To evaluate the
ocular complications that result from the use of silicone oil and gas.
of retinal detachment complicated by PVR remains controversial. Although
some cases are managed successfully by pars plana vitrectomy and with temporary
tamponade provided by intraocular gas, others eventually redetach with
this technique. Preliminary reports indicate that prolonged tamponade with
liquid silicone results in improved anatomical success, but the eventual
visual outcome may be prejudiced by silicone-related complications, particularly
glaucoma and keratopathy. The addition of hydraulic reattachment by simultaneous
fluid/gas exchange to vitrectomy surgery has proved to be an important
development. Although complications are few with these procedures, subsequent
redetachment is frequent.
The Silicone Study
was a randomized trial to investigate the relative merits of silicone oil
or gas as tamponade modalities. All study patients underwent vitrectomy
and were randomized intraoperatively either to silicone oil or to gas.
Two groups of eyes were entered into the study: eyes that had not had a
prior vitrectomy (Group 1) and those that had undergone previous vitrectomy
outside the study (Group 2).
element in the study was a standardized surgical procedure for PVR. This
surgical procedure, intended to relieve retinal traction with vitrectomy
techniques, was followed by assessment of the relief provided by an intraocular
air tamponade. The eye was randomized to silicone oil or gas only after
completion of the entire surgical procedure to eliminate investigator bias
that might develop through knowledge of the treatment modality. Patients
were examined 5 to 14 days following the randomization and again at 1,
3, 6, 12, 18, 24, and 36 months after that date. Repeated surgery was permitted
for either treatment modality. The Fundus Photograph Reading Center staff
processed and analyzed photographs taken at all the clinics, graded the
preoperative severity of PVR on the basis of baseline visit photographs,
and confirmed the macular status at followup visits.
of the study were visual acuity of 5/200 or greater and macular reattachment
for 6 months following the final surgical procedure. The successful outcomes
and complication rates of the two modalities were compared.
included but were not limited to PVR of Grade C-3 or greater according
to the Retina Society Classification and visual acuity of light perception
began on September 1, 1985, and was completed June 30, 1991. A total of
151 eyes were randomized to receive either SF6 gas or silicone oil (113
in Group 1 and 38 in Group 2). Four hundred and four eyes were randomized
to receive either C3F8 gas or silicone oil (232 and 172 in Groups 1 and
Implications for Clinical Practice Outcomes Comparing Group 1 Versus Group
have stressed the perceived differences in pathologic anatomy and outcomes
in eyes undergoing primary vitrectomy (Group 1 eyes) compared with eyes
that have already failed at least one prior vitrectomy for PVR (Group 2
eyes). In those nonrandomized retrospective studies, Group 2 eyes have
had poorer anatomic and visual results than Group 1 eyes. In the Silicone
Study, anatomic and vision results and prevalence of complications suggest
that the differences in outcomes between Groups 1 and 2 were not as great
as previously believed.
pressure (IOP) abnormalities were a common postoperative complication in
eyes with PVR. Chronically elevated IOP was found in 5 percent of the eyes;
chronic hypotony was found in 24 percent of the eyes. Chronically elevated
IOP was more prevalent in silicone oil eyes than in C3F8 gas eyes. Chronic
hypotony was more prevalent in C3F8 gas eyes than in silicone oil eyes,
more prevalent in eyes with anatomical failure, and correlated with poor
postoperative vision, corneal opacity, and retinal detachment. The presence
of diffuse contraction of the retina anterior to the equator should alert
the vitrectomy surgeon that the eye is likely to be hypotonous postoperatively.
in the Silicone Study:
from the Silicone Study, we compared the cohort of eyes that underwent
relaxing retinotomy with the cohort of eyes that did not in regard to preoperative
and intraoperative findings and to visual and anatomic outcomes and complications.
We concluded that eyes undergoing vitreous surgery for the first time for
the treatment of PVR can be treated successfully in most instances by conventional
techniques without the need for relaxing retinotomy. Retinotomy may be
required more frequently in patients undergoing repeat vitreous surgery
for PVR. In those patients, silicone oil and C3F8 gas appeared to be equally
effective tamponade modalities. In eyes undergoing retinotomy that have
not been previously vitrectomized, silicone oil may initially increase
the likelihood of visual success and may decrease the likelihood of hypotony
at 6 months; however, long-term observations at 24 months suggested a trend
toward worsening in silicone oil-filled eyes and improvement in gas-filled
After Silicone Oil Removal:
advisability of silicone oil removal from these complex eyes remains controversial,
we used data from the Silicone Study to compare visual and anatomic outcomes
in the cohort of eyes from which oil was removed with visual and anatomic
outcomes in the cohort of eyes in which oil was retained. Compared with
the oil-retained eyes evaluated at a comparable time after silicone oil
injection, oil-removed eyes at the examination before oil removal were
more likely to have attached retinas, have visual acuity 5/200, and not
be hypotonous. Eyes with attached retinas at the time of oil removal generally
showed improvement in visual acuity at the last followup examination. In
a matched-pair cohort analysis comparing oil-removed eyes with oil-retained
eyes, there was an increased risk of recurrent retinal detachment at the
last followup examination in the oil-removed eyes. However, in oil-removed
eyes with attached retinas at the last followup examination, overall visual
acuity improved and the incidence of complications decreased.
Abnormalities in the Silicone Study:
Study was the first study to document that the postoperative incidence
rates of corneal abnormalities are equivalent between oil and gas. The
incidence of corneal abnormalities in eyes randomized to gas was higher
than expected, and the incidence of corneal abnormalities in eyes randomized
to silicone oil remained high in spite of the use of an inferior iridectomy.
Successful surgical repair of the retinal detachment with a single operation
and prevention and early management of silicone oil-corneal touch should
help to prevent corneal abnormalities. If rubeosis iridis or severe aqueous
flare is present, preoperative treatment with intense topical and possibly
periocular steroids might help to reduce preoperative and postoperative
inflammation, which may mediate corneal damage.
Macular Pucker in the Silicone Study:
is a term that describes wrinkles and folds in the central retina resulting
from contraction of an epiretinal membrane. A limited manifestation of
PVR, macular pucker is observed within 6 months in 4 to 13 percent of eyes
after successful conventional surgery for retinal detachment without PVR.
Using data from the Silicone Study, we found that the 6-month point prevalence
rate of postoperative macular pucker was 15 percent. The occurrence of
macular pucker following successful surgery for retinal detachments complicated
by severe PVR was not influenced by the choice of intraocular tamponade.
Using the Silicone Study Classification System:
As part of
the study, a Silicone Study classification system for PVR was developed
based on the characteristic patterns of retinal distortion produced by
the contraction of proliferative membranes on the retina or within the
vitreous base. This classification was designed to document the extent
and anatomic distribution of PVR present preoperatively and to help standardize
the surgical treatment. Using data from the Silicone Study, we demonstrated
that identification of the anteroposterior extent of the PVR was prognostic
of visual acuity and hypotony at 24 months. The joint knowledge of the
location of PVR (using the Silicone Study classification system) and the
tightness of the funnel for retinas with 9 to 12 clock hours involved by
fixed folds (using the Retinal Study classification system) has prognostic
utility for eyes presenting with anterior plus posterior PVR.
of Outcome in Anterior Versus Posterior PVR in the Silicone Study:
Silicone Study classification system, we compared preoperative and intraoperative
findings, and vision and anatomic outcomes and complications, in the cohort
of eyes with anterior PVR and the cohort of eyes with only posterior PVR.
We found that anterior PVR was more prevalent in these Silicone Study eyes
than was posterior PVR and had a worse prognosis. Eyes with anterior PVR
and clinically significant posterior PVR changes had a better visual prognosis
if silicone oil rather than C3F8 gas was used.
Outcome in the Silicone Study:
At the time
of study closeout (June 30, 1991), the National Eye Institute funded an
extension of the Silicone Study to provide long-term followup in the cohort
of eyes (randomized to silicone oil or long-acting gas) with attached maculas
at the 36-month followup examination. During 6 years of followup, attachment
of the macula was maintained for all eyes. No significant differences in
the rates of complete retinal attachment, visual acuity greater than 5/200
or glaucoma were found between treatment groups. In contrast, gas-treated
eyes had more hypotony. Success in the first operation for PVR is paramount
in obtaining better visual results. Overall, surgery for PVR had a high
likelihood of retinal reattachment, and if anatomically and visually successful
at 3 years, there is an excellent chance that the results will be maintained
over the long term.
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