Full text of DOI:10.1007/s004170100330

Graefe’s Arch Clin Exp Ophthalmol
(2001) 239:635–642
C L U B J U L E S G O N I N
DOI 10.1007/s004170100330
Karin Kobuch
Dirk Henning Menz
Hans Hoerauf
Joachim Hans Dresp
Veit-Peter Gabel
New substances for intraocular tamponades:
perfluorocarbon liquids, hydrofluorocarbon
liquids and hydrofluorocarbon-oligomers
in vitreoretinal surgery
Abstract Perfluorocarbon liquids
application, side-effects are similar
Published online: 30 August 2001
© Springer-Verlag 2001
(PFCLs) and heavy fluorocarbon liq- to those observed with PFCLs. Sub-
uids (HFCLs) are being increasingly stances of this group, such as F6H6,
used as soft tools during vitreoretinal F6H8, O44, and O62 are used intra-
surgery. However, since long-term
intraocular tolerance is still unsatis-
operatively and are currently being
investigated for clinical long-term
factory, at present complete removal application. With the aim to avoid
at the end of surgery is recommend-
ed. With the aim to improve long-
emulsification and to improve intra-
ocular tolerance, we have developed
term intraocular compatibility and to HFCL-oligomers consisting of 2–4
enlarge the spectrum of clinical ap-
plications, modified HFCLs have
been developed. HFCL-oligomers
with a higher viscosity represent the
latest perspective. All three groups
of fluorocarbon liquids will be com-
pared with respect to their physical
HFCL molecules with increased vis-
cosity. The oligomers were tolerated
well in rabbit eyes for up to 4
months. In contrast to PFCLs or
monomers, they did not emulsify nor
show vascular alterations. ERGs re-
turned to normal after removal of the
and chemical properties, experimen- oligomer from the eye. Histology of
tal and clinical results, and prospects the retina showed mild alterations.
for clinical applications. Common
features of PFCLs, HFCLs and
HFCL-oligomers are biological in-
ertness, specific gravity higher than
water, immiscibility with water or
Conclusion: according to physical
properties, experimental intraocular
compatibility and stability against
emulsification, HFCL-oligomers are
promising candidates for improved
blood, and a high gas binding capac- long-term tamponade of the lower
ity. In PFCLs such as decalin, oc-
tane, or phenanthrene, all carbon at-
oms of the carbon backbone are
completely fluorinated. In experi-
mental and clinical use, emulsifica-
tion, vascular changes and structural
alterations of the retina have been
described. By only partial replace-
ment of hydrogen atoms by fluorine,
the specific gravity of HFCLs is re-
duced, whereas lipophilic properties
increase. Thus HFCLs are potential
solvents for intraocular silicone oil
remnants. However, after long-term
retina. At present, indications for an
application in human eyes have to be
determined in clinical trials.
K. Kobuch · V.-P. Gabel (
University Eye Hospital,
)
✉
Franz-Josef-Strauss-Allee 11,
93042 Regensburg, Germany
e-mail:
veit-peter.gabel@klinik.uni-regensburg.de
D.H. Menz
Pharm Pur, Augsburg, Germany
J.H. Dresp
Bausch and Lomb Surgical,
Munich, Germany
H. Hoerauf
University Eye Hospital, Lübeck, Germany

636
Background
PFCLs, HFCLs, HFCL-oligomers:
common physical and chemical properties
Since perfluorocarbon liquids (PFCLs) were first intro-
duced into vitreoretinal surgery by Haidt and Clark [21] Common features of PFCLs and HFCLs including the
and Chang et al. [8, 9, 10], they have been used increas- oligomers are biological inertness, immiscibility with wa-
ingly and successfully as intraoperative soft tools for ma- ter or blood according to the high interfacial tension, and
nipulation and reapposition of the retina [4, 7, 11, 37]. a high gas binding capacity. They are heavier than water
However long-term intraocular tolerance of PFCLs is still with a specific gravity ranging between 1.34 and 2.03
unsatisfactory, so that at present complete removal at the g/cm3. Both interfacial tension and specific gravity deter-
end of surgery is recommended [2, 3, 6, 7, 14, 46, 47]. mine the shape of the intraocular substance-droplet rang-
Attempts have been made to modify the physical and ing between a round, easily rolling bubble or a quickly
chemical properties of PFCLs in order to improve the in- sinking mass with a horizontal liquid level. The refractive
traocular tolerance [26, 30, 45] and the spectrum for ap- index varies between 1.27 (perfluorooctane) and 1.33
plications of this very suitable and variable group of sub- (perfluorophenanthrene). Since these substances are mis-
stances. Thus the first generation of heavy, fully fluorina- cible with each other, the refractive index can be adjusted
ted carbon liquids, such as perfluorodecalin, perfluorooc- to the demands of the surgeon and the patient between
tane and perfluorophenathrene, has recently been supple- 1.27, clearly distinguishable from that of intraocular fluid
mented by new partially hydrogenated hydrofluorocarbon or residual vitreous, and 1.34, close to the refractive in-
liquids (HFCLs), which feature reduced specific gravity dex of the vitreous. PFCLs and HFCLs for clinical use
and increased lipophilic properties. This new group of are highly purified. Differences in the molecular structure
partially hydrogenated fluorocarbon liquids, such as of PFCLs, HFCLs, and HFCL-oligomers (Table1) define
F6H6, F6H8, O44, and O62 are advantageous for intraop- different physical and chemical properties (Table2) lead-
erative manipulation of the retina during macular rota- ing to new perspectives for clinical applications.
tion. Due to their lipophilic, silicone oil solvent proper-
ties, they have the potential to remove intraocular silicone
oil remnants. Long-term intraocular clinical tolerance of PFCLs, HFCLs, HFCL-oligomers:
HFCLs is currently under investigation [51].
The latest perspective represent hydrofluorocarbon oli- experimental and clinical results
gomer liquids (HFCL-oligomers) (OL62 LV/HV), a new
specific characteristics,
group of substances with increased viscosity, which we Perfluorocarbon liquids
have developed recently with the aim to improve long-term
tamponade therapy especially for pathologies of the lower In PFCLs, all carbon atoms are completely fluorinated.
retina. The properties, experimental results and new thera- In comparison to the closely related gaseous fully fluor-
peutic potential of HFCL-oligomers will be presented.
inated fluorocarbons such as C3F8, which are also wide-
Table 1 Chemical structure
of fluorocarbon liquids
(FCLs), PFCLs, HFCLs, and
HFCL-oligomers (yellow:
hydrogen;green: fluorine)
HFCLs, for example the octane
O62, are obtained by partial
fluorination of hydrocarbon liq-
uids. Two to maximal four O62
molecules can be oligomerised
to OL62 LV (low viscosity) or
OL62 HV (high viscosity)

637
Table 2 Physical and chemical
properties of PFCLs, HFCLs,
and HFCL-oligomers as com-
pared to silicone oil
ly used in ophthalmology, they possess a higher molecu-
Second, after long-term intraocular application of
lar weight and consist of more than five carbon atoms. PFCLs, vascular damage was evident in FLA findings.
PFCLs are hydrophobic and lipophobic. They have a Vascular occlusions, avascular zones, aneurysms and
very low viscosity and, due to the heavy fluorine atoms, leakage of dye are demonstrated as compared to the
a high specific gravity (Table2).
same vascular area before treatment (Fig.2). Trypsin di-
PFCLs are used as soft tools to manipulate, unfold gested flat mounts of the vessels [28] show loss of per-
and reappose the retina intraoperatively in cases of com- icytes and endothelial cells [24]. Similar vascular altera-
plicated retinal detachment, during macular rotation, or tions have been related to oxygen toxicity [1, 44]. We
for removal of dislocated lenses [5, 6, 9, 15, 29, 33, 34, conclude, based on our hypothesis, that these vascular
36, 37, 39, 40, 50]. However, at present complete remov- alterations can be caused by high pO2 and low CO2 lev-
al of the substance at the end of surgery is recommended els. Histologically, alterations of the retina were more
because intraocular long-term tolerance is unsatisfactory striking in the lower retina, the area of permanent con-
as demonstrated in animal experiments or described in tact with the PFCL, as compared with the upper retina
clinical reports after use in humans [7, 12, 13, 14, 16, 22, (Fig.3). Preretinal foam cells containing optically empty
32, 35, 41, 46]. Intraocular droplet formation does occur vacuoles were found along the inner side of the
within the first few days, demonstrated here in a rabbit retina, mainly around the vessels. Retinal thinning and
eye 5 days after injection. Simultaneously, flakey white penetration of all retinal layers by vacuoles was occa-
precipitates appear in the residual vitreous and build sionally noted. Hypertrophy of Müller cells and structur-
membrane like structures around the bubbles, which may al disturbances in the plexiform layers was observed.
prevent reconfluence and indicate disturbance of the
blood retinal barrier and leakage of protein (Fig.1) [20].
Experimentally, functional and morphological alterations Hydrofluorocarbon liquids
of the retinal blood supply were found in two respects:
first, an immediate vasoconstriction with an up to 30% The hypothesis that the high specific gravity of PFCLs is
reduction in retinal blood flow was measured in rabbit a causative factor for long-term intraocular tissue dam-
eyes after injection of PFCL [25]. Measurements of both age led to the development of HFCLs with reduced spe-
pO2 and pCO2 in the PFCL before injection and than in- cific gravity [42]. In HFCLs, reduction of the specific
traocularly after injection of PFCLs revealed high pO2 gravity is accomplished by only partial replacement of
(160 mm Hg) and low pCO2 (3 mm Hg) levels in com- hydrogen atoms by fluorine atoms. Corresponding to the
parison to normal intravitreal values (pO2 15 mm Hg, number of carbon atoms, which are either fluorinated or
pCO2 50 mm Hg). Consequently we suggested that vaso- hydrogenated, the substances are called F6H6 (perflu-
constriction could be explained as an additive vasocon- orohexane), F6H8 (perfluorohexyl-octane), O62 (perflu-
strictive effect due to high pO2 together with low pCO2 orohexyl-ethane) or O44 (perfluorobutyl-butane). Partial
in PFCLs, when injected intravitreally. The fact that va- fluorination leads to a stepwise reduction in specific
soconstriction could be avoided or blood flow even in- gravity, from 2.03 g/cm3 (perfluorophenanthren) to 1.32
creased by adaption of pO2 and pCO2 in PFCLs to nor- g/cm3 (F6H8). Simultaneously, hydrogenation causes
mal values or to reduced pO2 and increased pCO2 levels, augmented polarisation leading to increased lipophilic,
further supports our hypothesis [17, 25].
silicone-solvent properties of the substances. Thus, rep-

638
Fig. 1a–c Optical properties and intraocular stability of FCLs, in-
jected into rabbit eyes (a) 5 days after injection of decalin, droplet
formation has occurred. Flakey precipitates have formed in the re-
sidual vitreous and around the decalin bubbles; (b) similar altera-
tions of the initially clear substance occurred in eyes with O62 or
O44 and (c) no droplet formation and clear optical media are
shown here in a rabbit eye, 8 weeks after injection of OL62 HV.
The refractive index of the substitute is very close to that of nor-
mal vitreous
reduced force on the retina is needed. According to their
surface tension properties combined with the reduced
specific gravity, they form a rounded, easily rolling drop-
let on the retina, which may be especially advantageous
for retinal manipulations as in macular rotation. After
long-term intraocular application, experimental as well
as clinical findings are not much different from those ob-
served after the use of PFCLs. Emulsification occurred
after about 1 week after injection (Fig.1). Vascular alter-
ations, an immediate vasoconstrictive effect and long-
resenting the first biocompatible intraocular silicone sol- term structural damage, are shown in Fig.2, 6 weeks af-
vent, HFCLs potentially allow removal of silicone oil ter injection of O62.
remnants from the eye or wash out of silicone oil con-
Histology of the inferior retina revealed structural al-
taminations from intraocular lenses. Initial clinical appli- terations similar to those observed after application of
cations have been reported [51]. However, if PFCLs, PFCLs, despite the lower specific gravity of HFCLs
HFCLs and silicone oil are used in succession intraoper- (Fig.3) [18]. Based on calculations, the downward force
taively, “silicone oil in HFCL solutions” can build dense of intraocular PFCLs cannot exceed 1–2 mm Hg and
opacifications which may obscure the vision of the sur- thus remains within the normal range of intraocular ten-
geon and are difficult to remove [23]. Therefore, for sion. So both histological findings and calculations do
combined intraocular use, a definite sequence of applica- not support the hypothesis that the specific gravity of
tion and exact knowledge of solubility properties is man- PFCLs is a major factor for retinal damage [17, 18, 42,
datory for the surgeon.
48]. At present, the long-term tolerance of HFCLs in hu-
For clinical intraoperative short-term application, man eyes is under investigation in a clinical study. Thus,
HFCLs offer advantages over PFCLs in cases where a for further optimisation of an intraocular tamponade

639
Fig. 2a–d Fluorescein angiography of the rabbit’s retinal blood
vessels (a) before and after injection of (b) PFCL (identical area
of the vascular system),(c) HFCL and (d) OL62 HV. As compared
to the normal, untreated contralateral eye (a), vascular occlusions,
rarefication, aneurysms and leakage of dye have developed
6 weeks after injection of PFCL (b) or O62 (c), whereas the vas-
cular system appears normal 8 weeks after OL62HV-injection (d)
centre, HFCL-oligomers represent a new class of com-
pounds. They differ from HFCLs in many respects such
as surface properties and lipophilic properties. The spe-
cific gravity of these substances, 1.62, is very suitable
for tamponade of the lower retina. The refractive index is
almost identical with that of normal vitreous, which is an
advantage for the patient but may make it difficult for
the surgeon to distinguish the intraocular oligomer bub-
therapy, in particular for the lower retina, as an alterna- ble from intraocular fluid. For special surgical demands,
tive to silicone oil, the major goals remain to improve in case of removal, better visualisation can be achieved
the optical properties of the substitute by avoiding intra- by mixing the oligomer with a PFCL, which has a differ-
ocular droplet formation and to reduce intraocular side- ent refractive index.
effects.
The intraocular compatibility of two HFCL-oligomers
with different viscosity, OL62 LV of 90 mPas and OL62
HV of 1750 mPas respectively, was evaluated in rabbit
eyes. After gas compression of the vitreous [43], 1.2 ml
of either substance was injected intravitreally. The eyes
Hydrofluorocarbon oligomers
With the idea that higher viscosity can improve the me- were observed for up to 3 months and examined by slit
chanical properties of an intraocular tamponade and thus lamp, ophthalmoscopy, and fluorescence angiography
reduce emulsification and intraocular complications, we (n=4 in each group). ERGs were performed with the sub-
have developed HFCL-oligomers. By joining two to stance in the eye and after removal of the oligomer. At
maximal four HFCL molecules, viscosity reaches values the end of the observation time, the eyes were enucleated
ranging between 90 (OL62 LV, low viscosity) and 1750 and processed for light and electron microscopy.
mPas (OL62 HV, high viscosity), which still guarantee
Both substances were easy to handle. They were tol-
an easy handling and injectability through fine needles erated without any inflammatory reaction. Droplet for-
but can improve intraocular stability and reduce droplet mation did not occur in any eye during the whole obser-
formation. Due to the star-shaped molecular structure vation period. The substance, the residual vitreous and
with the polar, hydrogenated end of the molecule in the all optical media remained clear, as shown in Fig.1, 8

640
Fig. 3 Light microscopy of the rabbit’s lower retina 6 weeks after
application of either PFCL (a), HFCL (b), or HFCL-oligomer (c).
In general, the retinal architecture remained well preserved. Some
hypertrophy of Müller cells was evident in all specimens. Vacuoli-
sation of the inner retinal surface and slight disarrangement of the
plexiform layers was more marked after OL62 HV administration;
preretinal vacuole containing foam cells on the inner retinal sur-
face were seen less frequently
long-term observation, the retinal blood vessels appeared
well preserved in FLA (Fig.2) and on histology. As pO2
and pCO2 levels in HFCL-oligomers are identical to that
of PFCLs or HFCLs at the time of injection, it is not
clear at present, why the experimental intraocular vascu-
lar long-term tolerance of HFCL-oligomers is different
from that of PFCLs or HFCLs [24,27]. Hypothetically,
very slow gas diffusion properties of oligomers com-
pared to PFCLs and HFCLs could reduce the toxic ef-
fects of oxygen to the retinal vessels.
weeks after injection of OL62 HV. In contrast, droplet
While the oligomer was in the eye, ERGs showed a
formation and precipitates were demonstrated 5 days af- general reduction in amplitude of about 30% as com-
ter injection of decalin and 7 days after injection of O62 pared to the contralateral untreated eye (n=2), which is
(Fig. 1). The interface between the oligomer and the re- in accordance with the known insulating properties of
sidual vitreous was visible as a fine line (Fig.1). Vascular FCLs. Ten days after removal of the oligomer from the
constriction was noticed briefly after injection, but after rabbit eye, the ERG had returned to the normal value of

641
the control eye (n=2; data not shown). Histological alter- for removal of intraocular silicone oil remnants. HFCL-
ations of the lower retina were comparable to those after oligomers with increased viscosity proved stable against
PFCL or HFCL application or to those that have been intraocular emulsification. The appropriate physical and
described in the upper retina after long-term administra- chemical properties and the excellent experimental long-
tion of silicone oil [19, 24, 31]. They consisted in hyper- term biocompatibility and biostability point towards a
trophy of Müller cells, structural disturbance of the outer very good suitability of the oligomers for tamponade of
plexiform layer, and occasional foam cells and vacuoli- the lower retina and as a long-term vitreous substitute.
sation on the inner retinal surface (Fig. 3) [27]. Current- At present, clear guidelines and indications for an appli-
ly, oligomers are being evaluated in porcine eyes before cation of HFCL-oligomers in human eyes have to be de-
clinical trials are planned.
termined in clinical trials.
Acknowledgements Cooperation Arbeitsgemeinschaft Glaskör-
perersatz (AGGE) Germany: Prof. Michael Foerster, University
Eye Hospital, Benjamin Franklin, Freie-Universität, Berlin; Prof.
Veit-Peter Gabel, Prof. Johann Roider, Dr. Karin Kobuch, Univer-
Conclusions
†
For the future, PFCLs, HFCLs, and HFCL-oligomers
may represent a group of substances which can be em-
ployed and combined favourably according to special
surgical needs. High gas-binding capacities of PFCLs,
HFCLs, and oligomers offer new perspectives for the
treatment of the ischaemic retina [25, 38, 49]. HFCLs
with reduced specific gravity are presently introduced in-
to clinical use for intraoperative management of the de-
tached retina, but also for extended term application or
sity Eye Hospital, Regensburg; Prof. Klaus Heimann, University
Eye Hospital, Köln; Prof. Anselm Kampik, University Eye Hospi-
tal, Ludwig-Maximilians-Universität München; Prof. Horst Laqua,
Dr. Hans Hoerauf, University Eye Hospital, Lübeck; Prof. Peter
Wiedemann, Dr. Frank Faude, University Eye Hospital, Leipzig;
Dr. Martin Winter, University Eye Hospital, Kiel; Prof. Erhard
Kemnitz,Institut für anorganische und allgemeine Chemie, Hum-
boldt-Universität, Berlin; Dr. Dirk Henning Menz, Pharm Pur
GmbH, Augsburg; Dr. Joachim Dresp, Bausch & Lomb Surgical
GmbH, München
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