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RESEARCH ARTICLE
Axon numbers and landmarks of trigeminal
donor nerves for corneal neurotization
Eva Gyo
¨riID
1
, Chieh-Han John TzouID
1
, Wolfgang J. Weninger
2
, Lukas ReissigID
2
,
Ursula Schmidt-Erfurth
3
, Christine Radtke
1
, Roman Dunavoelgyi
3
*
1Division of Plastic and Reconstructive Surgery, Department of Surgery, Medical University of Vienna,
Vienna, Austria, 2Division of Anatomy, Medical University of Vienna, Vienna, Austria, 3Department of
Ophthalmology and Optometry, Medical University of Vienna, Vienna, Austria
*roman.dunavoelgyi@meduniwien.ac.at
Abstract
Purpose
Corneal anesthesia leads to chronic corneal injury. This anatomical study characterizes the
donor nerve branches of the supratrochlear and supraorbital nerves used for corneal
neurotization.
Methods
In 13 non-embalmed cadavers, the supratrochlear and supraorbital nerves were dissected
and distances to anatomical landmarks measured. Cross-sections of supratrochlear and
supraorbital donor nerves were harvested and histomorphometrically analyzed to assess
the number of myelinated axons.
Results
The donor axon counts were 3146 ±1069.9 for the supratrochlear and 1882 ±903 for the
supraorbital nerve distal to the supraorbital notch. The supratrochlear nerve was dissected
on the medial upper eyelid 2 cm lateral to the facial midline and the branch of the supraor-
bital nerve 1 cm medial to the mid-pupillary line.
Conclusion
The supraorbital and supratrochlear branches of the trigeminal nerve are potent donor
nerves for corneal neurotization in the treatment of neuropathic keratopathy and can be reli-
ably dissected using anatomical landmarks.
Introduction
Corneal anesthesia is a serious condition that leads to corneal injury through impaired protec-
tive sensation, which causes chronic erosions and infections, which may result in loss of vision
in severe cases [1]. The cornea is innervated by the ophthalmic division of the trigeminal nerve
PLOS ONE | https://doi.org/10.1371/journal.pone.0206642 October 31, 2018 1 / 12
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OPEN ACCESS
Citation: Gyo¨ri E, Tzou C-HJ, Weninger WJ,
Reissig L, Schmidt-Erfurth U, Radtke C, et al.
(2018) Axon numbers and landmarks of trigeminal
donor nerves for corneal neurotization. PLoS ONE
13(10): e0206642. https://doi.org/10.1371/journal.
pone.0206642
Editor: Leila Harhaus, BG Trauma Center
Ludwigshafen, GERMANY
Received: July 16, 2018
Accepted: October 16, 2018
Published: October 31, 2018
Copyright: ©2018 Gyo¨ri et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Funding: The study was funded by the Austrian
grant “Medical Research Fund of the Mayor of
Vienna” (project no. 17010) to RD, https://www.
wien.gv.at/gesundheit/einrichtungen/med-wiss-
fonds/. The funders had no role in study design,
data collection and analysis, decision to publish, or
preparation of the manuscript.
[2]. Corneal sensitivity is important for initiating the blink reflex and preserving the integrity
of the corneal epithelium [3].
Multiple congenital and acquired etiologies of corneal anesthesia have been identified,
which lead to the clinical condition described as neurotrophic keratopathy [1,3,4]. The most
common causes of neurotrophic keratopathy are viral infections such as herpes simplex or her-
pes zoster keratoconjunctivitis [4,5]. Acquired causes of corneal anesthesia include chemical
burns, physical injuries and corneal surgery [4]. Intracranial pathologies affecting the trigemi-
nal nerve or ganglion, lesions in the posterior fossa and pathologies affecting the brainstem
can also lead to neurotrophic keratopathy [4]. Systemic conditions like diabetes or demyelinat-
ing diseases can also affect the corneal sensitivity [1,4].
Congenital corneal anesthesia is either complete or partial, and typically affects both eyes
[2,6]. Cases of unilateral congenital corneal anesthesia have been reported, which can be asso-
ciated with anesthesia in other areas of the face supplied by the first and second division of the
trigeminal nerve [2]. Congenital cases can be either syndromatic, or non-syndromatic. Syn-
dromatic cases can be associated with ocular, neurological and systemic conditions, like the
VACTERL association, Goldenhar syndrome or Moebius syndrome [2].
With multiple etiologies causing corneal anesthesia, the cellular pathophysiological mecha-
nisms are complex and not yet fully investigated [4]. The cornea is densely innervated by sen-
sory, sympathetic and parasympathetic nerves, which each express specific neurotransmitters
[4]. Substance P and calcitonin gene-related peptide are highly expressed in sensory corneal
nerves, while sympathetic nerves contain neurotransmitters like noradrenaline, serotonin and
neuropeptide Y [4]. Altered neurotransmitter levels are a crucial mechanism leading to neuro-
throphic keratopathy [4]. Experimental studies showed that altered levels of cAMP, cGMP and
Substance P affect corneal epithelial cell regeneration in corneal anesthesia [2,7].
Despite the complex pathophysiology of corneal anesthesia, the treatment of neurotrophic
keratopathy was mainly symptomatic and included artificial tears, lubricants, bandage contact
lenses, protective glasses, punctual occlusion and tarsorrhaphy to avoid severe consequences
of corneal injury [2,8]. Surgical reinnervation of the anesthetic cornea was first described
by Terzis and colleagues in 2009. Six patients with unilateral facial palsy and neurotrophic ker-
atopathy were treated with corneal neurotization surgery using direct nerve transfers [3].
Through a bicoronary incision, the contralateral supraorbital and supratrochlear nerves were
used as donor nerves [3]. Corneal sensation was restored, but the method did not gain wide-
spread popularity, due to the bicoronary approach and extensive sensory donor nerve deficit
[5].
In 2014, Elbaz and colleagues published a minimally-invasive technique where autologous
sural nerve grafts are used for corneal neurotization to reduce the extent of surgical exposure
and to reduce donor site morbidity [5]. Depending on the etiology of corneal anesthesia, the
contralateral or ipsilateral supratrochlear nerves were used as donor nerves, with a minimally-
invasive access through small incision in the tarsal folds [5,9]. This method includes a side-to-
end coaptation of a sural nerve graft to the supratrochlear nerve, thus limiting the donor nerve
deficit by preserving the continuity of the donor nerve [5,9]. The authors reported improved
corneal sensation 6 months after neurotization, which is determined by the regeneration dis-
tance, given peripheral nerve regeneration of approximately 1 mm per day [9]. Postoperative
in vivo confocal microscopy showed successful corneal reinnervation in the stromal and sub-
basal corneal layers [10]. Some of the treated patients subsequently underwent corneal trans-
plantation after successful restoration of corneal sensation [5,10].
Ting and colleagues described favorable long-term outcomes after corneal neurotization,
which were confirmed by in vivo confocal microscopy and histopathological measures [11].
Benkhatar and colleagues successfully used the great auricular nerve as a nerve graft instead of
Donor nerves for corneal neurotization
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Competing interests: The authors have declared
that no competing interests exist.
the sural nerve for minimally-invasive corneal neurotization in a patient with unilateral neuro-
trophic keratopathy [12]. The nerve graft was coapted end-to-end to the contralateral supra-
trochlear nerve [12]. A minimally-invasive case of corneal neurotization using the ipsilateral
supraorbital nerve was described by Jacinto and colleagues in a patient with corneal anesthesia
from a local injury to the long ciliary nerves [13]. In this case report, the direct transfer of the
supraorbital nerve was performed while avoiding a bicoronary incision. In this case, the inter-
position of a nerve graft was not necessary, thus avoiding an additional sensory donor nerve
deficit and longer regeneration distances [13].
In all reported cases of corneal reinnervation, donor nerve branches of the supratrochlear
or the supraorbital nerve, were used [3,5]. They are distal branches of the ophthalmic division
of the trigeminal nerve and provide sensation to the forehead region, the upper eyelid and the
cornea [3,5].
As recent reports of corneal neurotization demonstrated reproducible, successful reinner-
vation in the anesthetic cornea, the donor nerves have not yet been further characterized. In
this study, we aimed to describe the supratrochlear and supraorbital nerves as donor nerves
for corneal neurotization and to analyze the number of myelinated axons available for sensory
reinnervation of the anesthetic cornea. The detailed analysis of available donor nerve branches
is crucial, because their axonal load determines the reinnervation capacity and the subsequent
donor nerve deficit. Terzis and colleagues described 900 myelinated axons as a cut-off value
for donor nerve branch selection in cases of facial reanimation surgery [14]. However, these
values might not directly translate to corneal reinnervation, as donor branches of the facial
nerve a motoric donors and regeneration distances through cross-face nerve grafts are signifi-
cantly higher. The optimal number of donor axons for corneal reinnervation is not yet estab-
lished. In this anatomical study, we aimed to provide detailed data of trigeminal donor nerve
characteristics. The second aim of this study was to describe reliable anatomical landmarks to
guide intraoperative donor nerve dissection.
Materials and methods
The study was performed under the approval of the ethics commission of the Medical Univer-
sity of Vienna (protocol number 1826/2016) and followed the guidelines of the Helsinki Decla-
ration of 1975 and the regulations concerning the use of body donor materials for science
and teaching. Written pre-mortem consent for anatomical research was obtained from each
individual.
Anatomical dissection
Thirteen fresh, non-embalmed white cadavers (7 female and 6 male) were dissected for this
study. The exclusion criteria for anatomical specimen selection were periorbital scars and cra-
nial trauma. All dissections were performed under surgical loupe magnification. Measure-
ments were obtained bilaterally using a standard surgical ruler. Through a tarsal incision, the
supratrochlear nerve was identified and the distances to the facial midline, the medial corner
of the eyelid, the mid-pupillary line and the nasocranial margin of the orbita were measured
(Fig 1). Subsequently, the supraorbital nerve was dissected using a supraciliar incision. The
distances to the facial midline, the medial corner of the eyelid and the mid-pupillary line were
measured (Fig 1).
Sural nerve grafts were harvested with minimally invasive technique through a lateral retro-
malleolar incision using a nerve stripper. Proximally, 2 to 3 small skin incisions of 15 to 20
mm were performed to aid nerve graft harvesting, depending on the branching pattern of the
Donor nerves for corneal neurotization
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Fig 1. Anatomical landmarks. The facial midline (solid arrow), the medial canthus (dashed arrow) and the mid-
pupillary line (dotted arrow) were used as landmarks to provide guiding distances for donor nerve branch dissection of
the supraorbital and supratrochlear nerves in this anatomical study.
https://doi.org/10.1371/journal.pone.0206642.g001
Donor nerves for corneal neurotization
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sural nerve [15]. Nerve grafts of approximately 15 cm length were used for corneal neurotiza-
tion, as previously described by Bains and colleagues [9].
As clinically described in unilateral cases of neuropathic keratopathy, the contralateral
supratrochlear or supraorbital nerve can be used as the donor nerve branches and the sural
nerve graft was passed from the donor side to the recipient side through a subcutaneous tunnel
(Fig 2A). On the insensate side, the sural nerve graft was pulled through a craniomedial con-
junctival incision and guided to the superior fornix using a Wright Fascia Needle (Fig 2B). The
fascicles at end of the nerve graft were separated and the ends trimmed (Fig 2C). The 4 to 5
individual fascicles of the nerve graft were placed under the conjunctiva (Fig 2D), spread out
evenly and sutured to the sclera with perilimbal 10–0 Nylon interrupted sutures (Fig 2E) as
described previously [5,9]. The nerve graft was coapted to the donor nerve with interrupted
10–0 Nylon epineural sutures. In a clinical situation, the patient’s eye would have been closed
with a temporary tarsorrhaphy for one week [5].
Nerve cross-sections and myelinated donor nerve counts
Cross-sections of the supratrochlear and supraorbital nerves were obtained for histomorpho-
metric analysis. The samples were harvested at the site of coaptation to the autologous nerve
graft to assess the available donor nerve counts for corneal reinnervation. Samples of the
Fig 2. Neurotization of the anesthetic cornea using a sural nerve graft and supratrochlear donor nerve. Cadaveric dissection to
neurotize the right cornea using the contralateral supratrochlear nerve as a donor, which is dissected through a small skin incision
on the upper eyelid. A subcutaneous tunnel connects the donor and recipient side (A). The sural nerve is used as an autologous
nerve graft and pulled through the to the superior fornix with a Wright Fascia Needle (B). The fascicles of the sural nerve graft are
separated (C) and tunneled under the conjunctiva (D). The 4 to 5 fascicles are placed around the limbus and sutured to the sclera
using 10–0 Nylon interrupted sutures (E).
https://doi.org/10.1371/journal.pone.0206642.g002
Donor nerves for corneal neurotization
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supraorbital nerve were harvested proximally in the cranial part of the orbita and further dis-
tally after its passage through the supraorbital notch. Additionally, biopsies of the sural nerve
graft were harvested. Nerve biopsies were fixed in 2.5% glutaraldehyde and processed as previ-
ously described [16,17]. Characteristics of nerve cross-sections and myelinated nerve fibers
were measured using a semi-automated image analyzing software (LUCIA-M, Nikon Labora-
tory Imaging, Prague, Czech Republic) [17]. Axon diameters were marked by the investigator
for an area covering at least 30% of the nerve cross-section. The image analysis software was
subsequently used to calculate the axon numbers of the entire nerve biopsy.
Statistical analysis
Mean values and standard deviations were reported for all anatomical measurements and his-
tomorphometric criteria. The different myelinated donor axon counts were analyzed by one-
way ANOVA and post-hoc Bonferroni corrections. A two-sided p-value of <0.05 was consid-
ered statistically significant.
Results
Anatomical dissection
Seven female and 6 male cadavers were dissected for this study. The mean age was 79.4 ±9.5
years. Cause of death was pneumonia in 3 cases, cardiovascular events in 3 cases and cancer in
1 case. In 6 cases, the exact cause of death was not available, however, all included anatomical
specimen met the criteria of no periorbital scars or trauma.
Anatomical landmarks
In this cadaver study, the supratrochlear nerve (Fig 3A) was dissected through a short trans-
verse incision on the medial upper eyelid under surgical loupe magnification. The mean dis-
tance to the supratrochlear nerve was 20.1 ±2.8 mm lateral to the facial midline and 14 ±2.9
mm medial to the mid-pupillary line. The supratrochlear nerve was found 2.7 ±1.6 mm lateral
to the medial canthus and 2 mm caudal to the craniomedial orbital rim.
The supraorbital nerve (Fig 3B) was accessed through a supraciliary incision at the medial
third of the eyebrow. The supraorbital nerve was 19.6 ±3.1 mm lateral to the facial midline
and 11.8 ±2.4 mm medial to the mid-pupillary line. The mean distance to the medial canthus
was 1.7 ±0.6 mm.
As practical dissection guidelines for the supratrochlear and supraorbital nerves as donor
nerves with limited skin incisions, the supratrochlear nerve can be located through a tarsal
incision approximately 2 cm lateral to the facial midline and 2 mm caudal to the craniomedial
orbital rim. The supraorbital nerve can be dissected through a supraciliary incision approxi-
mately 1 cm medial to the mid-pupillary line.
Myelinated donor nerve fiber counts
Nerve biopsies were obtained for histomorphometric analysis of myelinated axons and nerve
cross-sections were evaluated. The supratrochlear nerve contained 3146 ±1069.9 myelinated
axons in 2 ±1.5 fascicles (Fig 4A). The supraorbital nerve branch distal to the supraorbital
notch, which was dissected through a supraciliary incision, included 1882 ±903 myelinated
axons in 6 ±3.8 fascicles (Fig 4B). The proximal part of the supraorbital nerve, which was dis-
sected proximal to the orbital rim through a tarsal approach, contained 6035 ±1675.2 myelin-
ated nerve fibers in 4 ±2.2 fascicles. The sural nerves harvested as autologous nerve grafts
contained 3179 ±1524.5 myelinated nerve fibers in 7 ±3.8 fascicles (Fig 4C).
Donor nerves for corneal neurotization
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Fig 3. Donor nerve branch dissection using anatomical landmarks. The donor branch of the supraorbital nerve distal to the
supraorbital notch accessed through a supraciliary incision and found approximately 1 cm medial to the mid-pupillary line (A). The
supratrochlear nerve branch was located 2 cm lateral to the facial midline and dissected through a small transverse incision on the
medial upper eyelid (B). The sketch on the left side displays the anatomical landmarks (see Fig 1).
https://doi.org/10.1371/journal.pone.0206642.g003
Fig 4. Nerve biopsies. Cross-sections of nerve biopsies of the supratrochlear nerve (A), the supraorbital nerve (B) and the sural
nerve graft (C) were analyzed histomorphometrically to determine the myelinated axon counts.
https://doi.org/10.1371/journal.pone.0206642.g004
Donor nerves for corneal neurotization
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The myelinated axon counts of cross-sections of the proximal supraorbital nerves were sig-
nificantly higher than those of the distal supraorbital nerves (p <0.001), the supratrochlear
nerves (p = 0.003) and the sural nerves (p = 0.001). The myelinated axon counts of the supra-
trochlear nerve and the distal supraorbital nerve biopsies did not differ significantly.
Discussion
Reinnervating the anesthetic cornea provides a therapeutic treatment option for neuropathic
keratopathy, which was previously managed symptomatically [3,5,9]. Corneal neurotization
was first described by Terzis and colleagues and has been successfully performed in few
patients worldwide [3,9,11]. Corneal reinnervation is either performed by direct nerve trans-
fers [3,13] or by interposition of nerve grafts [5,9,11,12]. This study analyzed the characteris-
tics of the supratrochlear and supraorbital nerve branches of the trigeminal nerve used as
donors for corneal neurotization. Additionally, reliable anatomical landmarks for donor nerve
branch dissection were described for both, the supratrochlear and the supraorbital nerve
branches.
The main findings of this study were the robust donor nerve counts of the trigeminal donor
nerve branches: the supratrochlear nerve contained approximately 3150 myelinated axons and
the supraorbital nerve 1880 distal and 6000 proximal to the supraorbital notch, respectively.
The high numbers of myelinated axons available for sensory reinnervation of the anesthetic
cornea concur with the clinical reports of successful postoperative outcomes in patients with
neuropathic keratopathy [3,5,10,11].
The data of this anatomical study described the supratrochlear and supraorbital nerve
branches as strong donor nerves, however, the optimal number of donor axons has not yet
been determined. The previously reported cut-off point of 900 myelinated axons [14] for
donor branch selection in facial reanimation surgery may not be directly translatable to cor-
neal reinnervation surgery, because regeneration distances are significantly longer and the
axonal input required for adequate motor reinnervation may differ from the axonal load nec-
essary to restore corneal sensation. The high axon counts of all available trigeminal donor
nerves, confirm that distal donor nerve branch selection, which reduced the donor nerve defi-
cit, is possible. The supraorbital nerve proximal to the supraorbital notch contains significantly
more myelinated donor axons than its distal branch and the supratrochlear nerve. It remains
to be determined if choosing a stronger donor nerve branch for end-to-side coaptation to the
nerve graft leads to superior results compared to harvesting a smaller, more distal donor nerve
branch for end-to-end coaptation and creating a partial sensory donor nerve deficit.
The different techniques of corneal neurotization involved either direct nerve transfers
through a bicoronary dissection [3], or a minimally-invasive technique using small tarsal and
supraciliary incisions with interposition of nerve grafts [5,9]. Recently, Leyngold and col-
leagues described an endoscopic technique to dissect the supraorbital nerve for corneal neuro-
tization [18,19]. The nerve fascicles are coapted around the limbus using microsurgical
technique in all surgical methods, using either direct nerve transfers or nerve grafting [3,5,9].
When autologous nerve grafts were used, the proximal coaptation of the nerve graft to the
donor nerve was performed with micro-sutures and fibrin glue [9]. Here, the donor nerve
branch selection and coaptation method influences the amount of donor nerve fibers that will
grow through the nerve graft and subsequently reinnervate the cornea. As indicated by Elbaz
and colleagues, depending on the size of the selected donor nerve branch and the clinical pre-
sentation, end-to-side or end-to-end coaptations of the nerve graft can be performed [5].
Larger donor nerve branches are more suitable for end-to-side coaptations, where the end of
the nerve graft is sutured to the side of the donor nerve, which preserves donor nerve function
Donor nerves for corneal neurotization
PLOS ONE | https://doi.org/10.1371/journal.pone.0206642 October 31, 2018 8 / 12
[20]. In neuropathic keratopathy, future experimental studies are needed to determine the
number of donor nerve axons growing into the nerve graft and reinnervating the cornea. Pre-
vious studies have shown that the number of axons growing into nerve grafts is generally less
predictable after end-to-side coaptations than after end-to-end coaptations [20,21]. There are
numerous clinical and experimental examples of successful regeneration through end-to-side
nerve coaptations [21–28], but in cases of corneal neurotization their applications and benefits
compared to end-to-end coaptations remain to be determined. Choosing smaller donor nerve
branches and opting for end-to-side coaptations while preserving the continuity of the donor
nerve reduces the sensory donor nerve deficit and may be beneficial for the patient, given
recent clinical reports of successful corneal neurotization using these less invasive techniques
with interposition of nerve grafts [5,9,11] compared to the more invasive direct nerve transfer
through a bicoronary approach [3]. The additional sensory deficit of the sural nerve graft is
limited to the dorsolateral foot and clinically acceptable for the majority of patients [15].
Through improved minimally invasive techniques, the skin incisions in both the donor nerve
dissection in the face and the dorsal to the lateral malleolus are limited and the scars are cos-
metically acceptable [5]. Benkhatar and colleagues recently proposed using the great auricular
nerve instead of the sural nerve graft [12]. The smaller diameter of the nerve graft, which is
more compatible to the donor nerve branches than the sural nerve, and the harvest site were
cited as main benefits of this technique [12]. The length of the harvested great auricular nerve
was 7 cm [12], which is shorter than the sural nerve graft of approximately 15 cm used by
other authors [5]. Clinically, the appropriate nerve graft selection will depend on donor nerve
selection and anatomical features of the patient, which determine the regeneration distance
that needs to be covered.
In the present study, distances to anatomical landmarks for simple donor nerve branch dis-
section were described. The supratrochlear nerve can be found 2 cm lateral to the facial mid-
line and 2 mm caudal to the orbital rim, whereas the supraorbital donor nerve branch distal to
the supraorbital notch can be dissected 1 cm medial to the mid-pupillary line. The described
anatomical landmarks are easily clinically applicable and facilitate reliable donor nerve
dissection.
Clinical studies demonstrated successful corneal neurotization which improved patients’
vision by avoiding corneal injuries associated with corneal anesthesia and providing improved
conditions for subsequent corneal transplantation [5]. After corneal neurotization, in vivo
confocal microscopy confirmed the successful reinnervation of stromal and subbasal corneal
layers and documented the presence of new sensory nerve fibers [10]. Ting and colleagues
underlined the importance of neurotrophic factors providing trophic support after corneal
neurotization [11]. It is yet unclear how many ingrowing nerve fibers are required to achieve
clinically adequate results. Soluble factors released by trigeminal neurons, which stimulate cor-
neal epithelial cells, and neurotrophic factors expressed by corneal epithelial cells that promote
nerve regeneration have been shown to play a crucial role in the pathogenesis of neurotrophic
keratopathy [4]. Their role in corneal reinnervation will be the focus of future investigations.
The cornea is the most densely innervated surface tissue due to the complex innervation and
branching patterns of corneal nerves [29]. Corneal nerves are heterogeneous and innervate dif-
ferent nociceptors: about 20% are mechano-nociceptors, 70% are polymodal nociceptors and
10% are cold-receptors [30]. The role of nociceptor excitation and sensitization after corneal
reinnervation remains to be explored in experimental studies and will improve our under-
standing of the underlying cellular mechanisms of corneal neurotization.
The present study showed that both the supraorbital and the supratrochlear nerve are
potent donor nerves that can be reliably dissected using clinical landmarks. Limitations of the
Donor nerves for corneal neurotization
PLOS ONE | https://doi.org/10.1371/journal.pone.0206642 October 31, 2018 9 / 12
study were the advanced age of the cadavers and the limited information about preexisting
neurological conditions available from the donors.
Conclusion
The supraorbital and supratrochlear branches of the trigeminal nerve are potent donor nerves
for corneal neurotization, that can be reliably dissected using anatomical landmarks. Restoring
sensory innervation to the cornea provides a therapeutic treatment option for patients suffer-
ing from neuropathic keratopathy.
Supporting information
S1 Table. Supporting information for nerve biopsies. Histomorphometric analysis of nerve
biopsy characterizing fascicle numbers and myelinated axon counts.
(XLSX)
Acknowledgments
The authors thank Maria Prieto Barea and Andrea Ofner for creating the anatomical sketch.
They also thank Sonja Wolf and Melanie Schmid for the histomorphometric analysis of nerve
cross-sections.
Author Contributions
Conceptualization: Eva Gyo¨ri, Roman Dunavoelgyi.
Data curation: Eva Gyo¨ri.
Formal analysis: Eva Gyo¨ri, Roman Dunavoelgyi.
Funding acquisition: Eva Gyo¨ri, Roman Dunavoelgyi.
Investigation: Eva Gyo¨ri, Chieh-Han John Tzou, Roman Dunavoelgyi.
Methodology: Roman Dunavoelgyi.
Project administration: Eva Gyo¨ri.
Resources: Wolfgang J. Weninger, Lukas Reissig, Ursula Schmidt-Erfurth, Christine Radtke.
Supervision: Wolfgang J. Weninger, Ursula Schmidt-Erfurth, Christine Radtke.
Visualization: Eva Gyo¨ri, Chieh-Han John Tzou.
Writing – original draft: Eva Gyo¨ri.
Writing – review & editing: Chieh-Han John Tzou, Wolfgang J. Weninger, Lukas Reissig,
Ursula Schmidt-Erfurth, Christine Radtke, Roman Dunavoelgyi.
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