Endoscopic Corneal Neurotization: Technique and Initial Experience

Corneal Neurotization: Paving the Path to Reinnervation

Neurotrophic keratopathy (NK), a degenerative corneal disease characterized by the loss of innervation to the cornea, has historically required long-term supportive treatment with a poor prognosis for rehabilitation. Corneal neurotization restores corneal sensation, permanently addressing the underlying pathophysiology of NK. Surgical approaches to corneal neurotization are expanding and undergoing refinement as more centers perform this intervention. This article describes the indications, surgical approaches, outcomes, and future directions of corneal neurotization.

Corneal neurotization for the treatment of neurotrophic keratopathy

PURPOSE OF REVIEW

Corneal neurotization, a surgical technique that restores corneal sensation by transferring a healthy sensory nerve to the neurotrophic cornea, has emerged as a treatment of moderate to severe neurotrophic keratopathy. This review provides an overview of the indications, surgical techniques, and outcomes of corneal neurotization.

RECENT FINDINGS

Corneal neurotization can be performed via direct nerve transfer or indirect nerve grafting, with comparable long-term outcomes. Advances such as minimally invasive and endoscopic techniques, nerve allografts, and alternative donor nerves have expanded its accessibility. Studies show significant improvements in corneal sensation, epithelial integrity, and ocular surface health, with younger patients achieving faster and more complete recovery. The procedure has demonstrated efficacy across diverse neurotrophic keratopathy etiologies and is increasingly considered earlier in disease progression.

SUMMARY

Corneal neurotization offers a promising, long-term solution for neurotrophic keratopathy by addressing the root cause of corneal anesthesia.

Corneal Neurotization for Neurotrophic Keratopathy: A Multicenter Experience

PURPOSE

Corneal neurotization is an emerging technique that offers potential for visual rehabilitation in neurotrophic keratopathy. This study reports on a multicenter experience and outcomes for both direct and indirect methods of corneal neurotization.

METHODS

Retrospective case series. Sixteen patients with neurotrophic keratopathy who underwent corneal neurotization across 5 centers in Australia and Israel were identified for inclusion. Corneal neurotization was performed via direct neurotization from the ipsilateral or contralateral supraorbital/supratrochlear nerve or by the use of an interpositional sural nerve graft. Change in corneal sensitivity (measured in millimeters by the Cochet-Bonnet aesthesiometer), visual acuity, and corneal health.

RESULTS

Over a mean follow-up period of 31.3 months (range: 3 months-8 years), mean corneal sensitivity improved from 3.6 mm (range: 0-25 mm) to 25.3 mm (range: 0-57 mm). Visual acuity improved on average from 20/380 to 20/260. Twelve of 16 patients (75.0%) improved in at least 2 out of the 3 main outcome measures. Nine patients (56.3%) showed an improvement in visual acuity; 13 (81.3%) showed an improvement in average corneal sensitivity; and 11 (68.8%) showed an improvement in corneal health. There were no intraoperative or postoperative complications.

CONCLUSIONS

Corneal neurotization is an emerging surgical treatment option for the management of neurotrophic keratopathy. With appropriate case selection, outcomes are favorable and complication rates are low, for a condition that is otherwise challenging to manage. Patients with severe neurotrophic keratopathy should be considered for this surgical treatment option.

Corneal Neurotization: Essentials for The Facial Paralysis Surgeon

Deficits in corneal innervation lead to neurotrophic keratopathy (NK). NK is frequently associated with facial palsy, and corneal damage can be accelerated by facial palsy deficits. Corneal nerves are important regulators of limbal stem cells, which play a critical role in epithelial maintenance and healing. Nonsurgical treatments of NK have undergone recent innovation, and growth factors implicated in corneal epithelial renewal are a promising therapeutic avenue. However, surgical intervention with corneal neurotization (CN) remains the only definitive treatment of NK. CN involves the transfer of unaffected sensory donor nerve branches to the affected cornea, and a variety of donor nerves and approaches have been described. CN can be performed in a direct or indirect manner; employ the supraorbital, supratrochlear, infraorbital, or great auricular nerves; and utilize autograft, allograft, or nerve transfer alone. Unfortunately, comparative studies of these factors are limited due to the procedure's novelty and varied recovery timelines after CN. Regardless of the chosen approach, CN has been shown to be a safe and effective procedure to restore corneal sensation and improve visual acuity in patients with NK.

Insights on the Choice and Preparation of the Donor Nerve in Corneal Neurotization for Neurotrophic Keratopathy: A Narrative Review

The article introduces neurotrophic keratopathy (NK), a condition resulting from corneal denervation due to various causes of trigeminal nerve dysfunctions. Surgical techniques for corneal neurotization (CN) have evolved, aiming to restore corneal sensitivity. Initially proposed in 1972, modern approaches offer less invasive options. CN can be performed through a direct approach (DCN) directly suturing a sensitive nerve to the affected cornea or indirectly (ICN) through a nerve auto/allograft. Surgical success relies on meticulous donor nerve selection and preparation, often involving multidisciplinary teams. A PubMed research and review of the relevant literature was conducted regarding the surgical approach, emphasizing surgical techniques and the choice of the donor nerve. The latter considers factors like sensory integrity and proximity to the cornea. The most used are the contralateral or ipsilateral supratrochlear (STN), and the supraorbital (SON) and great auricular (GAN) nerves. Regarding the choice of grafts, the most used in the literature are the sural (SN), the lateral antebrachial cutaneous nerve (LABCN), and the GAN nerves. Another promising option is represented by allografts (acellularized nerves from cadavers). The significance of sensory recovery and factors influencing surgical outcomes, including nerve caliber matching and axonal regeneration, are discussed. Future directions emphasize less invasive techniques and the potential of acellular nerve allografts. In conclusion, CN represents a promising avenue in the treatment of NK, offering tailored approaches based on patient history and surgical expertise, with new emerging techniques warranting further exploration through basic science refinements and clinical trials.

Corneal Neurotization: Preoperative Patient Workup and Surgical Decision-making

Background

The use of sensory nerve transfers to the anesthetic cornea has transformed the treatment of neurotrophic keratopathy by restoring ocular surface sensation and activating dysfunctional epithelial repair mechanisms. However, despite numerous reports on surgical techniques, there is a scarcity of information on the interdisciplinary management, preoperative assessment, and surgical decision-making, which are equally critical to treatment success.

Methods

This Special Topic presents a standardized, interdisciplinary preoperative workup based on our 10-year experience with corneal neurotization in 32 eyes of patients with neurotrophic keratopathy.

Results

Our assessment includes a medical history review, ophthalmic evaluation, and systematic facial sensory donor nerve mapping for light touch and pain modalities. This approach enables evidence-based patient selection, optimal surgery timing, and suitable donor nerve identification, including backup options.

Conclusions

Based on a decade-long experience, this special topic highlights the importance of interdisciplinary collaboration and provides a practical roadmap for optimizing patient selection and surgical decision-making in patients undergoing corneal neurotization.

Corneal Neurotization—Indications, Surgical Techniques and Outcomes

Corneal neurotization is a promising surgical approach for the treatment of moderate to severe neurotrophic keratopathy. This technique aims to restore corneal sensation by transferring healthy nerves, either directly or via a conduit, to the anesthetic cornea. This review provides a report on the current state of development, evidence, and experience in the field. We summarize the data available from clinical reports and case series, placing an emphasis on the diversity of the surgical techniques reported. While these data are encouraging, they also highlight the need for a consensus in reporting outcomes and highlight how the next step will involve validating putative outcome parameters when researching and reporting corneal neurotization surgery.

Corneal neurotization in the management of neurotrophic keratopathy: A review of the literature

Neurotrophic keratopathy (NK) is a rare degenerative disease in which damage to the corneal nerves leads to corneal hypoesthesia or anesthesia. Neurotrophic corneal ulcers are notoriously difficult to treat and can lead to blindness. Corneal neurotization (CN) is a recent surgical technique aimed at restoring corneal sensation and may offer a definitive treatment in the wake of NK. Herein, we review the surgical techniques utilized in direct and indirect CN. Technical considerations, outcomes, current limitations and future perspectives are also discussed. This article highlights the key points of this promising procedure and biological aspects that will help provide the best treatment options for patients with severe NK.

A Surgeon's Armamentarium for Ocular Management in Facial Paralysis: A Comprehensive Review

OBJECTIVE

To review the current management paradigm of the eye in patients with facial paralysis.

METHODS

A PubMed and Cochrane search was done with no date restrictions for English-language literature on facial synkinesis. The search terms used were "ocular," "facial," "synkinesis," "palsy," "neurotization," and various combinations of the terms. A total of 65 articles were included.

RESULTS

Facial paralysis may result in devastating ocular sequelae. Therefore, assessment of the eye in facial paralysis is a critical component of patient management. Although the management should be individualized to the patient, the primary objective should include an ophthalmologic evaluation to implement measures to protect the ocular surface and preserve visual acuity. The degree of facial paralysis, lacrimal secretion, corneal sensation, and position of the eyelids should be assessed thoroughly. Patients with the anticipated recovery of facial nerve function may respond to more conservative temporizing measures to protect the ocular surface. Conversely, patients with expected prolonged paralysis should be appropriately identified as they will benefit from surgical reconstruction and rehabilitation of the periorbital complex. The majority of reconstructive measures within a facial surgeon's armamentarium augment coverage of the eye but are unable to restore blink. Eyelid reanimation restores the esthetic proportionality of the eye with blinking and reestablishes protective functions necessary for ocular preservation and function.

CONCLUSIONS

Ocular preservation is the primary priority in the initial management of the patient with facial paralysis. An accurate assessment is a critical component in identifying the type of paralysis and developing an individualized treatment plan.

Neurotrophic keratopathy: current challenges and future prospects

Neurotrophic keratopathy (NK), or neurotrophic keratitis, is a degenerative condition that results from decreased innervation to the cornea. The cornea is innervated by the ophthalmic branch of the trigeminal nerve. Neurotrophic keratopathy is most commonly caused by herpes keratitis however, any condition that disrupts the normal corneal innervation can cause NK. Neurotrophic keratopathy is a clinical diagnosis and is classified into three stages based on the disease severity. Stage 1 has mild epithelial defects, such as punctate keratopathy, stage 2 disease has persistent epithelial defects, and stage 3 is defined by the presence of ulcers. Current treatment modalities consist of medical and surgical options. Stage 1 is treated with lubrication through artificial tears, eyelid taping, and punctal plug/cautery. Stage 2 treatment can involve therapeutic contact lenses, topical autologous or allogenic serum, tarsorrhaphy, botulinum toxin injections, and possibly anti-inflammatory medications. Stage 3 disease may require human nerve growth factor, amniotic membrane transplantation, conjunctival flap, or corneal neurotization. New therapies, such as matrix regenerating therapy, plasma rich in growth factors, Thymosin β4, Substance P/Insulin like growth factor-1, and nicergoline represent exciting future options.KEY MESSAGESNeurotrophic keratopathy is a rare degenerative disease defined by decreased innervation to the cornea that is associated with significant morbidity.Treatment options range from lubrication alone to various medical and surgical treatments.Matrix regenerating therapy, plasma rich in growth factors, Thymosin β4, Substance P/Insulin like growth factor-1, and nicergoline are exciting novel therapies that will influence how neurotrophic keratopathy is treated in the future.

Blink Reflex in Neurotrophic Keratopathy: An Electrophysiological Evaluation

PURPOSE

Neurotrophic keratitis (NK) is a rare condition which may result in visual loss. This case review investigates if there may be an association between NK and the blink reflex in the absence of facial nerve palsy and lagophthalmos.

METHODS

This is a retrospective case review of 5 patients with trigeminal nerve damage referred to the oculoplastic department with suspected anesthetic corneae. Information on etiology, symptoms, duration, associated medical conditions, medications, examination findings including Mackie stage of keratopathy, management of keratopathy, and blink electrophysiology results was obtained.

RESULTS

All 5 patients demonstrated absence of corneal sensation. All patients had preserved facial nerve function with no evidence of lagophthalmos. Keratopathy ranged from Mackie stage 0-2. Management ranged from ocular lubricants to Botulinum-toxin-induced ptosis. Blink studies demonstrated reduction in amplitude as well as increased latency in 2 patients, conferring reduced blink strength. Two patients demonstrated an absent blink reflex on the affected side. One patient had blink latency within the normative range; this patient recovered corneal sensation and was discharged.

CONCLUSIONS

Our finding of reduced amplitude in blink studies offers both a factor in pathogenesis of NK and a potential therapeutic target. Additionally, blink studies may provide prognostic information for recovery and therefore guide management. We suggest performing blink electrophysiology in patients with trigeminal nerve damage to assess nerve function.

Corneal Neurotization: A Meta-analysis of Outcomes and Patient Selection Factors

BACKGROUND

Corneal neurotization describes reinnervation of the anesthetic or severely hypoesthetic cornea with a healthy local nerve or graft. Preliminary evidence has shown corneal neurotization to improve corneal sensation, visual acuity, and ocular surface health. Factors that improve patient selection and lead to better neurotization outcomes have yet to be elucidated, limiting ability to optimize perioperative decision-making guidelines.

METHODS

A systematic review with meta-analysis was performed of the MEDLINE and Embase databases using variations of "corneal," "nerve transfer," "neurotization," and "neurotization." The primary outcomes of interest were corrected visual acuity, NK Mackie stage, and central corneal sensation. Regression analyses were performed to identify the effects of surgical technique, duration of denervation, patient age, and etiology of corneal pathology on neurotization outcomes.

RESULTS

Seventeen studies were included. Corneal neurotization resulted in significant improvement in NK Mackie stage (0.84 vs 2.46, P < 0.001), visual acuity (logarithm of minimum angle of resolution scale: 0.98 vs 1.36, P < 0.001), and corneal sensation (44.5 vs 0.7, P < 0.001). Nerve grafting was associated with greater corneal sensation improvement than nerve transfer (47.7 ± 16.0 vs 35.4 ± 18.76, P = 0.03). Denervation duration was predictive of preneurotization visual acuity (logarithm of minimum angle of resolution scale; R2 = 0.25, P = 0.001), and older age (ß = 0.30, P = 0.03) and acquired etiology (ß = 0.30, P = 0.03) were predictive of improved visual acuity.

CONCLUSIONS

Corneal neurotization provides significant clinical improvement in visual acuity, NK Mackie staging, and corneal sensation in patients who experience NK. Both nerve grafting and nerve transfer are likely to yield similar levels of benefit and ideally should be performed early to limit denervation time.

Minimally Invasive Corneal Neurotization Provides Sensory Function, Protects Against Recurrent Ulceration, and Improves Visual Acuity

PURPOSE

To measure sensory recovery after minimally invasive corneal neurotization, and to identify and quantify the extent to which patient and technical factors influence sensory recovery, ulceration rate, and visual outcomes.

DESIGN

Retrospective case series.

METHODS

This study included 23 patients with neurotrophic keratopathy who underwent indirect corneal neurotization. The primary outcome measure was corneal sensitivity with Cochet-Bonnet aesthesiometry (CBA), and the secondary outcome measure was epithelial breakdown.

RESULTS

Over a 7-year period, 28 eyes of 23 patients (mean age, 15.6 ± 13.6 years) were included in the study. The CBA measurements improved from 3.5 ± 9.1 mm at baseline to 44.1 ± 18.2 mm at 24 months after surgery (P < .001). Maximum CBA was reached after 11.1 ± 6.2 months (median, 9 months). Compared to eyes neurotized with a contralateral donor nerve, eyes with an ipsilateral donor nerve achieved a higher mean CBA (36.0 ± 10.9 vs 10.4 ± 14.0 mm, P = .001) at 3 months. Both the number of fascicles (Spearman correlation coefficient, r_s -0.474, P = .11) and insertions (r_s -0.458, P = .014) negatively correlated with the final CBA. Nine eyes (32.1%) experienced at least 1 episode of epithelial breakdown after surgery. Visual acuity improved in the neurotized corneas from logMAR 0.57 ± 0.79 at baseline to 0.39 ± 0.66 at 12 months (P = .043).

CONCLUSIONS

Corneal sensation improves over time after corneal neurotization. There is resultant improvement in visual acuity and protection against epithelial breakdown. It is important to maximize sensory recovery to protect against recurrent ulceration.

Direct Neurotization: Past, Present, and Future Considerations

ABSTRACT

Direct neurotization is a method that involves direct implantation of nerve fascicles into a target tissue, that is, muscle fibers, skin, cornea, and so on, with the goal of restoring aesthetic, sensation and or functional capacity. This technique has been implemented since the early 1900s, with numerous experimental and clinical reports of success. Applications have included both sensory and motor neurotization of muscle, as well as protective sensory provision for other organs. These techniques have been used to restore corneal sensation, repair brachial plexus injuries, reestablish tongue movement and function through direct tongue neurotization, and reinnervate multiple facial muscles in patients with facial paralysis. Most recently, these methods have even been used in conjunction with acellular cadaveric nerve grafts to directly neurotize skin. Indications for direct neurotization remain limited, including those in which neural coaptation is not feasible (ie, surgical or traumatic damage to neuromuscular junction, severe avulsion injuries of the distal nerve); however, the success and wide-range application of direct neurotization shows its potential to be implemented as an adjunct treatment in contrast to views that it should solely be used as a salvage therapy. The purpose of the following review is to detail the historic and current applications of direct neurotization and describe the future areas of investigation and development of this technique.

[Treatment of neurotrophic keratopathy in combined lesions of the trigeminal and facial nerves]

Ocular symptomatology in lesions of the facial nerve is associated with disturbed innervation of the circular muscle of the eye that leads to disruption of the protective function of the eyelids and the development of exposure symptoms, and is accompanied by a breach in corneal tear film integrity. The main clinical manifestation of the trigeminal nerve damage is the loss of sensory innervation of the cornea and disruption of the supply of neurotransmitters to its cells, manifesting as corneal hypo- or anesthesia. This triggers a cascade of pathological processes that lead to the development of neurotrophic keratopathy. In combined pathology of the facial and trigeminal nerves, a number of interrelated and mutually aggravating problems arise that require correction of lagophthalmos and functional restoration of the trigeminal nerve, since there is an interaction between the corneal epithelium and trigeminal neurons through trophic neuromodulators, which normally contribute to the proliferation of epithelial cells, their differentiation, migration and adhesion, and are essential for vital functions, metabolism and healing of surface lesions of the eye. Classical methods of treating neurotrophic keratopathy aim to protect the ocular surface, and are palliative or auxiliary, do not provide radical relief of the symptoms of neurotrophic keratopathy. Modern surgical technique of neurotization of the cornea allows restoring the structural growth of the nerve, which provides nerve trophism and corneal sensitivity, and is the only pathogenetically substantiated method of effective treatment of neurotrophic keratopathy. At the same time, direct neurotization has undeniable advantages over methods involving intercalary donor nerves, since neuropeptides from nerve fibers are immediately released into the recipient tissue and start reparative processes. Taking into account the accumulated positive experience of neurotization surgeries, scientific and clinical research should be continued in order to improve the most effective methods of corneal neurotization and promote their wider implementation into clinical practice.

Corneal Neurotization via Dual Nerve Autografting

Corneal neurotization is a fast-evolving surgical procedure for sensory reinnervation in neurotrophic keratopathy. After neurotization, prior reports document return of corneal sensation on average 8 months after surgery with 38 mm of sensation gain measured via cochet bonnet esthesiometer testing. Here, the authors describe a dual nerve grafting approach via simultaneous parallel sural nerve grafts from both the supratrochelar and supraorbital nerves to the affected contralateral cornea with return of sensation by postoperative week 11.

Clinical Outcomes and Patient Satisfaction After Corneal Neurotization

PURPOSE

The aim of this study was to assess clinical outcomes of corneal neurotization (CN) and determine patient perception of postoperative results.

METHODS

This was a retrospective study involving 29 eyes in 28 patients who underwent CN. Chart review data included demographic and clinical history; ophthalmic examination including visual acuity, ocular surface quality, and corneal sensation; surgical technique; and postoperative course. Subjective self-reported patient outcomes of surgical success were also assessed. Only eyes with at least 6 months of follow-up were included in the statistical analysis.

RESULTS

A total of 24 eyes and 23 patients were included in statistical analyses. The median postoperative follow-up time was 12.2 months (interquartile range 10.9-18.5 mo). Twenty-three eyes (92%) achieved improvement in ocular surface quality. Eleven of 13 (85%) demonstrated healing of persistent epithelial defects at their last follow-up. Patients gained a median of 2.3 cm in Cochet-Bonnet esthesiometry measurements of sensation. No significant difference was found between preoperative and postoperative visual acuity. All 17 patients who provided self-assessment of their surgical outcome indicated they would undergo CN again if given the choice. Most of the patients reported that the postoperative pain was tolerable, with a median pain score of 3.0 on a 10-point scale (interquartile range 0.0-4.0). Sixteen patients (94%) reported full or partial return of skin sensation along the donor nerve distribution.

CONCLUSIONS

CN provides improvement in corneal health and sensibility, with high patient satisfaction and minimal postoperative pain and morbidity.

Seeing through the evidence for corneal neurotization

PURPOSE OF REVIEW

Trigeminal anesthesia causes neurotrophic keratopathy, which may yield facial disfigurement and corneal blindness.

RECENT FINDINGS

We summarize approaches and evidence for corneal neurotization.

SUMMARY

Regional sensory nerve transfer appears safe and effective for therapeutic management of neurotrophic keratopathy. Prospective randomized clinical trials are necessary to confirm the utility of corneal neurotization.

The management of neurotrophic keratitis

PURPOSE OF REVIEW

The management of neurotrophic keratitis (NK) has evolved in the last decade. The present article reviews updated management guidelines of this entity, as well as future innovations in the field.

RECENT FINDINGS

The advent of confocal microscopy has allowed for the first time to image corneal nerves. In addition, multiple novel topical treatments such as nerve growth factor have improved the prognosis of this disease, with many other in the pipeline. Finally, corneal nerve restoration is now possible with corneal neurotization procedures.

SUMMARY

Many novel treatments based on agents that stimulate nerve regrowth are now available to treat NK. Improvement in neurotization procedures could also address advanced stages of this disease with surgery.

Assessment of Tactile Sensitivity Threshold Using Cochet-Bonnet Esthesiometer and Semmes-Weinstein Monofilaments and Their Use in Corneal Neurotization

PURPOSE

Although the Cochet-Bonnet esthesiometer (CBE) measures corneal sensitivity, it has heretofore only been tested on the index pulp. Tactile skin sensitivity thresholds are measured with Semmes-Weinstein monofilaments (SWM). This study measured skin sensitivity thresholds in healthy individuals using CBE and SWM, and compared both instruments in territories involved in corneal neurotization.

METHODS

Overall, 27 healthy individuals were tested by a single examiner at 9 territories on the face, neck, forearm, and leg, using 20-thread SWM and CBE with a diameter of 0.12 mm. Both sides were tested. Thresholds were compared for both instruments and between the different territories using Bayesian methods.

RESULTS

Mean sensitivity levels for SWM ranged from 0.010 to 1.128 g, while mean sensitivity levels for CBE ranged from 0.006 to 0.122 g. Thresholds measured with SWM were significantly higher than with CBE. Both instruments demonstrated higher thresholds in the leg territory than the forearm. However, the forearm presented higher thresholds than the head territories. No significant differences were found between the head territories themselves. Overall, right-side territories exhibited lower thresholds than left-side territories.

CONCLUSIONS

We have reported the first mapping of skin sensitivity thresholds using CBE. Thresholds measured with CBE and SWM were coherent. The use of CBE on the skin is particularly relevant to the field of corneal neurotization.

Corneal Neurotization: A Game-Changing Surgical Procedure for Neurotrophic Keratopathy

PURPOSE

The aim of this study is to describe techniques, results, and open issues of corneal neurotization (CN) for the treatment of neurotrophic keratopathy (NK).

METHODS

An overview of the most important studies of CN is provided. The 2 main surgical approaches (namely, direct CN and indirect CN) with specific advantages and disadvantages are described. The results regarding changes of corneal sensitivity and clarity, visual acuity, and in vivo confocal microscopy metrics are summarized. Ex vivo studies with histopathology of the neurotized cornea are reported. Intraoperative and early and late postoperative complications are described along with current open issues to be further clarified.

RESULTS

Corneal sensitivity improves after both direct and indirect CN. Corneal reinnervation allows the healing of NK in almost the totality of the operated eyes, determining a corresponding improvement of corneal clarity and visual acuity. Regeneration of corneal nerve fibers is confirmed by means of either in vivo confocal microscopy or ex vivo histopathology. Few self-limiting complications are reported during the postoperative course. Current open issues concern the identification of the technique of choice, the use of autograft or allograft, and the timing of CN either when performed alone or when combined with other surgeries.

CONCLUSIONS

CN represents a game-changing surgical procedure for NK, which has the potential to restore corneal sensitivity in all stages of the disease regardless of the mechanism of denervation. Further long-term results are needed to confirm its efficacy over time. The design of randomized clinical trials comparing CN with noninterventional therapies could further validate the adoption of this technique.

Corneal neurotization for neurotrophic keratopathy: Review of surgical techniques and outcomes

Neurotrophic keratopathy is a degenerative disease in which damage to the corneal nerves leads to corneal hypoesthesia. Injuries to neurotrophic corneas are notoriously difficult to treat and have traditionally been approached with supportive management. However, recent progress in the field of corneal neurotization has given new direction for addressing nerve loss directly by stimulating new nerve growth onto the cornea from nearby sensory nerves transferred to the perilimbal region. Herein, we review the surgical techniques utilized in corneal neurotization, including direct transfers and the use of nerve grafts. Considerations in surgical approach, as well as factors that influence prognosis and outcomes of the surgical intervention are also discussed.

Neurotrophic Keratopathy in Pediatric Patients

Purpose: This review provides an overview of the causes and treatment of neurotrophic keratopathy in the pediatric population.Methods: A thorough review of the current literature discussing neurotrophic keratopathy was conducted then summarized.Results:Fourty-nine papers were reviewed. Congenital and acquired causes of neurotrophic keratopathy exist in the pediatric population. Both medical and surgical approaches to treatment have been trialed, albeit to a limited extent, in pediatric patients. Conservative treatment includes topical lubrication and antibiotics to prevent concurrent infectious ulcer formation. Various neurotrophic factors have been trialed in the form of serum drops to restore corneal sensation when conservative measures fail. Surgically, different corneal neurotization techniques have been developed whereby a donor nerve is routed to the anesthetized cornea to restore innervation and sensation. Conclusions: Advances in the treatment of neurotrophic keratopathy have made corneal reinnervation and restoration of vision more easily attainable in pediatric patients.

Clinical and Morphologic Outcomes of Minimally Invasive Direct Corneal Neurotization

PURPOSE

To describe clinical outcomes of a minimally invasive technique for direct corneal neurotization to treat neurotrophic keratopathy.

METHODS

All cases of corneal neurotization for neurotrophic keratopathy performed by a single surgeon using minimally invasive direct corneal neurotization were reviewed. The supraorbital donor nerve was directly transferred to the cornea through an upper eyelid crease incision using either a combination of endoscopic and direct visualization or direct visualization alone. Detailed ocular and adnexal examinations as well as Cochet-Bonnet esthesiometry of the affected cornea were performed. Corneal histopathology and in vivo confocal microscopy after minimally invasive direct corneal neurotization were reviewed in one patient who underwent simultaneous penetrating keratoplasty.

RESULTS

Five consecutive cases in 4 patients were included, with a mean follow up of 15.8 months (range: 11-23 months). Average denervation time was 17.8 months (range: 6-24 months). Baseline corneal conditions were Mackie stage 1 (20%), Mackie stage 2 (40%), and Mackie stage 3 (40%). All patients demonstrated improvements in corneal sensibility and appearance postoperatively. All patients demonstrated stable or improved visual acuity. No patients developed persistent epithelial defects postoperatively, and all achieved return of tactile skin sensation in the donor nerve sensory distribution. In vivo confocal microscopy after minimally invasive direct corneal neurotization and simultaneous penetrating keratoplasty demonstrated regeneration of corneal nerves. Complications included an asymptomatic small bony excrescence lateral to the supraorbital notch in one patient and cataract progression in the patient who underwent penetrating keratoplasty.

CONCLUSIONS

Minimally invasive direct corneal neurotization is a safe and effective treatment of neurotrophic keratopathy.

Corneal Neurotization in the Setting of Facial Paralysis: A Comprehensive Review of Surgical Techniques

ABSTRACT

Neurotrophic keratopathy is characterized by decreased corneal sensitivity, decreased reflex tearing, and poor corneal healing resulting in corneal injury. Without proper sensory innervation, the cornea undergoes continuous epithelial injury, ulceration, infection and eventually results in vision loss. In situations where patients have concomitant facial paralysis, such as after resection of a large vestibular schwannoma, the ocular health is further impaired by paralytic lagophthalmos with decreased eye closure and blink reflex, decreased tearing, and potential lower eyelid malposition. In patients with a dual nerve injury, the ocular surface is in significant danger, as there is increased environmental exposure in conjunction with the inability to sense damage when it occurs. Immediate recognition and care of the eye are critical for maintaining ocular health and preventing irreversible vision loss. The first modern corneal neurotization procedure was described in 2009. The ultimate goal in corneal neurotization is to establish sub-basal plexus regeneration via transferring a healthy nerve to the corneo-limbal region. Corneal neurotization can be achieved either via a direct transfer of healthy nerve (direct approach) or via nerve graft interpositions (indirect approach). This is an emerging concept in the treatment of neurotrophic/exposure keratitis and over the past decade multiple direct and indirect approaches have been described in the attempt to restore corneal sensation and to prevent the devastating outcomes of neurotrophic keratitis. Knowledge of these techniques, their advantages, and disadvantages is required for proper management of patients suffering from neurotrophic keratitis in the setting of facial paralysis.

CORNEAL NEUROTIZATION IN A PATIENT WITH SEVERE NEUROTROPHIC KERATOPATHY. CASE REPORT

PURPOSE

Neurotrophic keratopathy (NK) is a degenerative corneal disease caused by damage to the trigeminal innervation due to a decrease in corneal sensitivity or complete anaesthesia. Impaired corneal innervation leads to morphological and metabolic disorders of the epithelium. In addition, it also leads to the development of recurrent or persistent epithelial defects in corneal ulcers, which may progress to stromal lysis and corneal perforation. One possible solution for severe NK is reinnervation of the anaesthetic cornea (corneal neurotization) using the supraorbital nerve and an autologous sensory nerve graft (indirect neurotization). This article presents the results of corneal neurotization in a young male patient with persistent epithelial defects and corneal ulcers due to corneal denervation.

RESULTS

A 22-year-old man with a history of neurosurgery for astrocytoma of the cerebellum and trunk on the right side at the age of 2 years, was observed for postoperative paresis of the right facial nerve with lagophthalmos in his childhood. The presence of asymptomatic dysfunction of the right trigeminal nerve was also noted. At the age of 22 years, after right eyeball contusion, the vision of the right eye decreased and a persistent epithelial defect developed, followed by corneal ulceration. Due to the exhaustion of therapeutic options in a young patient with corneal anaesthesia, the cornea was reinnervated via the contralateral supraorbital nerve using an autologous sural nerve graft. Five months after the surgery, the sensitivity of the cornea of the right eye began to recover. After amniotic membrane transplantation, the extensive epithelial defect healed, and the opaque corneal stroma gradually cleared up.

CONCLUSION

The reinnervation of the anaesthetic cornea (corneal neurotization) using the supraorbital nerve and the autologous sensory nerve graft represents a new solution for severe NK treatment. The severe corneal condition in our patient healed after the surgery.

Corneal Neurotization for Postherpetic Neurotrophic Keratopathy: Initial Experience and Clinical Outcomes

PURPOSE

To assess early outcomes of corneal neurotization for postherpetic neurotrophic keratopathy (NK).

METHODS

Retrospective analysis of patients who underwent corneal neurotization for postherpetic NK by a single experienced oculoplastic surgeon was performed. Collected data included stage and etiology of NK as well as comorbidities, prior treatment history, neurotization technique, donor nerve site, preoperative and postoperative examination findings (i.e., ocular surface quality, corneal clarity, corneal sensation by Cochet-Bonnet esthesiometry, and visual acuity [VA]), and follow-up duration. Differences between preoperative and postoperative values were analyzed by Wilcoxon signed-rank test.

RESULTS

Of 23 adult patients who underwent corneal neurotization, 3 (13%) had history of herpes simplex keratitis and/or endotheliitis, and 4 (17%) had history of herpes zoster ophthalmicus. One patient with herpes zoster ophthalmicus was excluded due to inadequate follow-up duration. Of the 6 patients included in the study, 3 (50%) had Mackie stage 1 disease, 1 (17%) had stage 2, and 2 (33%) had stage 3 with impending perforation, but all had markedly diminished corneal sensation, with a median denervation time of 11.8 months (interquartile range [IQR] 9.4-29.2 months). Following neurotization, median corneal sensation improved significantly from 1.6 cm (interquartile range 0.0-1.9 cm) to 3.6 cm (IQR 3.0-5.6 cm, p = 0.028), with 1 patient achieving full sensation by postoperative month 5. All patients with a persistent epithelial defect preoperatively showed complete corneal healing by their last follow-up visit. VA also improved postoperatively in all patients (p = 0.028). Median follow-up duration was 11.3 months (interquartile range 9.6-17.9 months).

CONCLUSIONS

Corneal neurotization can successfully reinnervate corneas previously devitalized by herpetic disease and halt the progressive nature of postherpetic NK. If utilized appropriately and early in the disease process, neurotization may reduce morbidity and maximize visual potential in postherpetic NK.

Direct Versus Indirect Corneal Neurotization for the Treatment of Neurotrophic Keratopathy: A Multicenter Prospective Comparative Study

PURPOSE

To analyze the comparative safety and efficacy of two techniques of corneal neurotization (CN) (direct corneal neurotization [DCN] vs indirect corneal neurotization [ICN]) for the treatment of neurotrophic keratopathy (NK).

DESIGN

Multicenter interventional prospective comparative case series.

METHODS

This study took place at ASST Santi Paolo e Carlo University Hospital, Milan; S.Orsola-Malpighi University Hospital, Bologna; and Santa Maria alle Scotte University Hospital, Siena, Italy. The study population consisted of consecutive patients with NK who underwent CN between November 2014 and October 2019. The intervention procedures included DCN, which was was performed by transferring contralateral supraorbital and supratrochlear nerves. ICN was performed using a sural nerve graft. The main outcome measures included NK healing, corneal sensitivity, corneal nerve fiber length (CNFL) measured by in vivo confocal microscopy (IVCM), and complication rates.

RESULTS

A total of 26 eyes in 25 patients were included: 16 eyes were treated with DCN and 10 with ICN. After surgery, NK was healed in all patients after a mean period of 3.9 months without differences between DCN and ICN. Mean corneal sensitivity improved significantly 1 year after surgery (from 3.07 to 22.11 mm; P < .001) without differences between the 2 groups. The corneal sub-basal nerve plexus that was absent before surgery in all patients, except 4, become detectable in all cases (mean CNFL: 14.67 ± 7.92 mm/mm² 1 year postoperatively). No major complications were recorded in both groups.

CONCLUSIONS

CN allowed the healing of NK in all patients as well as improvement of corneal sensitivity in most of them thanks to nerve regeneration documented by IVCM. One year postoperatively, DCN and ICN showed comparable outcomes.

Outcomes of corneal neurotisation using processed nerve allografts: a multicentre case series

Background

Corneal neurotisation is a rapidly evolving procedure treating neurotrophic keratopathy. The variety of surgical techniques used and corresponding outcomes after corneal neurotisation are not well understood. This study describes the techniques and outcomes in the largest case series of corneal neurotisation using processed nerve allografts to date.

Methods

This is a retrospective case series of patients who underwent corneal neurotisation with human cadaveric processed nerve allografts. All patients had preoperative and postoperative description of best corrected visual acuity and measurement of corneal sensation. Comparative studies after stratification of techniques were performed.

Results

A total of 17 patients were identified. The cause of corneal anaesthesia was prior infection in eight cases, trigeminal nerve palsy in eight cases and ocular trauma in one case. There were no intraoperative or postoperative complications. Following neurotisation surgery, the time to first gain of corneal sensation and maximal gain of sensation occurred at a mean of 3.7 months (range 1–8 months) and 6.6 months (range 3–15 months), respectively. The mean preoperative and postoperative corneal sensation as measured by Cochet-Bonnet aesthesiometry was 0.36 cm (range 0–3.2 cm) and 4.42 cm (range 0–6 cm), respectively (p<0.01). Visual acuity was unchanged after neurotisation. There were no statistical differences in outcomes based on end-to-end versus end-to-side coaptations, donor nerve selection or laterality of donor nerve.

Conclusion

Corneal neurotisation with processed nerve allografts is a safe and effective procedure. This study provides further evidence for the use of processed nerve allografts for corneal neurotisation.

[Neurotization of the cornea as pathogenically targeted method of treating neurotrophic keratitis in patients with facial paralysis]

Combined lesions of the facial and trigeminal cranial nerves are typical after neurosurgical treatment. Violation of the innervation of orbicularis muscle leads to inability to completely close the eyelids, while denervation of the cornea is often manifested as a long-term ongoing and recurring neurotrophic keratitis. The restoration of corneal innervation is a pathogenetically targeted treatment for this pathology. For this purpose, neurotrophic keratitis could be reversed via the method of corneal neurotization using contralateral n. ophthalmicus. The presented clinical case demonstrates the results of the first operation of neurotization of the cornea in a patient with combined lesions of the facial and trigeminal nerves.

Corneal Neurotization and Novel Medical Therapies for Neurotrophic Keratopathy

Purpose of Review

Neurotrophic keratopathy (NK) is a degenerative corneal disease characterized by decreased corneal sensibility and impaired corneal healing. In this article, we review surgical techniques for corneal neurotization (CN) and novel medical therapies for the treatment of NK.

Recent Findings

In recent decades, there has been a paradigm shift in the treatment strategies for NK. New minimally invasive direct and indirect CN approaches have demonstrated efficacy at improving best-corrected visual acuity and central corneal sensation while decreasing surgical morbidity. In addition, several targeted medical therapies, such as recombinant human nerve growth factor (rhNGF), regenerating agents (RGTA), and nicergoline, have shown promise in improving corneal epithelial healing. Of these options, cenegermin (Oxervate®, Dompé), a topical biologic medication, has emerged as an approved medical treatment for moderate to severe NK.

Summary

NK is a challenging condition caused by alterations in corneal nerves, leading to impairment in sensory and trophic function with subsequent breakdown of the cornea. Conventional therapy for NK depends on the severity of disease and focuses primarily on protecting the ocular surface. In recent years, numerous CN techniques and novel medical treatments have been developed that aim to restore proper corneal innervation and promote ocular surface healing. Further studies are needed to better understand the long-term efficacy of these treatment options, their target populations, and the potential synergistic efficacy of combined medical and surgical treatments.

[Corneal neurotization]

The previous treatment options for neurotrophic keratopathy (NK) were limited. Frequently performed surgical procedures for severe NK include amnionic membrane transplantation and tarsorrhaphy. Corneal neurotization describes the transposition of a healthy donor nerve along the limbal circumference to re-establish corneal sensation and trophic function. The nerve transfer can be performed either by directly transpositioning the supraorbital nerve as described here or by using a sural nerve interponate.

Corneal neurotization

PURPOSE OF REVIEW

Neurotrophic keratopathy is a devastating corneal condition that can lead to ocular morbidity and blindness. Current medical and surgical treatments poorly tackle the essential problem of corneal aesthesia and hence fail to provide a permanent cure. Recent advances in corneal neurotization techniques have shown promise to restore corneal nerves in neurotrophic keratopathy. This article aims at reviewing the current surgical advances, along with the current thoughts and evidence available for corneal nerve regeneration.

RECENT FINDINGS

Corneal neurotization was first introduced in 2009 by Terzis et al., but recently picked up more interest since 2014. Direct and indirect neurotization are being developed, and different nerves (sural nerve, great auricular nerve) have been explored for interposition between frontal nerve branches and the cornea. New endoscopic techniques are introduced for less invasive approaches. On the corneal front, confocal microscopy and esthesiometry studies have established that the regeneration of the corneal nerves is happening 6 months after the procedure.

SUMMARY

Neurotization is a budding revolutionary technique that shows promise of cure for neurotrophic corneas, but at this stage, it is still reasonably invasive and still reserved for selected patients.

Axon numbers and landmarks of trigeminal donor nerves for corneal neurotization

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 supraorbital 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 reliably dissected using anatomical landmarks.

Update on corneal neurotisation

Corneal neurotisation describes surgical restoration of nerve growth into the cornea to restore corneal sensation and trophic function. It represents an exciting and effective emerging treatment for neurotrophic keratopathy. Techniques described to date involve either direct nerve transfer or an interpositional nerve graft coapted to a healthy donor nerve. We review the experience to date with particular emphasis on a detailed review of techniques, outcomes and current thoughts.