Endoscopic Corneal Neurotization: Cadaver Feasibility Study

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.

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.

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.

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 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.

The supraorbital and supratrochlear nerves for ipsilateral corneal neurotization: anatomical study

Neurotrophic keratitis is a rare corneal disease that is challenging to treat. Corneal neurotization (CN) is among the developing treatments that uses the supraorbital (SON) or supratrochlear (STN) nerve as a donor. Therefore, the goal of this study was to provide the detailed anatomy of these nerves and clarify their feasibility as donors for ipsilateral CN. Both sides of 10 fresh-frozen cadavers were used in this study, and the SON and STN were dissected using a microscope intra- and extraorbitally. The topographic data between the exit points of these nerves and the medial and lateral angle of the orbit were measured, and nerve rotation of these nerves toward the ipsilateral cornea were attempted. The SON and STN were found on 19 of 20 sides. The vertical and horizontal distances between the exit point of the SON and that of the STN, were 7.3±2.1 mm (vertical) and 4.5±2.3 mm, respectively. The mean linear distances between the medial angle and the exit points of each were 22.2±3.0 mm and 14.5±1.9 mm, respectively, and the mean linear distances between the lateral angle and the exit points of the SON and STN were 34.0±2.7 mm and 36.9±2.5 mm, respectively. These nerves rotated ipsilaterally toward the center of the orbit easily. A better understanding of the anatomy of these nerves can contribute to the development and improvement of ipsilateral CN.

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.

Post-herpes neurotrophic keratopathy: Aetiopathogenesis, clinical signs and current therapies

Neurotrophic keratopathy (NK) is a degenerative corneal disease caused by damage of trigeminal innervation. This leads to epithelial defects, ulceration and, eventually, perforation. Both herpes simplex and varicella zoster keratitis are reported to be the main causes of NK. Furthermore, prognosis in this type of NK is poor. Classic clinical findings in post-herpes NK are spontaneous epithelial breakdown, round and central epithelial defects with smooth edges, stromal melting and thinning, scarring, and neovascularisation. Although several medical and surgical treatments have been reported, no therapies are currently available to definitely restore corneal sensitivity. Therefore, NK remains a challenging disease to treat. In this review a summary is presented of the pathogenesis, manifestations, and current management of post-herpes NK. The role of antiviral treatment and varicella-zoster vaccination is also discussed. A description is also presented on both medical and surgical novel therapies, such as regenerative drugs and corneal neurotization.

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.

Neurotrophic keratitis: current challenges and future prospects

Neurotrophic keratitis (NK) is a degenerative corneal disease caused by damage of trigeminal corneal innervation, which leads to spontaneous epithelial breakdown and corneal ulceration. The impairment of corneal sensory innervation causes the reduction of both protective reflexes and trophic neuromodulators that are essential for the vitality, metabolism, and wound healing of ocular surface tissues. A wide range of ocular and systemic conditions, including herpetic keratitis, ocular chemical burns, corneal surgery, diabetes, multiple sclerosis, and neurosurgical procedures, can cause NK by damaging trigeminal innervation. Diagnosis of NK requires careful investigation of any ocular and systemic condition associated with the disease, complete ocular surface examination, and quantitative measurement of corneal sensitivity. The clinical stages of NK range from corneal epithelial alterations (stage 1) to persistent epithelial defect (stage 2) and ulcer (stage 3), which may progress to corneal perforation. Management of NK is based on clinical severity, and the aim of the therapy is to halt the progression of corneal damage and promote epithelial healing. Although several medical and surgical treatments have been proposed, no therapies are currently available to restore corneal sensitivity, and thus, NK remains difficult and challenging to treat. The purpose of this review is to summarize available evidence on the pathogenesis, diagnosis, and treatment of NK. Novel medical and surgical therapies including the topical administration of nerve growth factor and corneal neurotization are also described.