In Vivo and Ex Vivo Comprehensive Evaluation of Corneal Reinnervation in Eyes Neurotized With Contralateral Supratrochlear and Supraorbital Nerves

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.

Evaluation of Corneal Nerve Regeneration After Minimally Invasive Corneal Neurotization

PURPOSE

To evaluate the corneal nerve regeneration after minimally invasive corneal neurotization (MICN) and to further clarify the recovery patterns of sensory and trophic functions of the corneal nerves.

DESIGN

A retrospective cohort study based in the Shanghai Ninth People's Hospital.

METHODS

Eighteen patients (18 eyes) who underwent MICN for neurotrophic keratopathy due to intracranial surgery was conducted to analyze their follow-up data at 6, 12, 18, and 24 months after surgery.

RESULTS

At 12 months postoperatively, the growth of the central and peripheral corneal nerve fiber density (CNFD) was 11.47±8.56 and 14.73±8.08 n/mm 2 with subsequent improvement slowing down, and the patient's corneal epithelium defect was healed ahead of the accomplishment of corneal nerve regeneration. The number of dendritic cells also reached its peak. At 18 months postoperatively, the recovery of central and peripheral corneal sensation was 37.22±23.06 mm and 39.38±18.08 mm with no subsequent improvement, and the growth of the central and peripheral corneal nerve branch density (CNBD) was 29.69±11.05 and 43.75±1.41 n/mm 2 , with a positive and significant correlation between corneal sensation and CNBD (at central r =0.632, P <0.005; at peripheral r =0.645, P <0.005). At 24 months postoperatively, mean CNFD, CNBD, and corneal sensation recovered significantly compared with preoperative, but a few patients' corneal sensation recovered insignificantly with good CNFD recovery and poor CNBD recovery.

CONCLUSIONS

After MICN, the trophic function of the corneal nerve recovers before the sensory function, and in particular, the recovery of sensation is based on the coexistence of the corneal nerve trunk and branches.

In-vivo corneal confocal microscopy: Imaging analysis, biological insights and future directions

In-vivo corneal confocal microscopy is a powerful imaging technique which provides clinicians and researcher with the capabilities to observe microstructures at the ocular surfaces in significant detail. In this Mini Review, the optics and image analysis methods with the use of corneal confocal microscopy are discussed. While novel insights of neuroanatomy and biology of the eyes, particularly the ocular surface, have been provided by corneal confocal microscopy, some debatable elements observed using this technique remain and these are explored in this Mini Review. Potential improvements in imaging methodology and instrumentation are also suggested.

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.

Neurotization of the human cornea - A comprehensive review and an interim report

We present a comprehensive review of existing literature on surgical corneal neurotization (SCN) as a treatment modality for neurotrophic keratopathy (NK) with an interim report of seven cases where SCN was performed using the indirect approach and followed up till 18 months postoperatively to look for improvement in ocular surface, corneal sensations, and nerve regeneration by using in vivo confocal microscopy (IVCM). A literature search was performed for publications with keywords “corneal nerves,” “neurotization,” “esthesiometry,” “corneal anesthesia,” and “neurotrophic keratopathy.” All literature available till December 31, 2020 was reviewed and included to describe NK and its management options, particularly SCN. NK is associated with absent or reduced corneal sensations and is managed using a step-ladder algorithm ranging from medical management for symptomatic relief to surgical corneal neurotization. Both direct and indirect approaches of SCN have a favorable outcome with reduced surgical morbidity in the indirect approach using sural nerve graft. Post neurotization, corneal sensation recovery may take up to 3–6 months, while nerve regeneration on confocal microscopy can take as long as 6 months–1 year.

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.

Comparison of the efficacy of topical insulin with autologous serum eye drops in persistent epithelial defects of the cornea

PURPOSE

To investigate the effect of topical insulin on epithelization in persistent epithelial defects (PED) refractory to usual treatment compared to autologous serum.

DESIGN

Retrospective, consecutive case-control series.

METHODS

The charts of 61 consecutive patients with PED treated with topical insulin (case group) and 23 treated with autologous serum (control group) were reviewed. Primary efficacy end points were the percentage of patients in which epithelization was achieved, as well as the rate and time until epithelization. Secondary efficacy point was need for amniotic membrane transplantation (AMT) or other surgeries.

RESULTS

Mean time between PED diagnosis and start of topical insulin was 22.7 ± 18.5 days (range 13-115) and the mean area was 14.8 ± 16.2 mm² (range 1.1-70.6). In the control group, mean time was 27.9 ± 16.8 days, mean epithelial defect area being 18.6 ± 15.0 mm² (range 1.7-52.9). No differences in baseline characteristics were found between groups (p > 0.05). Epithelization was achieved in 51 patients (84%) on insulin and 11 patients (48%) on autologous serum (p = 0.002). In those patients, mean time until reepithelization was 32.6 ± 28.3 days (range 4-124) in the insulin group and 82.6 ± 82.4 days (range 13-231) in the autologous serum group (p = 0.011). The need for AMT was significantly lower in the insulin group (p = 0.005). PED recurrence was higher in patients treated on autologous serum (43%) compared with insulin (11%) (p = 0.002).

CONCLUSIONS

Topical insulin is an effective treatment and safely promotes healing of PED. In our series, topical insulin presented better epithelization outcomes than autologous serum and could thus be considered as a first-line treatment.

Maternal serum eye drops to treat bilateral neurotrophic keratopathy in congenital corneal anesthesia: Case report and literature review

Purpose

To report the feasibility and the successful outcomes of a pediatric neurotrophic keratopathy (NK) owing to congenital corneal anesthesia (CCA) treated with allogeneic serum eye drops obtained from the mother as the only therapy.

Observations

A 18-month-old girl with generalized pain insensitivity presented with a large epithelial defect in the right eye (RE) and superficial punctate keratopathy (SPK) in the left eye (LE). Corneal sensitivity was completely absent in both eyes (BE). Peripheral serum eye drops obtained from the mother was prescribed and administered every 2 hours in BE. Two weeks after the beginning of treatment, compete healing of the epithelial defect in the RE was obtained, while the severity of the SPK in the LE markedly improved; in parallel, conjunctival hyperemia disappeared in BE. The treatment was continued over the course of 3 months with good tolerability and neither signs of recurrence of the epithelial defect nor other complications were noted.

Conclusions and Importance

Allogeneic serum eye drops obtained from the mother are effective in treating pediatric NK owing to CCA. This treatment may represent a readily available and inexpensive option when topical nerve growth factor is unavailable or corneal neurotization is not feasible.

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.

Regenerative therapy for the Cornea

The cornea is the outmost layer of the eye, unique in its transparency and strength. The cornea not only transmits the light essential for vision, also refracts light, giving focus to images. Each of the three layers of the cornea has properties essential for the function of vision. Although the epithelium can often recover from injury quickly by cell division, loss of limbal stem cells can cause severe corneal surface abnormalities leading to corneal blindness. Disruption of the stromal extracellular matrix and loss of cells determining this structure, the keratocytes, leads to corneal opacity. Corneal endothelium is the inner part of the cornea without self-renewal capacity. It is very important to maintain corneal dehydration and transparency. Permanent damage to the corneal stroma or endothelium can be effectively treated by corneal transplantation; however, there are drawbacks to this procedure, including a shortage of donors, the need for continuing treatment to prevent rejection, and limits to the survival of the graft, averaging 10-20 years. There exists a need for new strategies to promote regeneration of the stromal structure and restore vision. This review highlights critical contributions in regenerative medicine with the aim of corneal reconstruction after injury or disease. These approaches include corneal stromal stem cells, corneal limbal stem cells, embryonic stem cells, and other adult stem cells, as well as induced pluripotent stem cells. Stem cell-derived trophic factors in the forms of secretomes or exosomes for corneal regeneration are also discussed. Corneal sensory nerve regeneration promoting corneal transparency is discussed. This article provides description of the up-to-date options for corneal regeneration and presents exciting possible avenues for future studies toward clinical applications for corneal regeneration.

Alternative therapies for dry eye disease

PURPOSE OF REVIEW

Dry eye disease (DED) is a multifactorial disease affecting approximately 5-50% of individuals in various populations. Contributors to DED include, but are not limited to, lacrimal gland hypofunction, meibomian gland dysfunction (MGD), ocular surface inflammation, and corneal nerve dysfunction. Current DED treatments target some facets of the disease, such as ocular surface inflammation, but not all individuals experience adequate symptom relief. As such, this review focuses on alternative and adjunct approaches that are being explored to target underlying contributors to DED.

RECENT FINDINGS

Neuromodulation, stem cell treatments, and oral royal jelly have all been studied in individuals with DED and lacrimal gland hypofunction, with promising results. In individuals with MGD, devices that provide eyelid warming or intense pulsed light therapy may reduce DED symptoms and signs, as may topical Manuka honey. For those with ocular surface inflammation, naturally derived anti-inflammatory agents may be helpful, with the compound trehalose being farthest along in the process of investigation. Nerve growth factor, blood-derived products, corneal neurotization, and to a lesser degree, fatty acids have been studied in individuals with DED and neurotrophic keratitis (i.e. corneal nerve hyposensitivity). Various adjuvant therapies have been investigated in individuals with DED with neuropathic pain (i.e. corneal nerve hypersensitivity) including nerve blocks, neurostimulation, botulinum toxin, and acupuncture, although study numbers and design are generally weaker than for the other DED sub-types.

SUMMARY

Several alternatives and adjunct DED therapies are being investigated that target various aspects of disease. For many, more robust studies are required to assess their sustainability and applicability.

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.

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.

Topical insulin for refractory persistent corneal epithelial defects

PURPOSE

To evaluate insulin eye drops for persistent epithelial defects (PEDs) that are refractory to usual treatment in clinical practice and to analyze how it may improve epithelization.

METHODS

A prospective non-randomized hospital-based study was performed. Patients with PEDs that were refractory to conventional treatment were treated with insulin eye drops four times a day. Patients' demographics, PED etiology, concomitant treatments, and comorbidities were reviewed. The rate of PED closure and epithelial healing time were considered the primary outcome measures.

RESULTS

21 patients were treated with insulin drops (12 females and 9 males; mean age 72.2 years). Mean PED area before treatment was 17.6 ± 16.5 mm² (median 13.2; range 3.9-70.6). PED comorbidities included seven eyes with infectious keratitis (33%), five eyes with calcium keratopathy (24%), ocular surgery on three eyes (14%), three eyes with lagophthalmos (14%), two eyes with bullous keratopathy (10%), and one patient with herpetic eye disease (5%). The eyes of 17 patients (81%) with refractory PEDs had reepithelized and four patients (19%) had still presented an epithelial defect by the end of the study follow-up period, although it had decreased in size. In patients where PED closure was achieved, mean time until reepithelization was 34.8 ± 29.9 days (median 23; range 7-114). In the remaining patients, a mean area reduction of 91.5% was achieved for the PEDs.

CONCLUSION

Topical insulin can promote and accelerate corneal reepithelization of refractory PEDs. It also offers many other advantages, including excellent tolerance, availability, and cost-effectiveness.

In Vivo Evaluation of Corneal Nerves and Epithelial Healing After Treatment With Recombinant Nerve Growth Factor for Neurotrophic Keratopathy

PURPOSE

To evaluate the renewal of corneal nerve structure and function in patients with neurotrophic keratopathy (NK) treated with recombinant human nerve growth factor (rhNGF) eye drops.

DESIGN

Prospective, interventional, before-and-after case series.

METHODS

This study included 18 patients with NK with a persistent epithelial defect or corneal ulcer, treated with topical rhNGF, and age-matched healthy controls. Patients underwent clinical examination with corneal fluorescein staining, Schirmer 1 tear test, assessment of corneal sensitivity with the Cochet-Bonnet esthesiometer, and morphologic examination of the nerves by in vivo confocal microscopy (IVCM) at baseline and at 4 and 8 weeks of treatment. IVCM analysis was used to assess corneal sub-basal nerve density, number of nerve branches, and the diameter of nerve fibers.

RESULTS

A complete resolution of the epithelial defect was observed in all patients within 8 weeks. Schirmer 1 test showed a significant improvement of tear film secretion. Change from baseline in corneal sensation was significant (P < .001) but did not approach that of healthy controls. After 8 weeks of treatment, there was a significant increase in the mean nerve density in affected eyes as compared to baseline (P = .007) as well as in the number of nerve branches (P = .008) and nerve fiber diameter (P = .007).

CONCLUSIONS

Topical treatment with rhNGF was effective in promoting complete corneal healing of persistent epithelial defects and corneal ulcers in patients with NK. This was associated with an improvement of corneal sensitivity and an increase of sub-basal nerve density, diameter, and number of nerve branches, indicating improvement in structure and function of corneal nerves.