The Relationship between Corneal Nerve Morphology and Inflammatory Mediators and Neuropeptides in Healthy Individuals

Corneal subbasal nerve plexus reinnervation and stromal cell morphology with different cap thicknesses in small incision lenticule extraction

PURPOSE

The corneal cap thickness is a vital parameter designed in small incision lenticule extraction (SMILE). The purpose was to investigate the changes in corneal subbasal nerve plexus (SNP) and stromal cells with different cap thicknesses and evaluate the optimized design for the surgery.

METHODS

In this prospective, comparative, non-randomized study, a total of 108 eyes of 54 patients who underwent SMILE were allocated into three groups with different corneal cap thicknesses (110 μm, 120 μm or 130 μm group). The SNP and stromal cell morphological changes obtained from in vivo corneal confocal microscopy (IVCCM) along with their refractive outcomes were collected at 1 week, 1 month, 3 months and 6 months postoperatively. One-way analysis of variance (ANOVA) was used to compare the parameters among the three groups.

RESULTS

The SNPs in the three groups all decreased after surgery and revealed a gradual increasing trend during the 6-month follow-up. The values of the quantitative nerve metrics were significantly lower in the 110 μm group than in the 120 μm and 130 μm groups, especially at 1 week postoperatively. No difference was detected between the 120 μm and 130 μm groups at any time point. Both Langerhans cells and keratocytes were activated after surgery, and the activation was alleviated during the follow-up.

CONCLUSIONS

The SMILE surgeries with 110 μm, 120 μm or 130 μm cap thickness design achieved good efficacy, safety, accuracy and stability for moderate to high myopic correction while the thicker corneal cap was more beneficial for corneal nerve regeneration.

Inhibition of miR-144-3p/FOXO1 Attenuates Diabetic Keratopathy Via Modulating Autophagy and Apoptosis

Purpose

Diabetic keratopathy (DK) is a vision-threatening disease that occurs in people with diabetes. Mounting evidence indicates that microRNAs (miRNAs) are indispensable in nerve regeneration within DK. Herein, the role of miRNAs associated with DK, especially focusing on autophagy and apoptosis regulation, was investigated.

Methods

To identify differentially expressed miRNAs, we performed miRNA sequencing on trigeminal ganglion (TG) tissues derived from streptozotocin-induced type 1 diabetic mellitus (T1DM) and normal mice. MiR-144-3p was chosen for the subsequent experiments. To explore the regulatory role of miR-144-3p in DK, miRNA antagomir was utilized to inhibit miR-144-3p expression. Bioinformatic tools were used to predict the target genes of miR-144-3p, and a dual-luciferase reporter assay was then applied for validation. Autophagy and apoptosis activities were measured utilizing TUNEL staining, immunofluorescence staining, and Western blotting.

Results

Overall, 56 differentially expressed miRNAs were detected in diabetic versus control mice. In the diabetic mouse TG tissue, miR-144-3p expression was aberrantly enhanced, whereas decreasing its expression contributed to improved diabetic corneal re-epithelialization and nerve regeneration. Fork-head Box O1 (FOXO1) was validated as a target gene of miR-144-3p. Overexpression of FOXO1 could prevent both inadequate autophagy and excessive apoptosis in DK. Consistently, a specific miR-144-3p inhibition enhanced autophagy and prevented apoptosis in DK.

Conclusions

In this study, our research confirmed the target binding relationship between miR-144-3p and FOXO1. Inhibiting miR-144-3p might modulate autophagy and apoptosis, which could generate positive outcomes for corneal nerves via targeting FOXO1 in DK.

The impact of sensory neuropathy and inflammation on epithelial wound healing in diabetic corneas

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes, with several underlying pathophysiological mechanisms, some of which are still uncertain. The cornea is an avascular tissue and sensitive to hyperglycemia, resulting in several diabetic corneal complications including delayed epithelial wound healing, recurrent erosions, neuropathy, loss of sensitivity, and tear film changes. The manifestation of DPN in the cornea is referred to as diabetic neurotrophic keratopathy (DNK). Recent studies have revealed that disturbed epithelial-neural-immune cell interactions are a major cause of DNK. The epithelium is supplied by a dense network of sensory nerve endings and dendritic cell processes, and it secretes growth/neurotrophic factors and cytokines to nourish these neighboring cells. In turn, sensory nerve endings release neuropeptides to suppress inflammation and promote epithelial wound healing, while resident immune cells provide neurotrophic and growth factors to support neuronal and epithelial cells, respectively. Diabetes greatly perturbs these interdependencies, resulting in suppressed epithelial proliferation, sensory neuropathy, and a decreased density of dendritic cells. Clinically, this results in a markedly delayed wound healing and impaired sensory nerve regeneration in response to insult and injury. Current treatments for DPN and DNK largely focus on managing the severe complications of the disease. Cell-based therapies hold promise for providing more effective treatment for diabetic keratopathy and corneal ulcers.

The Role of Neuropeptides in Pathogenesis of Dry Dye

Neuropeptides are known as important mediators between the nervous and immune systems. Recently, the role of the corneal nerve in the pathogenesis of various ocular surface diseases, including dry eye disease, has been highlighted. Neuropeptides are thought to be important factors in the pathogenesis of dry eye disease, as suggested by the well-known role between the nervous and immune systems, and several recently published studies have elucidated the previously unknown pathogenic mechanisms involved in the role of the neuropeptides secreted from the corneal nerves in dry eye disease. Here, we reviewed the emerging concept of neurogenic inflammation as one of the pathogenic mechanisms of dry eye disease, the recent results of related studies, and the direction of future research.

Could contact lens dryness discomfort symptoms sometimes have a neuropathic basis?

Symptoms of dryness discomfort in soft contact lens wearers frequently lead to discontinuation from wear. The negative influence of pre-fitting tear dysfunctions appears likely to be exacerbated by the challenges to tear homeostasis caused by contact lenses. The corneal mechanisms for symptoms in contact lens wearers are different to those for dry eye disease because the cornea is insulated by the lens from ambient conditions as well as from lid wiper friction during blinking. Symptoms of dryness discomfort might be the consequence of increased lid wiper friction during blinking when the lens front surface becomes soiled and dry and exhibits very rapid tear break up. It is possible that some cases of contact lens intolerance and discontinuation could be a function of lid wiper neuropathy. In relation to the possibility of corneal neuropathy, a stagnant post-lens tear pool with the possibility of increased concentrations of metabolic by-products, cellular debris, and bacterial exotoxins, might have the potential to disturb the corneal epithelial and sub-basal nerves. Contributions by contact lens-induced inflammation to any neuropathic changes may partly depend on the degree to which inflammatory mediators are concentrated in a stagnant post-lens tear pool. It does not appear to be known if corneal neuropathic changes could develop under these conditions. The chances of neuropathic involvement may be greater if discomfort develops after a significant period of successful wear and there is a history of comorbid pain conditions. Esthesiometry and in vivo confocal microscopy in discontinued contact lens wearers may support a diagnosis of contact lens-related corneal neuralgia.