Corneal neurotization: a narrative review of techniques, outcomes, and surgical considerations

Background and Objective:Corneal neurotization is a novel surgical technique used to restore corneal sensation in patients with neurotrophic keratopathy.Neurotrophic keratopathy is a disorder characterized by dysfunction of the ophthalmic division of the trigeminal nerve,which provides sensory innervation to the cornea.Without sensation,the cornea is at risk of infection,ulceration,perforation,and ultimately,vision loss.Corneal neurotization has emerged as an innovative technique to reinnervate anesthetized corneas by transferring a healthy donor nerve to the affected eye around the corneoscleral limbus.As the field of corneal neurotization rapidly grows,there is a need to synthesize the existing body of literature on corneal neurotization and identify important areas for further research.In this review,we will discuss neurotrophic keratopathy and its current management strategies,followed by an overview of corneal neurotization techniques,outcomes,surgical considerations,and future directions.Methods:PubMed and Google Scholar searches were conducted to retrieve and analyze relevant original papers and reviews on neurotrophic keratopathy and corneal neurotization up until April 2022.Key Content and Findings:Currently,numerous techniques for corneal neurotization exist,including direct nerve transfers,as well as indirect neurotization via interposition nerve grafts.So far,corneal neurotization has been shown to be highly successful in restoring corneal sensation,improving visual acuity,and improving corneal epithelial health.To date,there have been no significant differences in outcomes between direct versus indirect neurotization techniques,different donor nerves,or autologous versus allogeneic interposition grafts.However,there is some evidence that corneal neurotization procedures may be more successful in pediatric patients.Conclusions:Corneal neurotization shows great promise in treating neurotrophic corneas and represents the first management option to date that addresses the underlying pathophysiological mechanism of neurotrophic keratopathy by restoring corneal sensation.As the use of corneal neurotization continues to broaden,additional studies will become important to compare techniques in a systematic manner,with larger sample sizes,as well as standardized outcome measures and follow-up time.

Dry eye and corneal sensitivity after small incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis:a Meta-analysis

AIM：To assess the corneal sensitivity and the incidences of dry eye after small incision lenticule extraction（SMILE） and femtosecond laser-assisted in situ keratomileusis（FSLASIK）.METHODS：The Meta-analysis was performed using Rev Man 5.3.We searched on Pub Med from inception to March 2016.Summary weighted mean difference（WMD） and 95% confidence intervals（CIs） were used to analyze the datum.Random-effects or fixed-effects models were chosen up to between-study heterogeneity.The main outcomes were composed of the Ocular Surface Disease Index（OSDI） scores,tear film break-up time（TBUT）,Schirmer Test and corneal sensitivity.RESULTS：Eight eligible studies including 772 eyes（386 in SMILE group and 386 in FS-LASIK group） were identified.The parameters have no significiant difference heterogeneity between SMILE and FS-LASIK group preoperatively.There were significant differences between the two groups in OSDI scores at one and three months postoperatively,in TBUT at one and three months postoperatively,in corneal sensitivity at one week,about one month and three months postoperatively.However,there was no significant difference observed in Schirmer Test at the follow-up periods.CONCLUSION：Compare to FS-LASIK,dry eye and the corneal sensitivity recover better in the SMILE group,in first three months after the surgery.

Experimental Study of Corneal Innervation in Diabetic Mellitus

The morphology of corneal innervation was studied in rabbits with alloxan-induced diabetes.The experimental rabbits were killed after 6,8,10, 12weeks.Corneal innervation was studied by histochemical techniques and transimission electron microscopy.The results revealed that in diabetic rabbits,from 6 weeks,the density of nerve-nets was markedly sparser,the fibers were thinner and the activity of nerves was lower than those of the control group.Ultrastructural changes showed swelling of axons,irregular distribution of fibril and degeneration of mitochondria of varying degree.With the progress of disease the above changes were becoming more marked gradually.It may be assumed that these changes are related to hyperglycemia.

Small incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomes

This review summarizes the current status of the small incision lenticule extraction(SMILE)procedure.Following the early work by Sekundo et al.and Shah et al.,SMILE has become increasingly popular.The accuracy of the creation of the lenticule with the VisuMax femtosecond laser(Carl Zeiss Meditec)has been verified using very high-frequency(VHF)digital ultrasound and optical coherence tomography(OCT).Visual and refractive outcomes have been shown to be similar to those achieved with laser in situ keratomileusis(LASIK),notably in a large population reported by Hjortdal,Vestergaard et al.Safety in terms of the change in corrected distance visual acuity(CDVA)has also been shown to be similar to LASIK.It was expected that there would be less postoperative dry eye after SMILE compared to LASIK because the anterior stroma is disturbed only by the small incision,meaning that the anterior corneal nerves should be less affected.A number of studies have demonstrated a lower reduction and faster recovery of corneal sensation after SMILE than LASIK.Some studies have also used confocal microscopy to demonstrate a lower decrease in subbasal nerve fiber density after SMILE than LASIK.The potential biomechanical advantages of SMILE have been modeled by Reinstein et al.based on the non-linearity of tensile strength through the stroma.Studies have reported a similar change in Ocular Response Analyzer(Reichert)parameters after SMILE and LASIK,however,these have previously been shown to be unreliable as a representation of corneal biomechanics.Retreatment options after SMILE are discussed.Tissue addition applications of the SMILE procedure are also discussed including the potential for cryo-preservation of the lenticule for later reimplantation(Mohamed-Noriega,Angunawela,Lim et al.),and a new procedure referred to as endokeratophakia in which a myopic SMILE lenticule is implanted into a hyperopic patient(Pradhan et al.).Finally,studies reporting microdistortions in Bowman’s layer and corneal wound healing responses are also described.