Treating Disorders of Innervation

Educational Objectives

The goal of this program is to improve management of innervation disorders that affect the cornea. After hearing and assimilating this program, the clinician will be better able to:

1. Develop strategies for management of innervation disorders that affect the cornea.

Summary

Neurotrophic keratopathy: herpetic disease often presents with severe neurotrophic keratopathy; however, causes (eg, dry eye disease) that contribute to mild manifestations are often underrecognized; traumatic or iatrogenic injury to cranial nerve (CN) V often yields a severe form of neurotrophic keratopathy

Innervation of the cornea: sensation on the cornea triggers a blink reflex (in which CN V inactivates CN III and activates CN VII to close the eye) and mediates the blink rate; reduced blink rate can occur with bilateral neurotrophic keratopathy; lack of sensation-triggered reflex tearing (and in turn, decreased reflex lacrimation and overall tear production) is the most common cause of dry eye and predisposes the ocular surface to injury; neurotransmitters and neurotrophic factors regulate immune response, maintain stem cell potency and the tissue in the epithelium, and regulate wound healing

Neurotrophic keratopathy after neurosurgery: development of neurotrophic keratopathy is relatively uncommon after surgery for trigeminal neuralgia; in one series from 1990, ≈20% of patients developed corneal anesthesia, but only 6 of these patients required ophthalmic surgical intervention; severity of neurotrophic keratopathy has no correlation with perceived sensation; Dhillon et al (2016) reported that postganglionic or severe extensive ganglionic injury created in the treatment of trigeminal neuralgia leads to more severe neurotrophic keratopathy compared with preganglionic lesions, because the ganglion and postganglionic fibers are secreting trophic factors onto the cornea to maintain the health of the ocular surface

Restoration of trophic factors

Topical therapies: trophic factors are found in autologous serum tears and amniotic membrane; topical recombinant nerve growth factor has been shown to reverse neurotrophic keratopathy and result in complete corneal healing for the majority of patients; some patients developed increased sensation or eye pain; recurrence of epithelial defect occurred in ≈15% of patients ≤1 yr

Corneal neurotization: offers the potential for long-term restoration of innervation to the anesthetic cornea, and it may restore sensation and trophic factors; in the seminal study (Terzis et al [2009]), patients had injury to CN V and VII; a coronal flap was done, and the supraorbital and supratrochlear nerves were dissected from the unaffected side and implanted into the affected side; durable response with restoration of sensation and improved clarity of the cornea were observed; although the procedure has become more common in recent years, evidence is lacking on other patient and surgical factors that may influence the severity of corneal breakdown and the success rates of corneal neurotization

Tarsorrhaphy: traditionally used for patients with injury to CN V and VII because the risk for corneal ulceration is high; patients with absent corneal reflex due to CN VII injury alone present with eye pain and irritation from exposure, epiphora, brow ptosis, upper lid retraction, and lagophthalmos; often, patients with concomitant CN V injury do not have pain but may have eye redness and decreased vision (indicating early-stage corneal ulcer)

Restoration of blinking: difficult after facial nerve injury; static strategies for lagophthalmos include spacers, stents, and slings to tighten the lower eyelid and adjust the paralytic ectropion and exposure caused by the inferior eyelid; tarsorrhaphy lifts the lower eyelid and brings the upper eyelid down, but it reduces the field of vision; placement of weights or magnets in the upper eyelid has been done but is not a mainstream treatment; reinnervation of the tiny fibers that activate the orbicularis oculi remains an ongoing field of study; one study found that adding an eyelid weight improves, but does not completely normalize, movement of the eyelid

Cross-face nerve and muscle grafting: a novel technique has been developed that raises the corners of the mouth and cheek along with the lower eyelid to produce a natural-appearing smile

Readings

Dhillon VK, Elalfy MS, Al-Aqaba M, et al. Corneal hypoesthesia with normal sub-basal nerve density following surgery for trigeminal neuralgia. Acta Ophthalmol. 2016;94(1):e6-e10. doi:10.1111/aos.12697; Peterson DC, Hamel RN. Corneal Reflex. [Updated 2023 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534247/; Terzis JK, Dryer MM, Bodner BI. Corneal neurotization: a novel solution to neurotrophic keratopathy. Plast Reconstr Surg. 2009;123(1):112-120. doi:10.1097/PRS.0b013e3181904d3a.

Disclosures

For this program, members of the faculty and planning committee reported nothing relevant to disclose.

Acknowledgements

Dr. Chang was recorded at the USC Department of Ophthalmology Winter Symposium, held December 9, 2023, in Los Angeles, CA, and presented by the Keck School of Medicine of the University of Southern California. For information on future CME activities from this presenter, please visit https://keckusc.cloud-cme.com. Audio Digest thanks the speakers and the Keck School of Medicine of the University of Southern California for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0.50 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0.50 CE contact hours.

Lecture ID:

OP620604

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.