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Corneal subbasal nerve morphology is not associated with reduction in corneal sensitivity to mechanical stimuli following single-step transepithelial photorefractive keratectomy (TransPRK), researchers report in a Journal of Cataract and Refractive Surgery study.
Ophthalmologists utilizing TransPRK remove the corneal epithelium and stroma in 1 step with 1 ablation profile. Postoperative complications include destruction of subbasal nerves and superficial stromal nerves. The objective of the study was to assess changes in the appearance of these nerves and their regeneration using in vivo confocal microscopy (IVCM), and evaluate how the changes affect the nerves’ function.
The researchers observed 51 patients (age 28.23±7.74 years, 29 women) with moderate myopia (mean -4.58±1.53 D myopia) who underwent TransPRK for both eyes between July 2019 and January 2020. The investigators conducted clinical exams before surgery and 1 week, 1 month, 3 months, 6 months, and 12 months after the surgery. One randomly selected eye per patient was assessed for blink frequency, corneal sensitivity, and IVCM analysis of corneal nerve regeneration in the central and peripheral ablation zone.
Prior to surgery, patients received a 0.5% topical antibiotic, and topical anesthetic drops (proparacaine 0.5%,). The cornea was flushed with balanced salt solution and ablation was performed. A therapeutic soft contact lens was placed on the eye after surgery, which remained until re-epithelization was complete. Patients received topical levofloxacin eye drops and fluorometholone 0.1% eye drops.
The researchers found that the Bowman layer was absent in all eyes following TransPRK. Corneal subbasal nerve plexus appeared at the anterior stromal. Nerve fiber regeneration at the margin of the ablation zone came predominantly from the peripheral cornea outside the ablation zone and spanned the ablation zone. Nerve fiber regeneration at the central cornea tended to stem from the ends of the corneal stromal nerves, forming the subbasal nerve in a radial direction before moving parallel to the ablation surface.
Immediately after Trans PRK, nerve fiber density, the quantity of branch points, nerve fiber width and total length of nerves plummeted after the procedure before gradually increasing. Many subbasal nerves did not contact the central corneal area.
The researchers report that mean central corneal sensation decreased 1 week postoperatively (P =.001) and returned to preoperative sensitivity within 1 month. They determined that corneal sensitivity and blink frequency were not linked with each other or with other observed variables. Blink frequency in 20 seconds did not change significantly, though most patients experienced slightly increased blink frequency by 1 month postoperatively.
“The results demonstrated that the structural changes of subbasal nerves were not parallel to their functions after TransPRK,” the study says.
Limitations of the study included limited follow-up time and the capabilities of Cochet-Bonnet esthesiometry.
Reference
Liu C, Yu A, Zhang C, et al. Structural and functional alterations in corneal nerves following single-step transepithelial photorefractive keratectomy. J Cataract Refract Surg. Published online December 3, 2021. doi:10.1097/j.jcrs.0000000000000872
