Pain Management in Corneal Collagen Crosslinking for Keratoconus: A Comparative Case Series

Molecular Mechanisms and Therapeutic Potential of Gabapentin with a Focus on Topical Formulations to Treat Ocular Surface Diseases

Gabapentin (GBP) was originally developed as a potential agonist for Gamma-Amino-Butyric-Acid (GABA) receptors, aiming to inhibit the activation of pain-signaling neurons. Contrary to initial expectations, it does not bind to GABA receptors. Instead, it exhibits several distinct pharmacological activities, including: (1) binding to the alpha-2-delta protein subunit of voltage-gated calcium channels in the central nervous system, thereby blocking the excitatory influx of calcium; (2) reducing the expression and phosphorylation of CaMKII via modulation of ERK1/2 phosphorylation; (3) inhibiting glutamate release and interfering with the activation of NMDA receptors; (4) enhancing GABA synthesis; (5) increasing cell-surface expression of δGABA_A receptors, contributing to its antinociceptive, anticonvulsant, and anxiolytic-like effects. Additionally, GBP displays (6) inhibition of NF-kB activation and subsequent production of inflammatory cytokines, and (7) stimulation of the purinergic adenosine A1 receptor, which supports its anti-inflammatory and wound-healing properties. Initially approved for treating seizures and postherpetic neuralgia, GBP is now broadly used for various conditions, including psychiatric disorders, acute and chronic neuropathic pain, and sleep disturbances. Recently, as an eye drop formulation, it has also been explored as a therapeutic option for ocular surface discomfort in conditions such as dry eye, neurotrophic keratitis, corneal ulcers, and neuropathic ocular pain. This review aims to summarize the evidence supporting the molecular effects of GBP, with a special emphasis on its applications in ocular surface diseases.

Intracanalicular dexamethasone insert for post-corneal crosslinking inflammation and pain: the LINK study

PURPOSE

To compare the efficacy of an intracanalicular dexamethasone insert with tapered topical steroid over 28 days after corneal cross-linking (CXL).

SETTING

Single private practice, outpatient setting.

DESIGN

Prospective observational randomized study.

METHODS

This prospective randomized study investigated the efficacy of a dexamethasone intracanalicular insert on post-CXL pain and inflammation in progressive keratoconus patients. 20 patients (40 eyes) were enrolled; half were randomized to the dexamethasone intracanalicular insert group; half were prescribed a 28-day topical tapering steroid regimen. All patients were evaluated for pain scores, rate of re-epithelialization, ease of the post-CXL regimen, and need for rescue pain medication after standard bilateral epithelium-off CXL on postoperative day (POD) 1, POD3, and POD4 to 7, as well as postoperative week (POW) 1, POW2, POW3, and POW4.

RESULTS

20 patients (40 eyes) underwent standard-of-care epithelium-off bilateral CXL for progressive keratoconus. 10 patients were randomized to receive prednisolone eyedrops on a tapering schedule after CXL; 10 patients received dexamethasone intracanalicular inserts at the time of CXL. Regardless of the postoperative steroid regimen, there was no significant difference in the rate of re-epithelialization or use of rescue pain medication between groups. There was a nominal, however, statistical difference in pain scores between groups, favoring prednisolone eyedrops. Both groups stated no difficulty in following postoperative regimens. There were no adverse events noted in relation to treatment or the CXL procedure.

CONCLUSIONS

Using a dexamethasone insert to alleviate pain and inflammation can be considered as a safe and efficacious part of a post-CXL regimen.

Pain mechanisms and management in corneal cross-linking: a review

Though corneal collagen cross-linking (CXL) is an increasingly available and effective treatment for keratoconus, few reports have considered its impact on pain-related physiology in depth. This comprehensive narrative review summarises mechanisms underlying pain in CXL and clinical care possibilities, with the goal of future improvement in management of CXL-related pain. Postoperative pain associated with CXL is largely due to primary afferent nerve injury and, to a smaller extent, inflammation. Chronification of pain after CXL has not been reported, even as long-term nerve damage without regeneration following standard CXL treatment is frequently observed. The lack of pain chronification may be due to the minimally invasive nature of the procedure, with its rapidly recovering superficial corneal wound, and to the positive anti-inflammatory changes of the tear film that have been described after CXL. Different CXL approaches have been developed, with the transepithelial epithelial-on technique (epi-on) associated with less postsurgical pain than the gold standard, epithelial-off technique (epi-off). After the first few days, however, the difference in pain scores and need for analgesics between epi-on and epi-off disappear. Patients experience relatively high-intensity pain the first few days post-CXL, and many strategies for acute pain control following CXL have been studied. Currently, no method of pain management is considered superior or universally accepted. Acute pain following CXL is a recognised and clinically significant side effect, but few CXL studies have systematically investigated postoperative pain and its management. This review aims to improve patient pain outcomes following this increasingly common procedure.

A New Surgical Technique to Deliver Riboflavin Beneath Corneal Epithelium: The Corneal Cross-Linking Epi-Pocket

PURPOSE

To describe a new technique to deliver riboflavin into the corneal stroma during Corneal Cross-Linking (CXL) without the removal of corneal epithelium.

METHODS

Keratoconus patients underwent CXL for progressive keratoconus. Riboflavin was delivered by manually creating an epithelial pocket (CXL Epi-Pocket). Verbal rating scale was recorded postoperatively. Best-corrected visual acuity, keratometric indices, corneal thickness and corneal densitometry were recorded at baseline and at 12-month follow-up.

RESULTS

Eighteen eyes of 18 patients were included in the study. At a 12-month follow-up, best-corrected visual acuity, K1, K2 and densitometry values were stable. Maximum keratometry (Kmax) reduced from 55.31 ± 6.21 (SD) to 52.34d ± 4.12d (SD) (P value = 0.032). the thinnest point went from 441 ± 21.18 (SD) to 425.4 ± 19.02 (SD) um (P value = 0.041). The verbal rating scale at 1, 2 and 3 days postoperatively were 1.76 ± 0.19 (SD), 1.02 ± 0.51 (SD) and 0.28 ± 0.14 (SD).

CONCLUSIONS

CXL Epi-Pocket is able to deliver riboflavin to halt the progression of keratoconus at a 12-month follow-up.

Crosslinking und Keratokonus

Ein Keratokonus führt zu einer progressiven Vorwölbung und Verdünnung der Hornhaut. Um dies aufzuhalten, kann ein Crosslinking durchgeführt werden. Dabei ist eine Behandlung nach dem „Dresdener Protokoll“ eine effektive und sichere Behandlungsmöglichkeit, aber auch zahlreiche neue Anwendungsprotokolle (akzeleriertes Crosslinking, transepitheliales Crosslinking) und sogar weitere Indikationen (refraktive Eingriffe, infektiöse Keratitis) wurden in den letzten Jahren veröffentlicht.

[Crosslinking and Keratoconus]

Keratoconus leads to a progressive protrusion and thinning of the cornea. In order to stop this, corneal crosslinking can be performed if the progression of the disease is proven. Crosslinking according to the "Dresden protocol" includes abrasion of the corneal epithelium, application of riboflavin eye drops and irradiation with UV-A light of an intensity of 3 mW/cm² for 30 minutes. The efficacy has been shown in several prospective randomized studies. One of the more recent developments is accelerated crosslinking, which allows a shorter irradiation time. On the other hand, the possibility of transepithelial crosslinking was presented, which does not require an abrasion of the cornea. This should reduce the occurrence of postoperative pain. The range of indications has also been expanded. Corneal crosslinking is used for post-LASIK keratectasia as well. It is also being considered for use in infectious keratitis. Topographically controlled crosslinking can likewise be used to try to positively influence the refractive power of the cornea. The risks of crosslinking include the occurrence of pain, haze or scarring, endothelial cell damage and, rarely, the occurrence of keratitis.

Corneal Cross-Linking for Keratoconus: Current Knowledge and Practice and Future Trends

Corneal collagen cross-linking (CXL) with riboflavin is an accepted universal standard of care for our keratoconus patients with progressive disease. It has been a game changer in how we manage keratoconus. Early diagnosis and treatment is essential in paediatric patients as younger patients progress more rapidly and have poorer transplant outcomes. There is an ongoing debate around standard, accelerated, and transepithelial protocols of CXL, the role of CXL, and the combination of laser refractive surgery. Future developments will improve CXL safety and efficacy and the scope of utilization, but we must be careful not to leap too far ahead with clinical applications before publication of basic science research and good clinical results with standardized protocols.