Age and Sex Variation in the Duration of Action and Corneal Touch Threshold (CTT) following Instillation of 0.5% Topical Ophthalmic Proparacaine and Tetracaine Hydrochlorides

Comparison of Proparacaine, Tetracaine, and Oxybuprocaine in Corneal Sensitivity Measurement

Purpose: This study aimed to determine the onset and duration of action of 3 commercially available topical anesthetic solutions in Brazil, using the Cochet-Bonnet esthesiometer (Luneau®, Paris, France) and to quantitatively assess patient-reported discomfort during application. Methods: A prospective, randomized, masked, and double-blind study was conducted, involving 40 eyes from 21 patients. Patients were administered each one of the topical anesthetics weekly, and corneal sensitivity was measured using the Cochet-Bonnet esthesiometer's corneal touch threshold (CTT). Patients rated the burning sensation using a visual analogue scale (VAS). Results: Among the 21 patients (42.9% male), with a mean age of 31.95 years (±standard deviation = 10.17, range = 22.0-58.0), corneal sensitivity significantly decreased 30 s after application, returning to baseline after 30 min for all groups (P < 0.0001). Significant differences in CTT were observed at 5 min, with proparacaine exhibiting a superior anesthetic effect (P = 0.0003), at 10 min, where tetracaine displayed the most substantial anesthetic effect (P = 0.0135), and at 20 min, where tetracaine demonstrated the highest anesthetic efficacy (P < 0.0001). VAS scores indicated the most intense burning sensation with tetracaine (P < 0.0001). Men reported experiencing more discomfort during instillation compared with women (P = 0.0168). Conclusions: Proparacaine exhibited the fastest onset of action among the 3 topical anesthetics and provided a more comfortable eye sensation during instillation. However, tetracaine demonstrated the longest duration of action despite causing more discomfort.

Comparative visual outcomes of the first versus second eye following small-incision lenticule extraction (SMILE)

BACKGROUND

This study aimed to compare the visual outcomes of the first operated eyes with those of the second operated eyes following small-incision lenticule extraction (SMILE).

METHODS

A total of 202 patients (404 eyes) underwent SMILE using the tear film mark centration method for myopia and myopic astigmatism correction. Baseline characteristics, objective optical quality, decentered displacement, induced corneal aberrations, and modulation transfer function (MTF) values were assessed. Linear regression analyzed the relationship between decentration and visual quality parameters, including corneal aberrations and MTF values.

RESULTS

No significant difference was observed in objective visual quality, efficacy, and safety indexes between the two groups (all P > 0.05). The average decentered displacement for the first and second surgical eyes was 0.278 ± 0.17 mm and 0.315 ± 0.15 mm, respectively (P = 0.002). The horizontal coma in the first surgical eyes were notably lower than in the second (P = 0.000). MTF values at spatial frequencies of 5, 10, 15, and 20 cycles/degree (c/d) were higher in the first surgical eyes compared to the second (all P < 0.05). Linear regression indicated that high-order aberrations (HOAs), root mean square (RMS) coma, spherical aberration, horizontal coma, vertical coma, and eccentric displacement were all linearly correlated. Furthermore, MTF values exhibited a linear relationship with eccentric displacement across these spatial frequencies.

CONCLUSIONS

There was no discernible difference in visual acuity, efficacy, or safety between the two operated eyes. Nonetheless, the first operated eyes exhibited reduced decentered displacement and demonstrated superior outcomes in terms of horizontal coma and MTF values compared to the second operated eyes following SMILE. The variations in visual quality parameters were linearly correlated with decentered displacement.

Neurophysiology of corneal neuropathic pain and emerging pharmacotherapeutics

The altered activity generated by corneal neuronal injury can result in morphological and physiological changes in the architecture of synaptic connections in the nervous system. These changes can alter the sensitivity of neurons (both second-order and higher-order projection) projecting pain signals. A complex process involving different cell types, molecules, nerves, dendritic cells, neurokines, neuropeptides, and axon guidance molecules causes a high level of sensory rearrangement, which is germane to all the phases in the pathomechanism of corneal neuropathic pain. Immune cells migrating to the region of nerve injury assist in pain generation by secreting neurokines that ensure nerve depolarization. Furthermore, excitability in the central pain pathway is perpetuated by local activation of microglia in the trigeminal ganglion and alterations of the descending inhibitory modulation for corneal pain arriving from central nervous system. Corneal neuropathic pain may be facilitated by dysfunctional structures in the central somatosensory nervous system due to a lesion, altered synaptogenesis, or genetic abnormality. Understanding these important pathways will provide novel therapeutic insight.

EFFECT OF ANESTHESIA DURATION ON INTRAVITREAL INJECTION PAIN: A double-blinded, randomized, comparative study

PURPOSE

To determine the effect of different durations of topical anesthesia on intravitreal injection (IVI) pain.

METHODS

This was a double-blinded, randomized, comparative study . Three hundred and twelve sequential eyes undergoing IVI were randomized to one of six groups according to the duration of topical anesthesia (from 1 to 30 minutes, one group for every 5-minute range, Groups 1-6). Topical anesthesia before IVI was standardized. Patients graded their pain using the visual analog scale and the Wong-Baker FACES scale at 15 minutes after the procedure.

RESULTS

The pain scores among the six groups were significantly different for the visual analog scale ( P = 0.013) and Wong-Baker FACES scale ( P = 0.024). The mean pain scores for Group 4 were 1.97 ± 1.04 (visual analog scale) and 2.02 ± 1.08 (Wong-Baker FACES scale) and were significantly lower than those of Group 1, 2, 5, or 6.

CONCLUSION

The duration of topical anesthesia significantly correlated with IVI pain. Preoperative 0.5% proparacaine hydrochloride drops were most effective in relieving IVI pain 11 to 20 minutes after topical administration.