The measurement of corneal sensation allows clinicians to assess the status of corneal innervation and serves as a crucial indicator of corneal disease and eye health. Many devices are available to assess corneal sensation, including the Cochet-Bonnet aesthesiometer, the Belmonte Aesthesiometer, the Swiss Liquid Jet Aesthesiometer, and the newly introduced Corneal Esthesiometer Brill. Increasing the clinical use of in vivo confocal microscopy and optical coherence tomography will allow for greater insight into the diagnosis, classification, and monitoring of ocular surface diseases such as neurotrophic keratopathy; however, formal esthesiometric measurement remains necessary to assess the functional status of corneal nerves. These aesthesiometers vary widely in their mode of corneal stimulus generation and their relative accessibility, precision, and ease of clinical use. The development of future devices to optimize these characteristics, as well as further comparative studies between device types should enable more accurate and precise diagnosis and treatment of corneal innervation deficits. The purpose of this narrative review is to describe the advancements in the use of aesthesiometers since their introduction to clinical practice, compare currently available devices for assessing corneal innervation and their relative limitations, and discuss how the assessment of corneal innervation is crucial to understanding and treating pathologies of the ocular surface.

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.