Presentations

Abstract

Introduction: Ocular surface discomfort, a common chief complaint among patient visits to eye care practitioners, has substantial impact on quality of life and healthcare costs. Pain may manifest directly as a result of tissue damage at the ocular surface (nociceptive pain) or may develop due to changes to the peripheral or central nerves in the sensory pathway (neuropathic pain). The peripheral afferent nerves are preferentially sensitive nociceptors arising from the densely innervated cornea and ocular surface. Hence, free nerve endings play an important role in detecting environmental stimuli but are susceptible to damage. Despite the high prevalence of ocular surface pain as well as neurotrophic keratopathy, a thorough understanding of its causative factors and tools for appropriate diagnostic evaluation remain notably absent in many eye clinics. We performed a cross-sectional observational study to compare corneal sensitivity measurements using a novel non-contact, instrument-mounted esthesiometer in a group of patients with a variety of ocular surface conditions.

Methods: In this cross-sectional study, corneal sensitivity was measured with a non-contact, non-invasive device delivering reproducible, constant-pressure air pulses at gradually increasing levels of intensity. To measure corneal sensitivity, participants were instructed to sit and direct their gaze straight ahead. The corneal esthesiometer was mounted to the slit lamp and measurements were performed according to the manufacturer instructions using the built-in LED positioning system. Measurements on eyes with ocular surface conditions were recorded in mbar units: mildly sensitive (2-3), normal (3-5), mildly insensitive (5-7), moderately insensitive (7-9), severely insensitive (9-10), and no sensation (>10). During cross-sectional chart review, parameters assessed included patient age, sex, ocular diagnosis, prior ocular surgeries, and data from corneal esthesiometry. Secondary outcomes included surveys regarding ocular symptoms. The Standardized Patient Evaluation of Eye Dryness (SPEED) questionnaire was utilized to assess the severity and frequency of ocular surface symptoms and scored as follows: mild (0-5), moderate (6-14), severe (15-40).

Results: A total of 206 patients (407 eyes) were included. The average age was 61 years. 60.7% (n=125) were female and 39.3% (n=81) were male. A significantly pronounced decrease in corneal sensation can be observed in subjects over the age of 50. The mean corneal sensitivity of subjects greater than 50 years of age (n=154) measured 4.30 mbar compared to that of subjects less than 50 years of age (n=52), which was 3.41 mbar (p=0.0002). Corneal esthesiometry measurements at the various intensity levels were as follows: mildly sensitive (n=181), normal (n=151), mildly insensitive (n=33), moderately insensitive (n=17), severely insensitive (n=12), and no sensation (n=13). Mean (M) esthesiometry measurements trended upward with increasing depth of corneal incisions in the ocular procedures performed: photorefractive keratectomy (M=3.82), partial-thickness corneal transplant (M=4.08), laser in-situ keratomileusis (M=4.54), cataract extraction with posterior chamber intraocular lens implantation (M=4.56), and full-thickness corneal transplant (M=4.93). When comparing subjects with symmetrical corneal esthesiometry measurements (n=138) to those possessing asymmetry differing by at least one intensity level (n=62) between their eyes, mean measurements were 3.70 mbar and 4.78 mbar, respectively (p<0.0001). SPEED questionnaire results showed 42% (n=87) mild, 34% (n=69) moderate, and 24% (n=50) severe with mean esthesiometry measurements of 3.81 mbar, 4.12 mbar, and 4.46 mbar, respectively, based on patients' subjective evaluations of their ocular surface symptoms (p=0.049).

Conclusion: The non-contact quantitative corneal esthesiometer is a non-invasive, diagnostic tool for detecting subclinical corneal dysesthesia and related pathologies. By using this device, ophthalmologists and optometrists are better able to prescribe specific treatment for early-stage neurotrophic disease and evaluate the effectiveness of each intervention. Early diagnosis and effective therapeutic implementation can avoid permanent damage of corneal nerves and prevent patients from facing irreparable vision loss.