SAN ANTONIO – Research from Deborah Antwi and colleagues suggests that repeated tear film instability alters the sensory threshold of the ocular surface.
She presented her group’s findings at the American Academy of Optometry annual meeting.
“We hypothesized that tear film instability stimulates and alters the response of underlying corneal sensory neurons, resulting in increased symptoms of ocular irritation,” Antwi said.
Detection thresholds were determined for 25 subjects who underwent cool, mechanical and chemical stimuli, using a Belmonte esthesiometer before, immediately after and 30 minutes after subjects completed 10 consecutive sustained tear exposure (STARE) trials.
During STARE trials, subjects kept the tested eye open as long as possible, to induce tear break-up and thinning.
Researchers calculated tear break-up as the percentage of tear break-up within the exposed cornea area.
Thresholds (mean ± SEM) before, immediately after STARE and 30 minutes later were 61.20 ± 4.94, 58.73 ± 4.54 and 52.40 ± 3.77 to cool, 39.53 ± 4.25, 40.27 ± 3.95 and 41.40 ± 3.49% CO2 to chemical and 82.70 ± 7.48, 67.53 ± 5.95 and 58.47 ± 3.83 to mechanical stimuli, according to the study.
Researchers found a significant difference between mechanical thresholds; before was significantly higher than immediately after and 30 minutes after.
Patient questionnaire scores before, immediately after STARE and 30 minutes later were 1.96 ± 1.05, 15.92 ± 2.14 and 5.16 ± 1.26, respectively.
Antwi said the increases in scores were significant immediately after staring for both visits.
Those with large changes in mechanical threshold had total area break-up of 7.24%, while subjects with minimal changes in threshold had total area break-up of 0.86%, occurring at more random locations within the exposed corneal area.
She suggested that larger areas of repeated tear break-up stimulate ocular surface neurons and are associated with an increase in symptoms and alterations in sensory thresholds.
Further, STARE trials induced tear break-up or extensive tear thinning in all subjects, with mechanical thresholds most affected.
Antwi concluded that stimulation of ocular surface polymodal nociceptors, possibly by local spikes of hyperosmolarity or surface drying within tear break-up, contributed to the changes in mechanical thresholds. – by Abigail Sutton
Antwi D, et al. Does repeated tear breakup affect sensory thresholds? Presented at: American Academy of Optometry annual meeting; San Antonio; November 7 – 10, 2018.
Disclosure: Antwi reports no relevant financial disclosures.