The nerve density in the cornea and its relation to photosensitivity and correlations in crossmodal sensitivity relationships
OA Version
Citation
Abstract
BACKGROUND: Photophobia is a symptom where the eyes are painfully sensitive to light and is a common symptom of various ocular diseases. Despite its prevalence, the inner workings of photophobia are poorly understood, making it challenging to treat. Corneal nerves play a key role in sensory perception, but their role in photophobia remains unknown. IVCM allows us to explore the cornea’s dense innervation, allowing us to gain insight into the connection between photophobia and corneal nerves. Additionally, QST allows us to measure pain thresholds across different stimuli such as thermal, visual and audio. By studying the correlations of these QST measures we may be able to improve our understanding of light induced pain and processing across different sensory modalities.
AIMS: This study aims to determine whether there is a significant correlation between corneal nerve fiber density and light pain thresholds. We aim to determine whether healthy volunteers who report low light discomfort thresholds also generally report enhanced sensitivity to other modalities of sensory stimuli.
METHODS: 28 participants (13 males and 15 females, mean age 21 ± 2.21) were assessed for thermal sensitivity (HPT) at three stimulation sites (forehead, forearm, and eyelid), photosensitivity (VPT), and auditory sensitivity. Corneal nerve density was measured with the IVCM. Statistical analysis included Friedman’s tests with post-hoc pairwise comparison with Bonferroni correction and Kendall’s tau-b correlations. A p-value of p<0.05 is significant.
RESULTS: Kendall’s tau-b correlation showed significant relationships between visual pain intensity and thermal pain intensity with each stimulation site as well as visual unpleasantness and thermal unpleasantness with each stimulation site. Kendall’s tau-b correlation showed that audio pain intensity significantly correlated with visual pain intensity and correlated with thermal pain intensity at the forehead and forearm only. Kendall’s tau-b correlation also revealed significant differences between VPT and visual unpleasantness. Kendall’s tau-b also showed a correlation between visual pain intensity and visual unpleasantness. Friedman’s analysis showed that a statistically significant difference was found in HPTs, with eyelid HPT being significantly lower than forehead HPT and forearm HPT. Friedman’s analysis also showed a significantly lower pain intensity at HPT was found at the eyelid when compared to the forearm. All audio sensitivity measures (pain intensity, sound intensity and unpleasantness) were significantly correlated between each other.
CONCLUSION: Although no significant correlation was found between VPT and HPT at any stimulation site, the positive relationship between thermal pain intensity ratings and visual pain intensity ratings as well as thermal and visual unpleasantness ratings suggests a potential shared mechanism underlying heightened sensitivity across sensory modalities. This may indicate that while absolute pain thresholds for visual and thermal pain may not be directly correlated in healthy participants, the way individuals experience pain across different modalities still may be interconnected. While our results partially support correlation between audio, thermal and photosensitivity, the inconsistent relationship across measures implies that generalized sensory hypersensitivity may involve distinct pathways for different modalities like intensity and unpleasantness. The location differences, forehead/forearm vs eyelid, suggest that nerve circuitry may modulate these relationships.
Description
2025
License
Attribution-NonCommercial-NoDerivatives 4.0 International