Abstract
Purpose :
In vivo confocal microscopy (IVCM) enables visualisation of corneal immune cells (ICs) in humans. The density and morphology of corneal ICs vary in the literature, even among healthy individuals. The reason(s) for this heterogeneity in corneal immune cell characteristics is unclear. This study sought to investigate potential seasonal environmental variations to the density and morphology of corneal ICs, in healthy individuals and those with seasonal ocular allergy.
Methods :
Twenty-six adults (n=16 healthy controls; n=10 untreated ocular allergy) were recruited in Melbourne, Australia. All participants attended two visits, to align with the high (Visit 1: Nov to Dec 2021) and low (Visit 2: Apr to Jun 2022) grass pollen seasons. Environmental (average daily temperatures, air pollution [PM10] and grass pollen levels); clinical (conjunctival staining, eyelid redness, eyelid roughness) and subclinical (corneal IC density and morphometry) parameters were analysed using 2-way repeated-measures ANOVAs to assess for both inter-group and inter-visit differences.
Results :
At Visit 1 (high pollen), mean daily temperatures, air pollution (PM10) and grass pollen levels were higher than at Visit 2 (p<0.01). Ocular allergy symptoms and eye rubbing frequency were higher in allergy participants, relative to controls at Visit 1 only (p<0.0001). Signs of ocular allergy (conjunctival staining, eyelid redness, eyelid roughness) were more severe in allergy participants than controls at Visit 1, but not Visit 2. Corneal IC density was quantified for each morphological subtype (immature, mature, globular) in both the central and inferior whorl regions. For each cell subtype, no differences in density were evident between groups at Visit 1 or 2, or between visits in each participant group. At Visit 1 (high pollen), the field area of mature immune cells was larger in healthy participants, and immature cells were less round and smaller in allergy participants, relative to the low pollen season (Visit 2; p<0.05).
Conclusions :
This study finds that IC densities are unchanged in the central and whorl regions of human corneas over a six-month period encompassing major changes in environmental conditions. The observed differences in IC morphology, which were distinct in healthy and allergy participants, suggest the potential influence of the local environment on human corneal immune status.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.