Regional Tear Film Quality Changes Across Eye Gaze Directions Revealed by Spatial Mapping and Threshold Sensitivity Analysis.

Objectives: This study aimed to determine whether eccentric gaze produces a regional, gaze-aligned redistribution of tear-film quality that is more apparent in spatial analysis than in whole-map summary measures. Methods: This was a secondary analysis of a previously acquired Medmont Meridia composite-topography dataset from 38 healthy participants, using only the Medmont data. Tear-film quality maps from the ahead, right, left, up, and down gaze were interpolated onto a common grid, aligned to a shared reference frame, and analysed using descriptive global measures, regional spatial mapping, and a threshold-based directional sector analysis. The threshold analysis used an operational cut-off of 0.35 to classify good-quality pixels, with lower values indicating better tear-film quality. Robustness was assessed by repeating the same analysis across nearby cut-offs from 0.30 to 0.40. As Placido-based topography measures reflection from the tear layer rather than the ocular surface itself, and as ocular rotation changes lid position and exposed ocular surface area, aligned comparisons were interpreted as comparisons of the exposed tear-film pattern rather than exact point-for-point anatomical tracking. Results: Global tear-film summary measures showed only modest variation with gaze direction, whereas spatial mapping revealed systematic regional redistribution of tear-film quality across eccentric gaze conditions. At the 0.35 operational threshold, the gaze-aligned good-pixel index was positive for right gaze (0.297 ± 0.200), left gaze (0.213 ± 0.174), up gaze (0.204 ± 0.219), and down gaze (0.308 ± 0.260). All four indices remained greater than zero after Holm correction (all pHolm < 0.001), and all remained greater than the matched ahead-gaze sector indices (all pHolm < 0.001). Threshold sensitivity analysis across cut-offs from 0.30 to 0.40 showed that the positive directional pattern was preserved for all gaze directions. Conclusions: Tear-film quality varies regionally with gaze direction, a pattern that was clearer in spatial maps and sector indices than in global summaries. Straight-ahead measurements may therefore provide an incomplete account of tear-film behaviour during eccentric gaze. As the analysis involved healthy participants and did not assess symptoms or diagnostic performance, the clinical relevance of this pattern requires validation in symptomatic populations.