Background: The aim is to investigate induced higher-order aberrations (HOA)s and astigmatism as a result of non-toric ortho-k lens decentration and utilise artificial intelligence (AI) to predict its magnitude and direction. Methods: Medmont E300 Video topographer was used to scan 249 corneas before and after ortho-k wear. Custom-built MATLAB codes extracted topography data and determined lens decentration from the boundary and midpoint of the central flattened treatment zone (TZ). An evaluation was carried out by conducting Zernike polynomial fittings via a computer-coded digital signal processing procedure. Finally, an AI-based machine learning neural network algorithm was developed to predict the direction and magnitude of TZ decentration. Results: Analysis of the first 21 Zernike polynomial coefficients indicate that the four low-order and four higher-order aberration terms were changed significantly by ortho-k wear. While baseline astigmatism was not correlated with lens decentration (R = 0.09), post-ortho-k astigmatism was moderately correlated with decentration (R = 0.38) and the difference in astigmatism (R = 0.3). Decentration was classified into three groups: ≤0.50 mm, reduced astigmatism by −0.9 ± 1 D; 0.5~1 mm, increased astigmatism by 0.8 ± 0.1 D; >1 mm, increased astigmatism by 2.7 ± 1.6 D and over 50% of lenses were decentred >0.5 mm. For lenses decentred >1 mm, 29.8% of right and 42.7% of left lenses decentred temporal-inferiorly and 13.7% of right and 9.4% of left lenses decentred temporal-superiorly. AI-based prediction successfully identified the decentration direction with accuracies of 70.2% for right and 71.8% for left lenses and predicted the magnitude of decentration with root-mean-square (RMS) of 0.31 mm and 0.25 mm for right and left eyes, respectively. Conclusions: Ortho-k lens decentration is common when fitting non-toric ortho-k lenses, resulting in induced HOAs and astigmatism, with the magnitude being related to the amount of decentration. AI-based algorithms can effectively predict decentration, potentially allowing for better control over ortho-k fitting and, thus, preferred clinical outcomes.

Purpose: To evaluate whether corneal topography map stitching can fully substitute the traditional single-shot capture methods in clinical settings. Methods: This record review study involved the measurement of corneal surfaces from 38 healthy subjects using two instruments: the Medmont Meridia, which employs a stitching composite topography method, and the Eye Surface Profiler (ESP), a single-shot measurement device. Data were processed separately for right and left eyes, with multiple gaze directions captured by the Medmont device. Surface registration and geometric transformation estimation, including neighbouring cubic interpolation, were applied to assess the accuracy of stitched maps compared to single-shot measurements. Results: The study evaluated eye rotation angles and surface alignment between Medmont topography across various gaze directions and ESP scans. Close eye rotations were found in the right-gaze, left-gaze and up-gaze directions, with rotation angles of around 8°; however, the down-gaze angle was around 15°, almost twice other gaze rotation angles. Root mean squared error (RMSE) analysis revealed notable discrepancies, particularly in the right-, left-, and up-gaze directions, with errors reaching up to 98 µm compared to ESP scans. Additionally, significance analyses showed that surface area ratios highlighted considerable differences, especially in the up-gaze direction, where discrepancies reached 70% for both right and left eyes. Conclusions: Despite potential benefits, the findings highlight a significant mismatch between stitched and single-shot measured surfaces due to digital processing artefacts. Findings suggest that stitching techniques, in their current form, are not yet ready to substitute single-shot topography measurements fully. Although stitching helps fit large-diameter contact lenses, care should be taken regarding the central area, especially if utilising the stitched data for optimising optics or wavefront 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.