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Henry B. Wallace, James McKelvie, Colin R. Green, Stuti L. Misra; Corneal Curvature: the Influence of Corneal Accommodation and Biomechanics on Corneal Shape. Trans. Vis. Sci. Tech. 2019;8(4):5. doi: https://doi.org/10.1167/tvst.8.4.5.
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Variation in the presence and magnitude of corneal conformational changes during accommodation may predict postoperative ectasia following refractive surgery and assist in the early diagnosis of corneal ectatic disorders. The current study aimed to establish a baseline for corneal refractive changes during ocular accommodation and to clarify the role of biomechanical factors in predicting these changes in a population without corneal pathology.
GALILEI G2 corneal tomography was assessed in 63 participants in both the accommodated and unaccommodated states. Four diopters (D) of physiological accommodation were induced using near-acuity calibrated words viewed through an externally mounted beam splitter mounted on a three-dimensional-printed frame. Corneal biomechanical characteristics were assessed with the CorVis-ST instrument, and statistical analysis was completed in R software.
Anterior chamber depth was reduced by 0.10 ± 0.07 mm with accommodation (P < 0.01). Areas of statistically significant change in corneal curvatures were seen in all participants with accommodation. Mean anterior instantaneous corneal power increased in the superior-nasal periphery (0.1 D, 95% confidence interval [CI] = 0.05–0.2 D) and decreased in the inferior-temporal periphery (0.1 D, 95% CI = −0.05 to −0.15 D). Corneal stiffness and the corneal deformation amplitude ratio predicted peripheral corneal curvature changes with accommodation (P < 0.05).
Corneal conformational changes occur during accommodation in normal subjects. Further studies are required to assess the magnitude of corneal changes during accommodation in patients with corneal ectasia.
An externally mounted beam splitter can be used to modify the visual target presented by clinical ocular imaging instruments. Corneal conformational changes during accommodation may be useful in the diagnosis of corneal ectasia.
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