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Could corneal biomechanics diurnal variations be affecting corneal response to an air puff in healthy eyes: preliminary evidence

Poster Details

First Author: M.Ariza-Gracia SPAIN

Co Author(s):    D. Pinero   B. Calvo   R. Perez-Cambrodi   J. Rodriguez           

Abstract Details

Purpose:

The response of the cornea when subjected to a non-contact tonometry test was found to be influenced by the intraocular pressure (IOP) and geometry, and not only by the mechanical properties of the tissue. A combined clinical and numerical study has been performed to evaluate whether diurnal changes in corneal biomechanics (pachymetry, curvature and IOP) influence the corneal response to a generic air puff in healthy eyes.

Setting:

Department of Ophthalmology, Medimar International Hospital (Alicante, Spain); Aragón Institute of Engineering Research (I3A). University of Zaragoza (Zaragoza, Spain); LaBS, Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”, Politecnico di Milano Italy.

Methods:

Diurnal variations in curvature (dioptres), corneal central thickness (CCT), pachymetry and IOP were obtained for 6 eyes in periods of 2 hours from 10.00 to 20.00. Corneal topography was measured using the Scheimpflug photography-based system Sirius (CSO, Italy) with a 1-micron resolution whereas IOP was measured using Goldman applanation tonometry with a 1-mmHg resolution. A patient-specific finite element (FE) corneal model was built using topographic data and a material model and properties for the eye reported in the literature. The model was used to simulate a non-contact tonometry test to obtain the maximum deformation amplitude (maxDA) of the corneal apex.

Results:

Dioptres (D), CCT (microns) and IOP (mmHg) showed diurnal changes (mean + standard deviation): 43.4±2.1, 570.9±17.4 and 12.3±2.7 respectively, with an average maximum absolute difference (%) of: 2.2±0.9, 3.0±1.3 and 21.5±4.8 respectively. Furthermore, there were localized differences in the corneal maps (dioptres and pachymetry) on the periphery of the corneal, and at the centre of the cornea, reaching a maximum difference of up to 20% near the periphery. The average numerical maxDA of the cornea (mm) was 0.98±0.08, which was found to be within the reported clinical results for healthy eyes, with an average maximum absolute difference (%) of 5.9±1.6.

Conclusions:

Results show an inverse correlation between variations in the IOP and in the CCT, indicating a clear interplay that influences the corneal response when subjected to an air-puff. Although maxDA seems not to be highly affected, IOP and CCT could locally vary up to a 20%. Hence, these variations may limit diagnostic of small biomechanical alterations based on non-contact tonometry. Therefore, the time of the day when a test is performed should be taken into consideration since diurnal changes in corneal biomechanics induce variability in the corneal deformation response that could lead to inaccurate clinical decisions.

Financial Disclosure:

NONE

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