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Yuta Ueno, Takahiro Hiraoka, Tetsuro Oshika; Age related changes in pachymetric mapping of normal corneas. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2453.
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Topographic analysis of corneal posterior surface has been conducted using scanning-slit videokeratoscope, Scheimpflug camera, and anterior segment optical coherence tomography (AS-OCT). Previous studies have shown that anterior and posterior corneal curvatures are not always in parallel with each other even in normal subjects. These studies also revealed that keratometric astigmatism calculated based on the measurements of anterior corneal curvature alone was different from the total astigmatism calculated based on actual measurements of both anterior and posterior corneal curvatures. This implies that corneal thickness is not uniform depending on the location. In the present study, corneal thickness profile was assessed with AS-OCT (CASIA, Tomey), and its directional difference was analyzed in relation to age in normal subjects.
948 eyes of 509 normal subjects (251 men and 258 women) ranging in age from 6 to 93 years (mean ± standard deviation, 53.8 ± 24.1 years) were enrolled. Eyes with corneal diseases or history of ocular surgery or contact lens use were excluded. Corneal thickness was measured across the cornea with AS-OCT and a pachymetric map was made for each eye. The corneal thicknesses on the annular ring of 3mm diameter around the corneal apex were averaged in each quadrant (superior, inferior, nasal, and temporal), and compared among 4 quadrants. The sum of corneal thicknesses in the vertical direction (superior quadrant + inferior quadrant) and in the horizontal direction (nasal quadrant + temporal quadrant) was also calculated. Subsequently, the difference in corneal thickness between the vertical and horizontal directions was analyzed in relation to age.
The cornea was the thickest in the superior quadrant in 800 eyes (84%), and the thinnest in the temporal quadrant in 688 eyes (73%). The sum of corneal thickness in the vertical direction was greater than that in the horizontal direction in 943 eyes (99%). The difference between them was 11.0 ± 5.8 µm, and showed a significant positive correlation with subjects’ age (r = 0.525, P < 0.0001).
In normal eyes, cornea is thicker in the vertical direction than in the horizontal direction, and the directional disparity increases with age. Therefore, it is quite important to consider the effects of corneal thickness profile on total astigmatism especially in elderly patients.
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