Corneal Thickness Profile and Posterior Corneal Astigmatism in Normal Corneas

      Purpose

      To analyze the influence of corneal thickness profile on posterior corneal astigmatism (PA).

      Design

      Prospective, observational study.

      Subjects

      We included 418 normal subjects (213 men and 205 women) ranging in age from 6 to 93 years (49.0±23.4 years, mean ± standard deviation) in this study.

      Methods

      Anterior and posterior corneal topography were evaluated using 3-dimensional anterior segment optical coherence tomography. Pericentral corneal thickness (PCT) in each quadrant (superior, inferior, nasal, and temporal) was measured, and average PCT in the vertical (superior + inferior) and horizontal (nasal + temporal) directions was calculated. Posterior corneal astigmatism was calculated as (1) assumed PA based on the anterior corneal curvature measurement and the keratometric index and (2) actual PA derived from the direct measurement of posterior corneal curvature.

      Main Outcome Measures

      Corneal thickness distribution and the difference between assumed and actual PA.

      Results

      The PCT was significantly greater in the vertical (546.0±31.8 μm) than in the horizontal direction (542.6±31.7 μm) ( P < 0.0001), and the difference between them was significantly correlated with subject age ( r = 0.518, P < 0.0001). The difference between assumed and actual PA significantly correlated with the discrepancy between vertical and horizontal PCT ( r = 0.819, P < 0.0001), as well as subject age ( r = 0.533, P < 0.0001).

      Conclusions

      Corneal thickness is greater in the vertical than in the horizontal direction, making the PA more against-the-rule pattern than calculated on the basis of the anterior corneal curvature measurement only. Such discrepancy is more prominent in older patients.

      Abbreviations and Acronyms:

      AS-OCT ( anterior segment optical coherence tomography), ATR ( against-the rule), CCT ( central corneal thickness), D ( diopters), KA ( keratometric astigmatism), OCT ( optical coherence tomography), PA ( posterior corneal astigmatism), PCT ( pericentral corneal thickness), WTR ( with-the-rule)
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      Linked Article

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