Comparison of Corneal Power and Corneal Astigmatism of Different Diameter Zones Centered on the Pupil and Corneal Apex Using Scheimpflug Tomography

Abstract

Purpose: Using Scheimpflug tomography to investigate the difference in corneal power and corneal astigmatism between 3- and 4-mm diameter zones centered on the pupil and corneal apex.

Methods: A total of 90 eyes were included in this study. Axial keratometry, total refractive power, and true net power centered on the pupil and corneal apex in 3- and 4-mm diameter zones were assessed. The paired sample t test and independent sample t test were used for data comparison.

Results: For corneal power and corneal astigmatism for the 3- and 4-mm diameter zones, the flat K values of axial keratometry, total refractive power, and true net power centered on the pupil (3-mm: 43.99 ± 1.69 D, 43.12 ± 1.71 D, 42.53 ± 1.67 D; 4-mm: 44.04 ± 1.67 D, 43.38 ± 1.71 D, 42.61 ± 1.65 D) were significantly higher than those centered on the apex (3-mm: 43.93 ± 1.69 D, 43.05 ± 1.71 D, 42.46 ± 1.67 D; 4-mm: 44.01 ± 1.67 D, 43.34 ± 1.69 D, 42.58 ± 1.65 D; all P < 0.02). However, the steep K and astigmatism magnitude values centered on the pupil (3-mm: 45.71 ± 1.73 D, 45.01 ± 1.73 D, 44.38 ± 1.69 D; 1.72 ± 0.83 D, 1.89 ± 0.86 D, 1.85 ± 0.84 D; 4-mm: 45.78 ± 1.73 D, 45.28 ± 1.74 D, 44.45 ± 1.68 D; 1.73 ± 0.84 D, 1.90 ± 0.85 D, 1.84 ± 0.85 D) were lower than those centered on the apex (3-mm: 45.81 ± 1.74 D, 45.10 ± 1.72 D, 44.50 ± 1.70 D; 1.88 ± 0.90 D, 2.05 ± 0.90 D, 2.04 ± 0.90 D; 4-mm: 45.85 ± 1.73 D, 45.34 ± 1.73 D, 44.51 ± 1.69 D; 1.83 ± 0.88 D, 2.00 ± 0.90 D, 1.93 ± 0.86 D; all P < 0.01). Compared with the 3-mm diameter zone, the corresponding 4-mm diameter zone showed higher corneal power centered on both pupil and corneal apex.

Conclusions: The difference in corneal power and corneal astigmatism, measured at 3 and 4 mm, centered on the pupil and the corneal apex should be noted in corneal refractive surgery and toric intraocular lens calculation.