Original articleCorneal regular and irregular astigmatism assessed by Fourier analysis of videokeratography data in normal and pathologic eyes1 ☆,
Section snippets
Subjects and methods
Corneal topography was obtained using videokeratography (TMS-2) in 200 eyes of 100 normal subjects, 58 eyes of 45 patients with keratoconus, and 24 eyes of 24 patients with suspected keratoconus, 100 eyes of 53 patients who had undergone LASIK, 101 eyes of 53 patients who had undergone PRK, and 79 eyes of 79 patients who had undergone PK. The measurements were repeated 4 times, and the best-focused, properly aligned image was chosen. The measurements were conducted by a nonmasked, experienced
Results
Color-coded maps representing each Fourier index are shown for a normal eye (Fig 1A), an eye with keratoconus (Fig 1B), an eye having undergone LASIK (Fig 1C), and an eye having undergone PK (Fig 1D). In a normal cornea (Fig 1A), the minimum amount of irregular astigmatism (asymmetry and higher order irregularity) is found. In keratoconus (Fig 1B), a prolate shape of the cornea is demonstrated in the spherical equivalent power map, and a large with-the-rule cylinder is shown in the regular
Discussion
In the current study, we defined the normal range of each Fourier index by adopting the mean±2×SD in 200 eyes of 100 normal subjects. Similar methodology has been applied in several other fields in medicine, such as systemic arterial pressure28, 29 and intraocular pressure. When the population conforms to the normal distribution, 96% of the samples are expected to lie within 2 SDs of the mean. In our normal group, the proportion of eyes that were included in the normal range was 96.0%, 98.5%,
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Manuscript no. 230013.
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None of the authors has a proprietary interest in any material or method mentioned.