The Reliability between Placido Topography and Scheimpflug Topography in Normal Corneas with Astigmatism less Than 0.50 Dc

Abstract

Purpose: This Clinical research was targeted to experimentally investigate the reliability between Placido topography and Scheimpflug topography in normal corneas with astigmatism ≤ ±0.50 Dc by comparing the refractive powers at the 4 main meridians (180⁰ - 90⁰) in order to study any differences between the two topographers and their reliability. Comparing the reliability measurements of Placido disk topography (CSO- Modi 02 Corneal Topographer with Phoenix Full & Pupil Module Software) with those of a high-resolution rotating Scheimpflug camera (Pentacam-Oculus,) and assess the agreement between these two topographers in measuring corneal power in normal eyes without astigmatism (≤ 0.50 Dc).
 Methods and Materials: Measurements were taken from 56 eyes corresponding to a proportion of patients, of which 26 were men with a mean age of ± 30 years and 30 were women with a mean age of ± 27 years. Refractive power maps were taken from the anterior cornea, having results for the steep meridian value (Ks), the flat meridian value (Kf), mean keratometric value (Km), and cornea astigmatism (Ks-Kf). The same examiner took all the data from measuring these 56 eyes. The results for each refractive map from the two topographers was taken with values for meridians (180⁰- 90⁰). Then the there was a statistical analysis comparing the values of (CSO) and (Pentacam) for those 56 eyes measured.
 Results: The statistical analysis for all meridians based on the results and as far as normal corneas with astigmatism ≤ ±0.50 Dc are concerned, the Placido topography (CSO) and Scheimpflug imaging technique (Pentacam), can be considered as equivalent in terms of diagnostic credibility and accuracy for primary health care, fitting contact lenses, etc. as the correlation coefficient r did not show any important differences for both instruments. For the 90⁰ meridian the correlation coefficient was 0.79, Significance level P=0.0001 and 95% confidence interval ranges from 0.67 to 0.87. For the 180⁰ meridian the correlation coefficient was 0.48, Significance level P<0.0001 and 95% confidence interval ranges from 0.25 to 0.66.
 Conclusion: In terms of diagnosis of pathology and follow-up, contact lens fitting especially for the anterior cornea surface these two instruments can work quite the same that’s why a small clinical practitioner should have at least a Placido topographer. Corneal topography is an important instrument in order to measure the shape and refractive power of the cornea. Corneal topography gives practitioners an important tool to fit contact lenses asses the power and the cornea shape and helps to evaluate complications of the contact lens in relation with the corneal surface. These instruments continue to develop techniques and software in order to investigate and evaluate corneal surfaces and the integrity of the tear film, so that they can provide better solutions for their contact lens patients.