Correlation between the dioptric power, astigmatism and surface shape of the anterior and posterior corneal surfaces

Abstract

A knowledge of the shape of the cornea is of major importance for the planning and monitoring of surgery, and for the correct diagnosis of corneal diseases. Many authors have studied the geometry of the second corneal surface in the central region and it has been stated that there is a high correlation between the central radii of curvature and asphericities of the two corneal surfaces. In this work we extend this study to a larger, central, 6-mm diameter of the cornea. Surface height data, obtained with an Oculus Pentacam from 42 eyes from 21 subjects, were analysed to yield surface power vectors. Corneal heights of both surfaces were also decomposed into low-order Zernike polynomials and the correlations between each of the power vectors and low-order Zernike coefficients for the two surfaces were studied. There was not only a strong correlation between spherical powers and Zernike defocus coefficients, but also between the astigmatic components. The correspondence between the astigmatisms in both surfaces found here can be of the utmost importance in planning optical surgery, since perfect spherical ablation of the first surface does not assure total correction of corneal astigmatism.

Influence of ocular dominance in the variability of the eye’s anterior segment measurements

“…This finding is in accordance with our previous results in Ref. [13], which lead us to make this study. In both studies measurements have not been done in total darkness, contrary to the recommendations of the Pentacam system -but in accordance with the normal clinical practice.…”

“…Results are also in accordance with those obtained by Mas et al [13]. In our opinion, the limited accuracy of the system does not allow to detect the small ocular movements although they influence the measurements since data obtained with the dominant eye are more stable that those with the other eye.…”

“…In a recent work, [13], the authors presented some results related with corneal morphology. In their data they distinguished between the left and the right eye, and found that bilateral symmetry was broken in many subjects, for different Zernike components.…”

Retinal image quality assessment through a visual similarity index

“…Therefore, the objective refraction, which is computed from the Zernike polynomial expansion of the 60 wavefront function, W 0 (x,y) [28], may not match up with the subjectively measured refraction. What we propose to overcome this problem is to modify the wavefront by changing the Zernike coefficients related to astigmatism and defocus in order to fit the subjective test.…”

Etiology and Clinical Presentation of Astigmatism

“…Using similar equipment, Mas et al (2009) compared the optics of the anterior and posterior corneal surfaces. Their data shows that there was a low correlation between the astigmatic components of both surfaces: for the power vectors J 0 of the first and second corneal surfaces, the regression line is: y = -0.13x + 0.17; r 2 = 0.49; p < 0.01.…”