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Evaluation of the shape symmetry of bilateral normal corneas in a Chinese population.

Bao F, Chen H, Yu Y, Yu J, Zhou S, Wang J, Wang Q, Elsheikh A - PLoS ONE (2013)

Bottom Line: The mean geometric center (x0, y0, z0) of both right and left corneas was located on the temporal side and inferior-temporal side of the apex in anterior and posterior topography map, respectively.Further, rotation angle γ along Z axis, which is related to corneal astigmatism, showed clear mirror symmetry.This characteristic could help in detection of pathological abnormalities, disease diagnosis, measurement validation and surgery planning.

View Article: PubMed Central - PubMed

Affiliation: The Affiliated Eye Hospital of WenZhou Medical College, Wenzhou, China.

ABSTRACT

Purpose: To investigate the bilateral symmetry of the global corneal topography in normal corneas with a wide range of curvature, astigmatism and thickness values.

Design: Cross-Sectional Study.

Methods: Topography images were recorded for the anterior and posterior surfaces of 342 participants using a Pentacam. Elevation data were fitted to a general quadratic model that considered both translational and rotational displacements. Comparisons between fellow corneas of estimates of corneal shape parameters (elevation, radius in two main directions, Rx and Ry, and corresponding shape factors, Qx and Qy) and corneal position parameters (translational displacements: x0, y0 and z0, and rotational displacements: α, β and γ) were statistically analyzed.

Results: The general quadratic model provided average RMS of fit errors with the topography data of 1.7±0.6 µm and 5.7±1.3 µm in anterior and posterior corneal surfaces. The comparisons showed highly significant bilateral correlations with the differences between fellow corneas in Rx, Ry, Qx and Qy of anterior and posterior surfaces remaining insignificantly different from zero. Bilateral differences in elevation measurements at randomly-selected points in both corneal central and peripheral areas indicated strong mirror symmetry between fellow corneas. The mean geometric center (x0, y0, z0) of both right and left corneas was located on the temporal side and inferior-temporal side of the apex in anterior and posterior topography map, respectively. Rotational displacement angle α along X axis had similar distributions in bilateral corneas, while rotation angle β along Y axis showed both eyes tilting towards the nasal side. Further, rotation angle γ along Z axis, which is related to corneal astigmatism, showed clear mirror symmetry.

Conclusions: Analysis of corneal topography demonstrated strong and statistically-significant mirror symmetry between bilateral corneas. This characteristic could help in detection of pathological abnormalities, disease diagnosis, measurement validation and surgery planning.

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Related in: MedlinePlus

The Cartesian coordinate system of bilateral corneas.Points A to D were chosen to test instrument measurement repeatability and analyze interocular symmetry. Rotation angles α, β and γ could be positive or negative according to right hand spiral law.
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pone-0073412-g002: The Cartesian coordinate system of bilateral corneas.Points A to D were chosen to test instrument measurement repeatability and analyze interocular symmetry. Rotation angles α, β and γ could be positive or negative according to right hand spiral law.

Mentions: The elevation maps of each anterior and posterior surface were exported in the form of up to 6361 elevation data points representing a middle circle of 9 mm diameter. A Cartesian coordinate system was employed with the X, Y and Z-axes in the horizontal (OD: temporal-nasal; OS: nasal-temporal), vertical (inferior-superior) and sagittal (posterior-anterior) directions, respectively. The data consisted of elevation zi at each point i on either the anterior or posterior corneal surface with Cartesian coordinates (xi, yi). zi was defined as the sagittal distance between point i and an XOY plane passing through the origin point O (the apex of anterior or posterior corneal surface), at which the instrument axis intercepts the cornea (Fig. 1). The data at four points including two in the central area: A (1, 0, zA) and B (−1, 0, zB), and two in the periphery: C (0, 3, zC) and D (0, −3, zD), were further used to test repeatability and symmetry of measurements (Fig. 2).


Evaluation of the shape symmetry of bilateral normal corneas in a Chinese population.

Bao F, Chen H, Yu Y, Yu J, Zhou S, Wang J, Wang Q, Elsheikh A - PLoS ONE (2013)

The Cartesian coordinate system of bilateral corneas.Points A to D were chosen to test instrument measurement repeatability and analyze interocular symmetry. Rotation angles α, β and γ could be positive or negative according to right hand spiral law.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3757004&req=5

pone-0073412-g002: The Cartesian coordinate system of bilateral corneas.Points A to D were chosen to test instrument measurement repeatability and analyze interocular symmetry. Rotation angles α, β and γ could be positive or negative according to right hand spiral law.
Mentions: The elevation maps of each anterior and posterior surface were exported in the form of up to 6361 elevation data points representing a middle circle of 9 mm diameter. A Cartesian coordinate system was employed with the X, Y and Z-axes in the horizontal (OD: temporal-nasal; OS: nasal-temporal), vertical (inferior-superior) and sagittal (posterior-anterior) directions, respectively. The data consisted of elevation zi at each point i on either the anterior or posterior corneal surface with Cartesian coordinates (xi, yi). zi was defined as the sagittal distance between point i and an XOY plane passing through the origin point O (the apex of anterior or posterior corneal surface), at which the instrument axis intercepts the cornea (Fig. 1). The data at four points including two in the central area: A (1, 0, zA) and B (−1, 0, zB), and two in the periphery: C (0, 3, zC) and D (0, −3, zD), were further used to test repeatability and symmetry of measurements (Fig. 2).

Bottom Line: The mean geometric center (x0, y0, z0) of both right and left corneas was located on the temporal side and inferior-temporal side of the apex in anterior and posterior topography map, respectively.Further, rotation angle γ along Z axis, which is related to corneal astigmatism, showed clear mirror symmetry.This characteristic could help in detection of pathological abnormalities, disease diagnosis, measurement validation and surgery planning.

View Article: PubMed Central - PubMed

Affiliation: The Affiliated Eye Hospital of WenZhou Medical College, Wenzhou, China.

ABSTRACT

Purpose: To investigate the bilateral symmetry of the global corneal topography in normal corneas with a wide range of curvature, astigmatism and thickness values.

Design: Cross-Sectional Study.

Methods: Topography images were recorded for the anterior and posterior surfaces of 342 participants using a Pentacam. Elevation data were fitted to a general quadratic model that considered both translational and rotational displacements. Comparisons between fellow corneas of estimates of corneal shape parameters (elevation, radius in two main directions, Rx and Ry, and corresponding shape factors, Qx and Qy) and corneal position parameters (translational displacements: x0, y0 and z0, and rotational displacements: α, β and γ) were statistically analyzed.

Results: The general quadratic model provided average RMS of fit errors with the topography data of 1.7±0.6 µm and 5.7±1.3 µm in anterior and posterior corneal surfaces. The comparisons showed highly significant bilateral correlations with the differences between fellow corneas in Rx, Ry, Qx and Qy of anterior and posterior surfaces remaining insignificantly different from zero. Bilateral differences in elevation measurements at randomly-selected points in both corneal central and peripheral areas indicated strong mirror symmetry between fellow corneas. The mean geometric center (x0, y0, z0) of both right and left corneas was located on the temporal side and inferior-temporal side of the apex in anterior and posterior topography map, respectively. Rotational displacement angle α along X axis had similar distributions in bilateral corneas, while rotation angle β along Y axis showed both eyes tilting towards the nasal side. Further, rotation angle γ along Z axis, which is related to corneal astigmatism, showed clear mirror symmetry.

Conclusions: Analysis of corneal topography demonstrated strong and statistically-significant mirror symmetry between bilateral corneas. This characteristic could help in detection of pathological abnormalities, disease diagnosis, measurement validation and surgery planning.

Show MeSH
Related in: MedlinePlus