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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

Values of γ rotational angles estimated for all 342 participants.For clarity of presentation, participants were split into two groups according to whether γ of right corneas was greater than 0 (A, C) or less than 0 (B, D).
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pone-0073412-g006: Values of γ rotational angles estimated for all 342 participants.For clarity of presentation, participants were split into two groups according to whether γ of right corneas was greater than 0 (A, C) or less than 0 (B, D).

Mentions: The analysis was extended to the angles of rotational displacement between the geometric and keratometric axes of corneal surfaces as shown in Figs. 5 and 6 and Table 5. Angle α had similar distributions in bilateral corneas (r = 0.81 and r = 0.72 for anterior and posterior corneal surfaces) with the same angle signs in fellow corneas making the correlation parameters positive (Fig. 5). Similar results were obtained for angle β although in this case the values for right and left corneas had opposite signs (both rotated towards the nasal side), and therefore the correlation parameters were negative: r = −0.72 and r = −0.52 for anterior and posterior surfaces, Fig. 5. Furthermore, angle γ, which was related to corneal astigmatism, also had opposite signs for right and left corneas with the absolute values indicating a high degree of mirror symmetry relative to the median vertical plane YZ in Fig. 6 (r = −0.47 and r = −0.44 for anterior and posterior surfaces).


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)

Values of γ rotational angles estimated for all 342 participants.For clarity of presentation, participants were split into two groups according to whether γ of right corneas was greater than 0 (A, C) or less than 0 (B, D).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0073412-g006: Values of γ rotational angles estimated for all 342 participants.For clarity of presentation, participants were split into two groups according to whether γ of right corneas was greater than 0 (A, C) or less than 0 (B, D).
Mentions: The analysis was extended to the angles of rotational displacement between the geometric and keratometric axes of corneal surfaces as shown in Figs. 5 and 6 and Table 5. Angle α had similar distributions in bilateral corneas (r = 0.81 and r = 0.72 for anterior and posterior corneal surfaces) with the same angle signs in fellow corneas making the correlation parameters positive (Fig. 5). Similar results were obtained for angle β although in this case the values for right and left corneas had opposite signs (both rotated towards the nasal side), and therefore the correlation parameters were negative: r = −0.72 and r = −0.52 for anterior and posterior surfaces, Fig. 5. Furthermore, angle γ, which was related to corneal astigmatism, also had opposite signs for right and left corneas with the absolute values indicating a high degree of mirror symmetry relative to the median vertical plane YZ in Fig. 6 (r = −0.47 and r = −0.44 for anterior and posterior surfaces).

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