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KMID : 1159320140160030373
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Korean Journal of Vision Science
2014 Volume.16 No. 3 p.373 ~ p.383
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Asphericity of the Central and Peripheral Cornea in Myopic Laser Refractive Surgery Patients
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Kim Jeong-Mee
Lee Koon-Ja
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Abstract
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Purpose: To evaluate changes in asphericity (Q-value) of the central and peripheral cornea in myopic corneal refractive surgery group compared with emmetropes and correlation between pre-operative refractive error (spherical equivalent) and Q-value of post-operation.
Methods: One hundred thirty five eyes of 68 subjects (23.49±2.5 years, range 20 to 29) who underwent myopic refractive surgery and 40 eyes of 20 emmetropes (22.50±1.7 years, range 20 to 25) were enrolled. Q-value was measured using a Pentacam Oculyzer topography (Oculus Inc.,Germany) for 6mm to 10mm zones. For analysis of post-op group, the group was classified by pre-op spherical equivalents of < -6.00 D(-4.41±1.09 D, range -1.25 to -5.58) and ≥-6.00 D
(-7.12±0.95 D, range -6.00 to -9.00) as two post-op groups.
Results: The mean Q-values in the emmetropes ranged between -0.34±0.12 (6 mm zone) to -0.52±0.09 (10 mm zone). There was a tendency to become more negative Q-values toward the peripheral zone. The negative Q-values with vertical meridian were greater than those with horizontal meridian in all diameters measured along the corneal meridian. However, the mean Q-values in post-op group ranged between 0.84±0.43 (6 mm zone) to 0.09±0.30 (10 mm zone).
There was a tendency for Q-values to become less positive Q-values toward the peripheral zone. The positive Q-values with vertical meridian in the post-op group were more than those with horizontal meridian in 6 mm, 7 mm and 8 mm zones measured along the corneal meridian. Whereas, the positive Q-values with vertical meridian in the post-op group were lower than those with horizontal meridian in 9mm and 10mm zones. There was a tendency for Q-values to become more
positive with increased pre-op spherical equivalent (P=0.000) and significant correlation between Q-value and pre-op refractive error in 6 mm, 7 mm and 8 mm zones (R=-0.725, R=-0.744 and R=-0.731, respectively).
Conclusions: Q-value was changed from prolate cornea (negative Q-value) to oblate cornea (positive Q-value) in myopic corneal refractive surgery group compared with emmetropes and Q-value according to corneal meridian in post-op group found to be different patterns compared with emmetropes. These changes in Q-value would be provided basic data for outcome of visual performance and for contact lens design and fitting in eyes with a new anatomical configuration induced by corneal refractive surgery.
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KEYWORD
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Corneal asphericity, Q-value, Asphericity coefficient, Corneal refractive surgery, Corneal topography
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