Transcript Correlation Between Corneal Biomechanics and Wavefront

Correlation Between Corneal
Biomechanics and Wavefront
Aberrations
Alejandro Rivera, MD
Private Practice
Mexico City
The author has no financial interest in any material or method
mentioned
Purpose
 The cornea is one of the main refractive structures of the eye and
therefore its contribution to the presentation of wavefront
aberrations is critical. There is no complete knowledge of the origin
of higher-order aberrations. The influence of intraocular pressure
(1), corneal thickness (2), eyelid pressure (3), tear film (4), age (5),
etc. has been studied. Altered biomechanical parameters in the
cornea as a result of refractive surgery can increase ocular image
errors. The purpose of this study was to know if in the normal
cornea there is a direct correlation between changes in the
biomechanical parameters and the presentation of wavefront
aberrations.
Methods
 The design was an observational series of patients without history of
ocular abnormalities. 230 eyes of 115 patients were retrospectively
evaluated. The data were taken from files of patients evaluated for
refractive surgery. The inclusion criteria were patients of age 18 to 35
years, without clinical signs of keratoconus or other ectatic diseases, no
contact lens use, no ocular pathology. The root-mean-square (RMS)
wavefront error of the combined coma-like aberrations was measured
by an Optical Path Difference Scan II ARK-10000 (Nidek Corporation,
Hiroishi-Cho, Japan). The Ocular Response Analyzer (Reichert
Corporation, Depew, USA) was used to determine the corneal
hysteresis (CH). The relationship between higher-order wavefront
aberrations and a biomechanical parameter such as corneal hysteresis
was statistically analyzed using the Analise-it for Microsoft Excel
program (Version 2.07, Analise-it Software, Ltd. Leeds, UK).
Results
 Using the Pearson Correlation Coefficient a negative correlation was
found between RMS Coma and corneal hysteresis (r = - 0.27, 2-tailed
p < 0.0001).
Pearson Correlation RMS Coma - CH
14
13
12
CH (mmHg)
11
10
9
8
7
6
5
0
0,5
RMS Coma (microns)
1
Conclusion
 Anterior corneal aberrations vary greatly from patient to patient (6) and
little of this is attributable to age, refraction, corneal thickness or
intraocular pressure. Changes in higher-order aberrations after
refractive or cataract surgery are well known and are believed to be a
consequence of variations in factors such as corneal thickness (2)
among other causes. Corneal hysteresis is a main biomechanical
parameter and it could be considered as playing a role in the origin of
wavefront aberrations. However, it was found in this study that in the
normal eye there is a negative correlation between RMS coma and
corneal hysteresis. The real sources of higher-order aberrations in the
normal eye are still unknown (1).
References
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2.
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5.
6.
Qu J, Lu F, Wu JX, Wang QM, Xu CC, Zhou XT, He JC. Wavefront
aberration and its association with intraocular pressure and central
corneal thickness in myopic eyes. J Cataract Refract Surg 2007; 33:
1447-1454.
Mierdel P, Krinke HE, Pollack K, Spoerl E. Diurnal fluctuation of
Higher order ocular aberrations: Correlation with intraocular pressure
and corneal thickness. J Cataract Refract Surg 2004; 20: 236-242.
Lieberman DM, Grierson JW, The lids influence on corneal shape.
Cornea 2000; 19: 336-342
Montés-Micó R, Phil M. Role of the tear film in the optical quality of
the human eye. J Cataract Refract Surg 2007; 33: 1631-1635.
Amano S, Amano Y, Yamagami S, Miyai T, Miyata K, Samejima T,
Oshika T. Age-related changes in corneal and ocular higher-order
wavefront aberrations. Am J Ophthalmol 2004; 137: 988-992.
Wang L, Dai E, Koch D, Nathoo A. Optical aberrations of the human
anterior cornea. J Cataract Refract Surg 2003; 29: 1514-1521.