Correlation Between Corneal Biomechanics and Wavefront Aberrations

1
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

2
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.

3
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).

4
Results

• Using the Pearson Correlation Coefficient a
  negative correlation was found between RMS Coma
  and corneal hysteresis (r - 0.27, 2-tailed p lt
  0.0001).

5
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).

6
References

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   JC. Wavefront aberration and its association with
   intraocular pressure and central corneal
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   2007 33 1447-1454.
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   Diurnal fluctuation of Higher order ocular
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3. Lieberman DM, Grierson JW, The lids influence on
   corneal shape. Cornea 2000 19 336-342
4. Montés-Micó R, Phil M. Role of the tear film in
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