Corneal High-Order Aberrations in Keratoconus

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Corneal High-Order Aberrations in Keratoconus
Juan C. Arciniega, MD Engy M. Mohamed, MD R.
Wayne Bowman, MD Steven Verity, MD James P.
McCulley, MD, FRCOphth (UK).
Department of Ophthalmology, The University of
Texas Southwestern Medical Center at Dallas,
Texas. USA.
Financial Disclosure
Juan C. Arciniega, Engy M. Mohamed, Steven Verity
and R. Wayne Bowman have no commercial
relationships. James P. McCulley is a
consultant of Alcon Inc.
This study was supported in part by grants NIH
EY12430, EY016664 and an unrestricted grant from
the Research to Prevent Blindness, New York, New
York.

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Background

• Keratoconus is a condition in which the cornea
  assumes a conical shape as a result of
  non-inflammatory progressive corneal thinning.
  The thinning and protrusion in keratoconus
  induces irregular astigmatism with and without
  myopia resulting in mild to marked impairment in
  both quantity and quality of vision. It is a
  progressive disease ultimately affecting both
  eyes, although only one eye may be affected
  initially.1

1. Kanski Jack, Clinical Ophthalmology. Sixth
   edition, Elsevier, 2007

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Purpose
To evaluate the use of the anterior and posterior
corneal surface high-order aberrations (HOAs) as
a tool to detect and grade keratoconus using the
Pentacam.
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Methods
A retrospective study of 111 eyes (62 patients
33 males) was performed. The eyes were divided
into 5 groups suspect group and four other
groups according to the Amsler-Krumeich
classification of keratoconus stage I to stage
IV groups. Anterior and posterior corneal HOAs
were obtained using the software provided by the
Pentacam system.
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Methods
The Amsler-Krumeich classification1 includes the
following stages
Stage I Eccentric steeping Myopia and astigmatism lt 5.00 D Mean central K readings lt 48.00 D
Stage II Myopia and astigmatism from 5.00 to 8.00 D Mean central K readings lt 53.00 D Absence of scarring Minimum corneal thickness gt400 µm.
Stage III Myopia and astigmatism from 8.00 to 10.00 D Mean central K readings gt53.00 D Absence of scarring Minimum corneal thickness 300 to 400 µm.
Stage IV Refraction not measurable Mean central K readings gt55.00 D Central corneal scarring Minimum corneal thickness 200 µm

1. Alió Jorge, Corneal Higher Order Aberrations A
   Method to Grade Keratoconus. J Refract Surg. Vol.
   22   No. 6   June 2006

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Methods

Anterior Posterior Zernike (Z) coefficients
were used from Z3 to Z6 to calculate

• Coma-like aberration
• Spherical-like aberration
• Residual aberrations

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Results
The mean age of patients was 49.46.7 years. The
mean keratometric value was 43.3014 D The mean
thinnest point of corneal thickness was
450.887µm.
Number of Patients 62
Eye number 111
Right eye 58
Left eye 53
Males 33
Females 29
Stage I 43
Stage II 24
Stage III 8
Stage IV 21
Suspect 15
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Results
Patients Demographics
Suspect Stage I Stage II Stage III Stage IV
Age 41.918.5 44.511.8 41.916.6 43.115.9 43.912
Mean keratometric value 43.61.9 44.81.9 49.91.4 53.80.55 60.55.3
Corneal thickness 519.840.6 490.444.4 437.245.1 413.674.1 349.9117
Sphere -4.43.3 -5.13.5 -9.73.2 -8.73.7 -9.74.7
Cylinder 2.31.4 3.51.9 2.62.5 4.51.8 4.53
Spherical equivalent -3.23.1 -3.43.4 -5.53.3 -6.54 -7.44
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Results
Posterior coma-like aberration was the highest
posterior HOAs among all the groups and anterior
coma-like aberration was the highest of anterior
HOAs among all groups except for the suspect
group which had the anterior spherical-like
aberration as the highest. Anterior coma-like
aberrations increased progressively with the
groups while the posterior coma-like aberrations
did not show a gradually increase.
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Results

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Conclusion
Corneal higher-order aberrations, especially
coma-like aberrations, are significantly higher
in eyes with keratoconus than in keratoconus
suspects. Only anterior coma-like aberrations
measured by Pentacam were best in the early
detection and grading of keratoconus.