Characteristics of Ocular HigherOrder Aberrations in Patients with Pellucid Marginal Corneal Degener

1
Characteristics of Ocular Higher-Order
Aberrations in Patients with Pellucid Marginal
Corneal Degeneration

• Yoshinori Oie, MD,1 Naoyuki Maeda, MD,1 Ryo
  Kosaki, MD,1
• Kohji Nishida, MD,2 Takashi Fujikado, MD,3 and
  Yasuo Tano, MD1
• 1Department of Ophthalmology, Osaka University
  Medical School, Suita, Japan
• 2Department of Ophthalmology and Visual Science,
  Tohoku University Graduate School of Medicine,
  Sendai, Japan
• 3Department of Applied Visual Science, Osaka
  University Medical School, Suita, Japan
• Financial interest
• Dr. Maeda received research grant from Topcon
  Corporation.

2
Introduction

• Pellucid marginal corneal degeneration

• Pellucid marginal corneal degeneration is one of
  the non-inflammatory disorders that cause corneal
  ectasia.
• Pellucid marginal corneal degeneration differs
  from keratoconus in that the corneal protrusion
  occurs inferiorly, above a narrow band of clear,
  nonvascularized thinned corneal stroma that is
  concentric to the limbus.
• Both pellucid marginal corneal degeneration and
  keratoconus are considered to be
  contraindications of laser refractive surgery
  such as LASIK.
• Therefore, it is very important to detect
  pellucid marginal corneal degeneration and
  keratoconus in LASIK candidates to avoid
  postoperative keratoectasia.
• We investigated the characteristics of ocular
  higher-order aberrations of eyes with pellucid
  marginal corneal degeneration using Zernike
  vector terms.

thinning
Anterior protrusion
3
Methods

• The medical records of 20 eyes with pellucid
  marginal corneal degeneration (PMCD group),
  76 eyes with keratoconus (KC group), and 105
  normal eyes (control group) were retrospectively
  reviewed.
• Patients attended the outpatient clinic of the
  Department of Ophthalmology at Osaka University
  Medical School between February 2002 and May
  2006.
• The higher-order aberrations (HOAs) for the
  central 4 mm diameter to estimate photopic vision
  were obtained up to forth order with the
  Hartmann-Shack wavefront analyzer (KR-9000PW,
  Topcon, Corporation, Tokyo, Japan)
• All data from the KR-9000PW database were
  extracted by using a prototype program of
  calculating Zernike vector analysis.
• The magnitudes and orientations of trefoil, coma,
  tetrafoil, secondary astigmatism in addition to
  the magnitude of the spherical aberration and
  total HOAs (third order component (S3), fourth
  order component (S4) S3 S4) were compared
  among the three groups.
• The simulated retinal image of Landolt ring of
  pellucid marginal corneal degeneration,
  keratoconus, control eyes was also investigated.

4
Zernike vector terms
Axis 90
Axis 30
Slow triangular
Fast triangular
Axis 270
Axis 90
Inferior slow
Superior slow
Axis 45
Axis 45
5
Diagnosis of pellucid marginal corneal
degeneration and keratoconus

• Pellucid marginal corneal degeneration
• Inferior corneal thinning with ectasia of the
  cornea above the area of thinning, with no
  evidence of scarring, vascularization or lipid
  deposition by slit-lamp examination
• Keratoconus
• Central thinning of the stroma with Fleischer
  ring and/or Vogts striae by
  slit-lamp examination.
• Pellucid marginal corneal degeneration suspect,
  keratoconus suspect
• Typical topographic patterns of pellucid
  marginal degeneration or keratoconus was observed
  in the axial power videokeratographic map for
  visual inspection without any abnormal findings
  in the slit-lamp and visual acuity examinations.
• Eyes diagnosed with pellucid marginal corneal
  degeneration suspect and keratoconus suspect were
  excluded in this study.

Pellucid marginal corneal degeneration
Keratoconus
Crab-claw pattern
lazy 8 figure pattern
6
Results
Clinical Characteristics
The age in PMCD group was significantly higher
than in KC group. The proportion of gender was
significantly different among the three groups.
Chi-square test, Kruskal-Wallis one-way
analysis of variance (ANOVA) on Ranks
7
PMCD group
trefoil fast triangular pattern coma inferior
slow pattern spherical aberration positive the
simulated retinal image of Landolt
ring comet-like pattern with two tails oriented
right-inferiorly and left-inferiorly
total HOAs
KC group
total HOAs
trefoil slow triangular pattern coma inferior
slow pattern spherical aberration negative the
simulated retinal image of Landolt
ring comet-like pattern with one tail oriented
inferiorly
Control group
total HOAs
??????
No significant higher order aberration pattern
8
Each of the third- and fourth-order Zernike
vector terms on polar coordinates
Coma
Trefoil (tripled angle)
Axis PMCD group30KC group90 The mean axes of
trefoil in PMCD group were reverse to that of KC
group.
Axis PMCD,KC groups90 The mean axes of coma in
PMCD and KC groups were distributed around 90
degrees.
Tetrafoil (quadrupled angle)
Secondary astigmatism (doubled angle)
9
Simple averages of magnitude for total HOAs and
each Zernike vector term

1.4
PMCD


1.2
KC
control
1
0.8
0.6
RMS(µm)

n.s.
0.4

0.2
0
Secondary astigmatism
HOAs
trefoill
coma
tetrafoil
-0.2
Spherical aberration
The magnitude of coma in PMCD group was
significantly lower than that in KC group. The
magnitude of spherical aberration in PMCD group
was significantly higher than in KC group.
Kruskal-Wallis one-way analysis of variance
(ANOVA) on Ranks
10
The percentages of eyes with comet-like image
with two tails in simulated retinal images of
Landolt rings
The difference of the percentages among the three
groups was significant. p0.001, Chi-square test
11
Discussion

• We suggest that the inferior slow pattern of coma
  in PMCD and KC groups is caused by the
  inferosuperior asymmetric pattern in power
  distribution.
• The difference of the sign of spherical
  aberration might be also helpful to differentiate
  pellucid marginal corneal degeneration and
  keratoconus.
• We speculated that there might be the association
  between steep axis (infero-nasal and
  infero-temporal) and the direction of two tails
  in the retinal image in pellucid marginal corneal
  degeneration.
• The HOAs patterns of PMCD and KC groups are
  characterized by the following three patterns of
  trefoil, coma, and spherical aberration.

Fast triangular
Inferior slow
positive sphrical aberration



Pellucid marginal corneal degeneration
Slow triangular
Inferior slow
negative spherical aberration



Keratoconus
12
Conclusion

• Although pellucid marginal corneal degeneration
  and keratoconus are categorized as
  noninflammatory corneal thinning disorders, the
  patterns of higher-order aberrations in both
  groups have different characteristics possibly
  due to the difference in the position of the
  corneal apex relative to the entrance pupil.
• The eyes with pellucid marginal corneal
  degeneration and keratoconus may possess
  distinctively different quality of vision.