Predicting Visual Acuity after Descemet

1
Predicting Visual Acuity after Descemets
Stripping Endothelial Keratoplasty using Corneal
Topography, Pachymetry and Posterior Curvature
Asymmetry Indices

• Gowri Pachigolla, M.D., M. Bowes Hamill, M.D.,
  Douglas D. Koch, M.D., Mitchell P. Weikert, M.D.
• Cullen Eye Institute, Baylor College of Medicine,
  Houston, TX
• Authors have no financial interest

2
Introduction

• Posterior lamellar keratoplasty was introduced by
  Melles approximately 10 years ago and since then
  the surgical technique has evolved considerably.
• Descemets stripping endothelial keratoplasty
  (DSEK) involves transplanting a donor endothelial
  graft after the patients descemets membrane has
  been manually removed.
• Compared to penetrating keratoplasty, DSEK offers
  faster visual recovery, lower post-operative
  astigmatism and more predictable corneal powers.
  It also maintains the structural integrity of the
  globe with minimal alteration of the anterior
  cornea.
• Several studies have shown no significant change
  in refractive astigmatism, placido-based
  topographic astigmatism or keratometry, while
  there have been reports of improvement in surface
  regularity and surface asymmetry indices after
  DSEK. 1,2

References 1 Koenig SB, Covert DJ, Dupps WJ Jr,
et al. Visual acuity, refractive error, and
endothelial cell density six months after
Descemet stripping and automated endothelial
keratoplasty (DSAEK). Cornea. 200726670-4. 2
Chen ES, Terry MA, Shamie N, et al.
Descemet-stripping automated endothelial
keratoplasty six-month results in a prospective
study of 100 eyes. Cornea. 200827514-20.
3
Introduction

• The hyperopic refractive shift that commonly
  occurs after DSEK has been correlated to
  nonuniform graft thickness resulting in a
  negative lens effect from grafts that are thinner
  centrally and thicker peripherally. 1, 2
• The largest published series of DSEK report over
  95 of patients attaining a BCVA of at least
  20/40 however few patients attain 20/20 with no
  clinicially identifiable cause of suboptimal VA.
  2-6
• Some surgeons feel that interface opacities and
  irregularities may contribute to sub-20/20 BCVA,
  but this has never been proven.

References 1 Dupps WJ Jr, Qian Y, Meisler DM.
Multivariate model of refractive shift in
Descemet-stripping automated endothelial
keratoplasty. J Cataract Refract Surg.
200834578-84. 2 Yoo SH, Kymionis GD, Deobhakta
AA, et al. One-year results and anterior segment
optical coherence tomography findings of descemet
stripping automated endothelial keratoplasty
combined with phacoemulsification. Arch
Ophthalmol. 20081261052-5. 3 Koenig SB, Covert
DJ, Dupps WJ Jr, et al. Visual acuity, refractive
error, and endothelial cell density six months
after Descemet stripping and automated
endothelial keratoplasty (DSAEK). Cornea.
200726670-4. 4 Chen ES, Terry MA, Shamie N, et
al. Descemet-stripping automated endothelial
keratoplasty six-month results in a prospective
study of 100 eyes. Cornea. 200827514-20.
5 Gorovoy MS. Descemet-stripping automated
endothelial keratoplasty. Cornea.
200625886-9. 6 Chen ES, Shamie N, Terry MA.
Descemet-stripping endothelial keratoplasty
improvement in vision following replacement of a
healthy endothelial graft. J Cataract Refract
Surg. 2008341044-6.
4
Purpose
Hypothesis
Donor graft decentration, either during donor
tissue preparation or final positioning within
the eye, and nonuniform graft thickness result in
corneal irregularities which limit BCVA.

• To evaluate the influence of asymmetries in
  corneal topography, pachymetry and posterior
  curvature on visual acuity after DSEK.

5
Methods

• Charts of patients having undergone successful
  DSEK with at least three months of follow-up were
  retrospectively reviewed. Corneal topography,
  pachymetry and posterior curvature were measured
  using the Galilei Dual Scheimpflug Analyzer.
• Inclusion criteria
• Absence of ocular comorbidities limiting visual
  acuity
• Galilei Analysis performed and available for
  review
• Pseudophakia
• Novel corneal asymmetry indices were developed
  and applied to data aquired from the Galilei
  Analyzer. These indices included Total Corneal
  Power Asymmetry Index (TCPAI), Corneal
  Pachymetric Asymmetry Index (CPAI), Posterior
  Elevation Asymmetry Index (PEAI) and Posterior
  Axial Curvature Asymmetry Index (PACAI).
• Linear regression analysis was used to evaluate
  the relationship between the individual indices
  and visual acuity.

6
Asymmetry Indices
The Asymmetry Index was applied to 4 different
parameters that were measured by the Galilei
Analyzer Total Corneal Power (shown
here) Corneal Pachymetry Posterior Elevation
(Float- BFS) Posterior Axial Curvature
The difference in corresponding values 180o away
on three concentric rings (2, 4, 6 mm) was
calculated
90o meridian
45o meridian
135o meridian
The average of these three values gives the
Asymmetry Index at the 180o meridian
The calculation was repeated for the 45o, 90o and
135o meridians. The values for the 4 meridians
were averaged to give a composite Asymmetry Index.
7
Results

• 54 eyes underwent successful DSEK by a single
  surgeon between May 2007 and June 2008 and
  satisfied the inclusion criteria
• 38 of these eyes had inadequate quality of
  Galilei Analysis
• 16 eyes (13 patients) were included in the study
• 9 eyes (8 patients) had adequate data for
  evaluation of posterior elevation and curvature
• Mean Asymmetry Indices (range)
• TCPAI 1.75 (0.81 5.55)
• CPAI 50.1 (13.4 128.9)
• PEAI 23.9 (16.8 37.1)
• PACAI 0.73 (0.53 0.98)
• Included 9 patients with posterior surface data

8
Results

• Average Age 74.6 years
• Indications for DSEK
• Fuchs Dystrophy- 13
• Pseudophakic Bullous Keratopathy- 3
• Visual Acuity
• Mean Preop BCVA- 20/78
• Mean Postop BCVA- 20/32 (plt0.05)
• Procedures
• DSEK- 14
• DSEK/Phaco/IOL- 2
• Donor Tissue
• Pre-Cut- 10
• Hand-Cut- 6
• Complications
• Dislocated graft- 4 (all succesfully rebubbled or
  spontaneously reattached)

9
Asymmetry Indices
There was no correlation between postoperative
visual acuity and three of the asymmetry indices
TCPAI, CPAI, and PEAI. While only 9 eyes had
adequate data of the posterior corneal surface,
there was a modest correlation approaching
significance between PACAI and postoperative
visual acuity.
10
Case 1 77 y/o female, 9 months after successful
DSEK (handcut donor). Corneal pachymetry is very
symmetric (CPAI 24.5), but posterior axial
curvature is highly asymmetric (PACAI 0.98).
Postop BCVA was 20/40.
11
Case 2 72 y/o female, 5 months after successful
DSEK (precut donor). Total Corneal Power (TCPAI
0.81) and Posterior Axial Curvature (PACAI 0.53)
are highly symmetric. Postop BCVA was 20/25.
12
Conclusions

• Asymmetry and irregularities in corneal
  topography, pachymetry and posterior curvature
  may limit best-corrected visual acuity after
  DSEK however, asymmetry indices evaluating
  pachymetry, total corneal power and posterior
  elevation, as measured by the Galilei Dual
  Scheimpflug Analyzer in this small data set, do
  not have significant predictive value in terms of
  visual acuity outcomes.
• A modest correlation exists between visual acuity
  and the Posterior Axial Curvature Asymmetry
  Index, but this relationship only approached
  significance.
• This study is limited by the small sample size as
  more than half of the 54 eyes reviewed had poor
  quality scans. Reasons for poor quality included
  inadequate Scheimpflug image, unsatisfactory
  placido quality and motion distance artifact.
  There is reason to believe that quality may
  improve with operator experience.
• The Galilei Analyzer, while certainly a useful
  diagnostic tool in certain clinical settings, may
  be limited in its ability to consistently and
  accurately evaluate the cornea after DSEK.