Predicting Visual Acuity after Descemet’s Stripping Endothelial Keratoplasty using Corneal Topography, Pachymetry and Po

1. Predicting Visual Acuity after Descemet’s 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. • Descemet’s stripping endothelial keratoplasty (DSEK) involves transplanting a donor endothelial graft after the patient’s descemet’s 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 1Koenig 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. 2007;26:670-4. 2Chen ES, Terry MA, Shamie N, et al. Descemet-stripping automated endothelial keratoplasty: six-month results in a prospective study of 100 eyes. Cornea. 2008;27:514-20.

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 1Dupps WJ Jr, Qian Y, Meisler DM. Multivariate model of refractive shift in Descemet-stripping automated endothelial keratoplasty. J Cataract Refract Surg. 2008;34:578-84. 2Yoo 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. 2008;126:1052-5. 3Koenig 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. 2007;26:670-4. 4Chen ES, Terry MA, Shamie N, et al. Descemet-stripping automated endothelial keratoplasty: six-month results in a prospective study of 100 eyes. Cornea. 2008;27:514-20. 5 Gorovoy MS. Descemet-stripping automated endothelial keratoplasty. Cornea. 2006;25:886-9. 6Chen ES, Shamie N, Terry MA. Descemet-stripping endothelial keratoplasty: improvement in vision following replacement of a healthy endothelial graft. J Cataract Refract Surg. 2008;34:1044-6.

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 theGalilei 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 |44.4 – ([43.2+43.8]/2)| |45.3 – ([43.5+43.6]/2)| |45.4 – ([43.0+43.1]/2)| 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 135o meridian 45o 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 (p<0.05) • 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.