1. Model of Hyperopic Shift After DSEK
Dana Wallace MD, Richard Hwang BS, and Natalie Afshari MD
Duke University Eye Center
The authors have no financial interests to disclose.

2. DSEK: A refractive neutral procedure?
Partial posterior lamellar transplant indicated in patients with endothelial dysfunction
Sutureless
No astigmatic effect
Now known to induce a hyperopic shift
Implications on “triple” procedures (CE/IOL/DSEK)
Covert DJ and Koenig SB. Ophthalmology 2007; 114:
Koenig SB and Covert DJ. Ophthalmology 2007;114:
Jun et al. Cornea 2009; 28:

3. Purpose
Changes in posterior curvature are responsible for the hyperopic shift that occurs in DSEK.
The magnitude of this shift remains unpredictable.
To derive a mathematical model that can be used preoperatively to predict the observed hyperopic shift after DSEK.
Gorovoy MS. Cornea 2006; 25:
Koenig SB, et al. Cornea 2007; 26:
Price FW Jr, Price MO. J Refract Surg 2005; 21:

4. Methods
Based on the assumptions of the thick lens equation and the Gullstrand model eye, we developed a mathematical model to predict the hyperopic shift that occurs after DSEK based on preoperative pachymetry and endothelial graft thickness.

5. Dcornea = Dant + Dpost - (d/n)(Dant)(Dpost)
Formula
Dcornea = Dant + Dpost - (d/n)(Dant)(Dpost)
Dant = refractive power of anterior surface
= (1/r1)(nant-nair)
r1 = radius of curvature of anterior surface
Dpost= refractive power of posterior surface
= (1/r2)(nant-naq)
r2 = radius of curvature of posterior surface
d = corneal thickness
n = refractive index

6. As applied to DSEK… Preoperative corneal power
Determined by preoperative pachymetry
Postoperative corneal power
Graft thickness of the graft was added to the corneal pachymetry
Graft thickness of the graft was subtracted from the posterior radius of curvature
The difference in these calculations reveals a hyperopic shift.

7. As applied to patients…
Preop Mrx
Preop
Pachymetry (μm)
Graft Thickness (μm)
Predicted Hyperopic Shift
Observed Hyperopic Shift 1
x092
643
103
+0.07
+1.25 2
x105
640
100
+0.06
+0.96 3
x165
142
+0.09
+0.375
Calculations were only performed in pseudophakic eyes.

8. Dcornea = (naq-nair)/radius of curvature
Interestingly, if we use the eye as only one refractive surface, the model is more accurate.
Dcornea = (naq-nair)/radius of curvature
Patient
Preop Mrx
Preop
Pachymetry (μm)
Graft Thickness (μm)
Predicted Hyperopic Shift
Observed Hyperopic Shift 1
x092
643
103
+0.58
+1.25 2
x105
640
100
+0.56
+0.96 3
x165
142
+0.80
+0.375

9. Other Factors to Consider
Endothelial graft is thicker peripherally than centrally
In the first few postoperative months, the graft edges thin faster than the vertex

10. A more accurate “r2”
Can current imaging modalities facilitate these measurements?
Pentacam
Anterior Segment OCT
Can we use a model of an ellipse to more accurately predict r2?

11. Conclusions
The hyperopic shift induced by DSEK is the result of changes in corneal thickness and posterior radius of curvature
Prediction of the hyperopic shift induced by DSEK is critical in the planning of refractive outcomes
Advances in anterior segment imaging will aid in more accurate prediction of refractive outcomes