Transcript Hyperopic Shift After DSEK

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.
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; 114:1272-1277.
Koenig SB and Covert DJ. Ophthalmology 2007;114:221-226.
Jun et al. Cornea 2009; 28: 19-23.
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; 25:886-889.
Koenig SB, et al. Cornea 2007; 26: 670-674.
Price FW Jr, Price MO. J Refract Surg 2005; 21:339-345.
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.
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
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.
As applied to patients…
Patient Preop Mrx
Preop
Pachymetry
(μm)
Graft
Predicted Observed
Thickness Hyperopic Hyperopic
(μm)
Shift
Shift
1
0.00-0.50x092
643
103
+0.07
+1.25
2
+0.25-1.25x105
640
100
+0.06
+0.96
3
0.00-0.25x165
640
142
+0.09
+0.375
Calculations were only performed in pseudophakic eyes.
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
Predicted Observed
Thickness Hyperopic Hyperopic
(μm)
Shift
Shift
1
0.00-0.50x092
643
103
+0.58
+1.25
2
+0.25-1.25x105
640
100
+0.56
+0.96
3
0.00-0.25x165
640
142
+0.80
+0.375
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
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?
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
