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Model of 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?.

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Model of Hyperopic Shift After DSEK

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  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; 114:1272-1277. Koenig SB and Covert DJ. Ophthalmology 2007;114:221-226. Jun et al. Cornea 2009; 28: 19-23.

  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; 25:886-889. Koenig SB, et al. Cornea 2007; 26: 670-674. Price FW Jr, Price MO. J Refract Surg 2005; 21:339-345.

  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. 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… Calculations were only performed in pseudophakic eyes.

  8. Interestingly, if we use the eye as only one refractive surface, the model is more accurate. Dcornea = (naq-nair)/radius of curvature

  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

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