Evaluation of Deep Lamellar Endothelial Keratoplasty (DLEK) Surgery Using Scatterometry and Wavefront Analyses

Abstract

Purpose:: To determine if post-surgical corneal interface abnormalities following deep lamellar endothelial keratoplasty (DLEK) cause increased light scattering or wavefront aberrations which could help explain decreased best corrected visual acuity in DLEK patients compared with penetrating keratoplasty (PKP) patients.

Methods:: A prospective comparative case series of clinically clear corneas of 4 eyes that had undergone DLEK surgery and 4 eyes that had PKP were studied. Normal control data for light scattering was collected from 12 right eyes and 11 left eyes with normal corneas. Corneal light scattering was measured with a scatterometer designed at the Johns Hopkins Applied Physics Laboratory, and wavefront analysis was performed using standard methods with a VISX CustomVue Hartmann-Shack wavefront sensor. Corneal scattering measurements were normalized by taking the ratio of the subject’s corneal light scattering to a reference material. A scattering index was calculated as the ratio of the normalized scattering for a given patient’s cornea to the average scattering of normal corneas. Astigmatism and higher-order aberrations were analyzed using standard data output from wavefront analysis and Zernike polynomial decomposition.

Results:: The mean scattering index (SI) was significantly higher following DLEK (1.78 + 0.29, mean + S.D) than following PKP (1.03 + 0.27) (p = 0.043). The higher-order root mean square (RMS) wavefront error was significantly higher following PKP (0.71 + 0.11 µm, mean + S.D) than following DLEK (0.44 + 0.12 µm) (p = 0.029). Zernike polynomial decomposition of the wavefront aberrations revealed that regular corneal astigmatism was the most important aberration component for both PKP and DLEK, but the PKP patients had significantly more regular astigmatism (1.7 D + 0.45 D, mean + S.D.) than did the DLEK patients (0.84 D + 0.27 D) (p = 0.029).

Conclusions:: Our data quantitatively support subclinical corneal haze as an explanation for the limited visual acuity following DLEK as compared to PKP. Intra-operative or post-operative modifications to reduce stromal haze following DLEK may result in better visual acuity outcomes.

Keywords: cornea: endothelium • cornea: clinical science