Scheimpflug Imaging Helps Predict Corneal Edema Resolution After DMEK

Findings of post hoc analyses published in JAMA Ophthalmology suggest that preoperative Scheimpflug imaging can help predict corneal edema resolution following Descemet membrane endothelial keratoplasty (DMEK).

DMEK is “a partial-thickness cornea transplant procedure that involves selective removal of the patient's Descemet membrane and endothelium, followed by transplantation of donor corneal endothelium and Descemet membrane without additional stromal tissue from the donor,” according to the University of Iowa Health Care.

DMEK has good clinical and patient-relevant outcomes, leading to operations earlier in the course of the disease so as to maximize visual rehabilitation, researchers explained. However, once morphologic changes have manifested in the cornea they can persist after successful replacement of the Descemet-endothelium complex and limit complete visual rehabilitation, they noted.

Due to high between-individual variations in healthy eyes, single measurements of central thickness and slitlamp examinations do not adequately assess corneal edema. To better understand the tomographic features and parameters of corneal shape and structure before and after restoring endothelial function in eyes with advanced Fuchs dystrophy, investigators developed a model based on preoperative features.

The model, derived from a statistical learning technique, was applied to derivation and validation cohorts, amassed from 2 separate prospective studies. All participants (n = 88) were scheduled for DMEK with or without phacoemulsification and posterior chamber intraocular lens implantation and had a minimum stable follow-up of at least 2 months after DMEK. Participants underwent high-quality Scheimpflug imaging before and after surgery.

For comparison purposes, 3 independent board-certified ophthalmologists evaluated tomographic features captured including irregularity of lines of equal corneal thickness and the displacement of the thinnest point of corneal thickness from its location. “To acknowledge that predictions of edema resolution in the clinic setting will be based on a single ophthalmologist’s rating, the validation cohort was rated by only 1 ophthalmologist,” authors explained.

Several Scheimpflug parameters were considered as potential predictors of edema resolution and used to develop a predictive model for corneal edema resolution in the derivation cohort. Demographic features were also considered and “the best-performing model was identified using linear least absolute shrinkage and selection operator regression.”

Of patients included in the analysis, the majority (61%) were female and median patient age was 68 years (interquartile range [IQR], 59-76).

Analyses conducted median of 13 months after DMEK (IQR, 9-16 months) revealed:

• Median corneal thickness was 77 μm lower (IQR, 51-94 μm) in the derivation cohort and 75 μm lower in the validation cohort (IQR, 54-96 μm) than before surgery.
• Per 10-μm edema resolution, eyes gained 0.66 Early Treatment Diabetic Retinopathy Study letters (95% CI, 0.09-1.23) in best-corrected visual acuity.
• 3 tomographic features were present in 68 of 100 eyes (68%) in the derivation cohort and in 18 of 32 eyes (56%) in the validation cohort before DMEK and in only 1 of 132 eyes (1%) after DMEK.
• In the validation cohort, the model showed high overall performance (R2 = 0.49; 95% CI, 0.37-0.62), discrimination (area under the curve 0.97; 95% CI, 0.86-1.00), and calibration (mean difference between predicted and observed edema 3.3 μm; 95% CI, −41.4 to 48.0 μm)

The 5 variables selected by the statistical learning model algorithm to predict edema resolution after DMEK included: nonparallel isopachs, focal posterior depression, anterior and posterior corneal backscatter, and central corneal thickness.

Overall, eyes without tomographic features of edema prior to DMEK experienced significantly less edema resolution after DMEK than eyes with tomographic features.

The study did rely on data from a single academic center and used an intermediate endpoint, marking limitations. In the future, investigations should explore whether implementing the model in clinical use results in improved decision making and better long-term outcomes, researchers wrote. It is also unknown if the model predicts disease progression in patients with clinically non-advanced Fuchs dystrophy.

“Applying this model in clinical practice and in research settings in conjunction with subjective, morphologic, and optical parameters of disease severity may allow for more precise and personalized counseling on outcomes and may help set realistic expectations for clinicians, patients, and their relatives after DMEK, which is an elective surgery,” authors concluded.

Reference

Zander D, Grewing V, Glatz A, et al. Predicting edema resolution after Descemet membrane endothelial keratoplasty for Fuchs dystrophy using Scheimpflug tomography. JAMA Ophthalmol. Published online February 18, 2021. doi:10.1001/jamaophthalmol.2020.6994