Postmortem ultrasound, OCT enhance study of posterior segment

Take-home:

Common imaging techniques-such as optical coherence tomography and ultrasound biomicroscopy-can be enlisted to help with research into retinal diseases when used to examine postmortem eyes, suggest findings from a collaborative research program.

Mitch McCartney, PhD, scientific director at the Lions Eye Institute for Transplant and Research (LEITR) in Tampa, discusses findings from a study showing high-frequency ultrasound can be used to screen eyes after death for disease-specific conditions. The study was presented at ARVO 2014.

Dr. Pavan

By Nancy Groves; Reviewed by Peter R. Pavan, MD

Tampa, FL-In what may be the first study of its kind, investigators used standard clinical imaging techniques on autopsy eyes to test a technique that could aid preclinical research. By correlating the findings of optical coherence tomography (OCT) with high-frequency (40 mHz) ultrasound biomicroscopy, they were able to image fine retinal structures in the eyes.

This technique could be applied to the study of eye diseases, such as age-related macular degeneration and diabetic retinopathy in the early stages, when they are often difficult to detect, said Peter R. Pavan, MD, ophthalmology professor and chairman, University of South Florida (USF) Morsani College of Medicine, Tampa.

“The goal is to be able to provide researchers with information about any pathology in the eye without having to disturb the eye in any way,” Dr. Pavan said. “We looked at techniques that we use in living patients to see how they could be applied to the donor eyes.”

Dr. Pavan and colleagues at USF and the Lions Eye Institute for Transplant and Research conducted the study.

To test the utility of postmortem ultrasound and imaging, fresh autopsy eyes transported to the laboratory were treated within 12 hours with 10% phenylephrine and 1% tropicamide, given in two rounds 3 minutes apart. The eyes were secured to a plastic foam head mount, and balanced salt solution was injected into the vitreous cavity. OCT raster line scanning images were obtained. After the eyes were re-oriented with the posterior pole facing forward, a UBM probe covered with a water-filled ultrasound transducer cover was placed over the back of the eye to obtain images of the macula and adjacent retina.

According to Dr. Pavan, UBM and OCT imaging of the macula identified much of the anatomy.

“The UBM showed recognizable landmarks in the posterior pole and correlated well with pathology seen on the OCT images, such as epiretinal membranes causing macular puckering,” he said, adding that postmortem retinal changes presented some limitations.

Variables for successful imaging

Optical coherence tomography of a postmortem eye shows an epiretinal membrane causing macular puckering. High-frequency ultrasound of the same macula also shows the epiretinal membrane and macular puckering. 

In earlier phases of this research, a team led by Timothy Saunders, MD, a fellow at USF, learned that time elapsed since death was the most important variable in postmortem imaging. The time from death to scan varied from 11 to 60 hours, and it was found that correlation of postmortem fundus imaging with histopathologic sections could not be performed in eyes older than 48 hours due to media opacity and tissue autolysis.

In that preliminary research, it was also determined that standard OCT imaging was the most consistently reliable technique for successful imaging, preferable to photography and autofluorescence. Dr. Saunders presented a poster on this work at the 2013 meeting of the Association for Research in Vision and Ophthalmology.

Following these discoveries, Dr. Pavan decided to test high-frequency ultrasound. This technique is highly sensitive but cannot be used in the retina of living eyes because it does not penetrate deeply enough. However, it could be used in the back of the autopsy eyes.

“We found that we could visualize some pathologies, especially those that involve thickening of the retina, and we could visualize some vitreoretinal interface problems, such as epiretinal membranes, that would affect the macular area,” Dr. Pavan said.

The technique is not 100% accurate, he added, but it is an attempt to provide some information to the researchers.

Peter R. Pavan, MD

P: 813/974-1530

E:  ppavan@health.usf.edu

Dr. Pavan did not report any commercial relationships.