PhD-student Peter Skov Jensen and the others in the laboratory are currently studying the mechanisms underlying diameter regulation of retinal capillaries (photo: Helene Bagger).

It is a sign of a warm collaboration when an ice-box with porcine eyes changes hands. The international food company Danish Crown supplies fresh tissue from pig eyes to The Department of Ophthalmology at Aarhus University Hospital; this is a unique way of exploring essential mechanisms in the human retina.

In the early morning a transport from Aarhus University Hospital rushes back to the hospital with an ice-box with 20-30 porcine eyes. The porcine eyes are collected at the international food company Danish Crown and less than one hour ago, the eyes were organs of a slaughter pig. During the period between the captive bolt pistol and the ice-box, the porcine eyes become valuable research material, which is transported to the laboratory at The Department of Ophthalmology at Aarhus University Hospital; it is important that the time of removal until use in the laboratory is as short as possible.

The Department of Ophthalmology has collaborated with Danish Crown for more than ten years and the tissue from the porcine eyes has been used in a number of studies. At the moment, the overall focus of the research activities is to discover methods for better treatment for patients with diabetes mellitus. Toke Bek, Professor, Consultant and DMSci explains why:
- Diabetes mellitus is a key research area because more than four per cent of the population have one of the two diabetes types. Approximately half of the patients with diabetes mellitus will develop vision threatening complications; this is a large number of patients which explains the importance of research in this area. Moreover, a number of other eye diseases are characterized by similar changes. When we study what happens to the retina in diabetic patients, we also obtain knowledge of these diseases.

Basic knowledge of healthy retinas

The study of porcine retinas is important because it can provide knowledge of the mechanisms in healthy blood vessels:
- The differences between the human and porcine retina is rather small. The retinas from Danish Crown provide detailed knowledge of the mechanisms underlying the dilatation and the contraction of blood vessels in the normal retina, says Toke Bek. He explains how visual problems in diabetic patients are caused by the impaired functioning of blood vessels in their retina leading to oxygen deficiency. The lack of oxygen will cause damage to the retinal photo receptors.
The study of the regulation of blood flow in normal tissue from Danish Crown provide information of how blood flow is regulated in the diseased retina, Toke Bek explains and underlines that the collaboration between Aarhus University Hospital and Danish Crown is unique.
- It is possible to study unique features of blood flow in our retinas because we have access to tissue with a post-mortem life of less than one hour old. This is decisive for our research results. Other Danish universities do not have this possibility because the distance between the laboratories and slaughterhouses is too far.

Research to be translated to clinical practice

The experiments on porcine eyes have resulted in the discovery of several substances with effects on porcine retinal arterioles that may be translated into clinical trials at The Department of Ophthalmology.
PhD-student Peter Skov Jensen is one of the researchers who have been studying porcine eyes for a number of years. He dissects the retina from the porcine eye and mounts it in an experimental setup, followed by the injection of contrast into the blood vessels for the study of diameter changes in the vessels.
- Previously, we were only able to study diameter changes in the larger retinal vessels, but now we use pipettes with a diameter of 1/20 millimeters which enables the study of diameter changes in the smallest vessels, the capillaries, where nutrients are exchanged with the tissue; this gives new opportunities for understanding diameter regulation of retinal vessels, says Peter Skov Jensen while demonstrating an image of the vessels filled with green contrast dye. He explains how the blood vessels are studied under microscope while different substances are introduced into the blood stream.
- This is how we can identify mechanisms for normalising the diameter regulation of retinal vessels in clinical practice, says Peter Skov Jensen.
A few times each year the laboratory can study retinas from pigs with diabetes mellitus from the University Hospital's own animal facility. Additionally, on rare occasions, the researchers can study human tissue retinal which has been donated for research after removal secondary to other eye diseases.

From pig to microscope

Every Friday, The Department of Ophthalmology calls Danish Crown to order porcine eyes for the following week.

Every morning a slaughter at Danish Crown removes the eyes from newly slaughtered pigs. The eyes are immersed in a cooled fluid in order to hinder postmortal degradation.

At 7:15, shortly after the eyes have been removed, the slaughter hands over the tissue to a representative from The Department of Ophthalmology at the Danish Crown car park.

After the return to the laboratory the retinas are dissected from the porcine eyes and are used for the experiments.

Porcine eyes are inexpensive – the research group pays the same price per kilo as for regular pork meat.