Icefish: one of the extremes in the animal kingdom aids ophthalmic research
25 March 2019 I Read more news
By Henrik Lauridsen, PhD, Department of Clinical Medicine, Aarhus University
Sight is one of our most important senses, and the retina of the eye is one of the most fascinating structures in humans and the animal kingdom generally.
The retina is one of the most energydemanding structures in the body, and a healthy retina requires a reliable and stable blood supply to meet its need for oxygen and nutrients.
In patients afflicted by wet age-related macular degeneration, weakening of the retina's outer layer causes the formation of new vessels – neovascularisation – behind the retina, and ingrowth or abnormal linkage of newly formed vessels in the outer layers of the retina. This results in an increase in fluid in the retina and impaired vision.
In patients with diabetic retinopathy, neovascularisation on the interior of the retina poses a risk of vision impairment, as the newly formed vessels tend to be fragile, and can easily rupture, which results in bleeding on the inside of the retina.
Animals reveal all
Given these risks in humans, it is astonishing that animals with extensive vascular ingrowth in the retina, do not, apparently, have the same problems.
Retinal structure is largely preserved in all animal species with a backbone (vertebrates), and by studying animals that deal with this problem perfectly, we can discover how neovascularisation of the retina can occur without any harmful effect. This situation is known
as the August Krogh principle, which states that for every medical problem ”...there will be some animal of choice or a few such animals on which it can be most conveniently studied”.
It turns out that the vertebrates with the largest ingrowth of retinal vessels are a family of Antarctic fishes named crocodile icefish or white-blooded fish. The name stems from the fact that these fish inhabit the icy waters of Antarctica's Southern Ocean, and are the only vertebrates that have none of the red oxygen-transporting pigment – haemoglobin – in their blood, which is why they are pale and have milky blood.