gms | German Medical Science

23. Jahrestagung der Deutschen Retinologischen Gesellschaft

Deutsche Gesellschaft für Retinologie

24.09. - 25.09.2010, Freiburg

Oxygenation of the human retina: ways to image retinal metabolism

Meeting Abstract

  • Einar Stefánsson - National University Hospital, Dept. of Ophthalmology, Reykjavik, Iceland
  • B. Ólöf - University of Iceland, Landspitali University Hospital, Reykjavik, Iceland
  • B. S. Ólafsdóttir - University of Iceland, Landspitali University Hospital, Reykjavik, Iceland
  • H. Sveinn - University of Iceland, Landspitali University Hospital, Reykjavik, Iceland
  • M. S. Hardarson - University of Iceland, Landspitali University Hospital, Reykjavik, Iceland

Retinologische Gesellschaft. 23. Jahrestagung der Retinologischen Gesellschaft. Freiburg i. Br., 24.-25.09.2010. Düsseldorf: German Medical Science GMS Publishing House; 2010. Doc10rg50

DOI: 10.3205/10rg50, URN: urn:nbn:de:0183-10rg507

Veröffentlicht: 21. September 2010

© 2010 Stefánsson et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

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We have developed a non-invasive spectrophotometric oximeter, which is based on a fundus camera (Figure 1 [Fig. 1]). The instrument measures the color of a blood in retinal blood vessels (Figure 2 [Fig. 2]). Due to the different colour of oxy- and deoxy-hemoglobin, the spectrophotometric colour measurement allows calculation of oxygen saturation in arterioles and venules in the human fundus. The instrument uses the normal flash of the fundus camera. Beams splitter, digital cameras and a computer analyze the image for oxygen saturation analysis (Figure 1 [Fig. 1]).

Sensitivity and reproducibility: In human studies the instrument measures changes in oxygen saturation in human arterioles and venules with the participants breathing 12, 21 or 100% oxygen. Reproducibility in repeated measurements is remarkably tight with the arterioles at 99 ± 4% (mean ± SD) and the venules 52 ± 5% (Hardarson et al 2006). It is notable that the standard deviation is lower than in intraocular pressure measurements and as good or better than what is seen in a retinal thickness measurements with the OCT. Long-term oxygen saturation measurements over 18 months show a remarkable stability in oxygen saturation in the human fundus and this reflects the biological stability of oxygen tension in the body as well as the technical stability of the instrument (Traustason et al 2009).

Light and dark: Previous animal studies have demonstrated that illumination influences the metabolism and oxygen tension of the retina (Stefánsson 1983, 1988, Linsenmeier, 1986). This effect can be detected in the human with the non-invasive oximeter which shows statistically significant changes in retinal oxygen saturation both in arterioles and venules when illumination changes from light to dark (Hardarson et al 2009).

Retinal vein occlusions: Hypoxia in retinal veins is seen in central retinal vein occlusion (CRVO). There is a statistically significant difference in oxygen saturation of blood between CRVO venules and those in the fellow eye. At the same time the oxygen saturation is variable in CRVO cases, both between eyes and also within each CRVO eye.

Similarly in branch retinal vein occlusion we see many cases with retinal hypoxia. The oxygen saturation is variable and in some cases the oxygen saturation is in the normal range or even high. Laser treatment improves oxygen saturation in retinal vein occlusion in many cases.

Diabetes: Venous oxygen saturation in patients with diabetic retinopathy is significantly higher than that of healthy controls. We believe that this is consistent with capillary non-perfusion and shunting, where blood bypasses the capillary bed and therefore does not give oxygen to the tissue to the normal degree. Glycosylated hemoglobin and decreased concentration of 2,3-DPG in blood may also increase the affinity of hemoglobin for oxygen in these patients and decrease the removal of oxygen from the blood to tissue resulting in increased venous saturation. Our data is similar to what has been reported by Hammer et al (2009).

Glaucoma: The oxygen saturation in retinal venules increases with worsening visual field in patients with open angle glaucoma. The arterio-venous difference in oxygen saturation decreases as the visual field gets worse. This is consistent with tissue atrophy, where oxygen consumption of the tissue is decreased as ganglion cells are lost. The oxygen saturation measurements in glaucoma may be consistent with the severity of disease. A small but significant improvement in oxygen saturation is found following glaucoma filtration surgery (Hardarson et al 2009). The retinal oximeter has also been used to evaluate the effect of glaucoma drugs on oxygen saturation (Traustason et al 2009, Siesky et al 2008, 2009).

Conclusion: Non invasive oximetry allows measurement of metabolic changes in the retina in ischemic and metabolic diseases of the eye. These include diabetic retinopathy, vein occlusions and glaucoma and will in the future extend to other diseases that influence the energy metabolism of the eye, such as age-related macular degeneration, retinopathy of prematurity and retinitis pigmentosa.

Until now, ophthalmologists have diagnosed and studied the progression of these diseases based on structural changes and impairment of visual function. In diseases like diabetic retinopathy where metabolic abnormalities are at the core of the pathogenesis, we presume that metabolic abnormalities precede structural and functional changes. It is our hope that non-invasive oximetry will not only increase our understanding of the pathophysiology of ischemic eye diseases, but also allow more detailed measurement of severity. Detailed metabolic measurements should allow treatment to be applied in proportion to the severity of disease.

The author has a commercial interest in Oxymap ehf., which produces oximeters.