Ophthalmology

Optimal function highly depends on an adequate blood supply

Organs can only function well if they are supplied with an adequate amount of blood. This applies to the eyes in particular. The blood supply to the eye must therefore be adapted to its current needs at all times. This is, among other things, to compensate for fluctuations in perfusion pressure, to adapt to changing neuronal activities or to keep the temperature around the fundus constant despite fluctuations in the outside temperature. For this reason, the blood flow at rest and the ability of the vessels to regulate the blood flow are of central importance.

Consequences of vascular disorders:

  • The relatively rare acute reductions in blood supply lead to infarction, e.g. of the retina or the papilla.
  • Chronic underperfusion, which occurs much more frequently, favours disease progression and in extreme cases the formation of neovascularisations.
  • Fluctuating oxygen supply due to disturbed vascular regulation increases local oxidative stress, a central factor in the pathogenesis of many diseases.
  • Hypoxia and oxidative stress damage the blood-brain barrier and therefore promote the formation of oedema and bleeding.

Significance of Imedos technology

  • Disturbed blood circulation often causes many eye diseases or becomes an important co-factor for the occurrence or progression of an eye disease. Imedos technology makes it possible to diagnose these vascular components and subsequently check the influence of a given therapy.
  • Interdisciplinary approach: For a number of systemic diseases such as diabetes, hypertension, lipometabolic disorders or rheumatism, the ophthalmologist can examine the blood vessels in the eye in order to provide colleagues from other disciplines with decisive information about the general state of health of the vessels (microvascular health) and the response to therapy or prophylaxis at a very early stage.

Imedos technology focuses on the retinal vessels as

  • A functioning retina is essential,
  • The vessels of the retina are optically accessible,
  • Retinal activity can be increased in a controlled manner by using flicker light and thus allows the measurement of the ability and capacity of the regulation of the blood vessels,
  • The retinal blood vessels are not autonomously innervated and so the function of the vascular endothelial cells can be measured specifically.

Why are vascular endothelial cells of particular interest?

The endothelial cells are significantly involved in the regulation of retinal blood flow. There are several trillion of these endothelial cells present in our bodies. Interestingly, the state of health of these cells in the retina is a very good indicator of the state of health of these cells in the whole body. In cardiovascular and cerebrovascular diseases as well as in primary vascular dysregulations, the vascular endothelial cells are always affected first.

Imedos technologies & solutions

Static vessel analysis using a static vessel analyzer (SVA)

The SVA measures the diameter of the retinal arteries and veins and provides the calculated vascular parameters CRAE, CRVE and AVR. Today, narrow arteries and wide veins are the best way to predict future cerebrovascular disease.

The calculated parameters show the cumulative effect of all influencing parameters on vascular health, such as smoking, stress, lack of exercise, etc. This allows the vascular risk to be detected at an early, asymptomatic stage. This is the basis for the earliest possible prophylaxis. Static vessel analysis is non-invasive and contact-free. This means that the examination itself is not stressful for the patient and can be performed without pupil dilation.

Dynamic vessel analysis using a dynamic vessel analyzer (DVA)

The DVA shows the state of health of microcirculation and the vascular endothelial cells in particular. This shows whether a disease such as hypertension, diabetes, dyslipidemia etc. has already damaged the vessels or not. Additionally, the DVA provides information on the quality and capacity of the autoregulation and in this way shows whether and how well the eye can still compensate for fluctuations in intraocular pressure and blood pressure.

In the same way as static vessel analysis, this examination is non-invasive and contact-free and therefore does not cause the patient any pain or discomfort at all.

IOPstim

If a spontaneous venous pulse is visible, the retinal venous pressure (RVP) is normal. If there is no spontaneous pulsation, the intraocular pressure (IOP) must be increased until the veins pulsate. This is how the RVP is derived. The IOPstim allows the IOP to be increased without unpleasant side effects, which then facilitates and improves the RVP measurement.

If the pressure in the retinal veins increases, the perfusion pressure decreases, which contributes to hypoxia. At the same time, transmural pressure, an important factor in the formation of oedema and bleeding, increases. Since blood from the optic disc flows through the retinal veins, increased RVP is also significantly involved in diseases of the papilla.

Areas of application for Imedos technology (symptoms in ophthalmology)

Retinal arterial occlusion

Using the SVA to examine the unaffected eye provides information about the general state of health of the blood vessels and therefore about the risk of further vascular occlusion – whether that be in the eye or in other organs.

Retinale venous occlusion

If a venous occlusion is caused by an arterial disease, is shown by static vessel analysis on the unaffected eye. It is often the case that the RVP is also increased in the other eye. Medically lowering the RVP improves the prognosis of the affected eye and reduces the risk of venous occlusion in the second eye.

Glaucoma

If damage progresses in a glaucoma patient despite normal or normalized IOP, static and dynamic vessel analysis will show whether and in what form a vascular disease is present. If both eyes are disturbed, it is usually a problem caused by arteriosclerosis and its risk factors. If, on the other hand, the static vessel parameters are inconspicuous and an examination with the DVA shows a disturbed endothelial function, then this is a treatable primary vascular dysregulation.

If the RVP is increased, the blood flow to the optic disc is reduced. In this case, not only the IOP but also the RVP must be reduced.

Diabetic retinopathy

Static vessel analysis reveals the risk for the development of diabetic retinopathy at an early stage. In case of non-proliferative retinopathy, it shows the risk of vascular complications, including the development of proliferative retinopathy.

The examination with the DVA shows whether and how well the retinal blood flow can still be regulated. An increased RVP increases hypoxia and therefore increases the formation of cotton wool spots and neovascularisations. Furthermore, a high RVP also increases transmural pressure, contributing to the formation of oedema, hard exudates and bleeding.

Central serous chorioretinopathy

In central serous chorioretinopathy (CSCR), ICG angiography can be used to detect local dysregulation of the choroidal vessels. However, frequently underlying dysregulation is also indicated by decreased responses in dynamic vessel analysis and an increase in RVP.

Retinitis pigmentosa (RP)

Here, the blood circulation of the eye is partly primary and partly secondary reduced. If the examination with the DVA shows an endothelial dysfunction, this indicates that one component must be primary. In most cases, the RVP is also increased. Both can be improved with therapy.

Perioperative visual loss

An acute loss of vision in connection with operations, e.g. after operations on the spine, is rare but serious. A disturbed regulative capacity, visible in the dynamic vessel analysis, explains a missing or insufficient adaptation, e.g. to special patient positioning. If the RVP is increased, this is a further explanation of the event and makes prophylaxis possible.

Altitude sickness

If the oxygen partial pressure decreases, some people develop altitude sickness. Those affected usually have pre-existing conditions (shown as reduced responses in the dynamic vessel analysis) and show a higher increase of their RVP compared to those not affected by altitude sickness.

Flammer syndrome (FS)

The FS describes a general predisposition to react differently to stimuli with the blood vessels. The consequences are particularly common on the eye. Often the RVP is increased, the reaction shown in the DVA is reduced, but the vessel diameters examined with the SVA are normal. If this constellation is present, the risk of developing an FS-associated disease is higher.

Recent studies and publications in this field using Imedos’ technology

  • Saruhan Y, Bollinger O, Gugleta K. Analysis of Retinal Vessel Pulsation with Electrographic Gating – Pulsation Amplitude and the Influence of Hyperoxia. Analyse der Gefäßpulsationen in der Netzhaut mittels EKG-Verankerung – Pulsationsamplitude und Effekte der Hyperoxie. Klin Monbl Augenheilkd. 2020;237(4):469–473. Abstract
  • Donicova, E., Ramm, L., Augsten, R. et al. The flicker response of venous oxygen saturation is significantly reduced in the early and late stages of age-related macular degeneration. Graefes Arch Clin Exp Ophthalmol 258, 31–37 (2020). Abstract
  • Hasan SM, Hammer M, Meller D. Correlation of the retinal parapapillary perfusion and the retinal vessel oxygen saturation in glaucoma patients. Invest Ophthalmol Vis Sci. 2019;60:1309–1315. Abstract