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Vascular diseases of the eye are pathological conditions, the first signs of which often emerge as part of internist check-ups and for the diagnosis of which ultrasound technologies are very important resources.

In particular, theecocolor doppler of the ocular vessels is a non-invasive diagnostic approach that allows the examination of blood flow and the early detection of many vascular abnormalities.

Ocular vascularisation

There are two systems that ensure the vascularisation of the eyeball: the retinal and that ciliary. Both are dependent on the ophthalmic artery, which is a branch of the internal carotid artery. The retinal circulation depends on the central retinal artery, while the ciliary vessel system is supplied by the ophthalmic artery, via the posterior and anterior ciliary arteries.

The short posterior ciliary arteries, of which there are about 20, cross the sclera all around the optic nerve and, with some branches, in the thickness of the sclera itself, form an arterial circle around the intrabulbar part of the nerve, called Haller's ring. The short posterior ciliary arteries then branch into the vascular layer of the choroid and capillarise in the choriocapillary layer.

The long posterior, medial and lateral ciliary arteries, after passing through the sclera, near the ciliary margin of the iris resolve into branches that form, at that margin, the great arterial iris circle.

The ciliary venous vessel system drains blood from the anterior part of the ciliary body via the anterior ciliary veins, while blood from the posterior part of the sclera takes the route of the posterior ciliary veins. Blood from the choroid is routed to the four whorling veins, one for each quadrant of the eyeball. All these vessels are tributaries of the ophthalmic vein.

Echocolour doppler

The echocolour doppler is a non-invasive and painless examination that combines conventional ultrasound and the doppler effect.

L'doppler effect is a physical phenomenon that occurs when the transmitter or receiver of a wave moves relative to each other. More precisely, the Doppler effect consists of a change in the apparent frequency of the wave due to the relative movement between transmitter and receiver.

Doppler ultrasound allows the presence, direction and speed of blood flow in major arteries and veins to be assessed and images of arteries and blood vessels to be obtained in colour instead of greyscale.

Specifically, two colours, blue and red, are used to highlight arteries and veins:

• The red-coloured arteries carry oxygen-rich blood from the heart to tissues throughout the body;
• veins, blue in colour, conduct oxygen-poor blood from the tissues to the heart.

The information gathered by means of the Doppler ultrasound, combined with the results of the morphological analysis carried out by means of conventional ultrasound, makes it possible to establish the health of the circulatory system examined and to assess the presence of any pathologies.

Eco-colour Doppler in Ophthalmology

There has long been a need in ophthalmology to be able to quantify the bulbar blood supply using non-invasive methods in order to better identify the vascular role in various ocular diseases.

Numerous investigative techniques have been developed, but the results obtained have made it possible to assess the vessels topographically without being able to know their blood flow, as in the case of fluorangiography, or have made it possible to extrapolate the choroidal flow indirectly, with POBF (Pulsatile Ocular Blood Flow) and oculo oscillo dynamography. In other cases with LDV (Laser Doppler Velocimetry) it was only possible to assess the flow of the central retinal artery in the case of perfect transparency of the dioptric media

The colour Doppler is a method that derives its importance from the fact that the use of the colour module allows the simultaneous visualisation of blood flow, even of vessels of small calibre, superimposed on the two-dimensional image.

How ocular blood flow is measured

In ophthalmology, the echodoppler probe is used to detect the movement of red blood cells in the ocular blood vessels. If they move towards the probe, the frequency increases; if they move away, it decreases.

Through this examination it is possible to observe:

• ophthalmic arteries and retinal veins
• ciliary vessels and optic nerve circulation
• pathological vascular changes

Eco-colour doppler specific advantages

The advantage of colour Doppler echo, compared to diagnostics that rely on static images, is that it can provide a suitable parameter to measure how the blood nourishes and irrigates the ocular structures and, therefore, is very useful in detecting pathological conditions characterised by vascular abnormalities, such as glaucoma, venous or arterial retinal occlusions, and diabetic retinopathy.

Ultrasound study of the ocular vascularisation

The study by ultrasound of the ocular blood circulation is favoured by a combination of conditions: the location of the organ, which is directly exposed to the external environment, and also the presence within the cavities of the eyeball of two particular substances, aqueous humour and vitreous humour.

• L'aqueous humour is a transparent, colourless liquid that fills the anterior chamber of the eye, located between the cornea and the crystalline lens. It is composed mainly of water, salts and protein substances, and is subject to continuous turnover. Aqueous humour is produced by the ciliary body and plays a key role in determining intraocular pressure and providing nutrients to the ocular structures.
• L'vitreous humour is a colourless, transparent, gelatinous connective tissue that occupies the vitreous chamber between the posterior surface of the crystalline lens and the retina. This mass helps to maintain the shape of the eyeball, promotes the diffusion of nutrients and protects against microtrauma from outside. In addition, the vitreous humour, being transparent, has a fundamental dioptric function within the refractive mechanisms, as under normal conditions it allows the unobstructed transmission of light to the retina.

Examination with ecocolour doppler may present contraindications, which are on the whole rather rare and may arise if there is a suspicion of a rupture of the eyeball following trauma or in patients with periorbital oedema.

Echocolour doppler in the clinical context

Among the neovascular ocular pathologies for which it may be useful to use colour doppler ultrasound, we must first mention diabetic retinopathy, which is the most frequent ocular complication of diabetes mellitus, both type 1 and type 2, and is the third leading cause of blindness in the world and among the leading causes of acquired blindness in adults of working age. Next are retinal venous occlusions, both venous and arterial, which can lead to sudden vision loss and account for about 2% of all causes of visual impairment.

Doppler echocolour is of great use especially when ophthalmoscopy is not possible due to opacities of the dioptric media that hinder visualisation of the posterior segment of the eye.

Doppler ultrasound can enable an early diagnosis, even before visual deficits appear, by detecting a reduction in the levels of blood flow that supplies the ocular tissues.

• Castilla-Guerra L, Gómez Escobar A, Gómez Cerezo JF. Utility of Doppler ultrasound for the study of ocular vascular disease. Rev Clin Esp (Barc). 2021 Aug-Sep;221(7):418-425. doi: 10.1016/j.rceng.2020.11.007. Epub 2021 May 29. PMID: 34059490.
• Mohamed IE, Mohamed MA, Yousef M, Mahmoud MZ, Alonazi B. Use of ophthalmic B-scan ultrasonography in determining the causes of low vision in patients with diabetic retinopathy. Eur J Radiol Open. 2018 May 11;5:79-86. doi: 10.1016/j.ejro.2018.05.002. PMID: 30069496; PMCID: PMC6066607.