Ultrasonography (US) is an important and reliable diagnostic tool for the complete and adequate evaluation of the vitreous chamber,
allowing radiologists to identify the most common pathologies in ophthalmologic emergency scenarios when clinical ophthalmoscopy is not diagnostic,
mainly due to opacification of the light-conducting transparent media.
The echo-structure of the eye and its superficial location allows its assesment through B-mode US combined with Color Doppler,
being able to rule out various conditions that would otherwise be difficult to differentiate in these scenarios,
such as retinal,
vitreous,
choroidal detachment, tumours,
and other pathological conditions that affect the posterior segment of the eye. In such cases the retinal detachment constitutes the most frequent entity.
The proper assesment of these through US enables a multidisciplinary approach to diagnosis and a more successful treatment and prognosis.
Ocular Anatomy
Understanding the anatomy and its sonographic correlation is essential in order to properly evaluate ocular structures through US and thus perform a differential diagnosis of the anterior and posterior segment pathologies,
especially of the latter.
The eyeball consists of three layers:
the sclera and cornea,
the protective outer layer that maintains its shape and pressure;
the retina,
the sensory inner layer; it extends from the optic nerve to the ora serrata (the most anterior part of the retina),
at an approximate distance of three quarters from the optic nerve to the iris;
the uveal tract, which constitutes the middlevascular layer and contains the choroid,
ciliary body,
and the iris.
It can also be divided into anterior and posterior segments by the lens. Fig.
1
The anterior segment contains aqueous humor and is further divided into anterior and posterior chambers,
separated by the iris.
The posterior part of the anterior segment is often small and difficult to visualize by imaging studies.
The posterior segment contains vitreous humor and it is also known as the vitreous chamber.
Normally,
the vitreous is strongly attached to the vitreous base,
macula,
margins of the optic disc,
and retinal vessels.
This segment is also formed by the retina,
choroid,
and sclera.
In the normal eye,
these three layers are attached,
but under certain pathologic conditions,
they may split away and form separated spaces.
The arterial supply comes mainly from the ophthalmic artery (OA),
branch of the internal carotid artery.
The main branches of the OA are: the central retinal artery (CRA),
which provides two thirds of the inner retina; and the posterior ciliary arteries,
which supply the choroid,
the optic disc and the outer third of the retina.
The superior ophthalmic vein provides venous drainage.
The optic nerve circulates alongside the OA and is sonographically seen as a hypoechoic band starting at the scleral zone,
sorrounded by the periorbital adipose tissue. Fig.
2