First step: complete examination and measurements
Radiologists must know how the healthy eye is visualized in an ocular ultrasound performance due to checking if there is any abnormality:
Anterior segment: most anterior echogenic structure are the soft tissues of the eyelid,
immediately posterior there is a curved,
thin,
echogenic band corresponding to the cornea.
The next echogenic and thin band is the anterior capsule of the lens,
and on each side of it,
the echogenic lines are the iris and ciliary bodies. The anechoic space between the cornea and the anterior capsule of the lens is the anterior chamber (Fig. 6).
The next echogenic band in depth is the posterior capsule of the lens,
between both capsules there is the lens,
which is anechoic.
Posterior segment: posterior to the lens,
an anechoic and echo-free wide space represents the vitreous chamber (Fig. 7).
The echogenic lateral and posterior limits of the vitreous chamber are the three layers which integrate the posterior ocular wall: retina,
choroid and sclera,
not distinguishable between them by the ultrasound mode B.
At the posterior aspect of the vitreous chamber,
the optic nerve may be seen as a hypoechoic band. Anterior to the optic nerve,
in the posterior ocular wall might be recognized the papilla as a thin echogenic swelling.
When colour Doppler is set it reveals the central retinal artery and vein as vascular structures alongside the optic nerve.
These neurovascular structures are surrounded by the markedly echogenic retroorbital fat.
Obtain measurements: it is advisable to measure the anteroposterior diameter of the ocular globe (normal is approximately 22-25 mm) (Fig. 8 ,
Fig. 9) and the optic nerve diameter (normal is under 5 mm) (Fig. 10).
Second step: gain modification
To modify the gain will reveal some information about the composition of the lesion which could be useful for guiding the diagnosis because the internal structure and echogenicity are correlated with the histologic composition of a lesion. In general terms,
a high cellularity lesion might show up the same echogenicity at any gain value whereas a lesion mainly composed by water or any other low cellularity tissue would not be expected to be seen in low gain values and it will progressively appear according to gain value rising.
On the one hand,
intraocular foreign bodies,
retinal detachments,
choroid detachments and intraocular tumours as nevi,
hemangioma or calcified retinoblastoma can be identified by ultrasonography in any range of the gain value,
lingering at low gain.
On the other hand,
vitreous haemorrhage,
subhyaloid haemorrhage,
vitreous membranes,
hyaloid and vitreous detachments and intraocular tumours as melanoma might not show up when ultrasonography is performed at low gain and will get echogenicity if gain value arises.
(Fig. 11 ,
Fig. 12 ,
Fig. 13 ,
Fig. 14 ,
Fig. 15)
Third step: vascularity
Colour Doppler ultrasound mode allows an assessment of the vascularity of any lesion or finding in ocular ultrasound performances.
To know which lesions are vascularized and to tie up the vascular anatomy of the eye with the ultrasonography findings may be indicative for the final diagnosis.
Retina and choroid both receive vascular support and will show it when Doppler mode is performed (Fig. 16).
The importance of this fact is facing doubts among three types of detachments: posterior vitreous detachment since vitreous has no vascular input,
will not show any flow under Doppler mode examination.
Besides,
in vitreous detachments,
might be seen the healthy retinal vascular structures on the posterior segment wall (Fig. 17).
If the aforementioned retinal vessels were not seen in the posterior wall,
associated retinal detachment should be reviewed.
Therefore,
if a retinal detachment occurs,
these membranes will present vascular flow under Doppler mode examination and the posterior wall might have altered it vascularity (Fig. 18).
Facing findings of posterior segment wall masses and intraocular tumours it is main to classify most common of them in vascular or avascular using colour Doppler mode.
This might help to dismiss some possibilities and guide to the final accurate diagnosis: most of the metastases,
hemangiomas and melanomas are vascular and show up vascular flow when Doppler ultrasound mode is performed (Fig. 19 Fig. 20, Fig. 21).
However,
nevi and drusen are avascular so do not show up vascular flow on Doppler mode (Fig. 22).
Colour Doppler mode assessment should always be performed because non expected vascular structures could come upon.
This occurs in persistent hyperplastic primary vitreous or persistent fetal vasculature,
pathology in which fetal vasculature persists inside the hyaloid canal and the aforementioned vasculature may be revealed in the middle of the vitreous chamber when colour Doppler mode examination (Fig. 23).
By last,
using colour Doppler should be helpful in a distinction between a non-tumoral process such as a large haemorrhagic choroidal detachment and a tumour by identifying internal or peripheric blood flow.
Fourth and fifth steps: convection and mobility
These two steps are compressed in the dynamic mode B scan.
To properly perform the convection assessment it is required to hold the probe stationary while the studied eye keeps still.
It becomes profitable when vitreous membranes or hemorrhages are found.
The main aim of this step is to ascertain about potential findings that could be masked by vitreous haemorrhage.
Moreover,
specific attention to this minor movement can greatly aid in the differentiation of posterior vitreous and retinal detachments and can help rule out intraocular solid mass lesions.
We suggest it should be evaluated before mobility to avoid misunderstandings with residuary moving structures after the eye movement.
The dynamic mode B scan to check mobility may be crucial in the assessment of membrane detachments because of each detachment exhibit distinctive and highly characteristic patterns of mobility.
Posterior vitreous detachment is seen as a freely undulating membrane that should swirl away from the region of the optic disc.
In contrast,
retinal detachment exhibits slight mobility because of being anchored to the optic nerve papilla and to the ora serrata.
Furthermore,
choroidal detachment will be motionless on dynamic B-scan.
(Fig. 24 ,
Fig. 25 ,
Fig. 26 ,
Fig. 27)