Abnormalities of the posterior segment are ideal cases for B scan ultrasound. In the examination, the most commonly seen B scans can be divided into four groups (remember that more than one abnormality may be present):

a. abnormalities of the vitreous
b. abnormalities of the retina/choroid
c. tumours
d. optic disc drusen
e. miscellaneous conditions

a. Abnormalities of the vitreous:

•     The scans usually show white opacities within the vitreous cavity. The main differential

    diagnosis being : vitreous haemorrhage, asteroid hyalosis and synchysis scintillans.
 
•     The three may look similar on the ultrasound but in the case of vitreous haemorrhage they

    may be associated posterior vitreous detachment or retinal tear.

Figure 1a	Figure 2a	Figure 3a
Of the three B scans above can you differentiate asteroid hyalosis from vitreous haemorrhage? answer Figure 1a is asteroid hyalosis. Figure 2a and Figure 3a are vitreous haemorrhages because of the associated posterior vitreous detachment (note the interface anterior to the globe)

b. Abnormalities of the retina/choroid

• The scans usually show elevated lesions projecting into the vitreous cavity. 

• The main differential diagnosis is between retinal detachment and choroidal detachment.

• In the case of choroidal detachment, the elevation is dome-shaped and has a smooth outline. On the other hand, retinal detachment has an irregular surface.

• Additional abnormalities to look for are:
• fluid level (especially in choroidal detachment)
• vitreous haemorrhage

Figure 2a	Figure 2b	Figure 2c
Figure 2d	Figure 2e	Figure 2f
Can you identify the above scans and any associated features? answer Figure 2a, 2d and 2c are choroidal detachments (note the smooth dome-shaped surface). Figure 2d also demonstrated suprachoroidal effusion. Figure 2c shows a vortex vein attached to the choroidal detachment. Figure 2b, 2e and 2f are retinal detachment. Figure 2b is a tractional retinal detachment note the presence of fibrosis radiating from the detachment. Figure 2f shows total retinal detachment with attachment at the optic disc.

c. Tumours

• The most likely tumour is choroidal melanoma. Occasionally you may be given retinoblastoma, the age is a clue.
• In choroidal melanoma, look for excavation, associated choroidal or retinal detachment and scleral invasion.

d Figure 3a Figure 3b d..

The above scans are taken from patients with choroidal melanoma. What do the scans show? answer Figure 3a shows a mushroom-shaped melanoma with vitreous haemorrhage. Figure 3b shows a raised dome-shaped lesion with choroidal excavation (note the choroid behind the lesion appears punch out). The A-scan of a choroidal melanoma typically shows low internal reflectivity.

d. Optic disc drusen

• If the ultrasound shows normal vitreous and absence of retinal or choroidal abnormalities, look for the presence of bright white area in the optic disc ie. drusen (See picture below).
• Although ultrasound has been used to detect papilloedema and glaucomatous optic disc, you are unlikely to be given such cases in OSE.

Figure 4a

e. Miscellaneous conditions

• a-b cover the most common cases seen in the OSE. The following scans have yet to appear in the OSE, could you diagnose the abnormalities ?

( In the OSE you can not ask for the clinical findings but if  any of the scans were to appear in the viva section of the final MRCOphth, always tell the examiners that you like to see the colour picture or perform a clinical examination. Like all imagings, the ultrasounds only supplement the clinical findings)

	This patient has significant difference in axial lengths between the two eyes. What does this scan show? answer Staphyloma.
	This patient requires high plus lens for good vision. What does the scan show? answer A dislocated lens
	This patient has a painful eye. What does the scan show? answer Posterior scleritis. Note the increase thickness of the wall and the typical 'T-sign' - caused by the spread of inflammation along the Tenon's space into the optic nerve sheath.