B-Scan Ultrasonography in Ocular Abnormalities

B-scan Ultrasonography, often called just B-scan or Brightness scan, offers two-dimensional cross-sectional view of the eye as well as the orbit. B-scan is used on the outside of the closed eyelid to view the eye.

This type of diagnostic tool is most helpful when there is difficulty examining the eye normally. There might be lid problems that make a routine examination difficult like edema or tarsorrhaphy or severe cataracts and keratoprosthesis. B-scan can help accurately view other eye structures like the lens, choroid, sclera, vitreous and retina. B-scan is helpful in diagnosing retinal detachment. B-scan is often a tool combined with an A-scan to help determine various eye abnormalities.

The eyeball’s fluid content and its superficial position make it ideally suited for examination with ultrasonography (USG). USG is the only practical method for obtaining images of the posterior segment of the eye when the light-conducting media are opaque. It is the most useful investigation prior to vitrectomy.

Advantages

• B-scan is a reliable, safe, cheap, and rapid investigation.
• B-scan helps in evaluating the posterior segment in the presence of opaque ocular media.
• B-scan is useful for preoperative planning.
• B-scan is the preferred screening modality in extraocular lesions.
• It is a feasible option in rural centres.

Various ocular conditions detected by B-scan

Cataract

Cataract is a degenerative disease of the lens that is usually seen in the older age-groups. It can sometimes be secondary to trauma, when the lens becomes opaque due to deposition of reflective material beneath the lens capsule. On B-scan, an immature cataract shows scattered opacities separated by clear zones. In a mature cataract, the lens has a completely opaque cortex and is seen as a very dense structure

Vitreous degeneration

In vitreous degeneration, the liquefied vitreous contains cholesterol crystals that move with eye movements. B-scan reveals multiple hyperreflective mobile foci within the vitreous chamber that show after-movements on a dynamic scan. This is also known as synchysis scintillans. There is no reduction of visual acuity in this condition. It is often bilateral and secondary to longstanding uveitis or may follow vitreous haemorrhage

Classic retinal detachment

Retinal detachment (RD) is usually due to a break or tear in the retina; it may also be caused by vitreoretinal traction due to contracting membranes or because of subretinal exudates. The detached retina is usually attached to the firm anchoring points of the ora serrata anteriorly and the optic nerve head posteriorly and, consequently, a total RD shows a funnel shape. Dynamic scan may reveal an undulating motion of the retinal membrane, particularly in a recent RD. With B-scan, it is possible to diagnose RD early so that reparative surgery can be carried out to seal the retinal tear using laser or cryotherapy.

Persistent primary hyperplastic vitreous

PHPV is a serious unilateral disorder of the vitreous that is seen in childhood. It presents as leukocoria (white pupil). There is failure of regression of the primary vitreous. The primary vitreous persists in a microphthalmic eye and B-scan shows a retrolental membrane, which may be dense; there is a persistent hyaloid artery extending from the retrolental region to the optic disc.

Retinopathy of prematurity

Retinopathy of prematurity is a bilateral condition that is associated with a history of prematurity and oxygen therapy in the postnatal period. This leads to the occurrence of retrolental fibroplasia, with development of dense retrolental membranes, a result of neovascularization from the retinal periphery leading to fibrotic changes in the anterior vitreous. The eyeballs are normal in size.

Choroidal melanoma

Choroidal melanoma, the commonest primary intraocular tumor in adults, arises from the choroid and ciliary body. Most of these lesions arise posterior to the equator of the eyeball. On B-scan, it is seen as a lenticular-shaped mass arising from the choroid. USG is used to assess scleral erosions and extraocular extension into orbital fat. Some tumors have a collar-button or mushroom shape. Blood flow within the tumor is seen on colour Doppler as pulsating channels or lakes of colour. Choroidal melanoma may be associated with retinal detachment. The tumor has a bilobed or ‘cottage-loaf’ appearance, which is caused by waisting as it breaks through Bruch’s membrane. The tumor usually demonstrates choroidal excavation. Colour Doppler reveals the vascularity of the lesion

Retinoblastoma

Retinoblastoma is the commonest primary intraocular tumour of childhood. It arises from the embryonic retinal epithelium of the primary optic vesicle. It is usually unilateral but may be bilateral in one-third of cases. It presents in childhood as leukocoria. The tumour projects from the retina into the vitreous chamber. Some tumours produce subretinal lesions and cause retinal detachment. Calcium deposits are commonly seen within the tumour. The calcium deposits, which are seen as highly reflective foci, are pathognomonic of the condition. The tumour outline is irregular. B-scan may help in the detection of optic nerve invasion resulting from extraocular spread of the tumour.

Phthisis bulbi

Phthisis bulbi is an end-stage condition following ocular trauma and haemorrhage. The eye is blind, small, and non-functioning, with extensive calcification. There is loss of the normal ocular shape.

Ocular trauma

Ocular trauma either due to blunt injury or penetrating injury can result in vitreous haemorrhage. There may be rupture and shrinkage of globe due to loss of vitreous as a result of a penetrating injury. There is distortion of normal ocular shape and intravitreal haemorrhage develops with or without concomitant posterior vitreous detachment. The foreign body that caused the injury may be seen within the eyeball, for example a metallic object in a missile injury or blasts. Sometimes penetrating foreign bodies like a wooden object or a metallic rod may be seen crossing the eyeball. Metallic foreign bodies show a posterior reverberation artefact.

Vitreous detachment

Vitreous detachment is seen in elderly individuals. It results from gel liquefaction and collection of fluid in the subvitreal space, which in turn, results in vitreous detachment. It is seen frequently in cataractous eyes on B-scan. B-scan shows reduced volume of vitreous gel. USG also shows marked mobility and elasticity of the detached vitreous, with a mirror image configuration when the eye is deviated to one side and then to the other.

Vitreous haemorrhage

Vitreous haemorrhage can result from tearing due to vitreoretinal traction, diabetic retinopathy, vasculitis, subarachnoid haemorrhage, and blunt trauma to the eye. The presence of blood cells in the vitreous gives rise to low-intensity echoes. Later, the haemorrhage may organize and develop fibrinous membranes.