CME article 10

 

CME: Ocular Ultrasound


 

The advent of real-time Ultrasound (US) has been of immense value in the work-up of patients with ocular disorders. It provides an instantaneous glimpse into the eye and in many instances yields information not obtainable by any other methods.

The cystic composition and superficial position of the eye are ideal for US examination. Opaque media caused by cataract, hemorrhage, or vitreous membranes conceal the intra-ocular contents from proper clinical examination. It is in cases like these that US is the most useful examination for assessment and prior to surgical procedures.

What follows is a brief look at the anatomy, and pathology of the eye, and the common abnormalities that can be picked up by US. This basic article has been written in view of the fact that many sonologists do not buy a special small parts probe and make do with the trans-vaginal probe for small parts. While this compromises quality for eye US, the fact that a TVS probe (5 or 6.5 MHz probe) can give decent information for evaluation of ocular pathology should not be lost on those reading this article.

Anatomy of the Eye

The eyeball is spherical in shape and has a diameter of about an inch. It is made of 3 concentric coats.
The outer fibrous coat of sclera and cornea.
The middle vascular coat of choriod, ciliary body and iris.
The inner nervous coat is the retina.
The refracting media from before backwards are cornea, aqueous humor, lens and vitreous body.

The sclera

It is thickest near the entrance of the optic nerve and thinnest behind the sclero-corneal junction where recti muscle insert. Sclera is fused posteriorly with dural sheath of the optic nerve. It provides insertion to the recti in front and the obliqui behind the equator.

Cornea

Cornea is transparent and forms the anterior 1/6th of the eyeball, it is separated from iris by the anterior chamber.

Choriod

Is a thin pigmented layer which separates posterior part of sclera from the retina.

Ciliary Body is the thickened part of the uveal tract lying posterior to the corneal limbus and suspends the lens.

Iris is the anterior part of the uveal tract with a circular pupil, it controls the amount of light entering the eye. It divides anterior segment of the eye into the anterior and posterior chambers.

Retina is the thin, delicate inner layer of the eyeball which is continuous with the optic nerve. Opposite the entrance of optic nerve, the circular area of 1.5 mm diameter is the optic disc which has a depressed area, the physiological cup.

Aqueous Humour

This is the clear fluid between the cornea and lens and is divided into anterior and posterior chamber by the iris.

Lens is a transparent biconvex structure with a diameter of 1 cm between the anterior and posterior segments. It is enclosed in a transparent capsule and is retained in position by the suspensory ligament (Zonule of Zinn).

Vitreous Body

This is the colorless jelly-like transparent mass which fills the posterior segment of the eyeball. It is enclosed in hyaloid membrane. Behind, it is attached to the optic disc and in front to the ora serrata. In between, it is free, and lies in contact with the retina.

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Fig 1 (Anatomy)


Indications

1) Opaque light-conducting media making direct vision by ophthalmoscopy impossible.
2) Suspected intra-ocular tumor, solid or cystic lesions
3) Differentiation between serous and solid retinal detachment. Sometimes, 
    a detachment may conceal a tumor. The subretinal area is clearly demonstrated on US
4) Examination of the vitreous
5) Localization of foreign bodies
6) Ocular Measurements
7) Proptosis

 

Pathology

 

Vitreous Hemorrhage (VH)

The vitreous is normally clear and echo-free but is subject to hemorrhage, especially in patients with diabetic retinopathy and trauma. Estimation of the extent of VH is important for prognosis as there may ne spontaneous clearing; if however the hemorrhage does not clear, thick echogenic membranes may develop and vitrectomy may have to be resorted to.

 

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Fig 2


Retinal Detachment (RD)

RD is divided into 2 main types:

Rhegmatogenous (arising from a retinal break or tear) and

Non-rhegmatogenous (or secondary detachment). 

Retinal breaks which result in detachment are usually caused by weakness in the peripheral retina due to degeneration, for example lattice degeneration in myopes and vitro-retinal traction from a detached vitreous.

Non-rhegmatogenous RD are of 2 types: Tractional and exudative

Tractional RD occurs when contracting vitreo-retinal membranes pull the sensory retina away from the pigment epithelium resulting in angular, fixed lesions. The proliferative retinopathies in diabetes and penetrating trauma are the main causes

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Fig 3


Exudative RD occurs when subretinal fluid from the choroids enters the subretinal space in inflammation (uveal effusion syndrome) or tumors.

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Seen here in Fig 4 is a melanoma causing RD.

 

Firm attachment of the retina exists at the ora serrata and the optic nerve head, ensuring that the RD does not extend beyond these sites. A classical, total RD therefore shows a funnel shaped appearance.

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Fig 5

and in a recent RD, dynamic scanning will show an undulating, sinuous motion of the retinal leaves. Retinal mobility is less marked if the RD is shallow, partial, or if there is a large amount of subretinal fluid, causing a tense, bullous detachment. A minority of RDs remain stationery for some years, but the majority, if untreated, will become total and progressively immobile, because of the development of preretinal fibrosis.

 

Choroidal Detachment (CD)

Complete CD shows fluid in the supra-choroidal space, limited by the choriodal anchoring points: anteriorly by the ciliary body, and hence the scleral spur, and posteriorly at the exit foramina of the vortex veins. A complete CD therefore appears on scanning as a biconvex indentation of the globe.

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Fig 6

If the vortex veins are absent or avulsed, the detachment may extend to the optic disc. CD may occur in association with RD, not only in exudative conditions, but also with rhegmatogenousus type of RD. US may reveal chorioidal tumor (melanoma, secondary deposit, or retinoblastoma) as the cause of exudative choroidal detachment, but the etiology also includes endogenous uveitis and infection.

 

Trauma & Intra-Ocular Foreign Bodies (IOFB)

Early assessment of intra-ocular damage enables vitrectomy and other microsurgical techniques to be performed before chronic internal, structural changes develop. US is also useful in localization of IOFB, particularly glass, metal or other reflective material.
Rupture of globe usually occurs in the equatorial region, and signs include distortion of the normal shape with loss of ocular volume, intra-vitreal hemorrhage, and intra-ocular air, particularly if there is sinus communication.

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Fig 7

 

Thyroid Opthalmopathy (TO)

Most patients with Grave’s disease develop changes of TO at some stage, and only about 3-5% of patients develop the sight threatening complication of  optic neuropathy, due to optic nerve compression by enlarged extra-ocular muscles. All extra-ocular muscles may be enlarged, but the severity of involvement can be assessed by US measurement of medial rectus muscle (normal is 4 mm). Typical enlargement mainly affects the muscle belly, with lesser involvement of muscle origin and insertion.

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Fig 8

Other features of TO include increased orbital fat and orbital edema (may be seen as echo-poor areas within the orbital fat), and / or there may be fluid within the Tenon’s capsule.

 

Microphthalmos

This may be congenital, associated with other cranio-cerebral anomalies or isolated, or acquired, due to trauma or infection. Phthisis bulbi is an end-stage condition following trauma and ocular hemorrhage. The eye is blind, small and eventually calcifies.

 

 

Retro-Orbital Tumors

The demonstration of a poorly reflective, irregular orbital mass, with good penetration of the sound beam is a strong indication of ocular malignancy.

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Fig 9

Tumors include mets from neuroblastoma, Ewing’s sarcoma of bone, Wilm’s tumor in children, metastasis from primaries in the bronchus, breast, prostate, kidney and GI, contiguous spread from paranasal sinuses in adults. Choroidal melanomas on US appear as lenticular shaped mass deeply embedded in, arising from the choroids, and may be associated with RD. Some melanomas have a cottage-leaf or mushroom shaped appearance caused by waisting as they break through Bruch’s membrane. This feature is pathgnomonic of melanoma.

All suspected tumors do need a CT/ MRI for accurate evaluation.

 

Dr. Rajesh Mayekar, MD
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This one is classic-Lens Prolapse