Ординатура / Офтальмология / Учебные материалы / Uveitis Text and Imaging Text and Imaging Text and Imaging 2009

Figure 13: B-scan echogram showing low reflective, homogenous echos in vitreous cavity suggestive of vitritis

Figure 14: B-scan echogram showing low reflective, homogenous echos in vitreous cavity and vitreous membranes suggestive of vitritis

Figure 15: B-scan echogram of a patient with endophtalmitis showing moderately high reflective homogenous echos in vitreous cavity and fixed vitreous membranes. Note the presence of choroidal thickening

Figure 16: B-scan echogram of a patient with vitreous haemorrhage showing echos that are less homogenous and more reflective than those produced by vitritis

The location, extent, and density of vitritis can be shown by ultrasonography. The localization of vitritis in the anterior or posterior vitreous or peripheral compartment can aid in tracing the point of origin of uveitis. The 20-MHz frequency probes can detect the typical snowbank in intermediate uveitis.9

The density of vitritis is estimated from the character of echoes and the area of vitreous involvement as determined from the B-scan. Movement of the eye causes low-amplitude echoes to move freely within the globe in vitritis (Figure 14) and helps to distinguish them from more fixed vitreous membranes seen in endophthalmitis. Choroidal thickening is frequently observed in endophthalmitis (Figure 15).

The echoes produced by vitreous hemorrhage are less homogenous and more reflective than those produced by vitritis (Figure 16).

Ultrasonography is useful in the detection of posterior vitreous detachment, a common finding in eyes with vitreous inflammation.10 The posterior vitreous hyaloid has a relatively weak reflection when compared to that of retina, usually disappearing when the sensitivity of the ultrasound gain is reduced below 70 dB. Posterior vitreous detachment may be complete or incomplete (Figure 17).

Incomplete posterior vitreous detachment with attachment to the optic disc can simulate retinal detachment (Figures 17A and 18)

Figure 17: B-scan echogram show low reflective vitreous echoes suggestive of vitritis associated with incomplete posterior vitreous detachment (Figure 17A) and complete posterior vitreous detachment (Figure 17B)

Figure 18: B-scan echogram shows retinal detachment as uniformly high reflectivity, attached to the optic nerve. The echo persists as the sensitivity is reduced below 70 dB

Figure 19: Fundus photograph (A) and B-scan echogram (B) in a patient with idiopathic panuveitis showing vitreous traction membrane (arrows) and retinal detachment (arrowhead)

Ultasonography is useful in monitoring the time course of the vitritis pocess. After resolution of vitreous inflammation , no echoes are detected but the vitreous membranes remain visible. This may lead to a traction retinal detachment (Figure 19).

RETINAL DETACHMENT

The retina in the normal eye appears on B-scan ultrasonography as a smooth, concave, acoustically opaque surface formed by echoes arising from the vitreoretinal interface (Figure 3 B). These echoes are contiguous with, and inseparable from the choroidsclera complex.

Detached retina appears as highly reflective membrane within the vitreous cavity. In retina detachment the echo persists as the sensitivity is reduced below 70 dB Attachment to the optic nerve suggests retinal detachment, which has less aftermovement

Figure 20: Vogt-Koyanagi-Harada disease. Fundus photograph

(A) shows areas of serous retinal detachment. A 20-MHz B echogram(B) shows diffuse, medium reflective choroidal thickening most marked in the peripapillary area (arrows) and serous retinal detachment (arrowheads). The limit between choroid and sclera is well defined (C, arrow) and there is accentuation of the Tenon’s surface posterior to the sclera (arrowheads)

when compared with posterior vitreous detachment (Figure 18).

Serous retinal detachment is a common finding in several inflammatory conditions, including Vogt-

Koyanagi-Harada disease, sympathetic ophthalmia, and posterior scleritis. It appears on B-scan ultrasonograms as a thin, continuous, shallow or bullous, acoustically opaque line of echoes separate from, and anterior to, echoes from the wall of the globe. The subretinal space in these conditions is acoustically clear (Figures 20-22). Ultrasonography can be used as a tool to monitor resolution of serous retinal detachment in response to corticosteroids (Figure 21).

Ultrasonography may be helpful in the detection and evaluation of other forms of retinal detachment complicating posterior uveitis: rhegmatogenous retinal detacment without or with proliferative vitreoretinopathy and traction retinal detachment (Figures 18 and 19).

CHORIORETINITIS

Ultrasonographic findings of chorioretinitis due to toxoplasmosis or other infectious or noninfectious causes include focally elevated fundus lesion and/or diffuse thickening of retinochoroid layer (Figure 23).11 Toxocariasis can present clinically as endophthalmitis that has opaque media. Echographic findings may include granulomatous lesion, which may be calcified, vitreous membrane extending between granulomatous lesion to the posterior pole, and posterior traction retinal detachment or retinal fold

(Figures 24 and 25).

The echographic findings of the cysticercosis is quite characteristic, with well-defined, oval-shaped cysts located within the vitreous cavity and/or the subretinal space.12 The scolex of the parasite appears as a very reflective, echo dense nodule attached to inner wall of the cyst (Figures 26 and 27). Movements of the cyst can also be demonstrated with kinetic evaluation.

CHOROIDAL AND SCLERAL CHANGES

On echography, the total chorioretinal thickness is about 1.5 mm in normal eye. The choroid thickness is about 0.5 to 1 mm in the posterior pole. Echography can detect choroidal and scleral thickening in the conditions like Vogt- Koyanagi-Harda (VKH) disease, sympathetic ophthalmia, and scleritis.

Although the diagnosis of VKH disease and sympathetic ophthalmia is based primarily on clinical presentation and fluorescein angiographic findings, inadequate pupillary dilation due to posterior

synechiae or dense vitritis may obscure the view of the fundus. In addition, presentation may be atypical and extraocular manifestations may be absent. In these instances, ultrasonography helps to establish the diagnosis.

Diagnostic ultrasound in acute VKH disease typically shows diffuse, low-to-medium reflective choroidal thickening most evident in the posterior pole. Associated findings include overlying serous retinal detachment located in the posterior pole or inferiorly, thickening of the sclera, and vitreous

Figure 26: Intraocular Cysticercosis. Vertical axial scan shows subretinal Cysticercosis with total retinal detachment on A and B-scan echogram

opacities (Figure 20). Ultrasonography may be used to follow gradual normalization of choroidal thickness in response to corticosteroid therapy (Figure 21).

The echographic manifestations of sympathetic ophthalmia include diffuse, medium-to high reflective thickening of the posterior choroid, serous detachment of the retina, and vitreous opacities (Figure 22).

Scleritis is an inflammatory condition that can affect either the anterior or posterior part of the sclera. The diagnosis of anterior scleritis is easy, where the assessment of posterior scleritis is difficult.

Echographic analysis of the posterior segment of eye especially sclera is very useful in establishing the presence of posterior scleritis.

Diffuse posterior scleritis shows high-reflective sclero-choroidal thickening. Scleral edema associated with fluid whithin Tenon’s space resulting in an echoluscent region just posterior to the sclera results in the classic “T” sign (Figure 28).

Nodular posterior scleritis presents as a single focal sclero-choroidal lesion. It may mimick an intraocular tumor choroidal melanoma, hemangioma, or metastatic carcinoma. It causes focal expansion of the ocular wall, and thickened sclera will be highly reflective with regular internal structure (Figure 29).

Echographic findings of infectious scleritis may include abscesses within the sclera, choroid, and even the orbit.13

Figure 27: Intraocular Cysticercosis. (A) Horizontal axial B-scan echogram showing intraocular Cysticercosis in vitreous cavity with adhesions to retinal wall and total retinal detachment; (B) A-scan shows thick highly reflective spike from the scolex (arrow), thin highly reflective spikes are also seen from capsular walls (C)

Echography can detect uveal effusion with choroidal detachment complicating severe intraocular inflammation in VKH disease, sympathetic ophthalmia, posterior scleritis, and other entities. B-scan ultrasonography typically shows a smooth, convex elevation with little aftermovement. The choroidal detachment is thicker than retina and inserts anteriorly near the lens and posteriorly near the equator of the globe (Figures 22D and E). It may result in angle closure and secondary glaucoma.

OTHER FINDINGS

Optic dis edema (Figure 30) and macular edema (Figure 31) may be detectable by ultrasonography in eyes with opaque media.

Figure 28: Diffuse posterior scleritis. Fundus color photograph (A)showing optic disc edema and retinal folds.10 MHz B echogram (B) showing diffuse retinochoroidal thickening (arrows) and acentuated episcleral space resulting in a typical T-sign (arrow heads). 20 MHz echogram (C) showing serous retinal detachment (arrow)

Figure 29: Posterior nodular scleritis: B and A-scan echograms show marked localized thickening of the sclera (arrow) that clinically presented as mass lesion

Figure 30: A 20 MHz echogram of a patient with Vogt-Koyanagi- Harada disease shows optic disc elevation due to optic disc edema (arrow) with diffuse, medium reflective choroidal thickening most marked in the peripapillary area (arrow heads)

DRAWBACKS

USG requires contact with the cornea, but can be done through lid also with mild sound attenuation. It involves mild discomfort in already inflamed eye. It requires experienced hands to perform and interpret the findings.

Figure 31: 20 MHz echogram of a patient with sarcoidosis uveitis showing a convex anterior projection of the vitreoretinal interface echo line in the macular region, followed by a localized anechoic area suggestive of cystoid macular edema (arrows)

KEY POINTS

1.USG is a non – invasive, quick, and easy to perform test.

2.The one dimensional amplitude-mode (A-scan ) and the two dimensional brightnessmode (B-scan) are the important ultrasound displays being used in ophthalmology

3.USG may be useful in the diagnosis of intraocular inflammatory conditions, especially when visualization of the fundus is poor because of opaque media or when the clinical presentation is atypical

4.USG is helpful in the detection and evaluation of vitritis, vitreous detachment, retinal detachment, focal retinochoroidal inflammation, choroidal and scleral thickening, and choroidal detachment

5.USG is a particularly useful diagnostic tool in Vogt- Koyanagi-Harada disease, sympathetic ophthalmia, and posterior scleritis

6.It can also be used as a tool to monitor the response to the therapy in these diseases

REFERENCES

1.Mundt GH Jr, Hughes WF Jr. Ultrasonics in ocular diagnosis. Am J Ophthalmol 1956;41:488-98.

2.Baum G, Greenwood I. The application of ultrasonic locating techniques to ophthalmology. II. Ultrasonic slit lamp in the ultrasonic visualization of soft tissues. Arch Ophthalmol 1958;60:263-79.

3.Bronson NR. Development of a simple B-scan ultrasonoscope. Trans Am Ophthalmol Soc 1972;70:365-408.

4.Ossoinig KC. Basic of clinical echo-ophthalmology. IV: Clinical standardization of equipment and techniques. In Bock J, Ossoinig KC (Eds): Ultrasonographica Meidca. Vienna, Wiener Med Akademie, 1971;83.

5.Ossoinig KC. Quantitative echography-the basic of tissue differentiation. J Clin Ultrasound 1974;2:33-46.

6.Ossoinig KC. Standardized echography: Basic principles, clinical applications, and results. Int Ophthalmol Clin 1979; 19:127-210.

7.Shammas HJ, Dunne S, Fisher YL. Three-dimensional ultrasound tomography of the eye. Eden Mills, Ontario, Canada, 1999.

8.Coleman DJ, Silverman RH, Lizzi FL, et al. Ultrasonography of the eye and orbit. 2nd edition. Lippincott Williams and Wilkins, 2006.

9.Doro D, Manfrè A, Deligianni V, Secchi AG. Combined 50and 20-MHz frequency Ultrasound Imaging in Intermediate Uveitis. Am J Ophthalmol 2006;141:953-5.

10.Hewick SA, Fairhead AC, Culy JC, Atta HR. A comparison of 10 MHz and 20 MHz ultrasound probes in imaging the eye and orbit. Br J Ophthalmol 2004;88:551-5.

11.Illingsworth RS, Wright T: Tubercles of the choroids. Br Med J 1948;2:365-68.

12.Fishman M, Kerman B, Foxman S. Intraocular Cysticercosis: Migratory. In Ossining KC (Ed): Ophthalmic echography. Dordrecht, Dr. W Junk, 1987;285.

13.Taravella MJ, Jihnson DW, Petty JG, et al. Infectious posterior scleritis caused by Pseudallescheria boydii clincopathologic findings. Ophthalmology 1997;104:1312- 6.

INTRODUCTION-HISTORY

The use of ultrasound frequencies in the 35 to 100 MHz range is a relatively new development in ultrasound imaging of the eye. In 1956, Mundt and Hughes1 demonstrated the use of Ultrasonography in Ophthalmology. The frequency used for conventional ultrasound is 10 MHz that has a depth of 4 cm and resolution of 940 microns. This is ideal for examination of posterior segment structures. To visualize anterior segment structures, we need a device with less penetration and more resolution i.e. more frequency. Ultrasound biomicroscope technology is based on the use of high frequency transducers incorporated into B-mode scanning device.2,3 Pavlin et al demonstrated the use of high frequency transducers and scanning devices on eye bank eyes4 and later in living tissue.5 The term ultrasound biomicroscopy (UBM) is applied to this technique because of its similarities to optical biomicroscopy, i.e imaging of the living tissue at microscopic resolution. UBM allows acquiring and viewing real-time high-resolution images of the anterior segment under magnification. Property of high resolution allows for determination of the relationships of structures in vivo without the need for histological specimens.

PRINCIPLE OF UBM

The basic principle of use of ultrasound in ophthalmic imaging remains the same. Ultrasound biomicroscopy uses all the essential components similar to conventional B-scan ultrasonography except for higher

frequency (35 to 100 MHz). UBM is based on hypothesis that by increasing the frequency, greater microscopic resolution can be obtained. Thus, high frequency used in ultrasound biomicroscopy leads to more resolution at the cost of penetration, e.g. 10 MHz would have penetration of 50mm while penetration is only 5 mm with 60 MHz. Increase in resolution results in visualization of the limited tissue depths. UBM can detect any pathologic conditions that fall within its penetration of approximately 4 to 5 mm.

The UBM system uses a piezoelectric co-polymer transducer attached to a microprocessor controlled RF signal generator to convert electrical signals into ultrasound waves of a specific high frequency. The transducer delivers the continuous ultrasound waves and receives the reflected signals back. Ultrasound waves pass through the various tissues of the eye at varying speeds, and are reflected back at different intervals depending on the density (acoustic impedance) of the tissues. Quality of image will depend on the direction of the returning echos. Sound waves reflected at an angle will lead to diminution of signal strength. Reflected waves are collected and assembled by the computer and magnified to provide a highresolution dynamic sectional B-scan image of anterior segment of eye. The B-scan image is a two-dimensional slice through the eye where changes in tissue density and tissue interfaces are shown by varying degrees of brightness (grayscale tones) that provide the visual contrast essential to identify and differentiate the tissue structures. UBM software can be further used to improve the image contrast or brightness to better

Figure 1: Photograph showing Paradigm UBM machine

highlight or identify interest areas without altering the original scanned file image.

THE ULTRASOUND BIOMICROSCOPY MACHINE

The UBM system consists of central processing unit (CPU) containing signal-processing unit with monitor, transducer, trackball unit, light pen, footswitch, gantry arm for precise motion control and accessories such as eyecups and printer or video. The entire hard ware is mounted on a motorised table (Figure 1).

The software necessary to operate and analyze is pre-installed. The CPU contains built in hard drives for patient image storage. The transducer is mounted to a gantry arm that articulates to remain fixed at a particular position for placing the probe over the patient’s eye (Figure 2).

Figure 3: “Start window” screen showing the various options that are displayed on starting the OCT machine

The commercial UBM systems use a 50 MHz transducer that gives a good compromise between resolution and penetration. The resolution of 50 Mhz is 40 microns and the depth is 4 mm.

TECHNIQUE OF ACQUIRING A SCAN

Switching on the system activates all components. On the start window, the menu and toolbars offer various options including patient and images, UBM, etc. (Figure 3). One can select the appropriate window and make data entry of new patients .

The patient is to be placed in a supine posture. After instillation of topical anesthetic drops, a scleral cup of appropriate size is inserted. There are four different sizes of reusable scleral cups i.e. 20 mm, 22 mm, 24 mm, and 26 mm in diameter (Figure 4).

Different size cups are used to keep the lids open and to allow the transducer to be immersed (Figure 5). The machine uses a fluid immersion technique to acquire the images. The scleral cups are filled with coupling solution, i.e. 1% methylcellulose solution.