rapid b-scanning of the vitreous · davidmcleod, marie restori, andjohni e. wright fig. 1...

British Journal of Ophthalmology, 1977, 61, 437-445

Rapid B-scanning of the vitreousDAVID McLEOD, MARIE RESTORI, AND JOHN E. WRIGHTFrom the Vitreous Clinic, Moorfields Eye Hospital, and the Ultrasonic Department,Department of Clinical Ophthalmology, Institute of Ophthalmology, London

SUMMARY Ultrasonic examination is an essential investigation in most patients awaiting vitrectomy.Rapid B-scanning of the vitreous is described utilising a new system capable of high resolutionand good tonal quality. Several patterns of haemorrhagic invasion of the vitreous cavity areillustrated, together with detachment, collapse, and retraction of the vitreous gel.

Diagnostic ultrasound has been used for many yearsfor the investigation of ocular and orbital diseases(Oksala, 1963; Baum, 1964; Purnell, 1966; Ossoinig,1972; Coleman, 1972; Bronson, 1972). Examinationmethods currently available include A-, B-, C-, andM-scanning and ultrasonic holography. Apparatuscapable of ophthalmic A-, B-, and C-scanning andholography was designed by Aldridge et al. (1974)and has been on clinical trial at Moorfields EyeHospital for the past three years. A report of itsuse in the investigation of orbital lesions is to bepublished shortly (Restori and Wright, 1977). Thispaper presents our experience of real-time B-scanning of the vitreous cavity, particularly inpatients being considered for vitrectomy.

Material and methods

EQUIPMENTA 10-MHz focused transducer is mechanicallyscanned in rectilinear fashion, each 4-cm sweepconstituting a B-scan section. Each sweep takesapproximately 140 milliseconds to complete, therebypermitting fast, almost real-time imaging of theglobe. A remote button (sited near the displayoscilloscope) controls the level of the B-scan section,which can be varied over a distance of 4 cm. Thislevel is displayed on a millimetre scale and can beconveniently compared with the position of thecentral B-scan section, that is, the section with thestrongest corneal echoes. B-scans may be taken inhorizontal, saggital, and oblique planes, and the4-cm-square scanning aperture can be completelyinvestigated in a few seconds. Variable system

Address for reprints: D. McLeod, FRCS, Moorfields EyeHospital, City Road, London EC1V 2PD

controls include gain, transmission pulse duration,scanning speed, and a swept gain facility to com-pensate for sound attenuation in the globe andorbit.The system is capable of good resolution and is

remarkably free of artefacts. The scanning mechan-ism has been built to a high standard of rigidity andprecision, and the instantaneous position of thetransducer is transferred to the display tube withminimum error. These are design criteria forholographic imaging and undoubtedly contribute tothe quality of the B-scan display.Adequate sensitivity and accurate echo registra-

tion allow weak echoes to be detected and displayed.The dynamic range of the system is 40 dB, and anamplifier to compress this 40 dB into the 20 dBdynamic range of an oscilloscope would improvethe grey scale appearance of the B-scan display.A time-gate has proved useful in selecting echoes

for amplitude quantitation from any B-scan section.The A-scan suffers no signal processing exceptoptional rectification and envelope detection.Polaroid Landpack film (type 107C) is used toobtain a permanent record of both A- and B-scandisplays; however, many of the grey tones are lost toPolaroid film and essential dynamic information isdifficult to capture on still photographs.

TECHNIQUEThe eye to be investigated is anaesthetised withoxybuprocaine HCl (Benoxinate) drops and theeyelids are retracted with a Barraquer speculum.The patient lies supine on a movable couch, and thetransducer is coupled to the eye by means of aSteridrape bath (Purnell, 1966) containing Ringer'ssolution at 36°C. The eye is positioned to lie in thecentre of the 4-cm-square scanning aperture, and is

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David McLeod, Marie Restori, and Johni E. Wright

Fig. 1 Rectilinear scanning in horizontal plane

scanned transversely at 1-mm intervals, initially withthe patient looking straight ahead (Fig. 1). Furtherscanning is then carried out during lateral andvertical deviations of the patient's gaze, therebyincreasing the amount of data obtained from theequatorial regions of the eye. If necessary, saggitalscanning is also performed, for example, to localiseradiolucent intraocular foreign bodies in 3 mutuallyperpendicular planes.

In dynamic studies the direction of gaze is changedsuddenly, and after-movements of the echoes areobserved for several seconds.

CLINICAL CORRELATIONUltrasonic findings have been correlated withophthalmoscopic and biomicroscopic appearanceswherever possible, for example, during vitrectomyperformed or witnessed by one of the authors(D. McL.).

Results

The vitreous cavity is the space behind the posteriorlens capsule and zonule and internal to the innerlimiting lamina of the ciliary epithelium, retina,and optic disc. This space is normally occupied bythe vitreous body, a relatively homogeneous aqueous

gel, so the vitreous cavity is normally spheroidal on

serial B-scanning (apart from the lenticular indenta-tion anteriorly) and is acoustically 'empty'.

Acoustic changes in the vitreous have beenclassified as follows:

I. ABNORMAL CONTENTS OF THE VITREOUSCAVITYThe presence of echoes within the vitreous cavityindicated:(1) persistence (or hyperplastic persistence) of

primary vitreous structures (Fig. 2a);(2) change in the physicochemical structure of the

vitreous body, for example, senile or myopicdegeneration; or

(3) invasion or infiltration of the vitreous bysubstances, cells, or other particles normallyforeign to this cavity (Fig. 2b).

II. CHANGE IN THE VOLUME AND SHAPEOF THE VITREOUS CAVITYThe volume of the vitreous cavity was increased inmyopic and buphthalmic eyes, an asymmetricalenlargement being interpreted as a staphyloma.Likewise in aphakia the vitreous cavity incorporatedthe posterior chamber, communicating with theanterior chamber via the pupil.

The volume of the vitreous cavity was reduced inmicrophthalmic eyes and in phthisis bulbi (wherechoroidal thickening compounded the effect ofscleral shrinkage on vitreous volume). An asym-metrical reduction in volume typically resulted fromsurgical explants and orbital tumours, and also fromdetachments and tumours of the retina and choroid(Fig. 2c).

III. CHANGE IN THE VOLUME AND SHAPEOF THE VITREOUS BODYThe vitreous body commonly occupied rather lessthan the total volume of the vitreous cavity, separat-ing from its surroundings anterior and/or posteriorto its firm annular attachment to the pars plana andperipheral retina (the 'vitreous base'). The vitreouscavity thus became divided into compartments-that is, the vitreous gel (formed vitreous) andprehyaloid or retrohyaloid spaces (fluid vitreous)-and the shapes of these compartments were mutuallyinterdependent. In many cases abnormal vitreo-retinal adhesions precluded complete posteriordetachment of the vitreous from the retina (Fig. 2d).

B-scanning of the vitreous cavity was most com-monly performed as part of the work-up of potentialcases for vitrectomy, and ultrasonic evaluation inthese patients was particularly directed towards:(A) localising and identifying material which had

invaded the vitreous cavity;(B) determining the presence of compartments

within the vitreous cavity; and ;(C) defining the borders of the vitreous cavity, in

particular detecting the presence of a retinaldetachment.

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439Rapid B-scanning of the vitreous

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Fig. 2 Classification of vitreousdisorders(a) Left eye: persistenthyperplastic primary vitreous(b) Left eye, deviated nasally:invasion of vitreous byhaemorrhage, densest posteriorly(c) Right eye, deviated nasally:ciliochoroidal detachmenttethering at scleral spur andvortex ampulla(d) Left eye: dense intragelhaemorrhage; foreign body trackand vitreoretinal adhesion nasally;thickened anterior and posteriorhyaloid membranes

(A) INVASION OF THE VITREOUS (Fig. 3)Extraneous intravitreal material gave rise to eitherlocalised or more generalised echoes from thevitreous cavity:

(1) Localised echoes. Inflammatory cells forminga vitreous abscess or granuloma produced a collec-tion of medium-amplitude echoes, as did haemor-rhages into relatively solid vitreous gel. Clottedblood was often confined within vitreous 'tracts' or

other intragel compartments (Fig. 3a), and in manycases the site of bleeding could be located by serialscanning of the globe (Fig. 3b). Stronger and more

discrete echoes arose from glial or fibrovasculartissue gSferating as a sequel to haemorrhage inthe gel,vor example, along the track of a perforatingforeign body (Fig. 2d). Similarly, sheets of glial or

fibrovascular tissue arranged as epiretinal mem-

branes gave rise to high-amplitude echoes whichtended to flatten the concavity of the vitreoretinalinterface (Fig. 3b).

Collections of high-amplitude echoes also resultedfrom intravitreal foreign bodies or a posteriorlydislocated lens.

(2) Dispersed echoes. Uveitis and vitreous haemor-rhage often resulted in low-amplitude echoesdisseminated within the vitreous cavity (Fig. 3c), apicture also seen occasionally in degenerativesyneresis. In general, inflammatory cells could notbe distinguished ultrasonically from red blood cells,and the amount of acoustic change was less thanthat expected from the degree of opacification of themedia to light.

Dispersed high-amplitude echoes were typical ofasteroid hyalitis.

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David McLeod, Marie Restori, and John E. Wright

Fig. 3 Invasion of the vitreous(a) Left eye, deviated temporally;dense haemorrhage in anterior gel;fine vitreous membrane tetheringposteriorly(b) Left eye: haemorrhage.fromfibrovascular proliferations;epiretinal membrane flattensconcavity of vitreoretinal interfaceposteriorly(c) Right eye: dispersed echoes invitreous gel.(d) Right eye, deviated temporally:diffuse echoes from blood inretrohyaloid space extending intothe central gel

(3) Diffuse echoes. Invasion of the vitreous cavityby inflammatory or red blood cells sometimes gaverise to diffuse low- amplitude echoes by scattering ofsound, producing a relatively uniform echo density(Fig. 3d).

(B) POSTERIOR VITREOUS DETACHMENT

(Figs. 4 and 5)Separation of the vitreous body from the retina was

often demonstrable, especially in patients with an

associated invasion or infiltration of the vitreouscavity. There were two basic acoustic patternsindicative of vitreous detachment:

(1) A thin sheet of echoes along the posteriorhyaloid interface, usually inserting into the retinajust anterior to the equator. This pattern was

typically found in those diabetic patients in whom a

relatively immobile membrane spanned the posteriorpart of the vitreous cavity, often attached to theoptic disc region by a thick rigid stalk. Echoes fromthe posterior hyaloid membrane were of loweramplitude and more discrete than the echoes fromfibrovascular tissue on the posterior aspect of thehyaloid membrane (Fig. 4a).

In senile and myopic posterior vitreous detachmentirregular low-amplitude echoes arose from themobile posterior hyaloid, while vitreous retraction-that is, gross anterior contraction and immobilisationof the gel (Fig. 4b)-was usually associated withhigh-amplitude echoes from a taut posterior hyaloidmembrane.(2) Localisation of diffuse or dispersed echoes to oneor other vitreous compartment, the other compart-ment being clear or containing a different echo

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Rapid B-scanning of the vitreous

Fig. 4 Posterior vitreousdetachment(a) Right eye: irregular echoesfrom posterior hyaloid membrane;fibrovascular stalk arising fromdisc(b) Left eye, deviated nasally:aniridic and aphakic; gelretraction and haemorrhage;thickened immobile anterior andposterior hyaloid membranes(c) Left eye: dense intragelhaemorrhage and two vitreoretinaladhesions(d)Right eye, deviated nasally:diffuse echoes from blood inretrohyaloid space and clear gel

density (Fig. 4c and d). Thus, intragel echoes wereoften bounded by a clear retrohyaloid space (Fig. 4c),or an acoustically clear gel was delineated by diffuseechoes from the retrohyaloid space (Fig. 4d). Insome patients the vitreous gel was immobile (Fig. 4d)or moved without significant change in contour,indicating gel contraction without collapse. In othercases, however, jerky after-movements of theposterior hyaloid interface characterised gel mobility.Extreme mobility of the gel was seen in myopeswith a bleeding retinal tear and in most cases ofvitreous haemorrhage due to retinal branch veinocclusion; such a pattern signified posterior vitreousdetachment with gel collapse (Fig. 5a and b).Echoes arising from one or other vitreous

compartment did not necessarily fill that compart-ment. For example, a gradual settling of a retro-

hyaloid bleed over the posterior pole sometimesoccurred during the course of ultrasonic examinationin the supine position (Fig. 5c). More commonly anapparent 'compaction' of intragel echoes along theposterior hyaloid interface resulted in a thickmembrane with a discrete, smooth, posteriorsurface (Fig. 5d), and at vitrectomy a dense non-fibrotic 'ochre' membrane was found. Such mem-branes were characteristically mobile, though thethicker the membrane the more restrained the gelafter-movements became. No ultrasonic evidence ofcompaction of blood from the retrohyaloid space onto the posterior aspect of the hyaloid interface hasbeen observed to date.The degree of contraction of gel volume, the

extent of residual vitreoretinal adhesion, and themobility of the gel were all variable. In eyes with a

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Fig. 5 Posterior vitreousdetachment(a) Left eye, not deviated: intragelhaemorrhage temporally; clearretrohyaloid space nasally.(b) Same eye as 5(a), deviatednasally: intragel haemorrhagenow on nasal side; clearretrohyaloid space temporally(c) Left eye: dense haemorrhagein retracted gel and thickenedposterior hyaloid membrane;retrohyaloid haemorrhagesediments on to posterior retina

(d) Left eye: dense intragelhaemorrhage showing 'compaction'posteriorly and tethering at themacula-an ochre membrane

minimally contracted mobile vitreous body the geltended to settle against the retina under theinfluence of gravity in the supine position. In suchcases dynamic testing was necessary in order toseparate the vitreous and retina and to identifypoints of true vitreoretinal adhesion, which might beextremely tenuous, for example, after neovascularisa-tion due to retinal branch vein occlusion. Tumoursor retinal detachments underlying the haemorrhagecould also be discovered in this way.

(C) DETACHMENT OF THE RETINA (Fig. 6)Detached retina produced a regular continuoussheet of high-amplitude echoes which encroachedon the vitreous cavity. When the detachment wasextensive and bullous, the membrane typicallyshowed undulating after-movements on dynamic

testing and was usually characterised by attachmentsat the ora serrata and optic nerve head (Fig. 6aand b). The site of communication between thevitreous cavity and the subretinal space in eyes withrhegmatogenous retinal detachment was detectedonly in cases of giant retinal tear or dialysis (Fig. 6cand d). The subretinal space was generally clear,though subretinal haemorrhage or tumour wasoccasionally present.

In many eyes there were also acoustic signs ofinvasion of the vitreous cavity by red blood cells orpigment cells (Fig. 6b) or evidence of posteriorvitreous detachment (Fig. 6a and d). In tractionretinal detachments a taut posterior hyaloid mem-brane typically inserted into the height of animmobile elevation of the retina. Alternatively, ifthe detachment resulted from transgel traction-band

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Fig. 6 Detachment of the retina(a) Left eye: detached retinatethers at the disc and ora

serrata; mobile posterior hyaloidmembrane(b) Left eye, deviated nasally:totally detached retina; pigmentinvasion of gel.(c) Left eye: giant traumaticretinal dialysis; gel attached tofolded temporal retina and parsplana; shallow nasal retinaldetachment(d) Right eye: giant retinal tear;folded-over temporal retina atdisc; detachment nasally; grossgel retraction and taut posteriorhyaloid membrane(e) Right eye, deviated nasally:vitreous retraction; epiretinalfibrosis; 'morning glory' retinaldetachment; retinal cyst(f) Left eye: retinal detachmentsecondary to anterior vitreoustraction; pars plana is detachedbut posterior retina is flat;posterior vitreous detachment(mobile on dynamic testing)

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formation or from severe contraction of epiretinalmembranes, the posterior hyaloid could be quitemobile. In eyes with massive preretinal retractionfibrous proliferation along the posterior hyaloidinterface typically resulted in a taut, immobile sheetof high-amplitude echoes across the vitreous cavity(Fig. 6d and e). Associated epiretinal membraneformation was suggested by retinal immobilitytogether with thickening and shortening of theretina (Fig. 6e), while in some cases the epiretinalmembranes were discernible between the retinal folds.Detached retina was usually readily differentiated

from a vitreous membrane, which generally gave riseto an irregular sheet of echoes of lower amplitudeand greater mobility than retina with discrete orabsent attachments posteriorly (Fig. 4a). Similarly,although elevation of the neuroepithelium sometimesextended anterior to the ora serrata in tractionretinal detachments (Fig. 6f), there was seldom anyreal source of confusion with a choroidal detachment(Fig. 2c). However, some difficulty was experiencedin differentiating a very shallow traction detachmentof the posterior retina from epiretinal fibrous tissueor a taut fibrous minimally detached posteriorhyaloid membrane. Similarly, a dense posteriorhyaloid membrane tethered by a wide adhesion tothe optic nerve-head sometimes simulated a totalretinal detachment. In such cases particular attentionwas paid to dynamic and tonal features such assigns of compaction.

Discussion

Recent advances in vitreous surgery have providedan added impetus to improving the ultrasonicassessment of the vitreous cavity. The B-scanmethod, which provides a cross-sectional image ofthe interior of the globe, is undoubtedly the mostuseful technique in the investigation of patientsawaiting vitrectomy. Standardised A-scan systems(such as the Kretztechnik 7200 mA) providequantitative data on intraocular echoes such thatdetached retina can be differentiated from a vitreousmembrane in many cases (Ossoinig, 1972). However,vital dynamic and topographic characteristics ofvitreous pathology are much more readily determinedby rapid B-scanning, and we use the A-scan toprovide supplementary information in relatively fewcases.Although contact scanning offers certain advant-

ages in respect of preparation time and patientacceptability, water-bath coupling eliminates prob-lems associated with working in the near-field of thetransducer and also permits echoes from the anteriorsegment to be displayed. Furthermore, a wide lineartransducer excursion allows landmarks on both sides

of the globe to be represented simultaneously,providing a good field of view of both anterior andposterior structures with minimal geometricaldistortion of the display. One potential problem oflinear scanning, of course, is the inability to displayflat structures which are not at approximately normalincidence to the sound beam. This can be overcomeby examining the eye in different directions of gaze,so structures become more favourably orientated tothe beam. Thus, compound scanning capability hasbeen found to offer no real advantage in theassessment of the vitreous cavity.The Moorfields system combines several features

essential for complete ultrasonic assessment of thevitreous cavity, in particular real-time imaging andgood tonal quality. Furthermore, resolution ismaintained despite spontaneous eye movements andduring dynamic testing. In our hands the limitedreal-time scanning facility and lack of tonal qualityof the Sonometrics Ophthalmoscan are considerabledrawbacks to adequate previtrectomy assessment.The possibility of operator-induced errors (such asoverwriting) from a manual scanning system, unlessused in conjunction with a scan converter, is afurther disadvantage.With the Moorfields B-scan system dynamic

vitreoretinal interrelationships can be graphicallyillustrated in a variety of conditions. Thus theindependent mobility of the vitreous gel and theposterior edge of giant equatorial retinal tears maybe contrasted with the attachment of vitreous gel todetached pars plana and peripheral retina in gianttraumatic retinal dialyses. In other rhegmatogenousdetachments the process of vitreous retraction canbe followed, the posterior hyaloid changing from athin mobile interface to a taut fibrous membrane(designated a 'cyclitic' membrane in some of theultrasonic literature). When associated with afunnelled 'morning glory' retinal detachment,echoes from this membrane contribute to the so-called 'triangle sign' (Fuller, 1976), which has beenconsidered to indicate inoperability of the retinaldetachment by vitrectomy and membranectomy.Nevertheless such detachments can sometimes be re-attached by silicone oil injection into the retrohyaloidspace. We believe gross shortening and fixed foldingof the retina are the best guides to inoperability.

Finally, repeated B-scanning has also allowed thedevelopment of posterior vitreous separation to befollowed in cases of haemorrhagic invasion of thegel. Such patients often complain of a furtherreduction in vision some time after initial visual loss,and dynamic testing suggests that a centrifugationor compaction of intragel particles has occurredowing to increased gel movement following vitreousdetachment. We hesitate to use the term 'organised

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vitreous membrane' to describe such an arrangementof haemorrhage, since 'organisation' implies massivefibrovascular invasion and immobilisation of a long-standing haemorrhage, none of which featurescharacterises ochre membranes.

We thank Mrs Sarah Cole for her help in typing themanuscript.

This work was supported by the Medical ResearchCouncil.

References

Aldridge, E. E., Clare, A. B., and Shepherd, D. A. (1974).Scanned ultrasonic holography for ophthalmic diagnosis.Ultrasonics, 12, 155-160.

Baum, G. (1964). Ultrasonography in clinical ophthalmology.Transactions of the American Academy of Ophthalmologyand Otolaryngology, 68, 265-276.

Bronson, N. R. (1972). Development of a simple B-scanultrasonoscope. Transactions of the American Ophthalmo-logical Society, 70, 365-408.

Coleman, D. J. (1972). Reliability of ocular and orbitaldiagnosis with B-scan ultrasound. American Journal ofOphthalmology, 73, 501-516.

Fuller, D. (1976). Ultrasonographic identification of massiveperi-retinal proliferation in eyes with opaque media.Presented at the tenth meeting of the Jules Gonin Club,Lausanne, June 1976. Modern Problems in Ophthalmology.In press.

Oksala, A. (1963). Experimental and clinical observations onthe echograms in vitreous haemorrhages. British Journal ofOphthalmology, 47, 65-70.

Ossoinig, K. C. (1972). Clinical echo-ophthalmography. InCurrent Concepts of Ophthalmology, Vol. 3, pp 101-13.C. V. Mosby: St. Louis

Purnell, E. W. (1966). Ultrasound in ophthalmologicaldiagnosis. In Diagnostic Ultrasound, p. 95. Edited by C. C.Crossman, J. H. Holmes, C. Joyner, and E. W. Purnell.Plenum Press: New York

Restori, M., and Wright, J. E W. (1977). In preparation.

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rapid b-scanning of the vitreous · davidmcleod, marie restori, andjohni e. wright fig. 1...

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