Television slit-lamp biomicroscopyTelevision slit-lamp biomicroscopy the slit lamp. This requires...

British Journal of Ophthalmology, 1978, 62, 644- 650

Television slit-lamp biomicroscopyA. J. BRON, D. V. KAUFMAN, AND D. HARWOOD

From the Eye Hospital, Oxford

SUMMARY The basic requirements for performing television slit-lamp biomicroscopy are outlined,and the methods of demonstrating particular features of ocular anatomy and ocular disease are

discussed. The technique has a particular role in teaching in the clinical setting.

Television has been used for many years to docu-ment and display ophthalmic procedures andclinical disorders. The modular construction of theZeiss series of biomicroscopes makes it possible tocarry out successful video-photography with theslit-lamp, using the same attachments employed fortelevising ocular surgery. This creates a mostvaluable teaching tool with some potential forresearch use. The following paper details therequirements for successful television slit-lampbiomicroscopy.

Materials and methods

Slit-lampA standard Zeiss slit-lamp may be used (Fig. 1) butthe results may be affected by differing combinationsof accessory equipment.

Video equipmentThe basic requirement for simple display work(surveillance) is a television camera and monitor.To record observations a videotape recorder (orVTR) is required. It is not the purpose of this paperto discuss the relative merits of different commercialequipment, since the final choice will depend onfactors of cost or the adaptation of existing equip-ment. The present report rests on experience gainedwith the Sony camera AUC 3420CE and portableVTR (AU 3420CE) (i.e.. the Sony 'Rover' system)and Pye 11 inch (28 cm) precision monitor(842843/01) for black-and-white. For colour aShibaden camera (HV 1500) x (HV9015) was usedwith a Hitachi 18 inch (45 cm) colour monitor(CM 181U). The Hitachi colour VCR with thePal-Secam cartridge system was used (SV 630).Also in the United States the Circon Camera andSony Trinitron monitor have proved satisfactory.The slit-lamp and video requirements are summa-rised in Table 1.

Address for reprints: Mr A. J. Bron, FRCS, The EyeHospital, Walton Street, Oxford OX2 6AN

TECHNICAL POINTS

Field of viewFor general surveillance of the eye in diffuse whitelight it is important to be able to display the wholeof the palpebral aperture without 'scanning' with

Monitor

Primarylightsource

a- Obj lensb- Mag. changec - Beam spl itter 70:30d- Photo adaptor

Video taperecorder

e- Primary light sourcef -Optional auxiliary light source (fibre optic)g- Junction boxFig. 1 The arrangement of the television slit-lampbiomicroscopy

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Television slit-lamp biomicroscopy

the slit lamp. This requires that the field of view in-the horizontal meridian at the lowest magnificationof the slit lamp is at least 3 0 cm. This is also im-portant when examining the tear film using fluores-cein in the conjunctival sac, since an excellentopportunity is afforded to watch both the marginalstrip of tears and precorneal tear film simultaneously.The fields of view for varying combinations of

the slit lamp, magnification change, and photo-adaptor combinations are given in Table 2.

LIGHT SOURCESThe primary light source (slit source) may be usedfor surveillance of the eye in diffuse illumination(white light) or for fluorescein work (blue light).

Table 1 Slit-lamp requirements for televisionhiomicroscopy

1. Zeiss slit lamp (100/16)or photo slit lamp

2. Objective lens100 mm125 mm Photoslit

3. Single beam splitter (70:30)

4. Photo-adapter137 mm107 mm

5. Magnification changeManualZoom

6. Illumination sources(a) Slit source (primary illuminant). Overload facility of value(b) Additional source (secondary illuminant)

7. Microscope height adjustment(a) Joystick (manual)(b) Column (manual)(c) Motorised

8. Video equipment(a) Camera(b) Monitor(c) VTR

Table 2

Photo- Smallest Smallest Smallestadapter horizontal diagonal vertical

Slit lamp number diameter diameter diameter(mm) (mm) (mm)

Regular Manual 137 15 19 11107 20 25 15

Zoom 137 12 15 9107 16 20 12

Photoslit Manual 137 20 23 15107 25 29 18

Zoom 137 16 18 14107 13 16 10

Diffuse illuminationThe pool of light can be enlarged to cover the wholeof the palpebral aperture by placing a standarddiffusing filter over the slit source. Alternativelyless costly diffusers are easily produced from paperor opalescent plastic sheets cut to size.

Fluorescein work

Exciter filterIt is important to use an interference filter (e.g.,Baird Atomic No. 5 Spectrotech SE 40 or BalzarFITC 4) to produce the blue exciter source, sinceeven with such a source the intensity of illuminationmay be less than optimal. With a blue exciter filterover the 1° source, opened wide, the pool of bluelight does not encompass the whole palpebralaperture. It would be useful to enlarge the pool oflight, but this problem has not yet been solved withexisting equipment. Two solutions have beenconsidered. (a) The pool of light can be enlargedby placing a diverging lens over the 1° light sourcein addition to the blue filter. However, this soreduces the intensity of illumination that thetechnique appears to have little application. (b)An alternative technique, which will probably beadopted ultimately, is to place the blue exciterfilter over a secondary (e.g., fibreoptic) light sourcewith delivery of the light close to the eye.

Barrier filterA barrier filter, such as a gelatin absorption filter(e.g., Ilford 110) placed over the objective lens ofthe slit-lamp is essential for examination of themarginal strip of tears, the preglobar and precornealtear films, and for negative and positive staining ofthe cornea (e.g., dry spots and ulcers). A matchedinterference filter is the ideal to provide maximumillumination, but a suitable absorption filter will do.A barrier filter is both unnecessary and unde-

sirable for the demonstration of the rings of appla-nation during applanation tonometry. Use of thebarrier filter reduces illumination to unsatisfactorylevels, and the rings are clearly visible without it.

Secondary light sourceA bright secondary illuminant is required, particu-larly to provide background illumination duringslit microscopy. Unfortunately the secondary sourceof the photoslit lamp is not intense enough. How-ever, it is easy to supply another lamp for thispurpose, and a fibreoptic source controlled by arheostat and located close to the objective lens ofthe slit lamp proves to be satisfactory.

Televising the slit imagePlacing the slit image on the screen is at first disap-

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A. J. Bron, D. V. Kaufman, and D. Harwood

Fig. 2 Slit picture of theanterior segment

Fig. 3 Lower lid margin seen bybroadfocal illumination

n ~~~~~~~~~~~~~~~...

"

pointing because of the great contrast between thelight on the object of interest, e.g., cornea or lens,and the surrounding structures, which are notilluminated directly. This problem is readily nego-tiated by adding a secondary fibreoptic source (seeabove) to provide background illumination. Thistechnique is identical to that required for slitphotography using a photoslit-lamp camera (Fig.2).

Scleral scatter illuminationWith the pupil dilated scleral scatter illuminationwill demonstrate epithelial corneal oedema. The

available intensity from the primary light source isnot adequate to do this well, however.

MANOEUVRING THE MICROSCOPEWhen recording sequences for clinical documenta-tion it is important to achieve smooth transitionsfrom one mode of examination to another. Theobserver must retain focus when shifting the micro-scope to different points of interest in the eye orwhen changing magnification. The following pointsmay be made:

Horizontal traverse of the microscope is achievedeasily and smoothly with the joystick control.

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Fig. 4 Perilimbal bulbarconjunctival vessels (diffuseillumination)

........ .... ................ . -:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..;..ha~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...MNAW..:

Vertical movement may be achieved adequately bymanual controls such as the knurled ring on thecentral column or, better, rotation of the joystickcontrol. Motorised controls with the switch are

within easy reach of the hand holding the joystick.The weight of the camera becomes a critical con-

sideration during the 'up' movement and may on

occasion demand manual assistance.The click-stop manual magnification change is

satisfactory, but not ideal, since a series of darkperiods occur on the screen at each change, whichinterrupts the continuity of observation. The foot-

Fig. 5 The iris collarette seen byh*diffuse illuminationh.. ....... ....:....I... ..

operated motorised zoom is ideal for televisionslit-lamp biomicroscopy because it allows the userto convert a survey picture into a detailed scrutinyat high magnification. Both the motorised zoomand vertical movements permit smooth titlingusing typescript. This can reduce editing problemsat a later date.

APPLICATIONS OF TELEVISION BIOMICROSCOPYThe majority of anterior segment features studiedwith the slit-lamp are amenable to scrutiny by slit-lamp television biomicroscopy.

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Fig. 6 Cortical lens opacitiesseen in the dilated pupil(photographs taken from 'stopframe' are of lower quality)

Fig. 7 Gonioscopy: a lightlypigmented open angle, with visibleiris processes

...........

The lidsThe lid margins, including lacrimal puncta andMeibomian orifices, may be demonstrated at highmagnification with diffuse or focal illumination(Fig. 3). Expression of Meibomian oil may be shownby catching the specular reflex from the oil dome.The palpebral conjunctival vessels may be shownwith diffuse illumination, or at high magnification,with red-free light.

The GlobeThe globe vessels are well demonstrated in diffuse

light, and at high magnification red-cell flow maybe demonstrated. To show the limbal vessels, i.e.,the marginal corneal arcade, retroillumination usingthe slit source is satisfactory, and a backgroundilluminant should also be used. The contour of theglobe can be examined in specular light from thetear film (Fig. 4).

The tear filmWith high magnification and reduced intensity ofillumination the typical coloured interference pat-tern produced by the surface Meibomian oil may

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Table 3 Video techniques

Primary Secondary Magnifi-Technique Purpose source source Filter cation Notes

Survey General detail + - Diffuser Any Low mag. to show whole of(diffuse illumination) palpebral aperture. High mag.

for conjunctiva, globe, vessels,Meibomian orifices andspecular reflex of tear film

Fine slit Thickness of objects in + + - Any (1) Show thickness and shape(focal) section. Also location of Added fibre- of cornea

depth of objects in section optic or (2) Depth of chamberother source (3) Opacities in cornea and lens

(4) Flare and cells in anteriorchamber?

Broad slit Used with slit angled + + - For punctate epithelial keratitis(focal) obliquely to illuminate opaque microcysts

objects which scatter light

Retroillumination Shows objects in silhouette; (Fine or + - Any Limbal vessels, e.g., pannus,(against iris) refractile objects broad slit) (May not be corneal lesions, e.g., clear

needed for microcysts, superficial cornealHP) disorder (SCD)

Retroillumination As above - - Any Ideal to show fine detail of(against red reflex: (Broad slit) structures in cornea or lens,slit offset to one side differing from surroundingor other to avoid structures in refractive index,corneal reflex) e.g., microcysts and SCD

Specular reflection To examine: + - - Any Endothelial mosaic is visible at(a) specular reflex of tear film, high magnification

e.g., interference pattern(b) Endothelial specular zone(c) Internal specular reflection

Scleral scatter To show light-scattering + - LP-HP Best at low power with TV(broad strip at either structures in the cornea, because of low emittence levellimbus) e.g., epithelial oedema

Dyes: (a) Negative staining follicles; + ?+ Blue exciter LP-HP HP poor at low light levels,Fluorescein fingerprint lines Large pool yellow barrier

(b) Positive staining punctate + ?+ Blue exciterepithelial erosion, ulcer Large pool yellow barrier

of light(c) Applanation + - Blue filter

only

HP = high power. LP = low power

be seen or accentuated by narrowing the palpebralaperture, using specular examination. The marginalstrip and tear film debris are also demonstrated.With the use of fluorescein and the appropriate

exciter and barrier filters (see above) the marginalstrip, prebulbar, and precorneal tear films aregraphically demonstrated, as is the replenishmentof the tear film which accompanies each blink.Negative and positive staining can also be shown.

The corneaNumerous features of corneal disease may bedemonstrated by slit, focal, and retroillumination.The fine detail of vesicular epithelial oedema,finger-print lines, and bleb-like dystrophies arewell seen by retroillumination against the iris or redreflex. Scars may be shown in slit section and diffuseor focal illumination, while density may be suggestedby retroillumination. The latter technique has also

proved ideal for demonstrating corneal vessels andsplits in Descemet's membrane in buphthalmos.Scleral scatter will demonstrate epithelial oedemaagainst the dilated pupil. Specular examination isjust capable of resolving the cells of the endothe-lium, but the tear film highlight diminishes thevalue of using this technique except to demonstratehow it is done. It should be possible in future tolimit the occurrence of such 'hot spots' on thescreen electronically.

The irisThe architecture of the iris and the mobility of thepupil are shown well by diffuse illumination (Fig. 5).

The lensWith the pupil dilated the detail of a clear lens,including the anterior clear zone, may be shown inslit section. Certain lens opacities may be shown in

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focal illumination (Fig. 6) while others are best seen

against the red reflex. Still other opacities may bedemonstrated as contour changes within the cortexby means of the specular technique.

The vitreousThe normal vitreous architecture is difficult todisplay, but significant opacities may be shown infocal and retroillumination.

The fundusWith a fundus contact lens in place the disc and itsvessels can be shown. Venous pulsation at the discmay be a striking phenomenon. Demonstration ofmacula and vessels, lesions such as new vessels, andhaemorrhage has been achieved but has not beenfully satisfactory. Colour is essential here, sincecolour contrasts are important.

GonioscopyThe angle structures are well seen, so that televisionhas particular teaching value in this area (Fig. 7).Some of the greatest problems encountered occur

when illumination is moved from a highly reflectingsurface such as the sclera to a poorly reflectingsurface such as the iris. This may be most marked,for instance, with a dark brown iris. The problemmay be overcome at times by using secondary illu-mination, but at others it may have to be acceptedthat in a given patient it may not be possible todisplay adequately a given mode of examination on

the television screen.

Discussion

The technique of television biomicroscopy has itsgreatest use in the teaching of medical students. Theteaching of ophthalmology is often condensed andmakes severe demands on the keenest of teachingstaff. One of the greatest problems relates to thedifficulty of making observations accessible to the

student. By using the television slit lamp the teachercuts down a great deal of the repetition whenstudents are obliged one by one to look down anobserver tube. Instead he can point out featureswhich appear on the screen and indeed may makeadjustments to the slit lamp while observing thescreen himself.

Observations which are usually not easy todemonstrate, such as the applanation rings or thechamber angle, can be discussed with the studentgroup looking at the phenomenon at the same time.The dynamic components of the features examined,such as blinking, blood flow, pupil constriction,pulsation of the applanation rings, and the venouspulse at the disc, all add to the interest generated bythe technique. It is clear that the resolution of mosttelevision systems is sufficient to demonstrate allthe clinical problems normally studied with thebiomicroscope. There is, however, room for im-provement, and it is likely that selection of low-weight, high-resolution cameras, of low-light-levelcameras, the use of image intensifiers, and improvedillumination sources will bring about these improve-ments. A streamlined custom-built television slitlamp, embodying some of the ideal features men-tioned above, would also be a welcome addition tothe clinical armamentarium.

Other uses and improvement may be foreseen forthe future. The use of a 'special effects generator'would allow the combination of clinical observa-tions with temporally related information on thesame screen. An example would be to combine theapplanation rings with the pressure reading dialduring tonometry, or of disc vessel pulsation duringophthalmodynamometry, with a simultaneous read-ing of force applied to the globe. It must be antici-pated that fluorescein angiography of the anteriorsegment will be feasible by this technique, and thatthe time after injection could similarly be displayedon the screen.

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