Instrument focus

Head-borne binocular indirect ophthalmoscopy is back

Bill Harvey tries out the Figure 1 latest variation of a classic Headset BIO is a flexible method of ophthalmoscopy system and – the Keeler Spectra Plus – allows a view from and finds much to many recommend it angles

think it is fair to say that head-set binocular indirect ophthalmoscopes are rarely used in general optometric practice. It is also true to suggest that fewer students leave our universities I with adequate skill in their use. But is this a merely an obsolete technique falling into obscurity? Or is it rather a reluctance to maintain one of the more specialised techniques which does have specific advantages in certain clinical scenarios? I would suggest the latter. slit-lamp BIO. The advantages include notice naevi. If one looks at a choroidal This article aims to offer an overview better clarity of retinal view through naevus using the macular stop of direct of the technique and its advantages media opacities. As someone who instrument, the pigmentation is clearly (and disadvantages), before then primarily sees elderly patients, the seen outside the area of illumination describing my experience with a new increased quality of retinal image but invisible under the beam. The headset BIO model, the Keeler Spectra provided by BIO is significant. The intensity of the light source of BIO Plus. reason for this improved vision instruments also serves to improve is that the incident light path and the resolution of lesions (something Binocular indirect reflected light path are separate, patients do not always appreciate) ophthalmoscopy unlike with direct ophthalmoscopy. Stereoscopic viewing is useful in Interestingly, indirect illumination also analysing the nature of certain lesions. ● Advantages has the benefit of exaggerating the Large areas of minimal elevation as There are several distinct advantages appearance of pigmented lesions. It may occur, for example, with a central offered by BIO and these have driven is very noticeable when first moving serous retinopathy are often difficult its rise in popularity, primarily of to indirect how much easier it is to to view but more easily detected with

20 | Optician | 16.05.08 opticianonline.net Instrument focus

a stereo view. Also, three-dimensional Table 1 structure is more easily assessed, such Properties of condensing lenses used for headset BIO as the presence of flyover vessels at the optic disc in a glaucomatous patient Lens power, size Working distance Magnification Typical field of A large field of view is usually cited from cornea at apex obtainable view (degrees) as the main advantage of an indirect (mm) technique. Using a 20D condensing 15D, 52mm 72 4.11X 36 lens, a field of view of more than 30 15D, 45mm 72 4.10X 31 degrees is realisable. For peripheral retinal examination, a wide field of 20D, 50mm 50 3.13X 46 view is preferable. However, too little 20D, 35mm 51 3.08X 34 magnification will lead to small lesions Pan retinal 2.2, 52mm 40 2.68X 56 being missed. A good compromise is 25D, 45mm 38 2.54X 52 afforded by the Pan Retinal 2.2 (Volk), 25D, 33mm 39 2.48X 39 which delivers a 56 degree field and 28D, 41mm 33 2.27X 53 a magnification of 2.68X. A wide field is also essential for retinopathy 30D, 43mm 30 2.15X 58 assessment. Any multifocal lesion is 30D, 31mm 31 2.09X 44 more easily assessed as to extent and 40D, 40mm 20 1.67X 69 relationship of individual lesions if 40D, 31mm 21 1.61X 57 seen in one single view. Recently, many practitioners have started using the Optos Panoramic system of non-mydriatic scanning laser and appropriate lens positioning, the ophthalmoscopy which also offers an retina may be viewed way out to the excellent field of view. It should be periphery. Obviously this is useful remembered that the image with this is in assessing the potential for retinal a composite of two confocal light beam breaks and tears, or monitoring the scans and is different to the ‘real world’ extent of lesions such as retinoschisis, view offered by the headset BIO. but may be further enhanced by the The view and magnification use of a scleral depressor with which are effectively independent of the tissues approaching the ora serrata are uncorrected refractive error of the achievable. patient. Adequate assessment of a high myope with a direct ophthalmoscope is ● Disadvantages Figure 2 The loupe system difficult due to the large magnification No technique is perfect and BIO does and usually requires use of a contact have some disadvantages. Obtaining is not sufficient for a good disc lens or supplementary trial lens to gain a good view takes time and patience. assessment for example. However, the a reasonable view. This is not necessary It had been a couple of years since brightness of the light source gives a with a BIO technique. last using a headset, so for this trial I good enough resolution to make out Headset BIO is available to patients wrongly predicted the ‘riding a bike’ vascular changes. who cannot be sat at the slit lamp. scenario and instead had to relearn Traditionally, this has usually been the technique, admittedly a little more Using a headset BIO implied to be babies and infants, easily than when I first tried as a The condensing lens captures the although anyone familiar with the student. Control of the patient is key emergent light from the patient’s ‘flying baby’ technique will know to gaining a good wide field image. eye and presents this for binocular that slit lamps are still useful. Indeed, Small movements of the light source, viewing. The larger the lens and the in this author’s experience, there is lens or patient eye are enough to cause bigger the pupil the wider the field many an elderly patient who is unable massive reflections or loss of image. of view obtainable. The lower the to position themselves adequately Another obvious point cited as a condensing lenses’ power the greater at the slit lamp for any length of disadvantage, but one that is soon the magnification and the smaller the time. Headset BIO is a more flexible adapted to, is the fact that the image field, as shown in Table 1. Higher- system and allows a view from many is inverted and reversed. Some power lenses are held closer to the angles with the patient seated or lying practitioners get around this by turning patient. The view is a bright wide field prostrate comfortably (Figure 1). their record card upside down before (about 10X wider than that of direct The increased working distance recording their findings, but familiarity ophthalmoscopy). There is reasonable is often quoted as useful in reducing soon makes this reinterpretation second stereopsis and negligible alteration patient to practitioner discomfort nature. in magnification with the refractive about their proximity to one another, The obvious correlate of a large field error of the patient or examiner. There but a good strong mint can do the job of view is a reduced magnification. is an addition of +2.00D or +2.50D I find. More seriously, the working Slit-lamp BIO allows the use of lower incorporated in the viewing system so distance allows a lower power viewing powered condensing lenses which, that presbyopic examiners can view the lens (typically a 20D) to be used and when combined with the slit lamp aerial image comfortably. therefore maintain a very large field magnification, allow perfectly good of view. This means that with a fully views of specific structures such as the Use of the Spectra Plus dilated pupil (perhaps with tropicamide disc and the macula. With the headset The first obvious point to notice about and phenyephrine used in conjunction) BIO and a 20D lens, magnification the Spectra Plus is that the viewing opticianonline.net 16.05.08 | Optician | 21 Instrument focus

Figure 3 ‘Helmet’ style headset BIO Figure 4 The viewing unit is set onto the two pins before the bridge

unit is mounted on a sporty frame. The patient that their eyes are going to be frame has been designed for multiple examined using a bright light but that functions, for example holding the it will not be at all harmful. Keeler loupe system shown in Figure 2. I recommends that practitioners use had only previously used the headset their discretion when deciding on shown in Figure 3 which, for accurate the brightness and duration of any usage, takes a good deal of time to set individual examination, the brighter exactly to fit the head such that the best light ensuring adequate view may view is gained and to maintain stability well override any potential for photic on the head during use. I found the damage. sports frame easy to fit and a simple Lengthy examination should be backstrap held it firmly in place. The avoided if the eye has already been viewing unit is set onto the two pins exposed to high light levels in the before the bridge (Figure 4). preceding 24 hours, for example The power to the unit is from a during retinal photography. portable battery pack (Figure 5) which Both eyes of the patient should is pre-charged from an overnight remain open throughout the exam charging unit and, when fully charged, (Figure 7). Screwing up one eye is sufficient to last a full day’s clinic. reduces the aperture in the remaining My previous experience had been with open eye. Patients may be lain flat a wall-powered unit. The portability if the chair allows it, but I managed of the battery unit was very useful in a adequate views on patients seated clinic with several bays, as might be the upright by simply moving myself into case in a hospital or a large practice. more doubled-up positions. If this was With the rheostat on the battery pack a technique to be used repeatedly for a (attached to my belt) set at its highest long time, I would strongly recommend setting, a beam was trained at a wall lying patients down to reduce the load around 40cm away. Each eyepiece may on the practitioner’s back. then be centred to view the circular The superior periphery is easiest to patch of light by adjustment of the examine first. This entails the patient sliding inter-pupillary distance control looking up and the examiner standing (Figure 6). The height of the beam is 180 degrees in the opposite direction, adjusted by tilting the internal mirror namely towards the patient’s feet. using the lever on the side of the unit. Once the red reflex is seen, the lens is It is essential with this technique that positioned with the steeper curvature the eyepieces are central. of the bi-aspheric lens facing the As with similar units, there is a examiner. The side facing the patient choice of two filters along with the has a silver or white band at the edge. clear filter-free option most commonly Holding the lens parallel to the used. A green filter is useful for patient’s iris plane and a short distance looking for vascular anomalies (as well from the cornea with the fingers as in cases of particularly light sensitive steadied on the patient’s forehead or patients) and a blue filter may be used cheek, the anterior segment of the eye for fluorescein angiographic viewing, is seen through the lens with a red a technique unlikely to be important to reflex in the pupil. an optometrist it must be said. Moving the lens away from the Patient preparation is equally eye, the fundus image fills the lens. important. Although I managed a few If moved too far, the retinal image variable quality views on younger disappears and anterior structure is patients undilated, dilation is essential seen again. to obtain a wide view. Instruct the The remainder of the retina may

22 | Optician | 16.05.08 opticianonline.net Instrument focus

Figure 5 The portability of the battery unit Figure 6 Adjusting the eyepiece to centre Figure 7 The patient must keep both was very useful the image eyes open be examined systematically, with the on my belt meant it was easier to me a consistent and accurate view and patient encouraged to move their eye interpret and respond to the patient’s initially took about four to five practice and the lens being tilted to reduce signals of discomfort. attempts to be reasonably confident reflection. The image gained was easy to of my view. The low magnification interpret and of a good enough means I will continue to use my Ease of use resolution to visualise, for example, Super 66D for maculopathy and my I found the set-up of the headset peripheral retinal degenerative changes. SuperField for diabetic retinopathy, very easy, much easier than the more Dilation is important and this could but would seriously consider headset traditional helmet-style instrument. I limit use in a busy high street setting. BIO as my main technique for many was impressed by the fact that the unit Careful rheostat use and introducing patients requiring a good peripheral was comfortable even after repeated the green filter while trying not to retinal scan, for example when uses. I like the portability of the unit dwell on the posterior pole of the complementing a search for tobacco enabling me to move around the patient meant that poor response from dust in a suspect myope. ● patient with ease and making it easier patients was minimal. Positioning the to examine those patients not able to be lens at a constant 5cm from the eye ● For further details on the Spectra Plus, lain out flat. The rheostat adjustment and tilting to avoid bad reflections gave contact Keeler on 01753 857177

opticianonline.net 16.05.08 | Optician | 23