Head Band Indirect Ophthalmoscopy
by S.Barnard. BSc(Hons).FCOptom.DCLP.FAAO.and A.Field..MSc.FCOptom.DCLP.FAAO.
In recent years head-band indirect ophthalmoscopes have been developed
that enable the practitioner to converge the entrance and exit
pupils. This very important improvement means that the optometrist
can examine every patient using this technique until he/she has
gained enough experience. Like SLM, dilation will then provide
a technique that will become a easy task for the optometrist.
The advantages of this method includes the provision of (a) an
excellent field of view (approximately 40°), (b) the
ability to move around the patient and therefore enlarge upon
the field of view, (c) a stereoscopic view, (d) excellent illumination
and (e) scleral indentation.
These characteristics lend head-band indirect ophthalmoscopy
to be secondary to SLM indirect ophthalmoscopy for the
routine examination of the fundi of patients in shared
care or co-management programmes involving glaucoma and diabetes.
However, the head-band indirect is particularly useful for examining
fine variations in the fundus colour that may be caused by tumours
for example, and for viewing the more peripheral areas of the
retina. Useful for suspected detachments, floaters associated
with photopsia, and high myopes. This facility may well be useful
in co-management programmes monitoring post-operative detachment
surgery, or the monitoring of peripheral lesions that may have
a predisposition to detachment.
The head-band indirect technique produces a real, inverted and
laterally reversed fundus image. Presently available lens powers
range from +14D to +30 D. Lower power lenses provide higher magnification
but offer a smaller field of view, and below about +20D, the lens
needs to be held further from the patient's eye and may not be
comfortable for steady positioning. Lenses above +20D may give
less magnification than is desirable.
General procedure for head-band binocular
indirect ophthalmoscopy.
Preparation
- Dilate your patient. This will usually take 20 to 30 minutes
following drug instillation. (see section on mydriasis).
- It will help to darken the room so that minimal lamp intensity
can be used.
- It will be preferable to have a patient chair that fully reclines,
enabling the practitioner to move around the patient and hence
gaining a full 360° traverse of the fundus. (Fig 1). If a reclining
chair is not available, the practitioner will have to make more
use of the patient fixating peripheral targets, and this will
often mean that a smooth traverse of the peripheral fundus is
not possible.(Fig 2)
Fig 1 |
Fig 2 |
- Instruct the patient to fixate a target in the primary position,
stare wide and to blink normally. The primary position for a
reclining patient will be immediately above his or her head. For
a seated patient this will be over the practitioner's shoulder.
Alignment of the head-band ophthalmoscope.
- Place the ophthalmoscope on the head and adjust the straps
for maximum comfort, and making sure that the viewing part of
the ophthalmoscope can be positioned in front of the practitioner's
eyes at a comfortable angle. Adjust the wearing position so that
the ophthalmoscope is not tilted in relation to the practitioner's
eyes. If worn, there is usually ample room for the practitioner
to wear his/her spectacles as well.
- If the practitioner is presbyopic, there is often a +2D lens
available to insert into the ophthalmoscope system
- Face a wall approximately 40 cms away, and adjust the illumination
mirror such that the illumination field is vertically centralised
to the observation ports.
- Move the viewing ports horizontally by adjusting the interpupillary
distance to align with the illumination field.
- Adjust the illumination system to give the required field,
usually the widest available. Set the illumination at a medium
intensity to start with. Use the yellow lens to reduce the amount
of blue light on the retina, and if available, using a diffuser
may widen the field of illumination.
- If being used on a non-dilated eye, make sure the system is
set with the illumination and viewing systems at maximum convergence.
This setting reduces the stereoscopic separation, and so should
be set to the maximum separation that is able to produce a stereoscopic
image.
Procedure.
- The practitioner should first illuminate the patient's pupil
area by pointing the head and hence the illumination towards the
patient's eye.
- Interpose the BIO lens close to the eye about 2 cm, and centre
the lens on to the pupil. The lens should be held with the more
convex side towards the practitioner. Many lenses have a white
or silver line indicating the side to be held closest to the patient.
- Pull back the lens away from the patient's eye, at the same
time taking care to keep the illumination centred on the pupil.
Whilst withdrawing the lens, the practitioner will find a distance
that provides an optimum field of view. This should be approximately
at the focus of the lens, i.e. 5cms from the pupil using a +20D
lens. The practitioner should make sure he/she is able to rest
some part of the hand on the patient's head to stabilise the BIO
lens.
Having obtained an image filling the BIO lens, the fundus may
then be examined by moving around the patient if reclining, or
by redirecting the patient's fixation if seated. It is at this
point that it becomes obvious that it is definitely preferable
to have the patient reclining if possible.
Fine tuning the fundus view
- Tilt the BIO lens to remove undesirable reflections.
- Adjust to system convergence to suit to pupil size.
- It may be helpful to adjust the illuminating mirror and point
the illumination system slightly higher or lower than centre.
- When looking to the peripheral retina, and hence though an
oblique pupil, it will be helpful to align the head with the long
axis of the oblique pupil. This will allow a wider exit pupil
for the stereoscopic viewing system, and hence help to keep your
stereoscopic image. With a reclining patient this is easy to do,
but examining a seated patient will when viewing the lateral aspects
of the retina, require the practitioner to tilt his/her head 90°,
and this is obviously not very comfortable.
Hints and tips for successful Head-band BIO.
- Practitioners should practise on non-dilated eyes. Practical
only with ophthalmoscopes that have converging systems.
- It is essential to have a steady hand, and the practitioner
must rest part of his hand on the patient's head.
This is particularly so with non-dilated pupils.
- Remember the Imaginary Convex Eye technique.
- A better peripheral view will be obtained using a +28D or
+30D lens and scleral indentation. However, a higher power lens
will reduce magnification. Conversely, a better view of the optic disc
will be obtained with lenses of a power in the +15D range.
- Fundus drawing should either be done from behind the patient
if reclined, or with the record card inverted if seated.
Scleral Indentation
To take full advantage of head-band binocular indirect ophthalmoscopy,
the practitioner should learn to perform scleral indentation.
The procedure is not as difficult or as uncomfortable for the
patient as may be imagined. Neither will indentation worsen
or cause retinal detachments. It is however relatively time consuming,
and therefore special arrangements for appointments will generally be necessary.
Preparation
- Have your patient ready as for head-band indirect ophthalmoscopy
previously described.
- The patient MUST be fully reclined. The practitioner
should preferably be seated so that his/her head height is just
a little higher than the patient's head.
- Instruct the patient to fixate a target immediately above
the head, stare wide and to blink normally. (Fig 3)
Fig 3
Alignment of the head-band ophthalmoscope.
Procedure.
- The optometrist should choose a thimble or other type of depressor
tool that feels comfortable to hold.
- Sitting to one side of the patient, the optometrist should
gently place the probe on the outside of the lid. A starting
position would be a little higher than the inner canthus, just
missing the caruncle, and at 180° to the observation angle. (See fig 3).
- The practitioner should next illuminate the patient's pupil
area by pointing the head and hence the illumination towards the
patient's eye, and interpose the lens as previously described.
- Next, the practitioner should very gently and tangentially
move the probe into the fold of the lid. It need not be moved
in very far, perhaps about 8 mm from the limbus. The patient should
not feel any untoward discomfort, and he/she should be instructed
to mention if the procedure becomes uncomfortable, as this will
probably mean the practitioner is pushing onto the eyeball.
- Look for the indentation in the lower field of the BIO lens,
as it will be inverted. Keep the depressor moving slightly to
aid finding the indented retina.
- Move around the patient to cover all angles, approximately
45° for each setting, and placing the probe at 180° to the point
of observation.
Hints and tips for successful scleral indentation.
- Practitioners should practise on non-dilated eyes, pupils
above about 4 mm will be usable. Practical only with ophthalmoscopes
that have converging systems.
Yes, it is possible.
- It is essential to have a steady hand, consequently the practitioner
must rest both hands on the patient's
head.
- The 3o/c and 9o/c positions can be indented
by placing the depressor slightly above on the upper lid (2o/c
and 10o/c), and sliding the probe downwards to move
it into the inner or outer canthal positions. If this is difficult,
indentation can be done applying the probe to the sclera without
the intervening lid, but topical anaesthesia should be used to
make your patient comfortable.
- Remember the Imaginary Convex Eye technique.
- A better peripheral view will be obtained using +28D or +30D
lenses.
- Fundus drawing should be done from behind the patient.
Pupil dilation
To obtain an adequate view when not practising, ophthalmoscopy
should be carried out under mydriasis.
Choice of drug
The drug of choice is tropicamide 0.5% or 1% ( Minims Tropicamide,
Mydriacyl) because it is both fast acting and of short duration
as compared to cyclopentolate hydrochloride. It will abolish
the pupil light reflex which is advantageous when carrying out
BIO and fundus photography. Post-examination visual needs of
the younger patient need to be considered since tropicamide has
the potential for causing significant, albeit short-lived, cycloplegia.
Phenylephrine is available in 2.5% and 10% concentrations. Minims
Phenylephrine are available in both percentages. The 2.5%
is generally adequate for most patients and the 10% concentration
is rarely indicated in optometric practice. Neither the light
reflex nor accommodation is abolished with sympathomimetics. Sphygmomanometry
should be carried out on all diabetic patients of 40 years of
age and older before the use of phenylephrine is considered.
To obtain optimal mydriasis a combination of both drugs is indicated
whenever possible, for example a drop of phenylephrine 2.5% in
each eye followed a few minutes later by a drop of tropicamide
1%.
Precautions
The use of phenylephrine is contraindicated in the presence of
vascular hypertension, a history of cardiac disorders, stroke
or aneurysms and when the patient is using certain medications
including monoamine oxidase inhibitors (e.g. phenelzine, Nardil),
alpha-2 adrenergic agonists (e.g. clonidine hydrochloride, Catapres,
Dixarit), adrenergic neurone blockers (guanethidine monosulphate,
Ismelin).
The use of sympathomimetics should be avoided in optometric practice
with long-standing diabetics particularly those with known marked
background, pre-proliferative or proliferative retinopathy. Such
patients are more likely to manifest a peripheral neuropathy which
may include sympathetic denervation. These patients may show "super-sensitivity"
to phenylephrine, the instillation of which may have an unwanted
and exacerbated effect on the cardiovascular system.
Guidelines for dilating patients with narrow angles
- Care must be taken in the presence of a very narrow or
shallow angle which has not been dilated previously. If the practitioner
is confident that mydriasis will provoke angle closure,
then an ophthalmological opinion should be sought.
(Van Herick, W., Shaffer, R.N., and Schwartz)
- If the patient has been dilated previously, with no induced
rise in ocular tension, the practitioner can dilate again.
- In all cases of angle grades 1 and 2, the patient's ocular
tensions should be checked before instillation of the drug(s)
and again 30 minutes after completing the examination. It should
be noted however that there can be rises in pressure some hours
later.
- The practitioner should always bear in mind that failure to
examine the fundus properly under mydriasis may lead to
serious retinal changes being missed. The risk of provoking
angle closure must be weighed against this in the knowledge
that, in due course, a predisposed patient is, in any event,
very likely to experience a sub-acute or acute glaucoma attack.
Post mydriatic management
- The use of a parasympathomimetic such as pilocarpine to routinely
reverse mydriasis is probably not indicated for most patients.
The visual effects of tropicamide and phenylephrine are either
very short in duration or insignificant and for most patients
there is little to be gained by the instillation of a miotic.
It should also be noted that pilocarpine may cause anterior displacement
and steepening of the lens in some eyes. Thus there may be a
very slight risk of provoking pupillary block glaucoma in predisposed
eyes. Hyperopic eyes and/or eyes with shallow anterior chambers
are considered to be more at risk (Doughty, 1995).
- In the very unlikely and rare event of a significant
rise (> 8 mm Hg) in ocular tensions due to angle closure
following tropicamide and/or phenylephrine mydriasis, the practitioner
should be aware of management strategies for the patient. Ophthalmologists
differ in their philosophies and individual optometrists should
discuss with their local consultant ophthalmologist what intervention
should be employed in these circumstances. One treatment strategy
would be to instil 1 drop of pilocarpine 1% or 2%. After 15 minutes
(q 15 min) the pressures and angle should be checked again and
another drop instilled if necessary. This procedure may be repeated
until the attack is broken For some patients 1 or 2 drops may
be sufficient to break the attack; in others, 4 to 6 drops might
be required (Doughty, 1995). One should proceed cautiously with
aggressive use of pilocarpine drops (q 15 min) if tonometry indicates
excessively high intraocular pressures (i.e. > 50 mm Hg) since
it has been suggested that such a use could exacerbate a pupil
block; lowering the intraocular pressure with an oral carbonic
anhydrase inhibitor should be the initial goal in such patients
prior to the aggressive use of the miotic.
Alternatively, the local ophthalmologist may prefer the optometrist
to instil one drop of pilocarpine before referring the patient
(preferably under escort) to the hospital Accident and Emergency
Department or even send the patient directly to A & E with
no pharmacological intervention. The optometrist should ensure
that there is a practitioner available to receive the patient.
References and further reading
Doughty, M. J. Drugs, Medication and the Eye, Chapter
9, Glasgow-Caledonian University, 1995
Field.A and Barnard N.A.S., Imaginary convex eye.
An aid to indirect ophthalmoscopy. Optometry Today, May 31, 22,
1993
Fingeret, M., Casser L., Woodcombe, H.T. Atlas of
Primary Care Procedures, Appleton & Lang, Norwalk, 1990
Prokopich, C..L., and Flanagan, J.G.
Indirect fundus biomicroscopy. Ophthal. Physiol. Opt. Vol 15
(Suppl 2), S38-S41, 1995
Van Herick, W., Shaffer, R.N., and Schwartz, A.
Estimation of width of anterior chamber. Am J Ophthalmol., 68,
626-629, 1969