Ординатура / Офтальмология / Английские материалы / Pickwell's Binocular Vision Anomalies 5th edition_Evans_2007

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PICKWELL’S BINOCULAR VISION ANOMALIES

CASE STUDY 14.2 Ref. F6102: 73-year-old man with

intractable diplopia who did not benefit from blurring

of the weaker image

SYMPTOMS & HISTORY: High myope, right macular haemorrhage 15 years

ago. Patient has had constant oblique diplopia associated with a strabismus for

over 10 years (initially fully investigated), particularly with television. The diplopia

is not changing and the patient does not drive. He has tried various prismatic

corrections, none of which have ever eliminated the diplopia. Wearing: R –

13.00 DS L – 9.50/ 0.50 135 with 4 down L and 5 out L effective prism

at pupil centres (patient said RE is partial correction).

INITIAL RESULTS & MANAGEMENT: VA with glasses: R3/60 L6/9. Refractive

error: R – 18.00 DS 6/60 L – 9.00/ 0.50 95 6/9 . Distance cover test with

usual glasses 6 esotropia. Unable to eliminate diplopia with prisms. Dilated

funduscopy, fields, pressures, etc. all OK. Explained to patient that RE is so blurred

and already only partially corrected. Suggested to him that we reduce RE

prescription to a 8.00 DS (to balance L) in the hope that he will then find the RE

easier to ignore, so no need to bother with decentring or prism. Patient agreed to

try this.

OUTCOME: Patient reported that diplopia was worse with new glasses, images

are further apart and he finds that this makes it harder to ignore the diplopia.

R lens was changed back to 13.00 and fine-tuned prism for maximum comfort.

With the final glasses, the patient reported that the double vision was easier to

tolerate than he could remember it ever being in the past.

Occlusion

Occlusion is the simplest method to treat intractable diplopia resulting

from binocular anomalies. There are various types of occluder, which are

listed in Figure 14.4.

Tarsorrhaphy and botulinum toxin are invasive, are associated with a

higher risk than other methods and achieve a very poor cosmetic outcome.

They are a last resort. If a simple eye patch fits well, then this method is vir-

tually guaranteed to achieve a satisfactory outcome in terms of completely

blocking out the image from the unwanted eye. However, the method is

unsightly and for most cases is best thought of as a temporary measure.

Similarly, the use of a blackened spectacle lens achieves a poor cosmetic

outcome and is best thought of as a temporary measure. But this approach

can be very helpful, for example, with elderly patients with diplopia from

a recent-onset deviation who are waiting to see an ophthalmologist.

For reasons of safety, glass Chavasse lenses have been superseded by

CR39 or polycarbonate lenses that can be frosted. An inexpensive translu-

cent occluder can be made with Favlon or with sticky tape (e.g. Scotch

tape) stuck on to a normal spectacle lens. A few diplopic patients who are

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particularly sensitive to any image in their non-preferred eye can still be

bothered by the image from translucent occlusion.

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months’ duration or more may be compatible with driving if there is

consultant support indicating satisfactory functional adaptation.

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Visual condition

Influence on retinal correspondence (likelihood of test

breaking down sensory adaptations and causing the

patient to revert to NRC)

Degree of dissociation

If the conditions of everyday vision are disturbed by

dissociating the eyes, it is likely that NRC will return

while the dissociation is present. The more complete

the dissociation, the more likely it is that NRC will be

present

Retinal areas stimulated

NRC is most likely to occur with bifoveal images.

HARC is more likely when the fovea of one eye is

stimulated simultaneously with a peripheral image in

the other eye

Eye used for fixation

HARC is likely when the dominant eye is used for

fixation but NRC is likely to return if the usually

strabismic eye takes up fixation

Constancy of deviation

If the angle of the strabismus is variable, HARC is less

likely to be firmly established (Ch. 12). In intermittent

strabismus NRC will return when the eyes are

straight. The same is true of patients with fully

accommodative strabismus when wearing their

refractive correction and in long-standing incomitant

strabismus in the position of no deviation

Relative illuminance of

NRC is more likely to occur if the illuminance of the

retinal images

image in the strabismic eye is less than that of the

fixating eye

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PICKWELL’S BINOCULAR VISION ANOMALIES

therefore determine the likelihood of a given test detecting HARC or causing

a patient who might normally have HARC to revert to NRC.

Differential diagnosis of HARC and suppression

The correction of significant refractive errors can influence the sensory sta-

tus as well as the motor deviation. For example, a clear retinal image may

help to overcome suppression. If the patient has a significant uncorrected

refractive error, or change in refractive error, then the practitioner should

assess the sensory status with and without the new correction.

There are two main approaches to differentially diagnosing HARC from

suppression:

(1) Battery of tests (Pickwell & Sheridan 1973). A sensitive test (e.g. Modi-

fied OXO test or Bagolini test) is used to determine the sensory adap-

tation (ARC or suppression) under natural conditions. Additional tests,

of increasing degrees of invasiveness (less naturalistic), are then used

to evaluate when the sensory adaptation breaks down and thus to esti-

mate the depth of the adaptation. These tests are described, in increas-

ing order of invasiveness, below after the sections on the Bagolini and

Mallett tests.

(2) Degrading the image (Mallett 1970). A sensitive test (e.g. modified OXO

test or Bagolini test) is used to determine the sensory adaptation under

natural conditions. Then, still using this test, the patient’s perception

is degraded until the sensory adaptation breaks down. Historically, a

red filter bar was used to degrade the image, but neutral density filters

are the preferred method (Mallett 1988a, Bagolini 1999), as used in the

Mallett Neutral Density filter bar. Alternatives to this are to use two

counter-rotated polarized filters, or Bangerter foils, or to decrease the

illuminance of the Nonius strips on the modified OXO test.

The first of these two techniques, using a battery of tests, is time-consuming

and uses equipment that is not available in most community eyecare prac-

tices. Hence, only the latter method will be described in detail.

Bagolini striated lenses

This test, combined with the cover test, can be used to differentially diag-

nose the four possibilities for binocular sensory status in strabismus (Ch.

12): NRC, HARC, unharmonious anomalous retinal correspondence

(UARC) or suppression. The Bagolini striated lens is a plano trial-case lens

that has a fine grating of lines ruled on it (Bagolini 1967). When the

patient views a spot light through a Bagolini lens a faint streak is seen

crossing the spot but the lens does not significantly disrupt vision (Cheng

et al 1998). In unilateral strabismus, one lens can be used before the devi-

ated eye to produce a vertical streak rather like a ‘see-through’ Maddox

rod, while the patient looks at a spot of light with both eyes open. If the

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streak appears to pass through the spot of light, HARC is demonstrated.

A central suppression area (Ch. 12) may result in a gap in the central part

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Bagolini lens test

e.g. 15 R SOT, Bagolini lens RE

LE image:

RE image:

HARC:

SUPPR:

NRC:

UARC:

of the streak but the patient may be able to report that the ends of it can be

seen in line with the spot (Fig. 14.5). If the streak and the spotlight are not

perfectly aligned (but within about 0.5 of one another) this does not neces-

sarily mean that there is UARC but can result from an imperfection in the

new anomalous sensory relationship. The diagnosis of UARC (which is very

rare: see Ch. 12) or NRC is confirmed by the presence of diplopia and con-

fusion (Fig. 14.5).

Occasionally, patients may change fixation to the normally deviating eye

and hence see the streak passing through the light. Close observation of any

eye movements during the test and a confirmatory cover test should be used

to verify that the eye behind the lens is still deviating. Unnecessary repeated

covering should be avoided because this could cause HARC to break down

to apparent UARC or suppression.

If the streak is misaligned and the patient is diplopic, then either NRC or

UARC is shown, depending on whether the angular separation of the spot

and the streak is the same as the angle of the deviation. With UARC, the

angle of the separation between the spot and the streak, the angle of

diplopia, is different from the angle of the strabismus. If the patient reports

diplopia during the Bagolini lens test but does not during everyday viewing,

it suggests that they have HARC that has ‘broken down’ under the very

slightly abnormal viewing conditions of the Bagolini test. Such cases are rare

and careful questioning may reveal that the HARC also breaks down when

the patient is fatigued, or in dim illumination. In these cases, the ‘pseudo-

binocular vision’ of HARC breaks down in an analogous way to the breaking

down of binocularity in a decompensated heterophoria. If the patient

reports an unstable perception of the streak in the Bagolini test, this can be

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indicative of an instability in the HARC. Again, this can be associated with

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PICKWELL’S BINOCULAR VISION ANOMALIES

marker in the strabismic eye may appear to be a different size, dimmer and

slightly misaligned with the other marker. This is because of inherent

imperfections in the anomalous alliance of receptive fields of unequal

dimensions and properties.

The absence of the strabismic eye’s Nonius marker indicates suppression

of the binocular field of that eye (Fig. 14.7). A neutral density filter bar (Fig.

14.6) can be used between the eye and the polarized visor to assess the depth

of HARC or of suppression, in a similar way to that described for the Bagolini

striated lens test above. The response should be checked with the cover test

and, if the patient is diplopic, the degree of diplopia can be investigated to

diagnose UARC or NRC, as with the Bagolini striated lens test.

As with any polarized test, the illumination should be increased by two to

three times to counteract the effect of the polarized filters. As with the

Bagolini test, the patient’s response should be monitored to determine

whether their ‘pseudobinocularity’ from the HARC has a tendency to break

down or to become unstable. If it does, then questioning may reveal that

symptoms occur in everyday life and treatment may be required (see below).

Both the Bagolini and Mallett modified OXO tests closely approximate

normal viewing conditions and these tests are very likely to reveal the sens-

ory status that exists under normal viewing conditions. They will detect

HARC in about 80% of cases of strabismus seen in optometric practice

(Mallett 1988a). For the reasons explained in the preceding section, the

tests described below create artificial viewing conditions and their results

are therefore unlikely to reflect the normal situation.

Other methods of differentially diagnosing HARC and

suppression

Four after-image tests have been discussed in detail by Mallett (1975) and

summarized in Mallett (1988a). The individual tests do not allow the depth

of HARC to be quantified but inferences about the depth of HARC can be

drawn by using all four tests. These tests are rarely used nowadays, but

more details can be found in Mallett (1988a).

The synoptophore can be used to investigate correspondence (Pickwell

1989, pp 129–131) but, owing to the artificial nature of the instrument,

the results can be very confusing and other methods (e.g. Bagolini lenses

or modified OXO) are likely to be a better use of clinical time. Stereoscope

cards can be graded in the same way as synoptophore slides to assess the

depth of suppression.

The single-mirror haploscope (Earnshaw 1962) comprises a rotatable

mirror, set at about 45° to the line of sight, bisecting two grey screens

placed at 90° to each other. One eye views the screen directly ahead while

the other observes its own screen through the mirror. The instrument pro-

vides a versatile alternative to the synoptophore, with slightly more natural

viewing conditions, but is not commonly found nowadays. Various other

haploscopic instruments have been devised but are not in regular use in the

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UK. Personal computers can be used with liquid crystal display (LCD) shut-

ter goggles, and some other computerized orthoptic testing systems use

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red/green dissociation. Another technique that creates abnormal (dissociat-

ing) viewing conditions is the red filter method (Siderov 2001).

Additional techniques for the investigation of suppression

Many polarized tests (e.g. Titmus and Randot tests) include tests of sup-

pression. Additional tests that are described elsewhere in this book are the

four base-out prism test (Ch. 16) and Mallett polarized letters test (p 82).

The Worth Four Dot Test can be used to assess suppression, as described

on page 220, with the inclusion of a cover test to check the motor status

during the test. However, this test creates unnatural viewing conditions,

overestimates the prevalence of diplopia and suppression (Bagolini 1999)

and is of limited value (von Noorden 1996, p 213).

Depth of suppression

Usually, it is most convenient for the practitioner to use the test that

detected the suppression to assess its depth, and several suitable tech-

niques have already been described. One very simple additional technique

is to find the depth of filter held before the non-suppressing eye that will

overcome the suppression. The method is to ask the patient to look at a

fairly detailed scene (to create normal viewing conditions) and to intro-

duce the filter bar before the non-suppressing eye, beginning with the

lightest filter. As the darker filters are moved before the eye, the retinal illu-

minance will be decreased until the patient reports diplopia or until the

strabismic eye moves to take up fixation. The depth of filter used will be a

measure of the suppression.

Extent of suppression scotoma

Almost all strabismic patients have either ‘total’ suppression or HARC. For

suppression to successfully prevent diplopia and confusion, there must be

suppression of all of the binocular field of the strabismic eye. This suppres-

sion is very different from the small areas (about 1°) of central suppression

that occur at the fovea and at the zero point of the strabismic eye in HARC.

Although these suppression areas may not be of major clinical significance

(Mallett 1988a), it used to be fairly common practice to measure their size,

using a form of binocular haploscopic perimetry. As with other aspects of

the investigation of sensory status, test procedures that interfere more with

normal binocular vision tend to produce artefactual results.

The situation is confused further by attempts to plot the extent of the

suppression area in patients with large-angle strabismus who do not have

HARC or diplopia. Clearly, these patients must be suppressing all the

binocular field of their strabismic eye, yet some investigative techniques

only detect an elliptical or D-shaped suppression area around the fovea

and zero point in such cases. The reason for this is that there will be deeper

suppression in this region and a test that creates artificial viewing condi-

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tions may only detect the suppression in this area and not the shallower