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

Another aspect that can help in the diagnosis of incomitant deviations is the

recognition of particular cranial nerve palsies, which are given below. Recent

reviews have detailed the pathway of the cranial nerves (Evans 2004e) and

the vasculature of these and the extraocular muscles (Evans 2004h) has

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recently been reviewed. A summary of the relative likelihood of a cranial

nerve palsy affecting a given nerve is given in Table 17.5 and Table 17.6 gives

INCOMITANT DEVIATIONS

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the prevalence of various aetiologies for such pareses. Von Noorden (1996,

p 406) noted that estimates of relative prevalence will vary depending on the

type of clinic. In his ophthalmological strabismus clinic, fourth nerve palsies

are seen by far most commonly, then sixth and then third nerve (cf. the data

in Table 17.5). The fourth nerve innervates the superior oblique and the sixth

nerve the lateral rectus. The third nerve innervates all the other extraocular

muscles and the levator (lid) muscle, and contains the parasympathetic sup-

ply to the muscle that constricts the pupil and to the ciliary muscles.

Richards et al (1992) reviewed the data from 4278 patients with ocular

cranial nerve palsies, noting that in many cases the cause was undetermined.

Of the congenital cases, 77% resulted from fourth nerve palsies. Patients

with multiple cranial palsies were most likely to have neoplasms or trauma

and fourth nerve palsies were least commonly tumours. Recurrent lateral

rectus palsies in children were generally benign.

Fourth nerve (superior oblique) palsy

A fourth nerve palsy is the most frequently diagnosed form of vertical stra-

bismus (Tollefson et al 2006). About three-quarters of superior oblique pare-

ses are congenital but many cases do not present until adulthood, when

they decompensate (Plager 1999), sometimes during pregnancy (Jacobson

1991) and sometimes secondary to a different extraocular muscle palsy (Metz

1986). In 92 patients presenting with superior oblique palsy under the age of

8 years, there were no cases where it was associated with the development of

new intracranial pathology (Tarczy-Hornoch & Repka 2004).

The trochlear nerve is the most slender cranial nerve and is the only

motor nerve that arises from the dorsal aspect of the central nervous system

(Warwick 1976, pp 282–290). Its long pathway means that it is particularly

prone to damage in closed head injuries (Table 17.6). According to Plager

(1999), more than half of acquired superior oblique palsies result from

trauma, one third are iatrogenic and other causes include tumour and, very

rarely, aneurysm. Sometimes, a superior oblique palsy can decompensate

following refractive surgery, particularly if monovision is induced (Schuler

et al 1999, Godts et al 2004). Contact lens monovision can also induce

decompensation (Evans 2006a).

Plager (1999) argued that to cause a superior oblique paresis trauma had

to be substantial, whereas von Noorden (1996, p 411) argued that it often

followed only a mild concussion. Trauma can cause bilateral superior oblique

palsies (discussed below), which can be asymmetric and thus easy to mis-

diagnose as unilateral (Lee & Flynn 1985).

Superior oblique palsies may be characterized by a head tilt away from

the affected side and in long-standing cases there may be a corresponding

facial asymmetry (Plager 1999). If the patient is asked to tilt the head to

the other side, the affected eye elevates (the Bielschowsky head tilting test;

p 296). The head tilt can disappear in early adolescence and there may be

binocular vision in the primary position of the eyes.

Superior oblique palsies can be very difficult to detect on motility test-

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ing (Brazis 1993) and patient descriptions of the position of gaze in which

there is maximum vertical diplopia are often unhelpful (Fig. 17.10 and

Appendix 13 with the cases on CD-ROM). The double Maddox rod test is

an extremely useful tool for investigating superior oblique palsies. This test

is discussed on p 286, where it is noted that it has only limited usefulness

for diagnosing bilateral superior oblique involvement (below). The cyclode-

viation may be manifest in the eye that is contralateral to the one that had

the original palsy.

Congenital palsies may be hard to detect, even with the double Maddox

rod or torsionometer tests (p 287) because of sensory adaptations (HARC

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or sensory cyclofusion) and motor cyclofusion (Phillips & Hunter 1999).

Another sign of congenital superior oblique palsies is that the patient may

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have vertical fusional reserves in excess of 10 (Finlay 2000). Reports of

image tilting are said to be diagnostic for acquired superior oblique palsy

The superior oblique muscle has been described as the ‘reading muscle’

and patients often adapt to reading by holding text higher than usual.

Bifocals and varifocals may therefore be contraindicated, or may require a

vertical prism in the near vision portion of the lens (Erickson & Caloroso

1992). Patients with superior oblique pareses who can achieve binocular

single vision and who have astigmatism over 1.00 DC, should have their

astigmatic axes determined under binocular viewing conditions (Rutstein &

Eskridge 1990). Prisms may be of benefit to patients with a small relatively

comitant deviation from a unilateral (Plager 1999) or bilateral (Lee & Flynn

Superior oblique palsies can be

difficult to diagnose and this is partly because of secondary sequelae, which

often obscure the original deviation (p 297). Typically, there will be an over-

action of the contralateral synergist (contralateral inferior rectus). In cases

that fixate with the non-paretic eye, there is often an overaction of the

ipsilateral antagonist (inferior oblique). This can cause the hypertropia to

be greatest when the eye with the original paresis looks up and in (von

Noorden 1996, p 412), although the mechanism for inferior oblique over-

Patients who habitually fixate with their paretic eye may develop an inhi-

bitional palsy of the contralateral antagonist (contralateral superior rectus).

This can cause the patient to report that the hyperdeviation is greatest

in up-gaze (Fig. 17.10). Von Noorden (1996, p 412) argued that this

occurs even when patients do not fixate with their paretic eye and is attrib-

utable to an overaction of the ipsilateral inferior oblique when the patient is

patients explain why reports

of vertical diplopia during the motility test so often lead to confusion in diag-

nosing a superior oblique paresis (Fig. 17.10). The key to uncovering whether

a superior rectus palsy results from a contralateral superior oblique paresis is

to test for a cyclodeviation and to carry out Bielschowsky’s head tilt test.

Some patients who fixate with their paretic eye also manifest a pseudo-

overaction of the contralateral superior oblique, which has been attributed

to a contracture of the ipsilateral superior rectus (von Noorden 1996, p 412),

which prevents the paretic eye from looking downwards when abducting

Surgical overcorrection of a unilateral superior oblique muscle paresis can

masquerade as an apparent contralateral superior oblique muscle paresis

(masked bilateral superior oblique muscle paresis). This is caused by a

persistence of the head tilt and side gaze misalignment pattern from the

original superior oblique muscle paresis (Ellis et al 1998).

Bilateral superior oblique palsy Bilateral superior oblique palsy is nearly

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always acquired, typically following closed head trauma (e.g. in a road

PICKWELL’S BINOCULAR VISION ANOMALIES

accident) or, uncommonly, from a tumour in the dorsal midbrain (Barr

et al 1997). Although it is rare, it should be suspected in all severe head

injuries (Lee & Flynn 1985). The condition can be asymmetric and may

appear to be unilateral on motility testing, so that bilateral cases are often

misdiagnosed as unilateral (Lee & Flynn 1985). It is unusual for a single

superior oblique muscle palsy to cause an excyclotropia over 8° (Spector

1993); a bilateral superior oblique palsy causes an excyclotropia that is

nearly always over 5° (Lee & Flynn 1985) and often over 10° (Plager 1999) or

12° (Spector 1993). However, Plager (1999) cautioned that this type of meas-

urement does not allow an infallible diagnosis and von Noorden (1996,

p 414) found little difference between the magnitude of the excyclotropia

for unilateral and bilateral cases. However, von Noorden (1996, p 414) listed

two signs that are never present in unilateral cases but may be present in

bilateral cases: right hypertropia in left gaze and left hypertropia in right

gaze, and a positive Bielschowsky test with the head tilted to either side.

Additionally, bilateral superior oblique palsies often cause subjective com-

plaints of torsion, a chin-down head posture and a V-syndrome.

Sixth nerve (lateral rectus) palsy

According to some authors, this is the most common ocular cranial nerve

palsy (Santiago & Rosenbaum 1999). The long intracranial path of the sixth

nerve makes it particularly susceptible to lesions associated with skull frac-

tures and raised intracranial pressure. Raised intracranial pressure is most

likely to have an effect on the nerve where it passes over the apex of the

petrous temporal bone (Fig. 17.5). Rare cases of benign intracranial hyper-

tension, which can result from endocrine disorders including obesity, can

result in sixth nerve palsy, headache and transient visual loss (Ramadan

1996). Because of the close association of the sixth and seventh cranial nerves

in the midbrain, the facial muscles also may be involved in some sixth nerve

palsies. Children may have a transient sixth nerve paresis following a viral ill-

ness, which should improve in about 6 weeks. However, prompt referral is

still appropriate. Vascular hypertension is a cause in adults.

Bacterial infection of the middle ear can spread to the petrous temporal

bone, affecting both the sixth and fifth (causing head pain) nerves. This con-

dition (Gradenigo’s syndrome) has become rare since antibiotics came into

general use. The sixth nerve may be involved in acoustic neuroma and these

cases will exhibit diminished hearing and corneal sensitivity (Swann 2001).

Lateral rectus palsy can be confused with Duane’s syndrome (p 310), and

the patient should be watched from the side during horizontal eye move-

ments to detect the retraction that is usually characteristic of Duane’s syn-

drome. Congenital bilateral lateral rectus palsy produces an alternating

convergent strabismus with equal acuities. If it is unilateral, the face is turned

towards the affected side. The degree of separation of the diplopic images

may be greater in the inferior than in the superior field on the affected side

(Percival 1928).

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Surprisingly, a lateral rectus palsy can produce a hyperdeviation as well

as a horizontal deviation, and there may be vertical diplopia (Slavin 1989).

INCOMITANT DEVIATIONS

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The hyperdeviation is maximal when the patient looks to the side of the

affected lateral rectus muscle (in up, down or straight lateral gaze) and may

also be present in the primary position and, to a much lesser extent, for

near vision. There can even be a cyclodeviation and, very rarely, a positive

Bielschowsky head tilt test (Slavin 1989). If the vertical deviation is more

than 5 then it may indicate a skew deviation (p 315) or that another

nerve or muscle is involved (Wong et al 2002).

A report of over 200 patients with sixth nerve palsy of unknown aeti-

ology found that 36% recovered in 8 weeks and 84% recovered in 4

months (King et al 1995). About half of those who failed to recover had

serious underlying pathology, emphasizing the need for optometrists to

refer any recent sixth nerve palsy. Another sign of underlying pathology is

an A-pattern: a small V-pattern should be expected in normal sixth nerve

pareses (Hoyt & Fredrick 1999).

Figure 17.9 (C and D) shows consecutive Hess screen plots for a patient

with a resolving lateral rectus palsy that was caused by vascular hyperten-

sion. This patient benefited from base-out prisms in her distance vision

spectacles, which reduced as the palsy improved. Fresnel prisms were not

tolerated because of blurring. A video clip of the motility test result for a lat-

eral rectus palsy can be found on the CD-ROM (Appendix 13).

Arnold–Chiari malformations are congenital structural defects in the

cerebellum. The indented bony space at the lower rear of the skull is

smaller than normal, causing the cerebellum and brain stem to be pushed

downward. Symptoms including dizziness, muscle weakness, numbness,

vision problems, headache and problems with balance and coordination.

There are three primary types of Arnold–Chiari malformation. The most

common is type I, which sometimes only produces symptoms in late

childhood or early adult years. Acute esotropia can be an early sign, as can

downbeat nystagmus (Russell et al 1992). The esotropia may be comitant,

divergence palsy (Lewis et al 1996) or lateral rectus palsy (Miki et al 1999).

Patients need to be referred for early decompression surgery (Russell et al

1992).

Third nerve palsy

If only the extrinsic muscles supplied by this nerve are affected, this is

external ophthalmoplegia. A paresis of the ciliary muscle and the iris sphincter

is known as internal ophthalmoplegia and when both the extrinsic and intrin-

sic muscles are affected there is total ophthalmoplegia. Some authors make

the distinction that if the lid muscles are involved it is ocular myopathy.

Total ophthalmoplegia is also known as complete oculomotor palsy; there will

be a divergent strabismus with slightly depressed eyes, ptosis and a loss of

pupil action and accommodation. Ophthalmoplegia can result from a

blow on the frontal region of the head, vascular disease (e.g. diabetes, hyper-

tension), neoplasia, aneurysm and ophthalmoplegic migraine (Swann 2001).

Other accompanying symptoms may therefore include headache, a tremor

of the contralateral limbs (due to the involvement of the red nucleus where

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the third nerve fibres pass) and other symptoms of diabetes (above).