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

OVERVIEW OF THE MANAGEMENT OF STRABISMUS

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an active process remains controversial (Lim 1999). The condition should

be differentially diagnosed from a bilateral sixth nerve palsy (where an

incomitancy will be detected on motility testing) but still requires referral

to investigate possible neurological causes.

Von Graefe and later Bielschowsky described a type of acute-onset

esotropia that is associated with high myopia. It usually occurs in young

adults at distance and then at near, and is associated with diplopia (von

Noorden 1996). Usually this is comitant (rarely, there is limited abduc-

tion), unlike another type of esotropia associated with very high myopia

( 15 D or more) in which there appears to be a limitation of motility in all

directions of gaze (von Noorden 1996). Indeed, acute onset esotropia in

adults was reported to be associated with some degree of myopia in nine out

of ten cases, but all cases regained stereoacuity after surgery (Spierer 2003).

When non-accommodative esotropia has become established for several

years, non-surgical treatment may not be successful. Prism relief may assist

(Ch. 14). Extraocular muscle surgery may be indicated when 20 or more

of esotropia remains after full correction of the refractive error or if optical

correction has no effect on the angle (Frane et al 2000). The chances of

achieving stereopsis after surgery for esotropia improve if the onset is after

the second year, but coexisting hypertropia worsens the prognosis (Kora

et al 1997).

Exotropia

Exotropia (constant or intermittent) affects about 1% of children by the age

of 11 years, with diagnosis most common at the ages of 3 years and 9 years

(Govindan et al 2005). The most common form of exotropia (Mohney &

Huffaker 2003) to occur under the age of 19 years is intermittent exotropia

(50%); other common types are exotropia associated with neurological

abnormalities (21%; mostly cerebral palsy or developmental delay), con-

vergence weakness (12%) and sensory exotropia (10%; mostly optic nerve

hypoplasia or cataract). Intermittent exotropia is more likely to be associ-

ated with neurological disease (e.g. developmental delay, cerebral palsy,

attention deficit disorder) if it is of the convergence weakness type rather

than the other types listed below (Phillips et al 2005).

The management options for intermittent exotropia were reviewed by

Coffey et al (1992) and negative lens therapy often achieves long-term suc-

cess (Caltrider & Jampolsky 1983). For many patients with intermittent

exotropia, the deviation reduces in angle and/or changes to an exophoria

over time, and this seems to happen regardless of the management of the

case (Rutstein & Corliss 2003). In contrast, another study found that more

than 50% of children with intermittent exotropia have an increase of

10 or more within 20 years of their diagnosis (Nusz et al 2006).

Divergent strabismus can be classified under four headings, there being

a different management and prognosis for each type.

(1) Divergence excess This presents typically as an intermittent divergent

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strabismus for distance vision only. It becomes most apparent during periods

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PICKWELL’S BINOCULAR VISION ANOMALIES

of inattention and day-dreaming, and is worse during ill health. Patients

are photophobic and bright light can cause the strabismus to occur (Eustace

et al 1973, Wiggins & von Noorden 1990). Most patients are female and

there is little refractive error. Because of its intermittent nature, the acuities

are generally good and nearly equal. There are usually no symptoms as there

are sensory adaptations when the eye is deviated. Patients usually seek

advice because some relative tells them that one eye sometimes deviates

(see also Ch. 8). Where the V syndrome exists, optometric treatment may

be more difficult.

Divergence excess is further discussed in Chapter 8, where the distinc-

tion is drawn between true and simulated divergence excess. It is also

noted in Chapter 8 that some authors have suggested that occlusion may

be an effective treatment for intermittent exotropia, although there have

been no randomized controlled trials.

The condition is usually improved by eye exercises designed to overcome

sensory adaptations and to build up the convergent fusional reserves. Also

useful are exercises to teach an appreciation of physiological diplopia and

the movement of the diplopic images during changes of fixation from near

to distance and back. If the patient has adequate accommodation and a mod-

erate to high AC/A ratio, it may be possible to help this deviation refractively

by prescribing distance glasses that are overminused with a near addition

(e.g. 2.00 DS at distance with a 2.00 add at near) to prevent the patient

developing an eso-deviation at near (Mallett 1988b).

(2) Near vision exotropia This is also called ‘convergence weakness type’

strabismus. The onset is usually in the mid-teens when binocular vision

breaks down for near fixation. It seems that binocular vision has been

maintained by the high convergence impulses that exist in children, but

in these cases it cannot be sustained for near when these impulses lessen.

Binocular vision may also break down for distance vision but the angle of

the strabismus is greater for near. These patients complain of symptoms

including diplopia. They are usually myopic and have equal acuities.

If the angle is over 20 , it is not possible to restore binocular vision by

optometric methods and the patient should be referred for a surgeon’s opin-

ion. In other cases, treatment may not be lasting. The approach is to correct

any significant refractive error and increase the convergent fusional reserves.

With smaller angles, prism relief is also useful. Some patients with adequate

amplitude of accommodation respond well to the prescribing of reading

glasses that are ‘overminused’. The minimum ‘negative add’ to transform the

near exotropia into a compensated exophoria should be prescribed and

the effect of this on distance ocular motor balance should be investigated.

Care must be taken to ensure that the glasses do not cause an eso-deviation

for distance vision or that they are only worn for reading. An alternative is

to prescribe executive bifocals and glaze them upside down (p 12).

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(3) Basic exotropia In these cases, there is a constant divergent strabismus

of approximately equal angle for distance and near vision. It is often

OVERVIEW OF THE MANAGEMENT OF STRABISMUS

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alternating with nearly equal acuities. As the onset is likely to be early in

life, there are no symptoms.

Any significant refractive error is corrected, following the general guide

of maximum minus or minimum plus. In children young enough to have

an adequate amplitude of accommodation, the effect of prescribing ‘nega-

tive additions’ to the prescription (overminusing or underplussing) can be

tried, as described in Chapter 14. Exercises for simultaneous binocular

vision may also be required. Divergent strabismus is sometimes accompan-

ied by a vertical component, which will make eye exercises more difficult.

Patients may be better with surgical correction for cosmetic reasons.

(4) Consecutive exotropia There are a number of circumstances in which a

convergent strabismus may become divergent. It is sometimes seen in

patients who had accommodative esotropia on which an operation was per-

formed in early childhood. No spectacles have been worn but in adolescence

or adulthood these patients develop symptoms due to the hypermetropia.

Correction of the refractive error relieves the facultative accommodation

and a divergent strabismus with diplopia occurs. A partial correction and

convergent fusional reserve exercises can sometimes help to maintain

binocular vision. Other cases need further surgery.

Vertical strabismus

About 1 in 400 people develop vertical strabismus by the age of 18 years

(Tollefson et al 2006). When vertical strabismus presents in adulthood it is

usually the result of an incomitant deviation (Ch. 17), usually fourth nerve

palsy (Tollefson et al 2006). This is a major reason why nearly 90% of cases

of vertical strabismus are hypertropia, and hypotropia is very likely to be

Brown’s syndrome (Tollefson et al 2006) (Ch. 17). Hypertropia can rarely

be exacerbated by convergence and accommodation (Thomas et al 2005).

Spasm of the near reflex

Aetiology

The term spasm of the near reflex (Rutstein 2000) is more accurate than its

synonym, convergent spasm (Bishop 2001), since all three components of the

near triad (convergence, accommodation, miosis) are typically involved

(Rutstein 2000). It usually has a psychogenic origin but can be organic

(Bishop 2001), when there may be other clinical findings such as nystag-

mus or papilloedema (Rutstein 2000).

Investigation

Symptoms include headache, visual discomfort, dizziness and print blur-

ring, doubling, becoming smaller or merging. A cycloplegic refraction is

indicated to rule out latent hypermetropia (Box 2.1). The condition is

characterized by intermittent and variable episodes of esotropia, pseudomy-

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opia and pupillary miosis. There may also be limited abduction and the

The presence of amblyopia in one eye is usually the first clue that

microtropia may be found. The amblyopic eye usually shows the crowding

phenomenon referred to in Chapter 13, i.e. single letter acuity is better than

line acuity. The foveal scotoma may also result in patients missing out letters

when reading lines of Snellen letters, or they may read the line more easily

backwards (see Fig. 13.1).

The patient should be tested for eccentric fixation (Ch. 13 and Appendix 6).

Eccentric fixation in microtropia is usually parafoveal and slightly nasal and

superior to the fovea in microesotropia. The other diagnostic features of stra-

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bismic amblyopia are summarized in Table 13.1.

This will depend on the type of test used. The TNO test measures random

dot stereopsis and the patient is unlikely to do better than 2000 of arc,

whereas the result from the Randot or Titmus stereotest circles, which

measure contoured stereopsis, may be as high as 100 of arc (Stidwill 1998).

Griffin & Grisham (1995) state that in microtropia central stereopsis is

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absent or greatly reduced, especially with random dot targets.