Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology Current Thought and A Practical Guide_Wilson, Saunders, Trivedi_2008

not cause, the onset of overaction in the opposite one

[39]. The best explanation for such an occurrence is that the first inferior oblique weakening was done fortuitously between the non-simultaneous appearances of the components of a bilateral disorder. Alternatively, one study suggested that some inferior oblique weakening procedures involve reattachment that limits elevation in abduction, causing apparent overaction of the opposite inferior oblique by Hering’s law [32].

In an otherwise typical case of congenital esotropia in which above-average hyperopia is also present, it is highly unlikely that the entire large-angle, constant deviation is the result of perpetually sustained accommodative effort at an age when the need for obtaining refined visual information is not yet well developed. Whether the customary “trial of the full refractive correction” is indicated is debatable in this setting. Postoperatively, this can change importantly. Accommodative esotropia (see Sect. 8.4) occurs as a sequel to infantile esotropia at high frequency and usually earlier than expected [3, 21], especially if hyperopia determined with cycloplegia is more than 3.50 D. The ophthalmologist should warn parents of this prominent possibility, or they will not understand the return of a deviation that, to them, seems identical to the earlier condition.

8.4Accommodative Esotropia

Accommodative esotropia is the most common form of childhood strabismus [15]. It can be present by itself or in combination with other strabismus entities. Intermittency of the deviation in a neurologically normal child between 2 and 3 years of age strongly suggests this diagnosis, although earlier presentation is certainly not rare (Fig. 8.4). With time, the deviation in the untreated patient becomes constant as abnormal sensory adaptations become established.

8.4.1Features

One variety of this disorder occurs because of an excessive demand for accommodation in a hyperopic patient whose innervation for accommodation and its

Fig. 8.4  Early-onset accommodative esotropia in a 1-year-old child

associated obligatory convergence (AC/A ratio) is in proper balance. The second category consists of patients whose hyperopia usually is in the normal range, but in whom the AC/A ratio results in an abnormally high convergence response. Normal and high AC/A ratios are distributed equally among patients with accommodative esotropia [21]. As a third variety, an occasional patient will present an identical clinical picture because of increased effort to overcome an insufficient accommodation ability. The extreme example of this is the aphakic child undercorrected for near vision, who despite loss of the organ of accommodation does not cease to exert neurogenic output in response to hyperopic blur.

Evaluation of accommodative esotropia requires cycloplegic refraction as well as measurement of the fusion-free alignment (e.g., by prism and alternate cover or corneal light reflex estimation). A rapid indicator that there is at least a partial accommodative component can be gained even before knowing the refractive error by observing a response to an empirically chosen + 2.50 or 3.00 D that reduces the near deviation below that at distance in the uncorrected state [20].

The preferred drug for cycloplegia is still disputed, with cyclopentolate and atropine each having strong proponents. Using cyclopentolate and examining after the appropriate interval of about 45 min, dynamic retinoscopy (comparing distance and near measurements) will seldom show more than a fractional degree of residual accommodation, giving a reliable result for most patients and obviating the need for multiple instillations, prolonged blur, and systemic side effects associated with atropine.

Amblyopia is uncommon prior to decompensation (see Sect. 8.4.3), unless there is the additional caus-

ative factor of anisometropia. About 30% of cases of accommodativeesotropiapersistbeyondtheexpected time of resolution of about 10−12 years of age. There are no reliable predictors of this occurrence; these cases show no differences in associated findings from those that do resolve by that time [26].

8.4.2Management

Purists continue to debate the proper measurement of the AC/A ratio. This should be of minor concern to the practitioner. No method directly measures the simultaneous innervational events of both accommodation and convergence. It is more useful to regard the AC/A as a concept rather than as a quantity. Whether the so-called gradient method is more accurate than the commonly employed distance-near alignment comparison [35] does not stand in the way of appropriate management decisions. Much of the dispute would evaporate if users of the distance-near comparison referred to it as just that, and not as the AC/A ratio.

Discouraging accommodative innervational effort is the cornerstone of management. The goal is to reduce the esodeviation to 8 PD or fewer, a result that allows the development of at least peripheral fusion [16]. Glasses or contact lenses (less usual in the young child) that correct substantially all of the patient’s hyperopia are worn during all waking hours. The author’s personal guide is to “hit hard, and ease up later.” It is unlikely that decompensation (see Sect. 8.4.3) will occur during the subsequent 18 months, allowing for fewer monitoring visits, e.g., every 8−9 months, than is usually advocated [27].

Less secure control requires closer scrutiny.

The controlled patient can receive periodic graded reduction of the initial prescription to facilitate acquiring a gradually expanding amplitude of fusional divergence that will maintain straight eyes under binocular conditions. Reductions are possible only unusually before age 5−6 years. They should not be arbitrary but instead determined by the measurement by simultaneous prism and cover while wearing the intended new power and with accommodation controlled. This need not be confirmed by a corresponding decrease in the cycloplegic measurement of the patient’s hyperopia. It is irrelevant whether there is a

corresponding change in the cycloplegic refraction, since the aim is to provide the least strength that will maintain proper alignment. It is the author’s practice to limit any single reduction to 0.75−1.00 D, even if it appears that more can be tolerated. If successful, the attempt is repeated at 4- to 6-month intervals. Many parents report transitory loss of control shortly after a prescribed reduction, but only occasionally is it necessary to reverse the reduction.

Bifocal additions, initially 2.50−3.00 D, are appropriate for high-AC/A cases, and under the “hit hard” guideline should be part of the original prescription when it is clear that the distance-near comparison calls for this measure, rather than being deferred until the effect of just the distance correction can be determined. It is important that the lower segment be set at about pupillary level, and specific instructions for this should be part of the prescription. Some ophthalmologists have been enthusiastic about progressiveaddition “lineless” bifocals [31], but these can cause monitoring difficulties. The bifocal strength can be periodically reduced in the same manner as indicated for the distance correction. While bifocals are no longer needed by age 10 years in many wearers, for some the need persists indefinitely [10].

Topical anticholinesterase “miotic” drugs, whose use in accommodative esotropia depends not on miosis but on facilitation of accommodation, once were considered an equally effective alternative treatment.

They are less popular now, in part because of difficulty in obtaining them but also because they proved to be less reliable for diagnosis and were not useful for anisometropia or for incorporation of small degrees of vertical prism that are sometimes needed. These agents were thought to overcome non-compli- ance with the wearing of glasses, but this often merely substituted one parent−child conflict for another. The author considers the best indication for the use of miotics to be as a temporary measure on occasions when wearing glasses would be awkward, such as in sports or, in older children, for social events. The dangers of retinal detachment and cataract formation from the use of these agents have been overstated for this age group. Pupillary cysts are the principal adverse side effect. They usually regress when the drops are discontinued or when topical 2.5% phenylephrine is included in the regimen.

Most ophthalmologists would decline to substitute extraocular muscle surgery for cases responding to

the measures described above. Very limited exceptions may apply to the patient requiring bifocals for an accommodative esotropia present in near viewing only [13], or in indefinitely persisting cases [11].

8.5Essential Intermittent Esotropia

This form of comitant esotropia presents as a recurring lapse of control of an underlying esophoria due to tonic imbalance of the horizontal rectus muscles.

Fusional divergence amplitudes are unable to comfortably overcome the tendency at all times, par-

Surgery is indicated when through neglect, noncompliance, or even with all appropriate treatment measures and full cooperation, a previously controlled patient no longer maintains straight eyes. The onset of this decompensation is gradual, distinguishing it from the acute, totally non-accommodative esotropia that can strongly imply serious neurologic disease. Decompensation may not be complete, so that the esotropia still responds, but only partially, to anti-accommodative measures. Decompensation is not a complication, but rather a disappointing, although foreseeable, feature of this entity, with a reported occurrence rate between 13 and 40% in various series [9, 23]. Whether a high AC/A ratio is a predisposing factor is disputable, but onset of accommodative esotropia prior to age 2 years suggests this outcome [4]. Because of normal early binocular visual experience, the existence of the capacity for at least peripheral fusion should be presumed, even when it cannot yet be tested reliably. This reinforces the need for vigorous therapeutic efforts to restore binocular single vision.

Base-out prisms address the sensory consequences but do not restore alignment and are, at best, only a temporary measure. Surgery is required, not to replace glasses but to allow optical treatment of the residual accommodative component to continue to be effective. Medial rectus muscle recessions are the first choice of most ophthalmologists, who adjust their customary quantitative schemes somewhat upward, either adding 0.5−1.0 mm of recession to each medial rectus, averaging the distance and near deviations, or basing the amount on the near esodeviation, which generally is the larger one. Preoperative prism adaptation is useful in planning surgery, not only in this disorder but in other settings as well [28], despite its disadvantages of multiple visits and additional delays. The accommodative portion that persists after surgery has a natural course similar to that of a purely accommodative deviation [24].

should be distinguished from the acutely presenting esotropia in children or adults that is constant from onset and that raises the suspicion of an abnormal intracranial process calling for neurologic consultation and imaging studies.

8.5.1Features

Patients with decompensating esophoria usually present at age 10 years or later, in contrast to the much earlier onset of accommodative esotropia. Diplopia and refined stereopsis are common and imply a long period of prior stability. Inferior oblique overaction and DVD are not prominent [14]. The monofixational fusion status occasionally seen may be an adaptation or an independent sensory state [16].

8.5.2Management

Non-surgical treatment of decompensating esophoria has limitations. Expansion of fusional divergence throughorthopticmeasuresisdifficultduetothemodest limits of even a normal amplitude and because of the prolonged rigorous effort required. Prisms base out to compensate for most or all of the esophoria can give symptomatic relief but tend to promote further erosion of the patient’s own control mechanism [36].

Above-average hyperopia can add an accommodative component to the existing stress on alignment and should be relieved optically.

Surgical correction is indicated when symptoms are severe and non-operative measures are ineffective. Recession of the medial recti or a unilateral recession/resection can be chosen, planned to correct the entire deviation, regardless of whether it is becoming constant or remaining intermittent and symptomatic [14].

8.6Undercorrected Esotropia

This designation refers to esotropia that continues after an attempt at elimination by surgery. To simplify management, if the undercorrection falls into the range where at least monofixational fusion is possible, i.e., 8 PD [16], it is for practical purposes a satisfactory result and does not require further treatment, as whatever binocular cooperation is possible is unlikely to be improved by a smaller misalignment; in addition, the cosmetic effect usually is acceptable as well.

Larger residual deviations are a different matter. If it was correct to begin the surgical task, it should be completed, provided that the conclusion that an undercorrection has occurred is deferred until it is present after the usual healing period of 6 weeks, as there is no urgency about recovering lost or slipped muscles.

If the undercorrection occurs after bilateral medial rectus weakening, lateral rectus tightening can be the follow-up operation. Prior unilateral recession/ resection on one eye can call for the same procedure on the other eye. Some surgeons have supplemented a less than maximal medial rectus recession, ascertained preferably by direct exploration of its position rather than from operative reports (Fig. 8.5), by further weakening, guided by the observation that the effect of the last few millimeters of recession is more profound than that of the first several. This procedure and double marginal myotomy should be last resorts because of their unpredictable results. Posterior fixation has been suggested [33] but is technically difficult if done posteriorly enough to be effective.

Fig. 8.5  Exploration of extraocular muscle insertion position, through a cul- de-sac incision

8.7Consecutive Esotropia (Overcorrected Exotropia)

It is generally accepted that initial modest overcorrection of exotropia is desirable because of anticipated postoperative outward drift, and that the likelihood of persisting esotropia is far less than that of recurrent exotropiaiftheeyesarestraightorexodeviatedimmediately after operation [25]. These observations were derived from patients receiving bilateral lateral rectus recession but are considered generally valid after unilateral recession/resection procedures as well. This type of overcorrection is not related to lateral rectus slippage, as abduction, although often limited just after operation, usually returns to normal quickly.

An occasional variant occurs when even successful correction of the exotropia unmasks an accommodative esotropia of the high AC/A ratio type [22]. One author has suggested that identification of these patients can be aided by determination of the AC/A ratio after occlusion has dispersed proximal fusion [8], but while this is useful for purposes of informed consent, the result is not avoidable by a modifying the surgical scheme.

Regarding management, initial overcorrection is appropriate surgical strategy, but the young patient is susceptible to a poor sensory outcome. As prevention, the author’s regimen includes majority-time occlusion for a deviation of more than 20 PD at the first (2−3 days) postoperative visit. Overcorrection of 10−20 PD still present after 2-week calls for continuing occlusion, which in both instances is maintained until alignment is within the range where fusion (monoor bifixational) is possible. Monitoring is done at 2-week intervals. Initial overcorrections of <10 PD are observed without this treatment. Trying to correct a varying alignment with prisms during this period has been less useful. Accommodationlowering measures are not employed unless they unequivocally affect alignment immediately, an unusual occurrence.

If the overcorrection has not improved at all in the first 2 postoperative weeks, this suggests its likely permanence; however, at least 6 weeks should be allowed to pass before reaching that conclusion. Treatment requires additional corrective surgery, preferably on muscles not included in the prior pro-

Take Home Pearls

•Binocular vision and moderate grades of stereopsis are possible for congenital esotropia patients if treatment restores proper alignment by age 2 years.

•If present, oblique muscle overactions and A or V patterns should be addressed in the surgical correction of esotropia.

•About 30% of patients with accommodative esotropia retain their disorder beyond

the age of expected disappearance. Such cases cannot be reliably predicted.

•Full control of accommodative esotropia should be gained before reducing optical correction to the minimum necessary to maintain straight eyes.

•Surgical correction of decompensated accommodative esotropia should be done for only the non-accommodative portion. Management of the remaining accommodative component is the same as for the patients without decompensation.

•While prism correction may have a role, surgical correction of decompensated esophoria is the most effective treatment for the patient with troublesome diplopia.

•Occlusion to avoid abnormal sensory adaptations in overcorrected exotropia is necessary until either the anticipated

“exodrift” occurs spontaneously or further surgery is accomplished.

•When divergence insufficiency esotropia presents acutely, thorough investigation and imaging studies should be obtained.

cedure. Accommodative esotropia unmasked by surgery to correct exotropia is managed as described in

Sect. 8.4.2.

observed in children and adults with central nervous system disease [19].

8.8Cyclic (Periodic) Esotropia

The hallmark of this unusual condition is a cycle of straight and crossed eyes, described as “alternate day esotropia” but often with a different interval [37].The cycles are strictly repetitive, unlike the early variability of accommodative and essential intermittent esotropia. The condition usually is benign but has been

8.8.1Features

Inferior oblique overaction, dissociated vertical deviation, and motor nystagmus are not characteristic of this entity. Abduction is not limited either in the straight or the esotropic phase. Adults may experience diplopia, but children usually have no symptoms. When the condition is still cyclic, the eyes are usually not misaligned long enough so that ambly-

opia or loss of fusion is a concern, unless there is anisometropia. Most such patients finally evolve to a constant esotropia.

more effective and usually emphasizes lateral rectus tightening. The author has noted that such patients may also show a usually modest A pattern, for which horizontal rectus displacement upon reinsertion is appropriate.

8.8.2Management

There are no effective non-surgical measures. Surgery is required and is equally effective whether done in the cyclic or the constant state [37]. The surgeon’s preferred procedure for other types of esotropia is appropriate here as well.

8.9Divergence Insufficiency

The term divergence insufficiency most often does not indicate a true abnormality of divergence, but rather is a shorthand description of an esodeviation that is larger at distance than at near. This is a somewhat unusual presentation in an untreated case; it is more to be expected in an undercorrected esotropia patient when the prior operation has been recession of the medial recti.

8.9.1Features

Especially when associated with the sudden onset of diplopia, a deviation with these characteristics suggests divergence paralysis and the possibility of prior head trauma, or an intracranial abnormality with or without elevated intracranial pressure [30]. This pattern is also seen in unilateral or bilateral sixth cranial nerve paralysis, in which observable abduction deficiency is present and/or the esotropia in right and left gazes is greater than in the primary position. Unless clearly long standing and asymptomatic, this condition calls for neurologic investigation and appropriate imaging studies [7].

8.9.2Management

Base-out prisms may be of limited help. For cases in which the designation is descriptive only, surgery is

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Contents

9.2Etiology and Classification  . . . . . . . . . . . . .   98

9.4.1Exophoria  . . . . . . . . . . . . .   99

9.4.2Infantile Exotropia  . . . . . . . . . .   99

9.4.3Sensory Exotropia  . . . . . . . . . .   99

9.4.4Consecutive Exotropia  . . . . . . . .   100

Core Messages

•Exotropic deviations include exophoria, infantile exotropia, sensory exotropia, consecutive exotropia, intermittent exotropia, and dissociated horizontal deviation.

•The decision whether to treat should be based on control, and how to treat is

based on the magnitude of the deviation.

•Burian’s classic treatment recommendations and classification of exotropia are based on some

assumptions that are probably incorrect. They need not be strictly followed.

•Intermittent exotropes with a true high AC/A ratio are uncommon but do exist. Standard surgery based on the distance angle frequently results in an overcorrection at near.

•Patients with fusional convergence insufficiency are different from exotropes with accommodative convergence insufficiency; the latter have a low

or absentAC/Aratio and are difficult to treat surgically; the former do well with orthoptic exercises.

•Patients with intermittent exotropia and monofixation syndrome have a poorer sensory outcome after surgery.

9.1Prevalence and Epidemiology

Exodeviations occur about one third as frequently as esodeviations, are more frequent in females than males, and have a higher prevalence in sunnier latitudes [18, 19, 29]. Exodeviations also occur more frequently in children with craniofacial anomalies (Fig. 9.1), neurologic impairment, or if there was a history of maternal smoking during pregnancy [13, 20]. There is probably a genetic component to the development of exotropia; however, it is most likely multifactorial [27].

9.2Etiology and Classification

Historically there has been disagreement about the etiology of exotropia. Theories have included an imbalance of the normal reciprocal relationship between convergence and divergence, mechanical and anatomic factors, and a combination of the two [55].

Traditionally exodeviations have been classified according to the relationship between the distance and near deviation. Burian’s modification of Duane’s classification is classic, [9, 10, 11, 17]; however, it implies some etiologies that are probably incorrect

[34, 37, 38, 41]. In spite of this, these categories are descriptive and have some clinical utility. They are:

1.Convergence Insufficiency Pattern: The distance deviation is at least 10 prism diopters (PD) less than the near deviation.

2.Basic Exodeviation: The distance deviation is within 10 PD of the near deviation.

Fig. 9.1  This boy has an exotropia shown here with his right eye deviating. He was born with multiple congenital anomalies and craniofacial abnormalities

9.3Sensory Adaptation

With intermittent exotropia, suppression is typically facultative. This means that when the eyes are aligned there is no suppression, and when the deviation becomes manifest the deviating eye is suppressed. The suppression scotoma may be regional in that it can include the fovea and much of the periphery. All the visual field of the deviating eye that overlaps the fixing eye may be suppressed [24, 25, 50, 51]. Of great clinical importance is the fact that most exotropic patients suppress while the image of regard falls on temporal retina of the deviating eye, but immediately see double if the image falls on nasal retina. This has important implications for the management of exotro-

10PD.

4.Simulated Divergence Excess Pattern: Initially the distance deviation exceeds the near deviation by at least 10 PD; however, special tests to suspend near fusion reveal a near deviation that will be within

10PD of the distance deviation.

This classification has more recently been modified by Kushner to include the role played by the fusional mechanism as well as accommodative convergence (see Sect. 9.4.5.6 for further discussion) [34, 37, 38, 39, 41].

sults of testing for retinal correspondence are inconsistent in exotropes. Many patients with intermittent exotropia have normal fusion with 40 s of stereopsis when they are aligned, and manifest suppression with no stereopsis when tropic.

Some patients with exotropia will experience panoramic vision (a wider binocular field) when tropic. In fact, unlike patients with esotropia who experience an expansion of their binocular visual field after surgery, some exotropes will indicate that they miss this wider field of vision after successful surgery. Von Noorden described the interesting case of an exotro-

pic rural mail carrier who was unhappy after his eyes were successfully aligned surgically [59]. Prior to surgery, he was able to watch the road with his dominant left eye, and simultaneously scan the mailboxes at the roadside with his right eye. After surgery, his binocular field was reduced to a normal range, but he missed the ability to use this panoramic vision.

9.4Types of Exodeviations

9.4.1Exophoria

An exophoria is a latent exodeviation that, by definition, is only manifest in the dissociated state, e.g., under cover, or with red-green glasses. Many adults have small-angle exophorias that are clinically insignificant, and they do not need treatment. Depending on the magnitude of the deviation and the patient’s fusional convergence amplitudes, an exophoria may cause headache or asthenopia. In this situation, orthoptic exercises or prisms incorporated in spectacles may be helpful. It is important to optimize visual acuity with a careful refraction, and to correct any anisometropia. If a patient reports intermittent diplopia, the deviation must be intermittently manifest and hence is an intermittent tropia instead of a phoria.

are not based on as sound clinical data due to the relative infrequent occurrence of this disorder. These guidelines include providing proper optical correction if appropriate, treating amblyopia, and operating to restore alignment. This should be done between 6 months and a year of age, provided that there are no medical or neurologic issues that require prior attention. A standard surgical formula for other forms of exotropia can be used to treat infantile exotropia; however, many surgeons prefer to not exceed 7 mm for bilateral lateral rectus recessions in infants. Sensorially, patients with infantile exotropia are similar to those with infantile esotropia. They typically develop subnormal fusion with deficient stereopsis, even after successful surgical realignment, and they have a high incidence of subsequently developing dissociated vertical divergence and dissociated horizontal deviations [22, 60].

9.4.3Sensory Exotropia

The normal anatomic configuration of the orbits tends to favor an exotropic position. If there is unilateral or bilateral vision impairment the fusion reflex will be impeded, and these anatomic factors will tend to cause an exotropia. This is referred to as a sensory

9.4.2Infantile Exotropia

Infantile (or congenital) exotropia shares many features with infantile esotropia, and some important differences. It is characterized by a constant exotropia that is present by 6 months of age. The deviation is often large, in the range of 35−60 PD; however, smaller deviations may be found. It is much less common than infantile esotropia and is much more likely to be associated with neurologic problems or developmental delay (Fig. 9.2). The child’s primary care doctor should be alerted to this frequent association and should pay careful attention to the child’s developmental milestones. If there is any doubt, referral to an appropriate specialist is advised. The guidelines for treating infantile exotropia are similar to those recommended for infantile esotropia; however, they

Fig. 9.2  This 5-month-old child has a constant exotropia, shown here with her right eye deviating, that was present since 2 months of age. She had been born prematurely and subsequently was found to have periventricular leukomalacia