Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

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Heterophoria

Heterophoria may present clinically with associated visual symptoms, particularly at times of stress or poor health, when the fusional amplitudes are insufficient to maintain alignment.

1Signs. Both esophoria and exophoria can be classified by the distance at which the angle is greater: (respectively, convergence excess or weakness, divergence weakness or excess and mixed).

2Treatment

•Orthoptic treatment is of most value in convergence weakness exophoria.

•Any significant refractive error should be appropriately corrected.

•Symptom relief may otherwise be obtained using temporary stick-on Fresnel prisms and may be subsequently incorporated into spectacles (maximum usually 10–12 Δ, split between the two eyes).

•Surgery may occasionally be required for larger deviations.

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Vergence abnormalities

Convergence insufficiency

Convergence insufficiency (CI) typically affects individuals, such as students, with excessive near visual demand.

1Signs. Reduced near point of convergence independent of any heterophoria.

2Treatment involves orthoptic exercises aimed at normalizing the near point and maximizing fusional amplitudes. With good compliance, symptoms should be eliminated within a few weeks but if persistent can be treated with base-in prisms.

3Accommodative insufficiency (AI) is occasionally also present. It may be idiopathic (primary) or post-viral and typically affects school-age children. The minimum reading correction to give clear vision is prescribed but is often difficult to discard.

Divergence insufficiency

Divergence paresis or paralysis is a rare condition typically associated with underlying neurological disease, such as intracranial spaceoccupying lesions, cerebrovascular accidents and head trauma. Presentation may be at any age and may be difficult to differentiate from 6th nerve palsy, but is primarily a concomitant esodeviation with reduced or absent divergence fusional amplitudes. It is difficult to treat; prisms are the best option.

Near reflex insufficiency

1Paresis of the near reflex presents as dual convergence and accommodation insufficiency. Mydriasis may be seen on attempted near fixation. Treatment involves reading glasses, base-in prisms and possibly botulinum toxin (orthoptic exercises have no effect). It is difficult to eradicate.

2Complete paralysis in which no convergence or accommodation can be initiated may be of functional origin, due to midbrain disease or may follow head trauma; recovery is possible.

Spasm of the near reflex

Spasm of the near reflex is a functional condition affecting patients of all ages (mainly females).

1Signs

•Diplopia, blurred vision and headaches are accompanied by esotropia, pseudomyopia and miosis.

•Spasm may be triggered when testing ocular movements (Fig. 18.47A).

•Observation of miosis is the key to the diagnosis (Fig. 18.47B).

•Refraction with and without cycloplegia confirms the pseudomyopia, which must not be corrected optically.

2Treatment involves reassurance and advising the patient to discontinue any activity that triggers the response. If persistent, atropine and a full reading correction are prescribed but it is difficult later to abandon treatment without recurrence. Patients usually manage to live a fairly normal life despite the signs and symptoms.

Fig. 18.47 (A) Spasmof the near reflex precipitated on testing ocular movements; (B) right esotropia and miosis

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Esotropia

Esotropia (manifest convergent squint) may be concomitant or incomitant. In a concomitant esotropia the variability of the angle of deviation is within 5 in different horizontal gaze positions. In an incomitant deviation the angle differs in various positions of gaze as a result of abnormal innervation or restriction. This section deals only with concomitant esotropia. A classification is shown in Table 18.1. However, all squints are different and not all fit neatly into a classification. For example, a microtropia may occur with a number of the other categories. It is more important to understand the part played by binocular function, refractive error and accommodation in the pathophysiology of each individual squint and to tailor treatment accordingly.

Table 18.1 -- Classification of esotropia

1. Accommodative

Early-onset esotropia

Up to the age of 4 months, infrequent episodes of convergence are normal but thereafter ocular misalignment is abnormal. Early-onset (congenital, essential, infantile) esotropia is an idiopathic esotropia developing within the first 6 months of life in an otherwise normal infant with no significant refractive error and no limitation of ocular movements.

Signs

•The angle is usually fairly large (>30 Δ) and stable.

•Fixation in most infants is alternating in the primary position (Fig. 18.48).

•There is cross-fixating in side gaze, so that the child uses the left eye in right gaze (Fig. 18.49A) and the right eye on left gaze (Fig. 18.49B). Such cross-fixation may give a false impression of bilateral abduction deficits, as in bilateral 6th nerve palsy.

•Abduction can usually be demonstrated, either by the doll's head manoeuvre or by rotating the child.

•Should these fail, uniocular patching for a few hours will often unmask the ability of the other eye to abduct.

•Nystagmus is usually horizontal.

•Latent nystagmus (LN) is only seen when one eye is covered and the fast phase beats towards the side of the fixing eye. This means that the direction of the fast phase reverses according to which eye is covered.

•Manifest latent nystagmus (MLN) is the same except that nystagmus is present with both eyes open, but the amplitude increases when one is covered.

•The refractive error is usually normal for the age of the child (about +1 to +2 D).

•Asymmetry of optokinetic nystagmus is present.

•Inferior oblique overaction may be present initially or develop later (see Fig. 18.51).

•Dissociated vertical deviation (DVD) develops in 80% by the age of 3 years (see Fig. 18.52).

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Fig. 18.48 Alternating fixation in early-onset esotropia. (A) Fixating right eye; (B) fixating left eye

(Courtesy of J Yangüela)

Fig. 18.49 Cross fixation in early-onset esotropia. (A) left fixation on right gaze; (B) right fixation on left gaze

(Courtesy of R Bates)

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Initial treatment

Early ocular alignment gives the best change of the child developing some degree of binocular function. Ideally, the eyes should be surgically aligned by the age of 12 months, and at the very latest by the age of 2 years, but only after amblyopia or significant refractive errors have been corrected.

•The initial procedure can be either recession of both medial recti or unilateral medial rectus recession with lateral rectus resection. Very large angles may require recessions of 6.5 mm or more. Associated significant inferior oblique overaction should also be addressed.

•Associated with peripheral fusion and central suppression (Fig. 18.50). This small-angle residual strabismus is often stable, even though bifoveal fusion is not achieved.

Fig. 18.50 Early onset esotropia. (A) Before surgery; (B) after surgery

Subsequent treatment

1Undercorrection may require further recession of the medial recti, resection of one or both lateral recti or surgery to the other eye, depending on the initial procedure.

2Inferior oblique overaction may develop subsequently, most commonly at age 2 years (Fig. 18.51). The parents should therefore be warned that further surgery may be necessary despite an initially good result. Initially unilateral, it frequently becomes bilateral within 6 months. Inferior oblique weakening procedures include disinsertion, recession and myectomy.

3DVD may appear several years after the initial surgery, particularly in children with nystagmus. It is characterized by the following:

•Up-drift with excyclorotation of the eye when under cover (Fig. 18.52B) or spontaneously during periods of visual inattention.

•When the cover is removed the affected eye will move down without a corresponding down-drift of the other eye (Fig. 18.52C).

•Thus DVD does not obey the Hering law. Although it is usually bilateral, it may be asymmetrical.

•Surgical treatment is indicated when the condition is cosmetically unacceptable. Superior rectus recession with or without posterior fixation sutures (see later) or inferior oblique anterior transposition are useful for DVD, although full elimination is seldom possible.

4Amblyopia subsequently develops in about 50% of cases as unilateral fixation preference commonly develops postoperatively.

5An accommodative element should be suspected if the eyes are initially straight or almost straight after surgery and then start to reconverge. It is therefore important to perform repeated refractions on all children and to correct any new accommodative elements accordingly.

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Fig. 18.51 Bilateral inferior oblique overaction. (A) Straight eyes in the primary position; (B) left inferior oblique overaction on right gaze; (C) right inferior oblique overaction on left gaze

Fig. 18.52 Dissociated vertical deviation. (A) Straight eyes in the primary position; (B) up-drift of left eye under cover; (C) up-drift of right eye under cover and down-drift of left eye

Differential diagnosis

1 Congenital bilateral 6th nerve palsy, which is rare and can be excluded as described above.

2Secondary (sensory) esotropia due to organic eye disease.

3Nystagmus blockage syndrome in which convergence dampens a horizontal nystagmus. Nystagmus can be elicited on abduction and the infant adopts a face turn to fixate in the adducted position.

4 Duane syndrome types I and III.

5Möbius syndrome.

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6Strabismus fixus.

Accommodative esotropia

Near vision involves both accommodation and convergence. Accommodation is the process by which the eye focuses on a near target, by altering the curvature of the crystalline lens. Simultaneously, the eyes converge, in order to fixate bi-foveally on the target. Both accommodation and convergence are quantitatively related to the proximity of the target, and have a fairly constant relationship to each other (AC/A ratio) as described previously. Abnormalities of the AC/A ratio are an important cause of certain types of esotropia.

Refractive accommodative esotropia

In this type of accommodative esotropia, the AC/A ratio is normal and esotropia is a physiological response to excessive hypermetropia, usually between +2.00 and +7.00 D. The considerable degree of accommodation required to focus clearly on even a distant target is accompanied by a proportionate amount of convergence, which is beyond the patient's fusional divergence amplitude. It cannot therefore be controlled, and a manifest convergent squint results. The magnitude of the deviation varies little (usually <10 Δ) between distance and near. The deviation typically presents at the age of 18 months–3 years (range 6 months–7 years).

1Fully accommodative esotropia is characterized by hypermetropia with esotropia when the refractive error is uncorrected (Fig. 18.53A). The deviation is eliminated and BSV is present at all distances following optical correction of hypermetropia (Fig. 18.53B).

2Partially accommodative esotropia is reduced, but not eliminated by full correction of hypermetropia (Fig. 18.54). Amblyopia is frequent as well as bilateral congenital superior oblique weakness. Most cases show suppression of the squinting eye although ARC may occur, but of lower grade than in microtropia.

Fig. 18.53 Fully accommodative esotropia. (A) Left esotropia without glasses; (B) straight eyes for near and distance with glasses

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Fig. 18.54 Partially accommodative esotropia. (A) Right esotropia without glasses; (B) angle is reduced but not eliminated with glasses

Non-refractive accommodative esotropia

In this type of accommodative esotropia the AC/A ratio is high so that a unit increase of accommodation is accompanied by a disproportionately large increase in convergence. This occurs independently of refractive error, although hypermetropia frequently coexists. It can be subdivided into:

1Convergence excess

•High AC/A ratio due to increased accommodative convergence (accommodation is normal, convergence is increased).

•Normal near point of accommodation.

•Straight eyes with BSV for distance (Fig. 18.55A).

•Esotropia for near, usually with suppression (Fig. 18.55B).

•Straight eyes through bifocals (Fig. 18.55C).

2Hypoaccommodative convergence excess

•High AC/A ratio due to decreased accommodation (accommodation is weak, necessitating increased effort, which produces over-convergence).

•Remote near point of accommodation.

•Straight eyes with BSV for distance.

•Esotropia for near, usually with suppression.

Fig. 18.55 Convergence excess esotropia. (A) Eyes straight for distance; (B) right esotropia for near; (C) eyes straight when looking through bifocals

Treatment

1Correction of refractive error is the initial treatment.

•In children under the age of 6 years, the full cycloplegic refraction revealed on retinoscopy should be prescribed, with a deduction only for the working distance. In the fully accommodative refractive esotrope this will control the deviation for both near and distance.

•After the age of 8 years, refraction should be performed without cycloplegia and the maximal amount of ‘plus’ that can be tolerated (manifest hypermetropia) prescribed.

•For convergence excess esotropia bifocals may be prescribed to relieve accommodation (and thereby accommodative convergence), thus allowing the child to maintain bi-foveal fixation and ocular alignment at near (see Fig. 18.55C). The minimum ‘add’ required to achieve this is prescribed.

•The most satisfactory form of bifocals is the executive type in which the intersection crosses the lower border of the pupil. The strength of the lower segment should be gradually reduced and eliminated by the early teenage years.

•Bifocals are best suited to hypoaccommodative esotropia where the AC/A ratio is not overly excessive and there is a reasonable chance of discarding bifocal correction with time.

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•At higher levels surgery is the better long-term option. The ultimate prognosis for complete withdrawal of spectacles is related to the magnitude of the AC/A ratio and to the degree of hypermetropia and associated astigmatism. Spectacles may be needed only for close work.

2Surgery is aimed at restoring or improving BSV, or to improve the appearance of the squint and so the child's social functioning.

•Surgery should only be considered if spectacles do not fully correct the deviation and after every attempt has been made to treat amblyopia.

•Bilateral medial rectus recessions are performed in patients in whom the deviation for near is greater than that for distance.

•If there is no significant difference between distance and near measurements, and equal vision in both eyes, some perform unilateral medial rectus recession combined with lateral rectus resection, whereas others prefer bilateral medial rectus recessions.

•In patients with residual amblyopia surgery is usually performed on the amblyopic eye.

•In partially accommodative esotropia surgery to improve appearance is best delayed until requested by the child to avoid early consecutive exotropia, and should aim to correct only the residual squint present with glasses worn.

•The usual first procedure for convergence excess esotropia is recession of both medial rectus muscles. This relies on fusion to prevent a distance exotropia; a few patients become divergent after surgery and need a further procedure.

•Medial rectus posterior fixation sutures (Faden operation) can also be used either as a first procedure, or in the case of under-correction following bimedial recessions.

Microtropia

Microtropia (monofixation syndrome), may be primary or follow surgery for a large deviation. It may occur in apparent isolation, but it is often associated with other conditions such as anisometropic amblyopia. Microtropia is more a description of binocular status than a specific diagnosis, for example a patient with fully accommodative esotropia may control to a microtropia rather than true bifoveal BSV with glasses. It is characterized by the following:

2Central suppression scotoma in the deviating eye.

3ARC with reduced stereopsis and variable peripheral fusional amplitudes.

4 Anisometropia is often present, commonly with hypermetropia or hypermetropic astigmatism.

5Symptoms are rare unless there is an associated decompensating heterophoria.

6Treatment involves correction of refractive errors and occlusion for amblyopia as indicated. Most patients remain stable and symptom-free.

Others esotropias

Near esotropia (non-accommodative convergence excess)

1 Presentation is usually in older children and young adults.

2Signs

•No significant refractive error.

•Orthophoria or small esophoria with BSV for distance.

•Esotropia for near but normal or lowAC/A ratio.

•Normal near point of accommodation.

3 Treatment involves bilateral medial rectus recessions.

Distance esotropia

1 Presentation is in healthy young adults who are often myopic.

2Signs

•Intermittent or constant esotropia for distance.

•Minimal or no deviation for near.

•Normal bilateral abduction.

•Fusional divergence amplitudes may be reduced.

•Absence of neurological disease.

3 Treatment is with prisms until spontaneous resolution or surgery in persistent cases.

Acute (late-onset) esotropia

1Presentation is around 5–6 years of age.

2Signs

•Sudden onset of diplopia and esotropia.

•Normal ocular motility without significant refractive error.

•Underlying 6th nerve palsy must be excluded.

3Treatment is aimed at re-establishing BSV to prevent suppression, using prisms, botulinum toxin or surgery.

Secondary (sensory) esotropia

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