Ординатура / Офтальмология / Английские материалы / Moorfields Manual of Ophthalmology_Jackson_2007

■Botulinum toxin : useful in assessing the risk of postoperative diplopia in ‘cosmetic’ cases not expected to achieve BSV. Also diagnostically useful in cases with weak potential BSV to see if this can be restored, and where several previous squint procedures make surgery unpredictable.

■Orthoptic exercises : aim to improve the quality of BSV, and are based on physiological diplopia and using the relationship between accommodation and convergence (e.g. bar reading, stereograms) in carefully selected patients with fully accommodative or convergence excess esotropia, or as an adjunct to surgery.

■Prisms : may help small-angle deviations, especially in distance esotropia.

■Surgery : performed to improve the appearance of the eyes and, where possible, to restore binocular vision. In general, if surgery is aiming to restore binocular function, it is performed once hypermetropia is satisfactorily corrected and amblyopia treated. The timing of surgery to improve appearance is largely a matter of patient (or parent) preference.

1.Constant esotropia with an accommodative element :

operate if cosmetically unsatisfactory with glasses. Consider medial rectus recession (MR− ) with lateral rectus resection (LR+) if the deviation is a similar size near and distance, or bilateral MR (bimedial) recessions if the deviation is larger at near. Undercorrect, as residual convergence tends to reduce over time: in the absence of BSV there is a high risk of consecutive exotropia.

2.Early-onset esotropia : requires early surgery, preferably before age 1 year, for any chance of binocular vision, but most patients suppress and there is a risk of consecutive exotropia. Surgery may involve bimedial recession, or medial rectus recession/lateral rectus resection. Patients usually need more than one procedure; however, multiple procedures mean a higher risk of consecutive exotropia as many patients continue to suppress. For cosmetically poor DVD consider bilateral inferior oblique anterior positioning or bilateral superior recti recessions (with Faden procedure for worse eye, if asymmetrical).

3.Late-onset esotropia : botulinum toxin or surgery if BSV not restored by glasses.

4.Convergence excess esotropia : notoriously difficult to manage. Start with bimedial recessions, with further

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Esotropia

surgery including Faden procedures or supramaximal medial rectus recessions.

5.Near esotropia : normally undertake bimedial recessions.

6.Distance esotropia : if not controlled with prisms, usually requires bilateral lateral rectus resections using adjustable sutures, although not all clinicians agree with this surgical approach.

7.Cyclic esotropia : consider medial rectus recession with lateral rectus resection as the deviation is usually a similar size near and distance.

Exotropia

Background Exotropia is a manifest divergent squint. The following relates to concomitant exotropia (angle of deviation the same in all positions of gaze and regardless of which eye is fixing). For incomitant strabismus, see page 601.

Classification

■Primary exotropia.

1.Constant.

a.Early-onset exotropia : typically associated with dissociated vertical deviation and manifest latent nystagmus. Much less common than early-onset esotropia and found particularly in Asian or African populations.

b.Constant primary exotropia : rare. Exclude secondary exotropia or decompensating intermittent exotropia. Be suspicious of an associated neurological or developmental problem.

2.Intermittent.

a.Distance exotropia : binocular single vision (BSV) at near; intermittent or constant exotropia at distance. Diplopia is very rare as suppression normally occurs on divergence. Subdivided into 2 types – true distance exotropia and simulated distance exotropia (see differential diagnosis below).

b.Near exotropia : BSV for distance; exotropia for near. Commoner in adults than children, e.g. existing near exophoria decompensated by presbyopic correction.

c.Non-specific exotropia : intermittent exotropia can present in any age group, and for either near or distance fixation.

■Consecutive exotropia : usually follows surgery for esotropia after a variable period of time. Usually constant but can be intermittent.

■Secondary exotropia : constant, secondary to visual impairment, usually >2 years of age.

Symptoms Ask about diplopia, although this is rare except in near and occasionally in consecutive exotropia. Intermittent exotropia commonly presents in toddlers or infants; ask about closure of one eye in bright sunlight. Ask about previous eye treatment or surgery.

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Signs VA is reduced in secondary esotropia. Amblyopia is common in consecutive exotropia but rare in intermittent exotropia.

Examination Perform a cover test for near and distance with and without spectacles. Perform the alternate cover test; a slowly recovering latent deviation may decompensate (become manifest) later. Examine eye movements. Intermittent exotropia may have a ‘V’ exo or ‘X’ pattern and can have slight limitations of adduction. Consecutive exotropias may have limitation of adduction from previous squint surgery. Reduced convergence can be associated with near exotropia. If VA is reduced, carefully exclude intraocular disease. Obtain refraction.

Investigations The accomodative convergence/ accomodation (AC/A) ratio is often high (> 5 : 1) in simulated distance exotropia, normal (3–4 : 1) in true distance exotropia, and low in near exotropia (< 3 : 1). Consider postoperative diplopia testing if there is no BSV, e.g. consecutive or secondary exotropia.

Differential diagnosis Distinguish true from simulated distance exotropia. Simulated distance exotropia can be controlled for near by a high AC/A ratio and/or fusional convergence. Disrupt fusion by occluding one eye for >45 minutes then measure the maximum true near angle.

distance exotropia or other exodeviations if the angle of deviation is much greater at distance. Consecutive exotropia usually requires exploration with medial rectus advancement and lateral rectus recession, using adjustable sutures in patients >10 years of age.

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Microtropia

Microtropia

Background Optimal binocular single vision (BSV) exists with bifoveal fusion. A subnormal variation of BSV can exist with foveal (central) suppression. Microtropia is a small-angle squint (<10 prism dioptres) with foveal suppression in the deviating eye and subnormal stereopsis. Motor fusion is present but the range may be reduced. Microtropia is commonly associated with anisometropia and amblyopia in the deviating eye. Microtropia can also occur after surgical or optical treatment for a larger-angle squint and can be present with other strabismus, e.g. a fully accommodative right microtropia.

Classification

■Microtropia with identity : no manifest deviation on cover test because the eccentric point of fixation coincides with the angle of squint and is used for monocular and binocular fixation. There is abnormal retinal correspondence (ARC) with the angle of anomaly (angle of squint) equal to the angle of eccentricity (angle between abnormal point of retinal fixation and normal fovea (p. 583).

■Microtropia without identity : a minimal flick deviation is seen on cover testing. Usually but not always esotropic. Central or eccentric fixation and ARC are more common than normal retinal correspondence. The angle of anomaly is larger than the angle of eccentricity.

History and examination Take a full history, perform cover testing, examine eye movements, and refract. Anisometropia is common.

Investigations Assess fusion, stereopsis, and measure any deviation with a prism cover test. The simultaneous prism cover test, rarely used in practice, measures the manifest component of the deviation where there is an associated heterophoria. The 4- dioptre prism test (base out for suspected microesotropia) usually shows no movement when the prism is placed in front of the deviating eye due to central suppression.

Treatment Fully correct refractive error (minus working distance). Consider amblyopia therapy, but if motor fusion is absent or poor there is a risk of intractable diplopia in patients >6 years (p. 589). Treatment is unlikely to produce bifoveal fixation. Treat decompensated microtropias as for concomitant strabismus.

Accommodation and

Convergence Disorders

Classification

■Isolated primary convergence insufficiency (CI).

■Primary CI with secondary accommodative insufficiency (AI).

■CI secondary to vertical deviation or decompensating near heterophoria (convergence weakness exophoria).

■Primary AI.

■Near reflex palsy (variably involving convergence, accommodation and pupil).

■Accommodative fatigue.

■Accommodative inertia.

History Patients can present at any age. Symptoms are associated with close work and include blurred vision, difficulty changing focus, horizontal diplopia, headaches,

eyestrain, and nausea. Check medication, as this may contribute to reduced accommodative responses, particularly antidepressants, muscle relaxants, antihistamines, and some antihypertensives.

Examination Assess ocular motility, as decompensating vertical deviations may be unable to converge. Check the near pupil response. In patients with near reflex palsy or marked AI or CI the pupils may fail to constrict, or even dilate, on attempted near fixation. Consider neurological assessment in convergence and accommodation paralysis.

Investigations Test the near point of convergence (NPC). The patient follows a small detailed target as it is slowly moved to within 8–10 cm of the nose on an RAF rule. Test three times. CI is diagnosed if this is not achieved, or if only with effort. Check accommodation under emmetropic conditions using the RAF rule; bring the target progressively nearer until blurred. Alternatively, use increasing plus and then minus lenses to determine the accommodative facility. Reduced accommodation is commonly associated with CI. Examine the prism fusion range, as this is often reduced.

Treatment Leave asymptomatic adults without treatment. Consider treating asymptomatic children if they have any other binocular imbalance. Treat with orthoptic exercises (pen and jump convergence, dot cards, stereograms, and voluntary convergence).

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Consider prisms if symptoms persist despite exercises. Convex lenses may be needed in those with AI. Botulinum toxin may provide some temporary relief in gross CI. Surgery is unhelpful, as CI recurs.

Incomitant Strabismus

Background Incomitant strabismus occurs when the angle of deviation differs depending upon the direction of gaze or according to which eye is fixing. It is associated mostly with defective eye movements, particularly neurogenic or mechanical lesions such as 3rd nerve palsy or thyroid eye disease, and less commonly with asymmetrical accommodative effort such as anisometropia.

History Establish when symptoms occurred (acute, chronic, congenital). Vague symptoms imply that the deviation is longstanding. Ask about diplopia (monocular or binocular; intermittent or constant; position of gaze when it occurs; vertical, horizontal, or tilted images), trauma, hypertension, diabetes, thyroid conditions, previous eye surgery or treatment. Neck ache may occur with recently acquired abnormal head posture (AHP). Longstanding AHP may be asymptomatic.

Examinations Note any AHP, nystagmus, lid malposition, and pupil reactions. Check spectacles for prisms. Perform cover test with and without any AHP. In paralytic strabismus the secondary deviation of the unaffected eye when fixing with the affected eye will be larger than the primary deviation when fixing with the normal eye, based on Hering’s law of equal innervation. Examine ocular movements and perform cover tests in the nine cardinal positions to establish overactions, underactions, and where the deviation is greatest. Compare subjective diplopia with objective findings. Check for bilateral asymmetric underactions. Examine ductions (movements tested monocularly with fellow eye covered) to differentiate underactions versus (mechanical) limitations.

Investigations

■Note the angle of deviation in primary position, fixing right and left eyes, and relevant positions of gaze with the prism cover test (PCT). Look for binocular single vision (BSV), stereopsis, and sensory and motor fusion. Patients with severe head injuries may lose motor fusion with intractable diplopia.

■Synoptophore : useful if BSV is not present in free space and for measuring torsion.

■Hess chart : based on simultaneous perception. Compare the patient’s results with the ‘normal’ grid on the chart. Different

size fields show incomitance. Observe the deviation in the primary position. The smaller field indicates the primarily affected eye (primary deviation), the larger field shows the secondary deviation. The greatest inward displacement compared to the normal field shows the primarily affected

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muscle(s), or in mechanical limitations the greatest restriction of movement. In the larger field the greatest outward displacement from normal indicates the main overacting muscle(s) – the contralateral synergist according to Hering’s law. Longstanding deviations may be more concomitant and identifying the primarily affected muscle can be difficult. In mechanical strabismus the outer field of the Hess chart tends to be compressed. A sloping field indicates an ‘A’ or ‘V’ pattern and not torsion.

■The field of BSV chart : usually plotted on an arc perimeter – shows the size, position, and usefulness of the area of BSV.

■Imaging : and other investigations may be required depending on the cause. See the appropriate sections for details

(p. 612, 3rd nerve palsy; p. 615, 4th nerve palsy; p. 618 6th nerve palsy).

Treatment Initial management of acquired incomitance includes advice about the use of an AHP, stick-on prisms, or occlusion. The prism is usually placed on one eye: the paralytic eye or the eye with the worst VA. The prism can be tilted to join both vertical and horizontal diplopia. It can also be placed on the top segment (or bifocal segment) of spectacles as required. Aim to join diplopia in the primary position and depression at least. Diplopia on extremes of gaze may not be correctable with prisms as this may lead to overcorrection in another position of gaze. Monitor patients, reducing prism strength as they recover or stabilize. Occlusion, (graded frosting, foils, frosted tape, or lenses) is used for large deviations or large incomitance, unsatisfactorily controlled with prisms, or where there is a lack of fusion. Longterm prisms can be incorporated into glasses for small deviations. Orthoptic exercises have a limited role except for associated convergence insufficiency. Treat amblyopia if age <8 years (p. 589).

Surgery for acquired incomitance is indicated for symptomatic deviations such as unsatisfactory control with prism/large AHP, and when the deviation is stable for at least 6 months. The type and number of operations depends on clinical findings. For neurogenic strabismus, weaken the overacting muscle(s). For mechanical strabismus, weaken the tight muscle(s).