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

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Alphabet patterns

‘V ‘or ‘A’ patterns may occur when the relative contributions of the superior rectus and inferior oblique to elevation, or of the inferior rectus and superior oblique to depression are abnormal, resulting in abnormal balance of their horizontal vectors in upand downgaze. They can also be caused by anomalies in the position of the rectus muscle pulleys leading to abnormal lines of action of the muscles. They are assessed by measuring horizontal deviations in the primary position, upgaze and downgaze and may occur regardless of whether a deviation is concomitant or incomitant.

‘V’ pattern

A ‘V’ pattern is said to be significant when the difference between upgaze and downgaze is ≥15 (allowing for a small physiological variation).

Causes

•Inferior oblique overaction associated with 4th nerve palsy.

•Superior oblique underaction with subsequent inferior oblique overaction, seen in infantile esotropia as well as other childhood esotropias. The eyes are often straight in upgaze with a marked esodeviation in downgaze.

•Superior rectus underaction.

•Brown syndrome.

•Craniofacial anomalies featuring shallow orbits and down-slanting palpebral fissures.

Treatment

By inferior oblique weakening or superior oblique strengthening when oblique dysfunction is present. Without oblique muscle dysfunction treatment is as follows:

1‘V’ pattern esotropia (Fig. 18.66A) can be treated by bilateral medial rectus recessions and downward transposition of the tendons.

2‘V’ pattern exotropia (Fig. 18.66B) can be treated by bilateral lateral rectus recessions and upward transposition of the tendons.

Fig. 18.66 ‘V’ pattern. (A) Esotropia; (B) exotropia

(Courtesy of Wilmer Institute)

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‘A’ pattern

An ‘A’ pattern is considered significant if the difference between upgaze and downgaze is ≥10 . In a binocular patient it may cause problems with reading.

Causes

•Primary superior oblique overaction is usually associated with exodeviation in the primary position of gaze.

•Inferior oblique underaction/palsy with subsequent superior oblique overaction.

•Inferior rectus underaction.

Treatment

Patients with oblique dysfunction are treated by superior oblique posterior tenotomy. Treatment of cases without oblique muscle dysfunction is as follows:

1‘A’ pattern esotropia (Fig. 18.67A) is treated by bilateral medial rectus recessions and upward transposition of the tendons.

2‘A’ pattern exotropia (Fig. 18.67B) is treated by bilateral lateral rectus recessions and downward transposition of the tendons.

Fig. 18.67 ‘A’ pattern. (A) Esotropia; (B) exotropia

(Courtesy of Wilmer Institute)

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Surgery

The most common aims of surgery on the extraocular muscles are to correct misalignment to improve appearance, and if possible to restore BSV. Surgery can also be used to reduce an abnormal head posture and to expand or centralize a field of BSV. However, the first step in the management of childhood strabismus involves correction of any significant refractive error and/or treatment of amblyopia. Once maximal visual potential is reached in both eyes, any residual deviation can be treated surgically. The three main types of procedure are: (a) weakening, which decreases the pull of a muscle, (b) strengthening, which enhances the pull of a muscle and (c) procedures that change the direction of muscle action.

Weakening procedures

The procedures for weakening the action of a muscle are: (a) recession, (b) disinsertion (or myectomy) and (c) posterior fixation suture.

Recession

Recession slackens a muscle by moving it away from its insertion. It can be performed on any muscle except the superior oblique.

1Rectus muscle recession

aThe muscle is exposed and two absorbable sutures are tied through the outer quarters of the tendon.

bThe tendon is disinserted from the sclera, and the amount of recession is measured and marked on the sclera with callipers.

cThe detached end of the muscle is sutured to the sclera at the measured distance behind its original insertion (Fig. 18.68).

2Inferior oblique disinsertion or recession

aThe muscle belly is exposed through an inferotemporal fornix incision.

bA squint hook is passed behind the posterior border of the muscle which must be clearly visualized. Care is taken to pick up the muscle without disrupting the Tenon's capsule and fat posterior to it.

cAn absorbable suture is passed through the anterior border of the muscle at its insertion and tied.

dThe muscle is disinserted and the cut end sutured to the sclera 3 mm posterior and temporal to the temporal edge of the inferior rectus insertion (Fig. 18.69).

Fig. 18.68 Recession of a horizontal rectus muscle

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Fig. 18.69 Recession of an inferior oblique muscle

Disinsertion

Disinsertion involves detaching the muscle from its insertion without reattachment. It is most commonly used to weaken an overacting inferior oblique muscle when the technique is the same as for a recession except that the muscle is not sutured. Very occasionally, the procedure is performed on a severely contracted rectus muscle.

Posterior fixation suture

The principle of this (Faden) procedure is to suture the muscle belly to the sclera posteriorly so as to decrease the pull of the muscle in its field of action without affecting the eye in the primary position. The Faden procedure may be used on the medial rectus to reduce convergence in a convergence excess esotropia and on the superior rectus to treat DVD. When treating DVD, the superior rectus muscle may also be recessed. The belly of the muscle is then anchored to the sclera with a non-absorbable suture about 12 mm behind its insertion.

Strengthening procedures

1Resection shortens a muscle to enhance its effective pull. It is suitable only for a rectus muscle and involves the following steps:

aThe muscle is exposed and two absorbable sutures tied into the muscle at a measured distance behind its insertion.

bThe muscle anterior to the sutures is excised and the cut end reattached to the original insertion (Fig. 18.70).

2Tucking of a muscle or its tendon is usually reserved to enhance the action of the superior oblique muscle in congenital 4th nerve palsy.

3Advancement of the muscle nearer to the limbus can be used to enhance the action of a previously recessed rectus muscle.

Fig. 18.70 Resection of a horizontal rectus muscle

Treatment of paretic strabismus

Lateral rectus palsy

Surgical intervention for 6th nerve palsy should be considered only when it is clear that spontaneous improvement will not occur. This is usually after at least 3 months have elapsed without improvement, typically at least 6 months from onset of the palsy. Treatment of partial and complete lateral rectus palsies is different.

1Partial palsy (paresis) is treated by adjustable medial rectus recession and lateral rectus resection of the affected eye, aiming for a

small exophoria in the primary position to maximize the field of BSV.

2Complete palsy is treated by transposition of the superior and inferior recti to positions above and below the affected lateral rectus

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Indications

The results of strabismus surgery can be improved by the use of adjustable suture techniques on the rectus muscles. These are particularly indicated when a precise outcome is essential and when the results with more conventional procedures are likely to be unpredictable; for example, acquired vertical deviations associated with thyroid myopathy or following a blow-out fracture of the floor of the orbit. Other indications include 6th nerve palsy, adult exotropia and re-operations in which scarring of surrounding tissues may make the final outcome unpredictable. The main contraindication is patients who are too young or unwilling to cooperate during postoperative suture adjustment.

Initial steps

a The muscle is exposed, sutures inserted and the tendon disinserted from the sclera as for a rectus muscle recession.

bThe two ends of the suture are passed, close, together, through the stump of the insertion.

c A second suture is knotted and tied tightly around the muscle suture anterior to its emergence from the stump (Fig. 18.73A). d One end of the suture is cut short and the two ends tied together to form a loop (Fig. 18.73B).

eThe conjunctiva is left open.

Fig. 18.73 Adjustable suture technique

Postoperative adjustment

This is performed under topical anaesthesia, usually a few hours after surgery when the patient is fully awake.

aThe accuracy of alignment is assessed.

bIf ocular alignment is satisfactory the muscle suture is tied off and its long ends cut short.

cIf more recession is required, the bow is pulled anteriorly along the muscle suture, thereby providing additional slack to the recessed muscle and enabling it to move posteriorly (Fig. 18.73C).

d If less recession is required, the muscle suture is pulled anteriorly and the knot tightened against the muscle stump (Fig. 18.73D). e Alignment is retested and adjustment repeated as required.

fThe conjunctiva is closed.

A similar technique can be used for rectus muscle resection.

Botulinum toxin chemodenervation

Temporary paralysis of an extraocular muscle can be created by an injection of botulinum toxin under topical anaesthesia and EMG control. The effect takes several days to develop, is usually maximal at 1–2 weeks following injection and has generally worn off by 3 months. Sideeffects are uncommon, although about 5% of patients may develop some degree of temporary ptosis. The following are the main indications for chemodenervation:

1To determine the risk of postoperative diplopia. For example, in an adult with a consecutive left divergent squint and left suppression, straightening the eyes may make suppression less effective resulting in diplopia. If postoperative diplopia testing by correcting the angle with prisms is negative then the risk of double vision after surgery is very low. If testing is positive then the left lateral rectus muscle can be injected with toxin so that the eyes will either straighten or converge and the risk of diplopia can be assessed over several days while the eyes are straight. If diplopia does occur the patient is able to judge whether it is troublesome.

2To assess the potential for BSV in a patient with a constant manifest squint by straightening the eyes temporarily. The deviation

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can then be corrected surgically if appropriate. A small proportion of patients maintain BSV long-term when the effects of the toxin have worn off.

3In lateral rectus palsy botulinum toxin can be injected into the ipsilateral medial rectus to give symptomatic relief during recovery and to see whether there is any lateral rectus action when there is medial rectus contracture (Fig. 18.74A). The temporary paralysis of the muscle causes relaxation so that the horizontal forces on the globe are more balanced, thus allowing assessment of lateral rectus function (Fig. 18.74B).

4Patients with a cosmetically poor deviation who have undergone multiple squint operations can be treated by repeated BT injections which may reduce in frequency with time.

Fig. 18.74 Principles of botulinumtoxin chemodenervation in left 6th nerve palsy

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Chapter 19 – Neuro-ophthalmology

NEUROIMAGING 784 Computed tomography 784 Magnetic resonance imaging  785

Angiography 788

OPTIC NERVE 789 Anatomy 789

Visual evoked potential 790

Signs of optic nerve dysfunction 790 Optic atrophy 790

Classification of optic neuritis 791 Demyelinating optic neuritis 792 Parainfectious optic neuritis 794 Infectious optic neuritis 794 Non-infectious optic neuritis 794 Neuroretinitis 795

Non-arteritic anterior ischaemic optic neuropathy  796

Arteritic anterior ischaemic optic neuropathy 796 Posterior ischaemic optic neuropathy 798 Diabetic papillopathy 798

Leber hereditary optic neuropathy 799 Hereditary optic atrophy 799 Nutritional optic neuropathy 800 Papilloedema 801

Congenital optic disc anomalies 802

PUPILLARY REACTIONS 812 Anatomy 812

Afferent pupillary defect 812 Oculosympathetic palsy (Horner syndrome)  813

Adie pupil 815

Other abnormal reactions 815

CHIASM 816 Anatomy 816 Physiology 822 Pituitary adenomas  823 Craniopharyngioma  826 Meningioma 826

RETROCHIASMAL PATHWAYS 827 Optic tract 827

Optic radiations  828

Striate cortex 829

OCULAR MOTOR NERVES 830 3rd nerve

 830 4th nerve  833 6th nerve  835

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SUPRANUCLEAR DISORDERS OF OCULAR MOTILITY 838 Conjugate eye movements

 838

Horizontal gaze palsy 839 Vertical gaze palsy 840

NYSTAGMUS 841 Introduction 841 Physiological nystagmus 841 Vestibular nystagmus 842

Motor imbalance nystagmus 843 Sensory deprivation nystagmus  845

Surgery for nystagmus 845 Nystagmoid movements 846

CAROTID STENOSIS 846 INTRACRANIAL ANEURYSMS 847

Anatomy 847

Neurological considerations 847 Neuro-ophthalmic considerations  848

OCULAR MYOPATHIES 849 Myasthenia gravis 849 Myotonic dystrophy 852

Chronic progressive external ophthalmoplegia  852

Eaton–Lambert myasthenic syndrome 854

NEUROFIBROMATOSIS 854 Neurofibromatosis type 1  854

Neurofibromatosis type 2  854

MIGRAINE 855 Clinical features 855 Treatment 858 Differential diagnosis  858

FACIAL SPASM 859 Essential blepharospasm  859

Hemifacial spasm 860

Neuroimaging

Computed tomography

Physics

Computed tomography (CT) uses X-ray beams to obtain tissue density values from which detailed cross-sectional images are formed by a computer. Tissue density is represented by a grey scale, white being maximum density (e.g. bone) and black being minimum density (e.g. air). Advanced CT scanners are able to acquire thinner slices leading to improved spatial resolution, together with faster examination times, without a proportionate increase in radiation dose. Images are acquired in an axial form and can be viewed in any plane using computer reconstruction. This multiplanar information can be an advantage over MR with regard to anatomical detail. CT is widely available, easy to perform, relatively inexpensive and quick but unlike MR it exposes the patient to ionizing radiation.

Contrast enhancement

Iodinated contrast material improves sensitivity and specificity but is contraindicated in patients allergic to iodine and in those with renal failure. Contrast is not indicated in acute haemorrhage, bony injury or localization of foreign bodies because it may mask visualization of these high density structures.

Indications

1Orbital trauma, for the detection of bony lesions such as fractures (Fig. 19.1A), blood, herniation of extraocular muscles into the maxillary sinus and surgical emphysema.

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