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

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Fig. 17.1 (A) Mild vitreous haemorrhage seen against the red reflex; (B) severe diffuse vitreous haemorrhage; (C) B-scan image showing vitreous haemorrhage and flat retina; (D) B-scan image showing vitreous haemorrhage and funnel-shaped retinal detachment

Asteroid hyalosis (Benson disease)

1Pathogenesis. Asteroid hyalosis is a common degenerative process in which tiny calcium-pyrophosphate globules collect within the vitreous gel (Fig. 17.2A). One eye is affected in 75% of patients; the condition rarely causes visual problems and in the majority of cases it is asymptomatic. An association with diabetes has been suggested but is unproven. The prevalence of asteroid hyalosis increases with age and affects 2.9% of those aged 75–86 years. It is more common in men than in women.

2Signs. Numerous tiny round yellow-white particles that vary in size and density (Fig. 17.2B and C). They move with the vitreous during eye movements but do not sediment inferiorly when the eye is immobile.

3US shows very high amplitude echoes (Fig. 17.2D).

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Fig. 17.2 Asteroid hyalosis. (A) Asteroid bodies illuminated by oblique light; (B) mild; (C) severe; (D) B-scan image

(Courtesy of J Harry and G Misson, from Clinical Ophthalmic Pathology, Butterworth-Heinemann, 2001 – fig. A)

Synchisis scintillans (cholesterolosis bulbi)

1Pathogenesis. Synchisis scintillans occurs as a consequence of chronic vitreous haemorrhage, often in a blind eye. The condition is usually discovered when frank haemorrhage is no longer present. The crystals are composed of cholesterol and are derived from plasma cells or degraded products of erythrocytes, and lie either freely or engulfed within foreign body giant cells.

2Signs. Numerous flat golden-brown refractile particles that tend to sediment inferiorly when the eye is immobile. Occasionally the anterior chamber may also be involved (Fig. 17.3).

Fig. 17.3 Synchisis scintillans in the anterior chamber of a degenerate eye

(Courtesy of P Gili)

Amyloidosis

1Amyloidosis is a localized or systemic condition in which there is extracellular deposition of a fibrillary protein. Vitreous opacification typically occurs in the familial amyloidosis that is also characterized by polyneuropathy, prominent corneal nerves and light-near dissociation of pupillary reactions.

2Signs. The vitreous opacities may be unilateral or bilateral and are initially perivascular. Later they involve the anterior vitreous and take on a characteristic sheet-like (‘glass wool’) appearance (Fig. 17.4A). The opacities may become attached to the posterior lens by thick footplates (Fig. 17.4B). Dense opacification resulting in significant visual impairment may require vitrectomy.

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Fig. 17.4 Amyloid deposits in the vitreous

Vitreous cyst

Vitreous cysts (Fig. 17.5) are rare congenital remnants of the primary hyaloidal system or ciliary body pigment epithelium. Treatment is seldom required, although laser photocystotomy or vitrectomy have been suggested in patients with annoying symptoms.

Fig. 17.5 Vitreous cyst

(Courtesy of W Lisch)

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Chapter 18 – Strabismus

INTRODUCTION 736

Definitions 736

Anatomy of extraocular muscles  736

Ocular movements 739 Sensory considerations 741

AMBLYOPIA 745

CLINICAL EVALUATION 746 History 746

Visual acuity 747 Tests for stereopsis 748

Tests for binocular fusion in infants without manifest squint  750

Tests for sensory anomalies 750 Measurement of deviation 755 Motility tests 758

Investigation of diplopia 759 Refraction and fundoscopy 763

HETEROPHORIA 765 VERGENCE ABNORMALITIES 765 ESOTROPIA 765

Early-onset esotropia 766 Accommodative esotropia  768

Microtropia 770 Other esotropias 770

EXOTROPIA 771

Constant (early onset) exotropia  771

Intermittent exotropia 771 Sensory exotropia 772 Consecutive exotropia 772

SPECIAL SYNDROMES 772 Duane retraction syndrome 772 Brown syndrome 773 Monocular elevator deficit 774 Möbius syndrome 774

Congenital fibrosis of the extraocular muscles  774

Strabismus fixus 774

ALPHABET PATTERNS 774 ‘V’ pattern

 776

‘A’ pattern  777

SURGERY 778

Weakening procedures 778 Strengthening procedures 779 Treatment of paretic strabismus 779 Adjustable sutures 780

Botulinum toxin chemodenervation  780

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Introduction

Definitions

1Visual axis (line of vision) passes from the fovea, through the nodal point of the eye to the point of fixation (object of regard). In normal binocular single vision (BSV) the two visual axes intersect at the point of fixation, with the images from the two eyes being aligned by the fusion reflex and combined by binocular responsive cells in the visual cortex to give BSV.

2Orthophoria implies perfect ocular alignment in the absence of any stimulus for fusion (uncommon).

3Heterophoria (‘phoria’) implies a tendency of the eyes to deviate when fusion is blocked (latent squint).

•Slight phoria is present in most normal individuals and is overcome by the fusion reflex. The phoria can be either a small inward imbalance (esophoria) or an outward imbalance (exophoria).

•When fusion is insufficient to control the imbalance, the phoria is described as decompensating and is often associated with symptoms of binocular discomfort (asthenopia) or double vision (diplopia).

4Heterotropia (‘tropia’) implies a manifest deviation in which the visual axes do not intersect at the point of fixation.

•The images from the two eyes are misaligned so that either double vision is present or, more commonly in children, the image from the deviating eye is suppressed at cortical level.

•A childhood squint may occur because of failure of the normal development of binocular fusion mechanisms or as a result of oculomotor imbalance secondary to a difference in refraction between the two eyes (anisometropia).

•Failure of fusion, for example secondary to poor vision in one eye, may cause heterotropia in adulthood, or a squint may develop because of weakness or mechanical restriction of the extraocular muscles or damage to their nerve supply.

•Horizontal deviation of the eyes (latent or manifest) is the most common form of strabismus.

•Upward displacement of one eye relative to the other is termed a hypertropia and a latent upward imbalance a hyperphoria.

•Downward displacement is termed a hypotropia and a latent imbalance a hypophoria.

5Anatomical axis is a line passing from the posterior pole through the centre of the cornea. Because the fovea is usually slightly temporal to the anatomical centre of the posterior pole of the eye, the visual axis does not usually correspond to the anatomical axis of the eye.

6Angle kappa is the angle subtended by the visual and anatomical axes and is usually about 5° (Fig. 18.1).

•The angle is positive (normal) when the fovea is temporal to the centre of the posterior pole resulting in a nasal displacement of the corneal reflex, and negative when the converse applies.

•A large angle kappa may give the appearance of a squint when none is present (pseudosquint) and is seen most commonly as a pseudoexotropia following displacement of the macula in retinopathy of prematurity, where the angle may significantly exceed +5°.

Fig. 18.1 Angle kappa

Anatomy of extraocular muscles

Principles

The lateral and medial orbital walls are at an angle of 45° with each other (Fig. 18.2A). The orbital axis therefore forms an angle of 22.5° with both lateral and medial walls. For the sake of simplicity this angle is usually regarded as being 23°.

•When the eye is looking straight ahead at a fixed point on the horizon with the head erect (primary position of gaze), the visual axis forms an angle of 23° with the orbital axis (Fig. 18.2B).

•The actions of the extraocular muscles depend on the position of the globe at the time of muscle contraction.

1 Primary action of a muscle is its major effect when the eye is in the primary position. 2 Subsidiary actions are the additional effects which depend on the position of the eye.

3Listing plane is an imaginary coronal plane passing through the centre of rotation of the globe. The globe rotates on the axes of

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Fick, which intersect in the listing plane (Fig. 18.3).

•The globe rotates left and right on the vertical Z axis.

•The globe moves up and down on the horizontal Xaxis.

•Torsional movements (wheel rotations) occur on the Y (sagittal) axis which traverses the globe from front to back (similar to the anatomical axis of the eye).

•Intorsion occurs when the superior limbus rotates nasally, and extorsion on temporal rotation.

Fig. 18.2 Anatomy of the extraocular muscles

Fig. 18.3 The listing plane and axes of Fick

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Horizontal rectus muscles

When the eye is in the primary position, the horizontal recti are purely horizontal movers on the vertical Z axis and have only primary actions.

1Medial rectus originates at the annulus of Zinn at the orbital apex and inserts 5.5 mm behind the nasal limbus. Its sole action in the primary position is adduction.

2Lateral rectus originates at the annulus of Zinn and inserts 6.9 mm behind the temporal limbus. Its sole action in the primary position is abduction.

Vertical rectus muscles

The vertical recti run in line with the orbital axis and are inserted in front of the equator. They therefore form an angle of 23° with the visual axis (see Fig. 18.2C).

1Superior rectus originates from the upper part of the annulus of Zinn and inserts 7.7 mm behind the superior limbus.

•The primary action is elevation (Fig. 18.4A); secondary actions are adduction and intorsion.

•When the globe is abducted 23°, the visual and orbital axes coincide (Fig. 18.4B). In this position it has no subsidiary actions and can only act as an elevator. This is therefore the optimal position of the globe for testing the function of the superior rectus muscle.

•If the globe were adducted 67°, the angle between the visual and orbital axes would be 90° (Fig. 18.4C). In this position the superior rectus could only act as an intortor.

2Inferior rectus originates at the lower part of the annulus of Zinn and inserts 6.5 mm behind the inferior limbus.

•The primary action is depression; secondary actions are adduction and extorsion.

•When the globe is abducted 23°, the inferior rectus acts purely as a depressor. As for superior rectus, this is the optimal position of the globe for testing the function of the inferior rectus muscle.

•If the globe were adducted 67°, the inferior rectus could only act as an extortor.

Fig. 18.4 Actions of the right superior rectus muscle

Spiral of Tillaux

The spiral of Tillaux is an imaginary line joining the insertions of the four recti and is an important anatomical landmark when performing surgery. The insertions are located progressively further away from the limbus in a spiral pattern; the medial rectus insertion is closest (5.5 mm) followed by the inferior rectus (6.5 mm), lateral rectus (6.9 mm) and superior rectus (7.7 mm; Fig. 18.5).

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Fig. 18.5 Spiral of Tillaux

Oblique muscles

The obliques are inserted behind the equator and form an angle of 51° with the visual axis (see Fig. 18.2D).

1Superior oblique originates superomedial to the optic foramen. It passes forwards through the trochlea at the angle between the superior and medial walls and is then reflected backwards and laterally to insert in the posterior upper temporal quadrant of the globe (Fig. 18.6).

•The primary action is intorsion (Fig. 18.7A); secondary actions are depression and abduction.

•The anterior fibres of the superior oblique tendon are primarily responsible for intorsion and the posterior fibres for depression, allowing separate surgical manipulation of these two actions (see below).

•When the globe is adducted 51°, the visual axis coincides with the line of pull of the muscle (Fig. 18.7B). In this position it can only act as a depressor. This is, therefore, the best position of the globe for testing the action of the superior oblique muscle. Thus, although the superior oblique has an abducting action in primary position, the main effect of superior oblique weakness is seen as failure of depression in adduction.

•When the eye is abducted 39°, the visual axis and the superior oblique make an angle of 90° with each other (Fig. 18.7C). In this position the superior oblique can only cause intorsion.

2Inferior oblique originates from a small depression just behind the orbital rim lateral to the lacrimal sac. It passes backwards and laterally to insert in the posterior lower temporal quadrant of the globe close to the macula.

•The primary action is extorsion; secondary actions are elevation and abduction.

•When the globe is adducted 51°, the inferior oblique acts only as an elevator.

•When the eye is abducted 39°, its main action is extorsion.

Fig. 18.6 Insertion of the superior oblique tendon

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Fig. 18.7 Actions of the right superior oblique muscle

Muscle pulleys

The four rectus muscles pass through condensations of connective tissue and smooth muscle just posterior to the equator. These condensations act as pulleys and minimize upward and downward movements of the bellies of the medial and lateral rectus muscles during upgaze and downgaze, and horizontal movements of the superior and inferior rectus bellies in left and right gaze.

•Pulleys are the effective origins of the rectus muscles and play an important role in the coordination of eye movements by reducing the effect of horizontal movements on vertical muscle actions and vice versa.

•Displacement of the pulleys can be one cause of abnormalities of eye movements such as ‘V’ and ‘A’ patterns (see below).

Nerve supply

1Lateral rectus is supplied by the 6th cranial nerve (abducent nerve – abducting muscle).

2Superior oblique is supplied by the 4th cranial nerve (trochlear nerve – muscle associated with the trochlea).

3Other muscles together with the levator muscle of the upper lid and the ciliary and sphincter pupillae muscles are supplied by the third (oculomotor) nerve.

Ocular movements

Ductions

Ductions are monocular movements around the axes of Fick. They consist of adduction, abduction, elevation, depression, intorsion and extorsion. They are tested by occluding the fellow eye and asking the patient to follow a target in each direction of gaze.

Versions

Versions are binocular, simultaneous, conjugate movements in the same direction (Fig. 18.8, top).

•Dextroversion and laevoversion (gaze right and gaze left), elevation (upgaze) and depression (downgaze). These four movements bring the globe into the secondary positions of gaze by rotation around either the vertical (Z) or the horizontal (X) axis of Fick.

•Dextroelevation and dextrodepression (gaze up and right; gaze down and right) and laevoelevation and laevodepression (gaze up and left; gaze down and left). These four oblique movements bring the eyes into the tertiary positions of gaze by rotation around oblique axes lying in the Listing plane, equivalent to simultaneous movement about both the horizontal and vertical axes.

•Torsional movements to maintain upright images occur on tilting of the head; these are known as the righting reflexes. On head tilt to the right the superior limbi of the two eyes rotate to the left, causing intorsion of the right globe and extorsion of the left.

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Fig. 18.8 Binocular movements

Vergences

Vergences are binocular, simultaneous, disjugate or disjunctive movements (in opposite directions) (Fig. 18.8, bottom). Convergence is simultaneous adduction (inward turning); divergence is outwards movement from a convergent position. Convergence may be voluntary or reflex.

Reflex convergence has four components:

1 Tonic convergence, which implies inherent innervational tone to the medial recti.

2Proximal convergence is induced by psychological awareness of a near object.

3Fusional convergence is an optomotor reflex which maintains binocular single vision (BSV) by ensuring that similar images are projected onto corresponding retinal areas of each eye. It is initiated by bitemporal retinal image disparity.

4Accommodative convergence is induced by the act of accommodation as part of the synkinetic-near reflex.

•Each dioptre of accommodation is accompanied by a constant increment in accommodative convergence, giving the ‘accommodative convergence to accommodation’ (AC/A) ratio.

•This is the amount of convergence in prism dioptres (Δ) per dioptre (D) change in accommodation.

Changes in accommodation, convergence and pupil size which occur in concert with a change in the distance of viewing are known as the ‘near triad’.

Positions of gaze

1Six cardinal positions of gaze are identified in which one muscle in each eye is principally responsible for moving the eye into that position as follows:

•Dextroversion (right lateral rectus and left medial rectus).

•Laevoversion (left lateral rectus and right medial rectus).

•Dextroelevation (right superior rectus and left inferior oblique).

•Laevoelevation (left superior rectus and right inferior oblique).

•Dextrodepression (right inferior rectus and left superior oblique).

•Laevodepression (left inferior rectus and right superior oblique).

2Nine diagnostic positions of gaze are those in which deviations are measured. They consist of the six cardinal positions, the primary position, elevation and depression (Fig. 18.9).

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