Clinical Orthoptics

Fiona J. Rowe

• Publisher: Wiley-Blackwell
• Year: 2012
• Print ISBN: 9781444339345
• eBook ISBN: 9781118341605
• Edition: 3
• Topic: Medicine
• Subtopic: Health Care Delivery

Clinical Orthoptics has become established as a basic reference text providing fundamental information on anatomy, innervation and orthoptic investigation, plus diagnosis and management of strabismus, ocular motility and related disturbances. It is aimed at trainee ophthalmologists and orthoptic undergraduate students. Qualified orthoptists, general ophthalmologists and optometrists will also find valuable guidance in these pages.

In this edition, the author has maintained the goal of producing a user-friendly, clinically relevant and succinct book, while revising it to reflect a variety of developments in the field.

FEATURES

• Essential reading for students of orthoptics and ophthalmolology
• Now fully revised and updated
• Generously illustrated with photographs and line drawings
• Includes diagnostic aids, case reports, and helpful glossary

SECTION III

10

Incomitant Strabismus

Incomitant strabismus is strabismus in which the angle of deviation differs depending upon the direction of gaze or according to which eye is fixing and is associated with defective movement of the eye or with asymmetrical accommodative effort.

Ophthalmoplegia is a group of conditions that have a variety of causative factors, where there is a paresis of two or more of the extraocular muscles.

When examining these patients, the angle of deviation may be different depending on which eye is fixing and how long the deviation has been present.

• Primary angle of deviation: The deviation when fixing with the unaffected eye in paralytic incomitant deviation.
• Secondary angle of deviation: The deviation when fixing with the affected eye in paralytic incomitant deviation.

Generally, with more recently acquired palsies, the strabismus will be quite incomitant with a significant difference between the primary and secondary angles of deviation. With time, the strabismus becomes less incomitant and it is harder to assess whether it is congenital or long standing. It is often difficult to differentiate between primary and secondary deviations, as relative concomitance usually occurs following long-standing incomitance.

Aetiology

Incomitant strabismus may be found in association with many disorders. The list below is designed to give an overall idea of the types of condition that can cause incomitance.

Congenital

Neurogenic

• In association with other congenital developmental disorders
• As an isolated feature

Form

• Aplasia; hypoplasia of nerve/nucleus
• Abnormal innervation
• Trauma during gestation/delivery
• Inflammation: Neonatal/antenatal

Mechanical

• Duane's retraction syndrome
• Brown's syndrome

Myogenic

• Developmental abnormality: Hypoplasia/hyperplasia/aplasia of extraocular muscles
• Abnormal attachments: For example, muscle insertions to the eyeball or to the orbital contents
• Fibrosis
• Adhesions: Intermuscular, muscle to orbit

Acquired

Neurogenic

• Trauma
• Inflammation, for example multiple sclerosis
• Vascular, for example hypertension
• Space-occupying lesions
• Metabolic disorder, for example diabetes

Mechanical

• Trauma: Development of fibrous tethers, fractures
• Space-occupying lesions
• Iatrogenic adhesions
• Secondary to myogenic inflammation, for example thyroid eye disease

Myogenic

Lesions at:

• neuromuscular junction, for example myasthenia gravis
• muscle fibre membrane, for example myotonia
• muscle fibre contents, for example dystrophies (chronic progressive external ophthalmoplegia), endocrine (dysthyroid eye disease), inflammatory (myositis)

Aid to diagnosis

Congenital and acquired defects often show different characteristics, which help in making the diagnosis. Table 10.1 shows the findings that might be expected when the patient is examined in the eye clinic.

Table 10.1 Differences between congenital and acquired defects.

	Congenital	Acquired
Presentation	Symptoms of decompensation Unaware of abnormal head posture Unacceptable cosmetic appearance	Diplopia and occasionally pain Aware of uncomfortable abnormal head posture
Ocular motility	Often full muscle sequelae	Muscle sequelae not fully developed
Binocular function	Extended vertical fusion range	Normal fusion range

There are also differences between neurogenic and mechanical defects, which are summarised in Table 10.2.

Table 10.2 Differences between neurogenic and mechanical defects.

	Neurogenic	Mechanical
Cover test	Deviation in primary position reflects the extent of palsy	Often only small deviation in primary position
Ocular motility	Movement is greater on ductions compared to versions No retraction of the globe	Movement is the same on ductions and versions Retraction may be noted
Hess chart	Space between inner and outer fields is equal and proportional Fields are displaced away from position of greatest limitation	Outer field is displaced close to inner field in the position of greatest limited movement
Forced duction test	Full passive movement	Limited passive movement
Intraocular pressure	Same in all positions of gaze	Increases when looking away from the position of limitation

Diplopia

Diplopia may be binocular or monocular and may be horizontal, vertical and/or torsional.

Causes of diplopia

Refractive error	Uncorrected
	Aniseikonia
Strabismus	Concomitant secondary strabismus
	Concomitant strabismus with loss of suppression
	Acquired strabismus due to cranial nerve palsy, trauma, systemic disease, iatrogenic (Trobe 1984)
Fusion deficit	Decompensation of long-standing heterophoria, acquired central fusion loss (Pratt-Johnson & Tillson 1988)
Retinal pathology	Retinal folds, retinal membrane, retinal traction (dePoole et al. 2005)
Visual field loss	Impairment of retinal correspondence with severe visual field loss, hemifield slide phenomenon (Rowe 1996)

Investigation

Case history	Question associated visual symptoms. Metamorphopsia, blur, distortion and illusory movements are typical of retinal pathology. History of closed head injury may indicate cranial nerve palsy or acquired central fusion disruption.
Diplopia type	Ascertain whether horizontal crossed (typical of exo-deviations) or uncrossed (typical of eso-deviations). Where diplopia is opposite to that expected, consider the presence of paradoxical diplopia due to sensory changes in long-standing concomitant strabismus (Castleberry & Arnoldi 2003). Torsional diplopia is typically seen with fourth nerve palsy (Woo et al. 2005). Impact of diplopia may be ascertained by questionnaire (Holmes et al. 2005).
Occlusion	Retinal diplopia will remain under monocular conditions whereas binocular diplopia will be eliminated with occlusion of one eye (Records 1980).
Pinhole test	Monocular diplopia is often relieved when looking through a pinhole.
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Table of contents

• Cover
• Dedication
• Title Page
• Title Page
• Preface
• Acknowledgements
• List of Figures
• List of Tables
• Section I
• Section II
• Section III
• Section IV: Appendices
• Index