Amblyopia and Strabismus 20141226 Amblyopia Definition Reduced visual

Amblyopia and Strabismus 眼科部 簡克鴻 2014/12/26

Amblyopia

Definition • Reduced visual acuity in the presence of optimal refractive correction and absence of eye and visual system abnormalities • Amblyopia arises from anomalous visual inputs to the immature brain.

Classification of amblyopia • Strabismic • Refractive – Isometropic – bilateral refractive error (myopia -6 D, hyperopia +5 D, astigmatism 2 D) – Anisometropic – unequal refractive error (myopia -6 D, hyperopia and astigmatism 1 -2 D) • Deprivational – obstructed visual axis

Spatial distortions of vision in the central visual field between normal eyes (upper row) and strabismic amblyopia (lower low).

Characteristics of amblyopia • Un-stationary vision • Crowding phenomenon • Better vision in dark illumination Crowding Bar

Treatment of amblyopia • Eliminate (if needed) any obstacle to vision, such as a cataract. – Strabismic and Deprivational type • Correct any significant refractive error. – Refractive type • Force use of the poorer eye by limiting use of the better eye. Different magnification in anisometropic correction

Extraocular muscles (EOM) Spiral of Tillaux

Right Superior Rectus Right Superior Oblique

Eye movements • Duction - moonocular eye movement • Version - binocular eye movements in same direction • Vergence - binocular eye movements in opposite direction

Ductions • X-axis– Elevation – Depression • Y-axis– Intorsion – Extorsion • Z-axis– Adduction – Abduction

Actions of the EOM from Primary Position Muscle Primary Secondary Tertiary Medial Rectus Adduction - - Lateral Rectus Abduction - - Inferior Rectus Depression Extorsion Adduction Superior Rectus Elevation Intorsion Adduction Inferior Oblique m. Extorsion Elevation Abduction Superior Oblique m. Intorsion Depression Abduction The superior muscles are intortors; the inferior muscles, extortors. The vertical rectus muscles are adductors; the oblique muscles, abductors

Versions Yoke muscles (paired muscles)- 2 muscles (1 in each eye) that are the prime movers of their respective eyes in a given position of gaze.

• Sherrington's law of reciprocal innervation – increased innervation and contraction of a given extraocular muscle are accompanied by a reciprocal decrease in innervation and contraction of its antagonist. – e. g. RMR and RLR in right eye adduction. • Hering's law of motor correspondence – equal and simultaneous innervation flows to yoke muscles concerned with the desired direction of gaze – e. g. RMR and LLR in right eye adduction.

Vergence

Basics for Strabismus • Ocular misalignment; To squint; To look obliquely • Prevalence – 1% in infants, 7% in children aged 6 -7 years.

Risk factors for strabismus • • Maternal Cigarette Smoking Drug abuse during pregnancy Neurological disorders (e. g. Cranial paralysis) Heredity Refractive errors Low birth weight Craniofacial anomalies Unilateral ocular disease

Problems from strabismus • Cosmesis • Abnormal stereopsis • Ocular disability (e. g. Amblyopia)

Terminology for Strabismus • Orthophoria • Heterophoria - latent ocular deviation that is controlled by fusional ability • Intermittent tropia - a deviation in which fusional control is present part of the time • Heterotropia - a manifest deviation in which fusional control is not present • Most people have a small heterophoria – normal limits

Nomenclature of Strabismus Pseudo-Esotropia

Tests for Strabismus Tests Light Reflex Tests Bruckner - qualitative Hirschberg - semi-quantitative; corneal light reflex test Krimsky – quantitative; prism and corneal light reflex test Cover tests – all quantitative Cover–uncover test - measures tropia only Alternate cover test - measures phoria plus tropia Prism-and-Cover tests Alternate prism-and-cover tests (APCT) - measures phoria plus tropia Simultaneous prism-and-cover test (SPCT) – measures tropia only Simultaneous prism under cover test (SPUCT) – measures dissociated deviation

Hirschberg Test Krimsky Test

Cover-Uncover Test Alternate Cover Test

Treatments for strabismus • Nonsurgical treatments – Spectacles, Prism, Occlusion, Botox injection • Surgical treatments

Nonsurgical treatments for strabismus Tape Occlusion Fresnel Prism

Indications for strabismus surgery • Improve prognosis – In congenital Esotropia • To develop fusion – In Exotropia • To maintain binocularity when intermittent and young • Improve cosmesis – On patient’s preference – Most common reason • Improve function – In binocular diplopia • Minimize visual disability in primary and down gaze – In torticollis • to improve psychological or behavior embarrassment