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

2. Amblyopia

3. 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.

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

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

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

7. 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

8. Extraocular muscles (EOM)
Spiral of Tillaux

10. Right Superior Oblique
Right Superior Rectus
Right Superior Oblique

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

12. Ductions X-axis- Y-axis- Z-axis- Elevation Depression Intorsion
Extorsion
Z-axis-
Adduction
Abduction

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

14. 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.

15. 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.

16. Vergence

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

18. 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

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

20. 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 (Exophoria 9PD, esophoria 7PD and 0 in vertical phoria)

21. Nomenclature of Strabismus
Psudo-esotropia
Pseudo-Esotropia

22. 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

23. Hirschberg Test
Krimsky Test

24. Alternate Cover Test
Cover-Uncover Test

25. Treatments for strabismus
Nonsurgical treatments
Spectacles, Prism, Occlusion, Botox injection
Surgical treatments

26. Nonsurgical treatments for strabismus
Tape Occlusion
Fresnel Prism

27. 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