This document discusses the etiology of heterophoria and heterotropia. Heterophoria is a latent deviation where the eyes are aligned when looking at an object but deviate on dissociation. Heterotropia is a manifest deviation where one eye is not directed at the object of regard. The document outlines various forms of each and discusses anatomical, refractive, and neurologic factors that can contribute to the development of heterophoria and heterotropia.

1. Etiology of Heterophoria
and Heterotropia
Tukezban Huseynova, MD
Specialist in Strabismus and Refractive Cornea,
Briz-L Eye Clinic, Baku, Azerbaijan
Tukezban@gmail.com

2.  Orthoforia occurs where both visual axes are directed
towards the fixation point and do not deviate on
dissociation.

3. Factors that determine the relative
position of the visual axes.
 Anatomical factors.
 Innervational factors.

4. Factors Responsible for the Manifestation of a
Deviation
 Abnormalities of Fusion Mechanism
 Reflexologic Theories

5. Heterophoria

6.  Where heterophoria is presented, both
visual axes are directed towards the fixation
point but deviate on dissociation.

7. Classification.
• Esophoria
- convergence excess
- divergence weakness
- non-specific
• Exophoria
- conveargence weakness
- divergence excess
- non-specific
• Hyperphoria/hypophoria
• Alternating hyperphoria/hypophoria
• Cyclophoria

8. Aetiology.
Esophoria
• Anatomical – enophthalmos, narrow IPD, extraocular muscle
anomalies
• Refractive – suprable hypermetropia, anisometropia
• High AC/A ratio
• Weak negative fusional reserves

9. Aetiology.
Exophoria
• Anatomical – exophthalmos, wide IPD, extraocular muscle
anomalies
• Refractive – acquired myopia, presbyopia, anisometropia
• Weak positive fusional reserves
• Passage of time

10. Aetiology.
Hyperphoria/hypophoria
• Refractive – high myopia (heavy eye syndrome)
• Weak vertical fusional reserves
• Anatomical – displaced globes, abnormal extraocular muscles,
ptosis

11. Heterotropia

12.  Heterotropia is a condition in which one or
other visual axis is not directed towards the
fixation point.

13. There are a number of different forms of heterotropia:
• Esotropia
• Exotropia
• Hypertropia
• Hypotropia
• Cyclotropia
• Dissociated vertical deviation (DVD)
• Dissiciated horizontal deviation (DHD)

14. Factors Causing the Deviation.
 Mechanical factors
 Structural anomalies of extraocular muscles
 Accommodation and refraction in comitant strabismus
 Fixation disparity
Previous eye surgeries or brain surgeries

15. Factors Causing the Deviation.
Other Innervational (Neurologic) Factors in
Comitant Strabismus.
 Paretic elements
 Anomalies of the brainstem
 Anomalies of convergence and divergence
 Vestibular system
 Anomalies of the visual pathway
 Brain damage
 Embryopathy

16. Thank You