Projection in Heterotropia Helen Griffiths Year 1 October

Projection in Heterotropia Helen Griffiths Year 1 October 2016

The plan for today…. . • Projection in normal BSV – recap • Types of strabismus • Projection in strabismus • Consequences of strabismus

Normal retinal correspondence • Fovea – Has the principal visual direction (PVD) – Projects straight ahead – Corresponds to the fovea of the other eye • Nasal retina – Projects temporally – Nasal retina RE corresponds with temporal retina of LE • Temporal retina – Projects nasally

Normal binocular single vision

Heterotropia • A condition in which one or other visual axis is not directed towards the fixation point

Types of Heterotropia • Esotropia - One eye deviates nasally when both eyes are open • Exotropia – One eye deviates temporally when both eyes are open

Types of Heterotropia • Hypertropia - One eye is deviated upwards when both eyes are open • Hypotropia – One eye is deviated downwards when both eyes are open

Projection in heterotropia • Diplopia Results from stimulation of non-corresponding retinal points by a single object • Confusion Results from stimulation of corresponding points in the two eyes by different objects

Esotropia

Esotropia Image from right eye on the right side

Esotropia • Homonymous (uncrossed) diplopia Image from an esotropic eye is seen on the same side eg. Right esotropia image from right eye seen on the right hand side

Exotropia • Heteronymous (crossed) diplopia Image from an exotropic eye is seen on the opposite side eg. Right exotropia image from right eye seen on the left hand side

Draw the following: Projection diagram: Right XT with normal retinal correspondence

Vertical heterotropia Hypertropia Object of fixation stimulates superior retina of the deviating eye which projects inferiorly Diplopic image from the deviating eye seen below the real target (seen by fixing eye) RE S F S cerebral projection RE

Vertical heterotropia Hypotropia Object of fixation stimulates inferior retina of the deviating eye which projects superiorly Diplopic image from the deviating eye seen above the real target (seen by fixing eye) F RE I F I cerebral projection RE

Adaptations To avoid diplopia and confusion • Suppression • Abnormal correspondence

Suppression • The mental inhibition of visual sensations • Occurs more readily in children • Foveal (central) suppression eliminates confusion • Nasal / temporal (peripheral) suppression eliminates diplopia

Abnormal correspondence • Sensory adaptation which allows strabismic patients to use both eyes without diplopia or confusion • Achieve abnormal binocular single vision • Further details in semester 2

Summary • Diplopia results from stimulation of noncorresponding retinal points by the same object • Confusion results from stimulation of corresponding points by different objects • Homonymous pathological diplopia occurs in esotropia • Heteronymous pathological diplopia occurs in exotropia

To do Read Von Noorden & Campos - chapter 13 p 211 – 222 NB: 220 – 231 on line Library or http: //www. cybersight. org/data/1/rec_docs/3285_5. 85 MB_Binocular_Vision_and_Ocular_Motility. pdf