PHYSIOLOGY TUTORIAL
What are the angles formed by extra ocular muscles with the visual axis in primary position? Explain the movements on the different direction of visual axis.
The relative importance of primary and secondary actions of extra ocular muscles depends on the direction of visual axis.
Medial and lateral recti lie on the horizontal meridian of the globe. Their functions are relatively simple and antagonistic. Contraction of medial rectus adducts and lateral rectus abducts the globe.
Superior and inferior recti subtend a 23° angle with the visual axis when the eye is in primary position.
When the eye is abducted 23°
The superior rectus acts solely as an elevator,
The inferior rectus acts solely as depressor.
When the eye is adducted 67°
The superior rectus acts solely to incyclotort the globe
The inferior rectus acts solely to excyclotort the globe.
Superior oblique –this vector plane subtends a 54° angle with the visual axis when the eye is in primary position.
When the eye is adducted 54°
Superior oblique acts solely to depress the globe
When the eye is abducted 36°
Superior oblique acts to incyclotort the globe.
Inferior oblique-subtends a 51° angle with visual axis when the eye is in primary position.
When the eye is adducted 51°
Inferior oblique solely elevates the globe.
When the eye is abducted 39°
Inferior oblique solely excyclotort the globe.
