The oculomotor apparatus and its pathology

Anatomy of the Oculomotor Apparatus

Before considering a problem of strabismus, it is necessary to recollect anatomy of the oculomotor apparatus, to determine con­ception of binocular vision.

The movement of the eye is carried out by 6 pairs of muscles: 4 straight muscles and 2 oblique muscles. They begin, except for in­ferior oblique muscle, from the tendon ring around the visual fo­ramen of the orbit. The inferior oblique muscle begins from the pe­riosteum of the anterolateral part of the orbit. The muscles are at­tached to the sclera at the following distance from a limbus:

• medial rectus muscle — 5-5.5 mm;

• lateral rectus muscle — 7 mm;

• superior rectus muscle — 8-9 mm;

• inferior rectus muscle — 6-6.5 mm;

• superior oblique muscle — 17-18 mm;

• inferior oblique muscle — 16-17 mm.

The blood supply of muscles is carried out by muscular arteries from the ophthalmic artery.

The function of muscles: the internal straight muscle turns the eye inward, external — outward, superior and inferior straight muscles — upward and downward accordingly, and also inward; superior and inferior oblique muscles — downward and upward accordingly, and also outward. Innervation of muscles: superior oblique muscle is innerved by the trochlear nerve, external straight muscle — by the abducent nerve, all others — by the oculomotor nerve. The formation of muscles comes to an end by 2-3 years of age.

The binocular vision is vision by two eyes, in which the images from both eyes merge into one, qualitatively new, volumetric im­age. It is absent in a newborn, therefore a position of the eyes in them is frequently wrong.

The binocular vision, as is shown by works of the great physi­ologists of our country. I. P. Pavlov, I. M. Sechenov, A. A. Ukhtomsky is a difficult conditionally-reflex function of higher sec­tions of the CNS which is provided by the corresponding activity of the visual, tactile, muscular, proprioceptive and other analyz­ers. It becomes complicated by binocular fixation at 2-3 months of life of the baby to a formed enough binocular vision by 2 years and up to the perfect action of stereoscopic vision at 6-12 years old.

Methods of Examination

Besides standard methods, other methods are applied: determi­nation of visual field (degree of the eye mobility in different sides); coordimetry (functional condition of the oculomotor muscles); test with a red glass in diplopia (determination of the affected muscle); investigation of convergence (convergence-trainer); investigation of accommodation (proximeter, near and far visual point); deter­mination of the squint angle by Golovin (on the perimeter) and by Girshberg according to a position of the corneal light reflection (if the light the corneal reflex is according to the pupillary edge — squint angle is 15°; up to middle of the iris — 25°; on the limbus — 45°; on the sclera — 60° and more than degrees); determina­tion of the character of vision (binocular, simultaneous, monocu­lar) by a colour test and with the help of tests with 2 pencils, by a "hole in the palm"; determination of the character of fixation in amblyopia (during ophthalmoscopy ask the patient to fix a label by a squinting eye and determine a site of the eye fundus, which it is projected on).