Greetings to all and sundry,
It is another beautiful day today and a wonderful opportunity to come your way once again with another one of our discussions concerning our eyes and their health. Before we move on though, i do hope you are doing amazing and having a wonderful time wherever you may be.
We previously looked at the visual pathway and the human visual perception and through that we got to understand how light is transduced to electricity and how it moves from the eye to the brain for interpretation and the various brain areas that are responsible for the various ocular functions relating to vision. For today we want to look at something related to that.
Ever wondered about how your eye moves? How you are able to look up or down or left or right? How come you are able to track an object moving through space or roll your eyes up and down. Some people can do amazing things with their eyes that make you wonder if it's real or perhaps a magic trick.
Well, all these are made possible by the various muscles in our we have in around our eyes. These muscles work much like how any other muscles work however they may have a bit of some variations to enable them function accurately. Today we are going to look at the 6 extraocular muscles and the function they play with respect to our ocular movements.
The Extraocular Muscles
There are 6 extraocular muscles that are attached to the eyeball within the bony orbit of the skull. These are the recti muscles and the oblique muscles. There are two oblique muscles and four recti muscles namely, lateral rectus, medial rectus, superior rectus, and inferior rectus muscle. The two oblique muscles include the superior oblique muscle and the inferior oblique muscle.
The muscles have a primary function, a secondary function, and a tertiary function thus they mostly do not work alone and whenever you experience an ocular movement you should know that definitely more than one muscle is involved in that.
Superior Rectus: The superior rectus muscle has the primary function of pulling your eyes up, in other words it is responsible for upwards movement or gaze. It also has the secondary function of rotating the eye ball nasally, action known as intorsion, then a tertiary function of moving the eye nasally known as adduction.
Inferior Rectus: The inferior rectus muscle has the primary function of pulling your eye ball downwards thus a down gaze, a secondary function of rotating your eyes temporally thus away from the nose and a tertiary function of adduction much like the superior rectus.
Note that the superior and inferior rectus has opposite functions and thus demand that the contraction of one comes with the relaxation of the other to ensure that the required movement is obtain.
- The Lateral Rectus: The lateral rectus muscle has only a primary function which can easily be guessed from its name. It moves or pulls the eyeball laterally thus responsible or help in a gaze away from the nose. That means right gaze for right eye and left gaze for left eye.
- The Medial Rectus: The medial rectus muscle much like the lateral rectus also has only a primary function which is the direct opposite of the lateral rectus, thus moving or pulls the eyeball nasally or towards the nose. What this means is that for the right eye it helps in the left gaze and for the left eye helps in the right gaze.
Note that the medial rectus and the lateral rectus also have opposing functions which would demand that the contraction gets the relaxation of the other for the movement to be possible.
The Superior Oblique: The superior oblique muscle rotates the eyeball inwards much like the secondary function of the superior rectus muscles and has the secondary function of the inferior rectus which is moving the eyeball down and a tertiary function of the lateral rectus muscle which is moving the eyeball away from the nose.
The Inferior Oblique: The inferior oblique muscle has the the primary function of rotating the eyeball outward much like the secondary function of the inferior rectus, a secondary function of moving the eyeball much much like that of the superior rectus and a tertiary function of moving the eyeball out or laterally just like that of the lateral rectus muscle.
The health of each of these individuals muscles may be tested using the Broad H test where your Optometrist may ask you to follow his finger movement with your eyes as he draws a big H in the air. Also, the status of your EOMs may be affected by their innervations as well as other medical conditions thus it is best to seek immediate treatment when you notice any restrictions with your ocular movement.
And so just as we have learnt our ocular movements are not controlled by only one muscle or innervation but the combined efforts of two or more to make us appreciate its work. These movement enable us to be able to focus our vision on objects so impulses can get into the eye and to the brain for us to appreciate vision.
It is important that noticing anything with respect to a misalignment involving your eyes, or any pain with ocular movement be reported to your Optometrist for a comprehensive examination. As usual i would end by saying that your eye is your window to the beautiful scenery of this world, avoid over the counter medication and always seek out professional consult. Thanks for reading and for your time. Have a blissful time.
Chiarandini, D. J., & Davidowitz, J. (1979). Structure and function of extraocular muscle fibers. Current topics in eye research, 1, 91–142.
Carrero-Rojas, G., Calvo, P. M., Lischka, T., Streicher, J., de la Cruz, R. R., Pastor, A. M., & Blumer, R. (2022). Eye Movements But Not Vision Drive the Development of Palisade Endings. Investigative ophthalmology & visual science, 63(11), 15. https://doi.org/10.1167/iovs.63.11.15
Somani, A. N., & Adesina, O. O. (2022). Neuroanatomy, Abducens Nucleus. In StatPearls. StatPearls Publishing.
Eckhardt, J., Bachmann, C., Sekulic-Jablanovic, M., Enzmann, V., Park, K. H., Ma, J., Takeshima, H., Zorzato, F., & Treves, S. (2019). Extraocular muscle function is impaired in ryr3-/- mice. The Journal of general physiology, 151(7), 929–943. https://doi.org/10.1085/jgp.201912333