The eye is an organ in constant motion. It enables us to see by capturing light and has the ability to distinguish shapes and colors. It is also a muscular organ, with a great capacity to adapt to the distance that separates us from the object of our attention. Let’s discover the unique capacities of this organ that allows us to observe the world around us.
The eye, a muscular organ made to move.
Also known as the oculomotor muscles, the muscles of the eye help move and maintain the eyeball within the bony cavity of the orbit. Surrounded by 4 straight muscles and 2 oblique muscles, the eye can thus move in all the desired directions, to analyze what surrounds us.
How do these eye muscles work?
Quite simply, if you want to look down, it’s the lower right muscle that comes into play. If you want to look up? Your upper right muscle will be involved in the movement. When you are cross-eyed, you bring your eye towards your nose. To do this, you use your internal right muscle to perform an adduction. The opposite, it is an abduction, and your eye will be oriented by the external right muscle towards your temple.
To look in the corner, direct your eye towards the temple and upwards, you will use your shortest oculomotor muscle: the inferior oblique muscle. For the opposite, towards the nose and downwards, it is the superior oblique muscle that will intervene, the longest. Feel free to test some eye movements after reading this paragraph, and try to analyse which muscle you have used!
Accommodation: when the eye “focuses”.
This expression, stolen from the world of photography, allows us to visualize the phenomenon of accommodation of the eye. It allows you to adapt your visual strength and improve your near and far vision. It is a natural phenomenon that relies on a slight deformation of the lens which will bulge slightly or relax, depending on the visual needs.
Its exact functioning depends on the ciliary bodies. These will contract to allow the eye to see into the distance. In the opposite case, the ciliary bodies will relax and converge to the maximum to allow clear near vision. This capacity of accommodation of the eye remains limited since the crystalline lens, whose shape bulges or relaxes, cannot be deformed indefinitely.
This accommodation is measured in diopters at your ophthalmologist’s during your consultation. Here we observe the ability of your eye to vary its convergence. The smallest distance at which your vision is clear is called punctum proximum and the largest distance at which your vision is clear is called punctum remotum.
The capacity of accommodation is not a fixed capacity of the human eye. It will evolve with age: a child can change from distant to extremely close vision in 350 ms, which is an accommodation capacity of 14 diopters. In childhood, the accommodation is very large, then it regulates, and finally reduces with age.
The reason for this reduction is simple: As we get older, the crystalline lens becomes rigid, which reduces the accommodative capacity of the eye, causing presbyopia. This is why it is necessary, at any age, to have an ophthalmological check up in order to make sure that the eye is aging properly!