Vision – what is it?
In the sense of eyes, vision is the ability of information to be perceived by the eye, be processed by the visual cortex and provide our brain with chemical responses to create an image. This is wholly dependent on the amount of light entering the eye and then, after this, the rest of the eye and the brain processing the light information.
What is it made up of?
The eye is not a perfect ball shape and has a diameter of 2.5cm and weighs approximately 8 grams. The layers are:
- Cornea; site of most refracted light to the retina. It gets oxygen from aqueous humor and tears
- Aqueous humor: watery fluid that nourishes the cornea and provides oxygen to it
- Pupil: Not a thing, just a hole that light goes through
- Iris: Limits the amount of light getting to the retina. It’s colour is determined by the amount of light reflecting through it – the same effect that makes the sky look blue
- Lens: suspended by ligaments attached to tiny eye muscles which are pulled to different tensions to focus the lens
- Vitreous humor: pressure of this sticky fluid keeps the eyeball spherical
- Retina: Light sensitive lining of the back of the eye for a large visual area
- Macula: Focus point of images directly in front of the eye
- Fovea: Indentation in the retina to allow focus of high-resolution vision (your HD!)
- Lens Imperfections
- The main function of the lens is to allow crisp formation of objects closer than 9 metres away. The closer the objects get, the more the lens has to adapt to bend light to ensure the objects image stays focussed for contact with the retina. This focus is called accommodation. Tiny muscles attached to the lens by ligaments are used to change it’s shape. If these muscles are relaxed, the lens flattens, the eye retains a perfect shape and the sight is normal.If the eyeball is too short front-to-back, light rays focus at a point behind the retina, causing the ability to see far away but not close up (the light needs a further distance to focus at the retina) = Long sightedness. If the eyeball is too long, light rays focus at a point in front of the retina, causing the ability to to see close up but not far away (the light needs less distance to focus at the retina) = Short sightedness.Muscles of the eye
- Extrinsic muscles (outside of the eyeball) hold the eye in place and move it in all directions. There are 6 of these muscles which have three different nerve supplies.Intrinsic muscles (inside the eyeball) are the ciliary muscles which control lens tension (and focus) and the pupil muscles that control its constriction and dilation.How the eyes link to the back of the head
- The eyes (as with most structures in the body) are surrounded by thin layers of tissue called dura. These layers include the meningeal and arachnoid layers which surround the brain and spinal cord. The link between the eyes and the back of the head is formed by what is called a myodural bridge – small ligaments that link the muscles of the occiput (the bottom of the skull) to the spinal cord.What can Osteopathy do for eyes
- It has been experienced with patients that neck position strain has resulted in pain at the posterior part of the eye – similar to a stabbing or sharp aching feeling. Whilst we must be sure that there is nothing wrong with your eyes and seeing an optician is advisable, we can treat the muscles at the back of the neck to determine if these are the cause. Treatment of this nature can be as simple as asking you to move your head into small and controlled positions. We can also look at how you are using your pillows at night or how you hold your head generally in order to create a successful recovery and management plan.
Shelley James
M.Ost