Understanding Vision
About your vision
The eye brings images into focus by bending or refracting light to retina at the back.
The cornea is a curved surface at the very front of the eye and is where the most powerful bending or refraction occurs. The crystalline lens sitting behind the coloured part of the eye also contributes to refraction but does most of the work in terms of focus when doing near tasks like reading up close. The pupils and iris form the aperture that allows more or less light to enter the eye.
For clear vision the light must be focussed on the retina specifically at the fovea.
Changing the shape of the cornea or changing the lens are most common ways in which to correct vision.
The reshaping of cornea is performed using laser whilst lens based procedures either insert an IOL into eye without removing crystalline lens or the crystalline lens is replaced by IOL.
The aim of refractive treatments, otherwise known as vision correction, is to reduce dependency on visual hardware such as glasses or contact lenses to see clearly.
Anatomy of the Human Eye
The eye is a sensory organ part of the nervous system that allows transmission of light and images to the brain via the Optic nerve.
Cornea – clear domed shaped structure at front of the eye
Iris – coloured part of the eye
Pupils – opening at centre of iris that regulates amount of light entering the eye.
Sclera – white part of the eye
Conjunctiva – clear, thin mucous layer of tissue that covers entire front of eye except cornea.
Crystalline Lens – sits directly behind the iris, helps focus eye when reading.
Aqueous Humor – the fluid behind the cornea
Vitreous – clear gel-like fluid that fills the chamber behind the lens.
Choroid – thin layer of tissue that forms the middle layer of the wall of the eye sandwiched between the retina and sclera.
Retina – light sensing layer lines the inner wall of the eye. Has light sensing cells called rods and cones that converts light into electrical impulses.
Optic Nerve – the sensing cells converge to carry electrical impulses to the brain.
Macula – small pin-head sized spot at the back of the eye allowing for central vision.
Fovea – lies in the centre of macula, with the highest concentration of cones that allow for fine acute central vision.
common eyesight conditions
Please read about some common eyesight conditions here:
Emmetropia
Emmetropia is the medical term for normal or 20/20 vision, it can be described as having perfectly focussed vision without the need for corrective lenses, visual aids, or hardware.
Myopia (Short/Near-Sightedness)
A visual condition whereby people see clearly up close and blurry at distance. The light is focussed at the front of the retina.
Hyperopia (Long/Far-Sightedness)
A visual condition whereby people see clearly at distance and blurry up close. The light is focussed past or behind the retina.
Astigmatism
Caused by an irregularly shaped cornea or lens that causes light to focus at different parts of the retina.
Presbyopia
A visual condition usually due to age whereby the crystlline lens is not able to “fatten” or change shape to focus when doing near tasks. Presbyopia is the gradual loss of the ability to focus for near tasks.
In its simplest form presbyopia is the loss of ability to focus on nearby objects. Close or near tasks become more difficult to perform as the lens in the eye becomes less flexible and more rigid. Close up tasks such as using mobile, reading, threading a needle become challenging without the aid of reading glasses or other visual hardware.