Short sight. If the eyeball is too long, of if the lens lacks elasticity, there will be good close-up vision, but the poor distant vision. This is easily corrected by spectacles.
Long sight. This is also frequently caused by the eyeball being too short from front to back. This too can be corrected by spectacles. A child is usually born long sighted, and diagnosis often allows complaints of eyestrain of fatigue.
Astigmatism. This is a very common defect, caused by the cornea on the front of the eye being imperfectly rounded, so that a distorted image is formed on the retina. Again spectacles can cure the problem by compensating for the defective cornea.
Optic Nerve child eyesight
At the back of each eye and optic nerve leads to an area of the brain called the visual cortex, where the information on the retina is processed and interpreted. We have a blind spot where the optic nerve leads away from the back of the eyes, although we are not aware of this, as the eyes compensate for it by overlapping in their fields of vision.
The image transferred to the retina is in fact upside down, and in 'decoding' the information received from the retina via the optic nerve, the brain turns it back the right way round again.
Structure Of The Eye child eyesight
Our eyes are often likened to a photographic camera because of the way in which they convert light into images in the process of seeing.
The eyes (which is spherical) has two lenses - the cornea, which is a fixed focus lens and consists of five layers, at the front of the eye, and an adjustable lens, simply called the lens, within the eyes.
Between the cornea and the lens is the outer one of two 'chambers' in the eye. At the back of this chamber. which is called the anterior chamber, is the iris, the coloured part of the eye. The anterior chamber itself is filled with a watery fluid called the aqueous humour, which is constantly being drained away and replaced. The iris is a circular, muscular diaphragm, in other words, a disc with an opening (like the aperture of a camera) at its centre. This opening is the pupil, which is adjusted by two sets of muscles, causing it to narrow or dilate (enlarge) according to the amount of light falling on the iris. This controls the amount of light that enters the eye, with the pupils dilating to admit more light when the light is dim and narrowing to admit less light when the light is bright.child eyesight
Fine Focus Lens
The fine focusing of light rays is done by the lens, which is situated just behind the iris. The lens is soft and elastic, and held round the edges by a muscle which changes the shape of the lens to adapt it to focusing on a range of objects at different distances from the eye.
The lens too is relatively near the front of the eye, and behind it lies the second chamber, known as the interior chamber, which makes up a large part of the eyeball. The chamber is lined with a light sensitive layer (equivalent to the film in a camera) called the retina.
The retina is actually made up of two different types of light sensitive cells called rods and cones. The rod cells are sensitive to low intensity light and are responsible for clarity of vision. The cones interpret colour and fine details of objects. They only function when the light level is high, explaining why we cannot distinguish colours and details in dim light.
The rods are most plentiful in the area of the retina at the back of the eye known as the macula, and this is where the lens focuses its sharpest image and where vision is best. Towards the edge of the retina is what is known as peripheral vision, which is all that indistinct area where we only half see.