The Human Eye
The information in this page has been provided by Hoya Lens Australia & New Zealand.
However normal and unremarkable it may seem to be able to look around and see, our eyes are vital to our wellbeing. Below you will find a concise explanation of some key componets of the Human eye. Slide your cursor over the sections and you will find a short explanation for each.
General Operation
When considering the eye as a camera, the pupli is the lens aperture. The retina operates as a kind of light-sensitive film. The light that falls on to this 'film' is then transferred to the brain through the optic nerves. The light stimuli are then translated into images. Together, the cornea and lens constitue the 'camera lens' that ensures that incoming light is refracted correctly. In order to see sharply, the focal point of the rays of light must fall onto the most sensitive part of the retina, which is called fovea.
Lens & Cornea
The lens and cornea play a vital role in accurate vision. In a healthy eye, these components ensure that the image is projected correctly onto the retina. This happens because both the lens and the cornea'refract' the light. In other words, in a healthy eye the refractive power of the eye is tuned correctly to the length of the eye. The length of the eye is the distance between the point at which light enters the eye and the point at which it hits the retina.
Cornea
The cornea is the principal determinant for the refractive capacity of the eye (70%). It consists of several cell layers. the exterior layers is easily regenerated when damaged, but the interior layer is highly sensitive to oxygen deprivation.
Pupil
The pupil determines the degree of light transfer through the eye. If there is a lot of light, the pupil contracts and vice versa. In healthy eyes, both pupils change size of the pupils: when looking at an object to close range the pupil narrows, while it becomes larger when we see something that excites us or touches our emotions.
Iris
When determining the colour of an individual's eyes, we look at the iris. If it contains a great quantity of pigment, the iris is brown; if it contains little pigment, the iris is blue or perhaps green. The back of the iris is always black and therefore does not allow light to pass through. However the opening at the center of the iris - pupil - does let through light.
Lens
the lens contain small muscles the lengthen or contract according to the distance at which an object is perceived. This causes the angle of light refraction whithin the eye to change. The capacity to focus clearly on objects at different distances is called accommodation.
Retina
When a ray of light hits the retina, a photochemical process occurs. This generates a stimulus that is transferred to the brain through the optic nerve. Actual imaging occurs in the brain. The cells of the retina consist of rods and cones, the cones are not photosensitive (sensitive to light), but actually perceive colour, while the rods are photosensitive and even perceive objects when there is little light.