Anatomy of the eye
The anterior segment of the eye consists of the cornea, a convex structure of transparent tissue; the majority of refractive surgery procedures are performed on this tissue for the correction of myopia, astigmatism and hyperopia. The edges of the cornea continue with an almost white band of tissue, called the sclera.
The iris lies behind the cornea; and it is this structure that determines the color of the eyes. The opening at the center of the iris is called the pupil and its diameter varies with the light intensity.
Behind the pupil and the iris lies the crystalline lens: this is a transparent lens, just slightly larger than a lentil, and it occurs naturally in the eye.
The crystalline lens can change its shape (a process known as accommodation) and this allows the eye to focus correctly in proportion to the distance that articles are positioned from the eye. The crystalline lens gradually starts losing its accommodation ability after 40 years of age. This marks the start of presbyopia, a natural phenomenon linked to the physiological ageing process of the eye.
If the crystalline lens becomes partially or completely opaque, a cataract is forming. In this case, it is advisable to intervene surgically as quickly as possible.
The posterior segment of the eye lies behind the crystalline lens. Here we find the vitreous, a clear gelatinous substance that fills all of the central portion of the eye. The retina is located on the internal posterior surface of the eyeball; this is the membrane that allows the eye to see: if we compare the eye to a photographic camera, the retina can be likened to the film.
The most important part of the retina, in visual terms, is the macula. This allows people to read, work at the computer and drive a car. If the macula is altered in any way (for example, in Age-related Macular Degeneration – AMD), the patient will perceive a sometimes considerable reduction in visual capacity.
Light reaches the retina once it has passed through the cornea, the pupil, the crystalline and the vitreous; here it stimulates special cells called photoreceptors: these transmit the stimulus to other cells that extend to form the optic nerve.
The optic nerve carries the impulses from the retina to the brain. The area of the brain called the visual cortex processes these impulses into images.
And this is how we see.
And to allow us to see properly, it is essential that all of the above-mentioned ocular elements function correctly.