Retina

These neurons are classified into three main groups:

• Photoreceptor cells (rods and cones)
• Bipolar cells
• Ganglion cells with axons

The retina is only firmly attached to the ora serrata (serrated junction between the retina and the ciliary body); elsewhere, it is held in place by the vitreous humour and intraocular pressure pressing the retina against the underlying choroid. In addition to providing nourishment for the retina, the choroid also serves to cool it, since the retina works like a large power plant.

The macula lutea (macula=spot and lutea=yellow) is an oval-shaped, highly pigmented yellow spot at the posterior pole of the eye. It has a diameter of around 5.5 mm. In its centre are the fovea and foveola (fovea centralis = pit at the rear of the retina), providing the most acute vision. The yellow pigmentation results from the rich concentration of the carotenoid pigment lutein. This pigment ensures that the effects of a specific type of optical aberration, chromatic aberration (different wavelengths of light are not focused onto exact the same focal plane) is largely compensated and that the rods and cones are protected from high-energy blue light (this is similar to the protection offered by sun cream).
All retinal nerve fibres run towards the papilla (blind spot) and end in the visual nerve to leave the eye in direction of the brain. Since there are no photoreceptors to detect light, no vision is possible in this area. Objects in this blind spot are not perceived. The papilla exhibits a depression or pit in the centre of the papilla (excavation), which is used to diagnose a range of pathological changes to the eye such as glaucoma.