Biomedical Engineering Reference
In-Depth Information
Rod
cell
Ganglion
cell
Horizontal
cell
Bipolar
cell
Cone
cell
Lights
Amacrine cell
Retina
Optice nerve
FIgUre 10.5
(See color insert.)
Structure of the retina.
Macula
Fovea
Blind Spot
Periphery
FIgUre 10.6
Functional division of the retina.
The resolution is at its highest point at the fovea level, rapidly diminishes in the first
10°, and then stabilizes in the peripheral retina. This peculiarity of the retina is the reason
why we perform eye movements; that is to say, they are activated by the need for letting
the image of the interested object to be projected on the fovea, where it will be possible to
analyze its tiniest details. The peripheral retina, with its convergent connections, is really
sensitive to light and insufficiently able to spatially segregate. The primary function of the
retina is then to receive the changes that can occur in the environment around the subject
and to trigger the foveation.
The eye movements are carried out by six muscles that are innervated by three cranic
nerves. We can see how the contraction of the medial recti induced a synergic contrac-
tion in the ciliary muscle. The activation of the accommodation, as an effect of hyperme-
tropy or induced with negative lenses, can also trigger a convergence movement. This
can lead to a wrong alignment of the converging visual axes, which can be noticed in the
