Boundaries:

This region is arbitrarily divided due to its unique function and to facilitate research and studies on this region. These imposed limits give the occipital lobe a TRIANGULAR SHAPE, which is formed; On the MEDIAL SURFACE, by the parieto-occipital sulcus, on the LATERAL SURFACE, by an imaginary line(called parieto-temporal lateral line) connecting the end of the parieto-occipital sulcus to preoccipital notch and on the INFERIOR side by another line(called parieto-temporal basal line) that connects the preoccipital notch to the beginning of the parieto-occipital sulcus(where it emerges from calcarine sulcus)

THE LOBES

The occipital lobe has further two lobes, which rest on the tentorium cerebelli (a process of dura matter that separates the cerebrum from cerebellum).These lobes are structurally isolated in their respective cerebral hemisphere by the cerebral fissure.

Sulci and gyri:

Following are the major sulci (fissure between the two convolutions of the brain) and gyri (a convolution on the surface of the brain between the sulci) present in the occipital lobe:

SULCI are transverse occipital, lateral occipital, lunate and superior and inferior polar sulcus.

GYRI are arcus parieto-occipitalis, superior occipital, inferior occipital and gyrus descendens.

FUNCTION

The main function of occipital lobe is processing of visual information and thus is related to the eyes and vision. The occipital lobe contains different areas related to visual communication. Following are the most important areas of the occipital lobe:

• The primary visual cortex (brodmann area 17) is the most important part of the occipital lobe. It receives and interprets information from the retinas (structure in eye which receives the image mainly) of the eyes.

• The secondary visual area (brodmann area 18+19) it relates the visual information received by the primary visual area to past visual experiences, thus enabling the individual to recognize and appreciate what he/she is seeing.

• The occipital eye field is present in the secondary visual area. The function of this eye field is believed to be associated with the movement of eye when it is following an object.

So the occipital lobe is associated with visual images and their interpretation which is essential for reading and comprehending what is being read and also important for understanding different signs and objects which we come across in our daily life.

CLINICAL ASPECTS

Damage to the occipital lobe causes:

• Defects in vision (visual field impairment)

• Loss of vision (blindness)

• Visual hallucinations

• Inability to recognize  words(word blindness)

• Difficulty recognizing drawn objects

• Inability to identify colors (color agnosia)

• Inability to recognize the movement of an object (movement agnosia)

• Inaccurately seeing objects (visual illusions)