GOAL: Relate the A/P of the central visual system to the evaluation of communication.

1. Trace the central visual system from the optic nerve to the occipital cortex (and the midbrain nuclear connections).

2. Demonstrate visual field screening

3. Relate visual field deficits to evaluation of communication disorders.



  1. The CENTRAL visual system can be said to begin at the Thalamus.


    1. One might question the separation of the visual system into peripheral and central sections.


      1. Cranial n.n are supposed to be part of the peripheral nervous system


      2. But the optic n.n are more "brain tracts" than they are "nerves" in a proper sense.


    2. Thalamic connections begin at the LATERAL GENICULATE NUCLEUS. At thislocation are the cell bodies for the forst parts of the central optic tracts


      1. Lateral geniculate neurons are arranged in a manner consistent with the retinal arrangement. In other words, the neurons are arranged like the rods and cones to which they are attached.


      2. Fibers (axons) from the lateral geniculate nucleus fan out toward the cerebral cortex in the OPTIC RADIATION.


      3. Disease at the Lateral Geniculate Nucleus level might result in localized (central) visual field deficits. The patient might complain of blindness on the center of the visual field, or in one or the other quadrants, and so on.


    3. Some fibers of the optic tracts communicate directly to the Midbrain.


      1. These synapse in two places: the SUPERIOR COLLICULUS and the PRETECTAL NUCLEUS


        1. The superior colliculus:


          1. Action potentials for consensual tracking.


            1. m.m. of tracking must act in unison


            2. Retinal impulses play a role.


            3. Fusal impulses from the muscle fibers play a more important role.


          2. Accommodation reflex.


        2. The Pretectal Nucleus.


          1. Action potentials for light reflex


          2. If disease here, light reflex will be disrupted


          3. While other oculomotor reflexes will not.


            1. EG: consensual pupillary constriction associated with convergence.


            2. Impulses descend to Ocular Nucleus from the cerebral cortex.


            3. Oculomotor reflexes are not directly dependent upon retinal stimulation.


        3. No matter, all the effectors are innervated ultimately by the Oculomotor Nerve.


    4. After the Lateral Geniculate NUcleus. , most of the fibers continue on to the Visual Cortex.


      1. First they pass through the posterior limb of the Internal Capsule


      2. The Visual Cortex is in the Occipital Lobe.


        1. The majority is in the walls of the CALCARINE SULCUS of this lobe.


          1. Visual fibers terminate in the lips of this sulcus.


          2. This is area 17


        2. The fibers that fan out of the lateral geniculate into the lobe are known as the OPTIC RADIATION


      3. Optic radiation fibers have two courses.


        1. One takes fibers directly into the occipital lobe.


          1. These are fibers from the superior retinal half.


          2. They terminate on the upper lip of the Calcarine Sulcus.


        2. The other loops around near the Temporal Lobe.


          1. This is loop of nerve fibers is called MEYER'S LOOP


          2. Looping fibers originate in the inferior halves of the retinae.


          3. These fibers terminate at the inferior lip of the Calcarine Sulcus.


          4. Lesions of the temporal lobe can produce visual disturbances


          5. Such lesions can also produce auditory disturbances.


          6. Hamilton doesn't mention direct fibers.


  2. VISUAL FIELD DISTURBANCES can result from disease of the central visual tracts.


    1. The visual field is that area of the environment the individual can see with both eyes open.


    2. Field disturbances are called ANOPSIA.


      1. Anopsia can be QUADRANTAL (1/4)


      2. They can be hemi-(1/2)


      3. They are HOMONYMOUS if the same portion is involved for both eyes.


      4. They are HETERONYMOUS if opposite portions of the visual field are involved for each eye.


    3. One screens visual fields with the confrontation test.


      1. Patient looks directly at the examiner.


      2. Examiner brings an object into the visual field from the four quadrants.


        1. Object is about halfway between examiner and patient.


        2. The patient signals when he/she sees the object.


        3. Patient should see object about the same time the examiner does.


      3. Temporal anopsia (heteronymous) would result from


        1. Damage to the optic chiasma in the center (nasal fibers cross)


        2. Damage to the lateral half of the chiasma would result in anopsia of the nasal field in the right eye.


      4. Left Homonymous hemianopsia would result from...


        1. destruction of the right optic tract


        2. right Lateral Geniculate destruction.


      5. Left homonymous superior quadrantal anopsia:


        1. Destruction of Meyer's loop fibers in the right Temporal Lobe.


        2. Destruction of the inferior lip of the right Calcarine Sulcus.


      6. Left inferior quadrantal anopsia results from


        1. Destruction of the direct optic tracts between the lateral geniculate nucleus and the calcarine sulcus (through posterior limb of internal capsule.


        2. Destruction of the superior lip of the calcarine fissure.


      7. Superior anopsia result from:


        1. Damage to the inferior retina


        2. Damage to the lower lip of the calcarine fissure


    4. Blind spots are Scotomata