40 Questions
What is the pathway of the visual information from the retina to the visual cortex?
Retina → Optic nerve → Optic chiasm → Optic tract → Lateral geniculate nucleus → Visual Cortex
What is the result of a lesion in the optic nerve?
Monocular visual loss with ability to compensate from contralateral side
What is the function of the ganglion cells in the retina?
To transmit visual information from the retina to the brain
What is the result of a Cecocentral scotoma?
Lesion of the retina that fuses with the blind spot
What is the structure that receives direct ganglion cell fibers from the retina?
Suprachiasmatic nucleus of the hypothalamus
What is the function of the aqueous humour in the eye?
To support the metabolism of internal eye structures, especially in the anterior segment
What is the structure that carries visual information from the eye to the brain?
Optic nerve
Lesions in which part of the visual pathway can cause visual field deficits?
All of the above
What is the function of the ganglion cells in the retina?
To transmit visual information from the retina to the brain
What is the blood vessel that supplies the retina?
Central Retinal Artery
What is the approximate rate of visual information leaving each eye?
10Mb/sec
Which type of RGCs are more sensitive to motion and have larger receptive fields?
Parasol/M-RGCs
What is the term for the atrophy of RGCs in the optic nerve due to lesions to the 2° neuron axons within the brain?
Wallerian atrophy
What is the approximate diameter of the fovea centralis?
1mm
Which part of the retina lacks blood vessels and contains densely packed cones?
Foveola
What is the result of an ischemic lesion of the proximal optic nerve?
Junctional scotoma of the ipsilateral eye and superior temporal crescent loss in the contralateral eye
Which retinal fibers do not cross in the optic chiasm?
Axons from the temporal retinas
What is the most common cause of a junctional scotoma?
Meningiomas
What is the target of the optic tracts in the subcortical visual structures?
Pretectum
Which pathway is involved in the reorientation to visual and auditory stimuli?
Tectospinal tract
What is the characteristic appearance of the optic disc due to axonal degeneration?
Pallor
Which part of the visual field is associated with the temporal retina?
Medial visual field
Where do ganglion cells from the nasal hemiretina project to?
Contralateral LGN
What is the characteristic visual field defect associated with lesions of the nasal hemiretina?
Band atrophy
Which visual field is wider superiorly than inferiorly?
Binocular visual field
During early development, which two structures interact to form the adult retina and lens?
Optic vesicle and lens placode
What is the function of horizontal cells in the retina?
To interconnect photoreceptors and bipolar cells
What is the direction of light and visual information travel in the vertebrate retina?
Light travels in one direction and visual information in the opposite direction
What is the function of Müller cells in the retina?
To support and nourish the retina
In which region of the retina are the layers thinnest?
Fovea and macula
What percentage of total ganglion cells are uncrossed fibers from the temporal hemiretina?
40%
Which part of the visual field is affected in Bitemporal Hemianopsia?
Superior visual field
What is the location of fibers from the superior visual field in the optic chiasm?
Superior chiasm
What is the term for the loop of contralateral fibers in the optic nerve?
Wilbrand's Knee
What is the characteristic visual field defect of a lateral compression of the optic chiasm?
Binasal Hemianopia
From which part of the retina do uncrossed fibers originate?
Temporal hemiretina
What is the term for the bilateral 'bowtie' atrophy of the optic disk?
Post-fixational blindness
What is the location of the lesion in a patient with Bitemporal Hemianopia caused by a pituitary adenoma?
Inferior-nasal fibers
What is the characteristic of ganglion cell fibers in humans and other primates?
A large number of fibers do not cross at the optic chiasm
What is the term for the progression of vision loss that can be used to locate the lesion?
Progressive visual deterioration
Study Notes
Visual Field and Retinal Fields
- The visual field is larger superiorly than inferiorly, and the temporal visual field is larger than the nasal visual field.
- The binocular visual field is wider superiorly than inferiorly.
- Temporal hemiretinas: 40% of ganglion cell fibers, receive images from medial visual field, and project to ipsilateral LGN (layers 2, 3, 5).
- Nasal hemiretinas: 60% of ganglion cell fibers, receive images from lateral visual field, and project to contralateral LGN (layers 1, 4, 6).
Main Visual Pathway (Retino-Geniculo-Calcarine)
- Retina: photoreceptors (rods and cones) -> bipolar cells -> 1° ganglion cells -> 2° optic nerve.
- 2° optic nerve -> 2° optic chiasm -> 2° optic tract -> 2° lateral geniculate nucleus -> 3° optic radiation -> 3° visual cortex (occipital lobe).
Visual Pathway Lesions
- Lesions in the retina or optic nerve can cause monocular visual loss, without the ability to compensate from the contralateral side.
- Lesions before the optic chiasm can cause blurred vision and loss of color vision (achromatopsia), while lesions after the chiasm will not.
- Local lesions in the retina can cause scotoma, which is a blind spot in the visual field.
- Cecocentral scotomas are lesions of the retina that fuse with the blind spot.
- Central scotomas and claudication are often symptoms of optic nerve ischemia.
Optic Chiasm
- The optic chiasm is the part of the brain where the optic nerves from each eye cross over to the opposite side.
- Ganglion cell axons from each nasal hemiretina cross at the chiasm.
- The suprachiasmatic nucleus of the hypothalamus receives direct ganglion cell fibers.
Retinal Anatomy
- The retina has 10 histologic layers, including photoreceptors (rods and cones), bipolar cells, and ganglion cells.
- The neural layer of the retina contains ganglion cells, bipolar cells, and interneurons.
- The pigmented layer of the retina is involved in the metabolism of the internal eye structure.
Optic Nerve
- The optic nerve is formed from the axons of ganglion cells.
- The optic nerve has a papillomacular bundle, which is a bundle of axons from the nasal retina.
- Lesions to the 2° neuron (RGC) axons within the brain can cause retrograde "Wallerian" atrophy of RGCs in the optic nerve.
Visual Field Defects
- Bitemporal hemianopia: a visual field defect characterized by bilateral blindness in the temporal fields.
- Binasal hemianopia: a visual field defect characterized by bilateral blindness in the nasal fields.
- Junctional scotoma: a central scotoma of the ipsilateral eye, and a superior temporal crescent loss in the contralateral eye.
Other
- The retina and optic nerve are outgrowths of the diencephalon, not technically part of the PNS.
- The lens placode and optic vesicle interact during early development to form the adult retina and lens.
Test your knowledge of the visual pathway, from photoreceptors to the visual cortex, including the main structures and potential lesions that can affect the visual field. Learn about the different types of scotomas and how they occur. Brush up on your understanding of the retino-geniculo-calcarine pathway and its components.
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