Tag: Visual Pathway

Visual Pathway

VISUAL PATHWAY

Q. 1 Which of the following represents the CORRECT visual pathway in humans?
 A Optic nerve–> optic tract–> optic chiasm –> optic radiation–> visual cortex
 B Optic nerve–> optic chiasm–> optic tract–> optic radiation–> visual cortex
 C Optic nerve–> optic radiation–>optic chiasm–>optic tract–> visual cortex
 D Optic nerve–> optic chiasm–>optic radiation–>optic tract–> visual cortex
Q. 1 Which of the following represents the CORRECT visual pathway in humans?
 A Optic nerve–> optic tract–> optic chiasm –> optic radiation–> visual cortex
 B Optic nerve–> optic chiasm–> optic tract–> optic radiation–> visual cortex
 C Optic nerve–> optic radiation–>optic chiasm–>optic tract–> visual cortex
 D Optic nerve–> optic chiasm–>optic radiation–>optic tract–> visual cortex
Ans. B

Explanation: Visual pathway starts with the optic nerve which consist of fibers carrying nasal and temporal field of vision from both the eye. Both the nerves join together to form the optic chiasm (here the nasal fibers decussates) and then divides into two optic tracts. These tracts terminates in the lateral geniculate body. The optic radiation begins in the lateral geniculate body forms a band that winds around the inferior and posterior horns of the lateral ventricle and terminates in the visual cortex or striate area (Brodmann area 17).

Ref: Thieme Atlas of Anatomy: Head and Neuroanatomy By Erik Schulte, page 358.


Q. 2

Lesion in which of the following part of visual pathway result in homonymous hemianopia?

 A

Chiasma

 B

Optic tract

 C

Optic nerve

 D

Occipital lobe

Q. 2

Lesion in which of the following part of visual pathway result in homonymous hemianopia?

 A

Chiasma

 B

Optic tract

 C

Optic nerve

 D

Occipital lobe

Ans. B

Explanation:

Homonymous hemianopia can be congenital, but is usually caused by brain injury such as from stroke, trauma, tumors, infection, or following surgery.

 
Vascular and neoplastic lesions from the optic tract, to visual cortex can cause a contralateral homonymous hemianopia. Injury to the right side of the brain will affect the left visual fields of each eye. The more posterior the cerebral lesion, the more symmetric (congruous) the homonymous hemianopsia will be.

 


Q. 3

Lesion at which part of visual pathway causes homonymous hemianopia?

 A

Optic tract

 B

Optic nerve

 C

Optic Chiasma

 D

Retina

Q. 3

Lesion at which part of visual pathway causes homonymous hemianopia?

 A

Optic tract

 B

Optic nerve

 C

Optic Chiasma

 D

Retina

Ans. A

Explanation:

A left homonymous hemianopsia can be caused by a lesion in the right optic tract or the right side of the brain. 

With a tract lesion, the pupillary reflex is lost if light is only projected from the blind hemifield; the pupil reacts when the lesion is posterior to the geniculate body in the optic radiations or occipital lobe. 
 
Transient homonymous hemianopsia may occur with migraine.
 
Ref: LeBlond R.F., DeGowin R.L., Brown D.D. (2009). Chapter 7. The Head and Neck. In R.F. LeBlond, R.L. DeGowin, D.D. Brown (Eds), DeGowin’s Diagnostic Examination, 9e.

Quiz In Between


Q. 4

A 9 year old child presents with sudden partial loss of vision in one eye. On examination, visual acuity is reduced, there is an absence of organic disease of ocular media, retina or visual pathway.

 
Assertion: Most common cause for development of amblyopia are visual deprivation, light deprivation or abnormal binocular interaction.
 
Reason: There is lack of formation of clear image on the retina of a young child.
 A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

 B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

 C

Assertion is true, but Reason is false

 D

Assertion is false, but Reason is true

Q. 4

A 9 year old child presents with sudden partial loss of vision in one eye. On examination, visual acuity is reduced, there is an absence of organic disease of ocular media, retina or visual pathway.

 
Assertion: Most common cause for development of amblyopia are visual deprivation, light deprivation or abnormal binocular interaction.
 
Reason: There is lack of formation of clear image on the retina of a young child.
 A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

 B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

 C

Assertion is true, but Reason is false

 D

Assertion is false, but Reason is true

Ans. A

Explanation:

Amblyopia refers to a partial loss of vision in one or both eyes in the absence of any organic disease of ocular media, retinal and visual pathway. In this condition visual acuity is reduced. It can be caused by visual deprivation, light deprivation or abnormal binocular interaction which impair formation of a clear image on the retina. Most sensitive period for the development of amblyopia is first 6 months of life.

Ref: Comprehensive Ophthalmology By A K Khurana, 4th Edition, Page 319.

Q. 5

The visual pathway consists of all of these except:

 A

Optic tract

 B

Geniculocalcarine tract

 C

Inferior colliculus

 D

Lateral geniculate body

Q. 5

The visual pathway consists of all of these except:

 A

Optic tract

 B

Geniculocalcarine tract

 C

Inferior colliculus

 D

Lateral geniculate body

Ans. C

Explanation:

C i.e. Inferior colliculus


Q. 6

Part (Arrow) in visual pathway as shown in photograph below is related to ? 

 A

Olivary mucleus.

 B

Lat. Geniculate body.

 C

Medial geniculate body.

 D

Trapezoid body.

Q. 6

Part (Arrow) in visual pathway as shown in photograph below is related to ? 

 A

Olivary mucleus.

 B

Lat. Geniculate body.

 C

Medial geniculate body.

 D

Trapezoid body.

Ans. B

Explanation:

Ans:B.)Lateral Geniculate Body.

Part (Arrow) in visual pathway as shown in photograph above represents optic tract.

Optic tract relays the information to Lateral geniculate body.

Visual Pathway

  • Vision is generated by photoreceptors in the retina.
  • The information leaves the eye by way of the optic nerve, and there is a partial crossing of axons at the optic chiasm.
  • After the chiasm, the axons are called the optic tract.
  • The optic tract wraps around the midbrain to get to the lateral geniculate nucleus (LGN), where all the axons must synapse.
  • From there, the LGN axons fan out through the deep white matter of the brain as the optic radiations, which will ultimately travel to primary visual cortex(Areas 17,18 and 19)

Quiz In Between



Visual Pathway

VISUAL PATHWAY


VISUAL PATHWAY

  • Visual pathway starting from retina.

Consists of:

  1. Optic nerve
  2. Optic chiasma
  3. Optic tracts
  4. Lateral geniculate bodies
  5. Optic radiations (geniculocalcarine pathway)
  6. Visual cortex

OPTIC NERVE

  • Also known as cranial nerve II.
  • Paired nerve that transmits visual information from the retina to the brain. 
  • Starts from the optic disc and extends up to optic chiasma, where the two nerves meet. 
  • It is the backward continuation of the nerve fibre layer of the retina, which consists of the second order neurons i.e. axon originating from the ganglion cells. 
  • Also contains the afferent fibres of the pupillary light reflex.
  • The fibres of optic nerve, numbering about a million.
  • The optic nerve  is about 47-50mm in length may be divided in the four parts :

1. Intraocular part (1 mm):

  • Begins at optic disc (optic nerve head) and exits the nerve through a hole in sclera that is occupied by a mesh like structure called the lamina cribrosa.
  • The nerve fibres from the retina leave the eye through pores (holes) in lamina cribrosa, a sieve – like structure made up of collagen meshwork.

2. Intraorbital part (30 mm):

  • Extends from back of the eyeball (at lamina cribrosa) to the optic foramina.

3. Intracanalicular part (6-9 mm):

  • It lies within the optic canal and closely related to ophthalmic artery which crosses obliquely over it.

4. Intracranial part (10 mm):

  • It lies above the cavernous sinus and converges with its fellow from contralateral side to form optic chiasma.

OPTIC CHIASMA

  • Both sides optic nerves converge with each other to form optic chiasma.
  • Posteriorly, chiasma is continuous with the optic tract.
  • Nerve fibres arising from the nasal halves of two retinae
  • Decussate at chiasma & go to the contralateral visual cortex through optic tracts.
  • While nerve fibres from temporal halves of the retinae & go to the same side of visual cortex.

OPTIC TRACTS

  • Cylindrical bundle of nerve fibres
  • Running outwards & backwards from posterolateral aspect of optic chiasma.
  • Each optic tract consists of fibres from the temporal half of the retina of the same eye & nasal half of the contralateral eye.

LATERAL GENICULATE BODY

  • Optic tracts terminate in the lateral geniculate body.
  • Fibres of second order neurons coming via optic tracts relay in neurons of lateral geniculate body.
  • Third order neuron originate from lateral geniculate body & extend into optic radiation.

OPTIC RADIATIONS

  • The optic radiations (geniculocalcarine pathway).
  • Extends from the lateral geniculate body to the visual cortex.
  • Inferor fibres of optic radiations subserve upper visual fields
  • Superior fibres subserve inferior visual fields.

VISUAL CORTEX

  • Located on the medial aspect of occipital lobe

In visual pathway

Sensory organs Photoreceptors (Rods & cones)
Neurons of first order Axon of bipolar cells (in Retina)
Neurons of second order Axons of ganglionic cell (Retina i.e optic disc,

Optic nerve, optic chiasma, optic tracts)

Neurons of third order Axons from nerve cells in lateral geniculate body (optic radiation)

Exam Important

Parts of optic nerve

  • Intraocular part: 1 mm
  • Intraorbital part: 25 – 30 mm
  • Intracanalicular part: 5 – 9 mm
  • Intracranial part: 10 – 16 mm

 Lesions of visual pathway

No

Site of lesion

Causes

Features

1

Normal

2

Optic nerve

Optic neuritis

Optic atrophy

Sarcoidosis

LHON

Traumatic avulsion

Complete blindness in affected eye

Loss of light reflex on the affected side and

consensual reflex loss on the other side

Near reflex present

Central/paracentral scotoma

3

Central chiasma

Pituitary tumors (MCC)

Suprasellar aneurysm,

Craniopharyngioma,

Glioma of Ill ventricle

Bitemporal hemianopia

Bitemporal hemianopic paralysis of

pupillary reflexes

3a

Lateral chiasma

Distension of 3rd  ventricle,

Atheroma of post.

communicating A

Binasal hemianopia

Binasal hemianopic paralysis of pupillary

reflexes

4

Optic tract

Geniculate body

Syphilitic meningitis,

gumma, tuberculosis,

tumors of optic thalamus

Incongruous (contralateral) homonymous

hemianopia

Contralateral Wernicke’s pupil (optic tract)

5

Optic radiations in

temporal lobe

(inferior fibres)

 

Superior quadrantic hemianopia (pie in the sky)

Normal pupillary reactions

5a

Optic radiations in

parietal lobe

(Superior fibres)

 

Inferior quadrantic hemianopia (pie on the floor)

Normal pupillary reactions

6

Optic radiations

 

Homonymous hemianopia

7

Anterior occipital

(visual) cortex

Occlusion of posterior

cerebral artery

Congruous homonymous hemianopia sparing macula

8

Tip of occipital cortex

 

Congruous homonymous macular defect

  • Optic atrophy (partial, descending) – occurs in lesions of chiasma, optic tract and geniculate body
  • Optic atrophy does not occur in lesions of optic radiations and visual cortex
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