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Defects of visual pathway

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Defects of visual pathway

  1. 1. Defects of visual pathway
  2. 2. Definition: The entire area that can be “seen” by the patient without movement of the head and with the eyes fixed on a single spot. Visual Fields Mapping of Visual Fields: •Confrontational method •Perimetry (Manual or Automated)
  3. 3. Visual Fields The image of an object in the visual field is inverted and reversed right to left on the retina. • Temporal field of left eye (red & purple) is seen by the nasal retina of the left eye • Nasal field of the left eye (green & yellow) is seen by the temporal retina of the left eye. • Superior field of the left eye (red & green) is seen by the inferior retina of the left eye. • Inferior field of the left eye (purple & yellow) is seen by the superior retina of the left eye. • Similarly, the image is inverted & reversed for the right eye. Retina of Left Eye Retina of Right Eye Binocular Visual Field Monocular Crescent of Right Eye Monocular Crescent of Left Eye
  4. 4. BLIND SPOT • Corresponding to optic nerve head • 15 deg temporal to point of fixation • Span – 5 deg horizontal -- 7 deg vertical
  5. 5. • SCOTOMA : focal region of abnormally decreased sensitivity surrounded by an area of normal sensitivity – ABSOLUTE – RELATIVE – POSITIVE – NEGATIVE
  6. 6. • QUADRANTANOPIA: Defective vision or blindness in approx. one-fourth of the visual field • HEMIANOPSIA: Defective vision or blindness in approx,. one- half of the visual field • HOMONYMOUS DEFECTS: Visual defects restricted to either the right or the left visual field (post-chiasmatic defects) • HETERONYMOUS DEFECTS: Visual defects involving parts of both the left & right visual fields • CONGROUS DEFECTS: Visual defects are equivalent in each monocular visual field • INCONGROUS DEFECTS: Visual defects are NOT equivalent in each monocular field • ALTITUDINAL DEFECTS: Visual defects are in the upper or lower aspect of the visual fields
  7. 7. LESIONS OF VISUAL PATHWAY
  8. 8. 1) LESIONS OF OPTIC NERVE : Causes: • Optic atrophy • Reterobulbar optic neuropathy • Acute optic neuritis • Traumatic Characterised by: complete blindness in affected eye with loss of both direct on ipsilateral & concensual light reflex on contralateral side. Near reflex is preserved.
  9. 9. 2)Lesions through proximal part of optic nerve : • Ipsilateral blindness. • Contralateral hemianopia • Abolition of direct light reflex on affected side & concensual light reflex on contralateral side. • Near reflex intact. Eg. Rt optic nerve Involvement in Proximal part
  10. 10. 3) Central lesions of chiasma (sagittal) • Causes: • Suprasellar aneurysm • Tumors of pituitary gland • Characterised by: • Bitemporal hemianopia • Bitemporal hemianopic • Paralysis of pupillary reflex. (Usually lead to partial descending optic atrophy)
  11. 11. 4)Lateral chiasmal lesions : • causes: • Distension of 3rd ventricle causing pressure on each side of optic chiasma • Atheroma of carotids & posterior communicating artery. Characterised by • Binasal hemianopia • Binasal hemianopic • parallysis of pupillary reflex (usually lead to partial descending optic atrophy)
  12. 12. 5)Lesions of optic tract : Causes: • Infections • Tumors of optic thalamus • Aneurysm of superior cerebellar or posterior cerebral arteries. Characterised by : • Incongruous homonymous hemianopia with C/L hemianopic pupillary reaction( wernicke’s reaction) • These lesions usually lead to partial descending optic atrophy & may be associated with C/L 3rd nerve paralysis & ipsilateral hemiplegia.
  13. 13. 6)Lesions of lateral geniculate body :  leads to homonymous hemianopia with sparing of pupillary reflexes & may end in partial optic atrophy.
  14. 14. 7)Lesions of optic radiations : Causes:  Vascular occlusion  Primary & secondary tumors  Trauma  Characterised by : TOTAL OPTIC RADIATION INVOLVEMENT COMPLETE HOMONYMOUS HEMIANOPIA( sometimes sparing macula)
  15. 15. LESIONS OF PARIETAL LOBE (involving superior fibres of optic radiations) INFERIOR QUADRANTIC HEMIANOPIA( PIE ON THE FLOOR) LESIONS OF TEMPORAL LOBE (involving inferior fibres of optic radiations) SUPERIOR QUADRANTIC HEMIANOPIA( PIE ON THE ROOF)
  16. 16. • Pupillary reactions are normal as fibres of light reflex leave the optic tracts to synapse in the superior colliculi. • Lesions of optic radiations do not produce optic atrophy as the 1st order neurons (optic nerve fibres) synapse in LGB.
  17. 17. 8)Lesions of visual cortex : pupillary light reflex is normal & optic atrophy does not occur following visual cortex lesions. Congruous homonymous hemianopia(sparing macula) Occlusion of posterior cerebral artery supplyin anterior part of occipiatl cortex Congruous homonymous macular defect Head injury/gun shot injury leading to lesions of tip of occipital cortex+

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