1. Disorders of chiasm and retrochiasm
Anatomy
Clinical features
3. Pituitary adenomas
3. Craniopharyngioma
4. Meningioma

2. the visual system consists of ( in order) :
The eye, especially the retina
The optic nerve
The optic chiasma
The optic tract ( the retrochiasm)
The lateral geniculate body
The optic radiation
Visual cortex
Visual association cortex

3. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.
The optic nerves from both eyes meet and cross at the optic chiasm
Information from the right visual field travels in the left optic tract. And vice versa. Each optic tract terminates in the lateral geniculate nucleus (LGN) in the thalamus

4. Anatomy of chiasm and pituitary gland
Upper nasal fibres
III rd ventricle
Macular fibres
Craniopharyngioma
Lower nasal fibres
Optic chiasm
Diaphragma sellae
Posterior clinoid
Anterior clinoid
Pituitary gland
The sella turcica is adeep saddle shaped depression in the superior surface of the body of the sphenoid
Dorsum sellae

5. The sella turcica is adeep saddle shaped depression in the superior surface of the body of the sphenoid in which the pituitary
gland lies.The roof of the selle is formed by afold of dura mater which strech from anterior to posterior clinoids (diaphragma sellae).The optic nerve and chiasm lie above the diaphragma sellae posteiorly the chiasm is continuous with the optic tract.

6. Normal anatomical variations
Central - 80%
Prefixed - 10%
Postfixed - 10%

7. The following anatomical variations in the location of the chiasm may be important
1- Central chiasm. Present in about 80% of normals , is located above the sellae so that expanding pituitary tumours will involve the chiasm first.
2-Prefixed chiasm .Present in about 10% of normals,is located more anteriorly,over the tuberculum sellae ,so that pituitary tumours involvethe optic tract first.
3-post fixed chiasm. Present in about 10% of normals,is located more posteriorly, over the dorsum sellae, so that pituitary tumours involve optic nerve first.
Lower nasal fibers .traverse the chiasm low and anterioly . They are therefore most vulnerable to damage from expanding pituitary lesions ,so the upper temporal quadrants of the visual fields are involved first.
2. Upper nasal fiber.traverse the chiasm high and posteriorly and therefor are invoved first by lesions coming from the chiasm e.g . Craniopharyngioma
If the lower temporel quardants of the visual field are affected more than the upper . apituitary adenoma is unlikely.
3.Macular fibers deccusate throughout the chiasm.

8. Approximately 25% of brain tumors occur in chiasmal area , almost half of these with an initial complaint of visual loss.

9. Main symptoms of chiasmal lesions :
Visual loss
Headache
Diplopia
Endocrine dysfunction

10. Main visual signs of chiasmal lesion:
Decreased visual acuity ipsilaterally
Incongruous homonymous hemianopsia ipsilaterally.
RAPD conralateral to the lesion.

11. Most lesions involving optic tract are usually large enough to involve the chiasm and optic nerve , thus producing an optic tract syndrome.
Retrochiasmal lesions characteristically have field defects that respect vertical
midline and visual acuity is not affected.
Retrochiasmal lesions results binocular fi eld defect involving contralateral space so both eyes manifest partial or loss total visual hemifield opposite the side of retrochiasmal lesion.such ahemianopia involving the same side of visual space in both eyes is homonymous,in contrast to chiasmal lesion which produce bitemporal hemianopia ,heteronymous in which opposite side of visual
Field are affected in each eye.

12. Visual field defect in chiasmal and retrochiasmal lesions
Incongruous homonymous hemianopsia.congruous refers to how closely the extent pattern of field loss in one eye matches that of the other.so identical field defects in either eye are highly congruous while mismatching field defects in both eyes are incongruous.

13. The more posterior the lesions, the more congruous the visual field
Because as the optic radiations pass posteriorly ,fiberes from corresponding retinal pointslies progressively closer together
Lesions of the optic radiations do not produce optic atrophy these because t hese fiberes are third order neurones that originate in the lateral geniculate body. But lesions of the optic tract may result in optic atrophy because the fibres in the optic tract are the axons of the retinal ganglion cells.

14. main ophthalmic test for diagnosing retrochiasmal lesions is:
“Visual field testing”

15. Pituitary adenomas ACTH PROLACTIN Cushing syndrome Basophil
Chromophobe
PROLACTIN
Acidophil
Growth hormone
Amenorrhoea
Infertility
Galactorrhoea
Hypoglandism
Impotence
Infertility
Gynaecomastia
Galactorrhoea
Acromegaly
Gigantism

16. Visual field defects in pituitary adenomasLE RE HM CF
Anteriorly
Decussating fibres
are most vunerable

17. Pituitary adenoma is the most common primary intracranial tumour to produce neuro-ophthamological features.
Typically presented in the middle age with
1.Headache.
2. Visual syptoms usually have avery gradual onset and may not be noticed by the patient until well established.

18. Craniopharyngioma In children with endocrine dysfunction
Presents
In children with endocrine dysfunction
In adults with visual field defects LE RE CF HM
The posteriorly crossing
fibres are most vunerable
Craniopharyngioma

19. Meningioma Typically affect middle-aged women LE RE Junctional scotoma
Tuberculum Sella
meningioma
Sphenoid ridge meningioma
Olfactory groove meningioma