Optic nerve Optic nerve subdivisions Intraocular segment : 1mm, neurological disorders may affect this part are inflammation (papillitis),edema & drusen Intraorbital segment 25-30 mm long, diameter is about 3-4mm Intracanalicular segment 5mm in length Intracranial segment 10mm in length 2
PUPILLARY LIGHT RESPONSE It is an objective indicator of anterior visual pathway function, in general, It is a practical and sensitive measure of optic nerve dysfunction. The speed and amplitude of the reflex depend on the overall intensity and speed with which the afferent neural signal is transmitted to the brain stem. Diseases of the retina, optic nerve, chiasm, and tract produce definite decreases in pupillary reactivity that last as long as the lesion persists. 8
VISUAL FIELDS AND PERIMETRY Definition of the visual field is: “that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction Perimetrymeasures the visual field and involves recording of visual function of the eye at topographically defined loci in space. Understanding the visual field as it relates to neuro-ophthalmologic diagnosis is a complex subject requiring knowledge of the anatomy of the optic pathways and contiguous related structures, of the intrinsic organization of retinal projection through the pathways and in the cortex, and of the nature of various lesions and the mechanisms by which they produce field defects. The specific localizing characteristics of field defects are discussed subsequently in the chapters dealing with topical diagnosis in the visual sensory system. 10
GOLDMANN KINETIC PERIMETRY. In manual kinetic perimeter, a stimulus of fixed size, luminance, and contrast on a defined background is moved from non-seeing to seeing areas until the appearance of the stimulus is detected by the patient. 13
Humphrey Visual Field Analyzer Graphic display produced by the Humphrey Visual Field Analyzer, central 30-2 threshold test. Center:Actual display arranged as dot-matrix printout; enlarged key components are shown surrounding the central display. Top right: GS,gray-scale graph. Top left: Num,numeric threshold values in decibels 14
Visual Loss Arising From Structures Anterior to the Optic Nerve. Retinal microembolization or hypoperfusion Retinal migraine Acute glaucoma (corneal edema) Reversible cataract (e.g.,acute hyperglycemia)retinal inhibition) Quinine, digitalis, clomiphene citrate Visual Loss Arising From Optic Nerve and Chiasm Obscurations preceding ischemic optic neuropathy Optic disc swelling Retro bulbar tumors Intracranial hypotension Visual Loss Arising From Postgeniculate Structures Carotid or vertebrobasilar ischemia occipital lobe cerebrovascular accidents Classic migraine Occipital trauma
Some of the Optic nerve clinical problems. A.Myelinated nerve fibers. Retina is white, opaque, with feathered edges B.Calcified astrocytichamartoma of retinal nerve fiber layer in tuberous sclerosis. C.Hypoplasia of the optic nerve. Disk is small and with pigment rim and surrounding paler ring. D.Inferior crescent. Disk is small and horizontally oval with scleral crescent at lower border. E.Pseudopapilledema; congenital elevated disk (compare with true papilledema, F). Note absence of central cup, vessels arise at disk apex. Vascular anomalies include excessive number of major disk vessels and multiple bifurcations. Nerve fiber layer does not obscure vessels at disk margins. F.Chronic moderate papilledema (compare with pseudopapilledema in E.) Note retention of central cup, flame hemorrhage at superior border, absence of anomalous vessel pattern, small arterioles are obscured in nerve fiber layer. 16
INFLAMMATORY OPTIC NEUROPATHIES:Optic neuritis. 17 Causes of Optic Neuritis Unknown origin Multiple sclerosis Viral infections of childhood (measles, mumps, chicken pox) with or without encephalitis Postviral, paraviral infections Infectious mononucleosis Herpes zoster Contiguous inflammation of meninges, orbit, sinuses Granulomatous inflammations (syphilis, tuberculosis, cryptococcosis, sarcoidosis) Intraocular inflammations
Optic neuropathies Clinical features of optic nerve disease The optic nerve head is the exit site for all retinal nerve fibres. Optic nerve lesions have the following clinical signs: Diminished visual acuity. Visual field defects which can be of various types depending on the underlying lesion, such as central scotomata, centrocaecalscotomata and altitudinal defects Diminished pupillary light reactions. Impairment of colour vision making coloured objects appear 'washed out'. Diminished light brightness sensitivity
defined as swelling of the optic nerve head secondary to raised intracranial pressure. It is nearly always bilateral although it may be asymmetrical.
All other causes of disc oedema not associated with raised ICP (e.g. optic papillitis, central retinal vein occlusion) are referred to as 'disc swelling' and usually produce visual impairment.
All patients with papilloedema should be suspected of having an intracranial mass until prooved otherwise . not all patients with papilloedema will have a tumour, as some may have benign intracranial hypertension or other pathology.
The following are its main features: Visual symptoms are absent and visual acuity normal. Optic discs showing hyperaemia and indistinctness of the disc margins, Loss of previous spontaneous venous pulsation. If venous pulsation is well preserved the diagnosis of papilloedema is unlikely Optic discs showing venous engorgement, elevation of the surface, partial obscuration of the small traversing blood vessels and obliteration of the cup flame shaped haemorrhages and cotton-wool spots.
Papilledema. A.Papilledema of raised intracranial pressure. In patient with frontal astrocytoma, right disk shows early edema of superior pole. B.Left disk of same patient shows more advanced edema, yet absence of hemorrhages, exudates, or engorgement. C.Fully developed Papilledema in a case of pseudo tumor cerebri. Multiple superficial infarcts of nerve fiber layer (“cotton-wool spots”). Veins are dilated and tortuous. D.Severe Papilledema associated with dural venous sinus thrombosis in young boy. Note exudative partial “star” figure at fovea. E.Chronic Papilledema of many months duration. F.Chronic Papilledema after detumescence of edema, revealing pallor and formation of retinochoroidal venous shunts. 21
Oculosympathetic palsy (Horner's syndrome) Causes of disruption of the sympathetic pathways include: Pancoast'stumour of the lung, (2) carotid and aortic aneurysms, (3) lesions in the neck (e.g. malignant cervical lymph nodes, trauma or surgery), (4) brain-stem vascular disease or demylination, (5) syringomyelia, (6) cluster headaches, (7) congenital (8) idiopathic. Clinical features are the following : The lesion is usually unilateral. Mild ptosis as a result of weakness of Müller's muscle. Slight elevation of the inferior eyelid due to weakness of the inferior tarsal muscle. Miosis resulting from the unapposed action of the sphincter pupillae. The pupillary reactions are normal to light and near. Reduced ipsilateral sweating, but only if the lesion is below the superior cervical ganglion. Heterochromia (irides of different colour) is occasionally present if the lesion is congenital. The pupil is slow to dilate.
Oculomotor nerve palsies Third (oculomotor nerve palsy) 26
The oculomotor nerve is responsible for elevation (superior rectus, inferior oblique), adduction (medial rectus), and depression (inferior rectus). It also provides innervation to the levator muscle to elevate the lid and parasympathetic innervation to the pupil causing constriction. A complete oculomotor nerve palsy results in ptosis, pupillary dilation, and the eye resting in the down and out position 27
The fourth cranial nerve is unique in that it is the only cranial nerve to exit dorsally from the brainstem. Patients with unilateral fourth nerve palsies complain of vertical and torsionaldiplopia. The diplopia is worse on gaze away from the involved superior oblique muscle and the patient may manifest a head tilt to the opposite side to eliminate diplopia The most common cause of an isolated fourth nerve palsy is trauma The magnitude of the head trauma need not be severe but fourth nerve palsies associated with minor head trauma can be the result of undiagnosed intracranial tumors. 29
Sixth nerve palsies are the most common of the oculomotor nerve palsies. Clinically it presents as a paralysis of the ipsilateral lateral rectus muscle which results in an abduction deficit toward the side of the lesion, esotropia, and horizontal diplopia While most patients with an acute acquired esotropia have a sixth nerve palsy, a thorough ophthalmic and neurologic evaluation is necessary to eliminate the other causes of abduction deficits