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November 30, 2016 00:17

A study of the cranial nerves .II pair : the optic nerve (n opticus.)

The optic nerve carries visual impulses from the retina to the cortex of the occipital lobe.

When collecting history trying to find out if there are any changes in the patient's vision.Changes of visual acuity (far or near) are the responsibility of the ophthalmologist.If episodes of transient violations of clarity, limitation of the visual field, or the presence of photopsia complex visual hallucinations must be a detailed study of all the visual analyzer.The most common cause of transient visual disturbances - migraine with visual aura.Visual disturbances often presents flashes of light or zigzag sparkling (photopsia), flicker, fallout area or field of view.The visual aura of migraine develops 0.5-1 hours (or less) to the attack of headache, lasts an average of 10-30 minutes (no more than 1 hour).Headache migraine occurs no later than 60 minutes after the end of the aura.Visual hallucinations photopsia by type (flash, sparks, zigzags) may be an aura of an epileptic seizure in the presence of the pat

hological focus, irritating bark in calcarine furrow.

acuity and her research

Visual acuity determined by ophthalmologists.To evaluate visual acuity using special tables with circles, letters, numbers.Standard table used in Ukraine, contain 10-12 rows of signs (optotypes), the size of which decreases from top to bottom on the arithmetic progression.Sight examined from a distance of 5 m, the table should be well illuminated.During normal (visual acuity 1) take a visual acuity, with which from this distance the examinee is able to distinguish the optotypes 10 minutes (counting from the top) line.If the examinee is able to discern the signs of the 9th row, his visual acuity was 0.9, 8-th row - 0.8, etc.In other words, reading each successive line from top to bottom indicates an increase in visual acuity of 0.1.Near vision checked using other special table or suggesting the patient to read the text from a newspaper (normally small newspaper font distinguish from a distance of 80 cm).If visual acuity is so small that the patient can not read anything either from what distance is limited to a score of fingers (doctor's hand is located at eye level of the subject).If this is not possible, the patient is asked to determine in which room: in the dark or lit - it is.Reduced visual acuity (amblyopia) or total blindness (amaurosis) occur in lesions of the retina or optic nerve.In this blindness disappears direct reaction of the pupil to light (due to interruption of the afferent pupillary reflex arc), but remains intact reaction of the pupil in response to healthy eyes lighting (efferent arc of the pupillary reflex, provided the fibers of cranial nerve III, remains intact).Slowly progressive decline in vision observed with compression of the optic nerve or chiasm tumors.

Signs violations.Transient short-term loss of vision in one eye (transient monocular blindness, or amaurosis fugax -. From the Latin for "fleeting") may be due to transient disturbances of blood supply to the retina.It is described by patients as "curtain, fallen from the top down" when it occurs, and how to "lift the curtain" at its reverse development.Usually, vision is restored within a few seconds or minutes.Acutely arisen and progressive for 3-4 days reduced vision, then the recovery within a few days, weeks, and often accompanied by pain in the eyes, is typical of optic neuritis.Sudden and persistent loss of vision occurs when fractures of the anterior cranial fossa in the field of the visual channel;vascular lesions of the optic nerve and temporal artery.When plugging the zone of bifurcation of the basilar artery and the development of bilateral occipital infarct with damage to the primary visual centers of both hemispheres of the brain there is a large "tubular" vision or cortical blindness."Tubular" vision due to bilateral hemianopsia with the preservation of the central (macular) vision in both eyes.Preservation of the narrow central field of view due to the fact that the projections of the macula area of ​​the occipital lobe at the pole supplied with blood from several arterial beds and occipital lobes infarcts often remains intact.Visual acuity in these patients is reduced slightly, but they behave like the blind."Cortical" blindness occurs in the event of failure of anastomoses between the cortical branches of the middle and posterior cerebral arteries in the areas of the occipital cortex, responsible for the central (macular) vision.Cortical blindness is different safety pupil reaction to light, as the visual pathways from the retina to the brain stem is not damaged.Cortical blindness with bilateral lesion of the occipital lobe and parietal-occipital areas in some cases may be combined with the denial of the disorder, achromatopsia, apraxia friendly eye movements (the patient can not direct attention toward the object in the peripheral visual field) and the inability to visually perceive the objectand touch him.The combination of these disorders is referred to as Balint's syndrome.

fields of study and their

field of view - the space station, which sees the fixed eyes.Preservation of field is determined by the state of the entire visual pathway (optic nerve, optic tract, optic radiation, the cortical area of ​​which is located in calcarine sulcus on the medial surface of the occipital lobe).Due to the refraction of light rays and chiasm in the lens and move the fiber optic retinal halves of the same name in the chiasm the right half of the brain is responsible for the safety of the left half of the visual field of each eye.The fields of view are evaluated separately for each eye.There are several methods of their approximate estimation.

  • alternately evaluation of individual fields of view.The doctor sits in front of the patient.The patient closes his eyes one hand, and the other eye is looking at the doctor nose.Hammer or wiggling fingers moved along the perimeter of the head of the subject to the center of his field of vision and the patient is asked to note the time of occurrence or hammer toes.A study carried out successively in all four quadrants of the visual field.
  • procedure "threat" is used in cases when it is necessary to explore the field of vision in a patient voice unavailable contact (aphasia, mutism, etc.).Doctor sharp "threatening" movement (from the periphery to the center) brings to straighten the fingers of his hand to the patient's pupil, watching his blinking.If the field of vision intact, the patient in response to an approaching finger flashing.Explore all of the field of view of each eye.

described methods relate to screening, more accurately detect defects in visual fields using a special device - the perimeter.

Signs violations.Monocular visual field defects are usually caused by disorders of the eyeball, the retina or optic nerve - in other words, the loss of the visual pathways in front of their chiasm (chiasma) causes a disturbance of the visual field of one eye only, located on the affected side.Binocular visual field defects (hemianopsia) can be bitemporal (both eyes fall temporal field of vision, that is, the right of the right eye, the left - left) or homonymous (each eye drop of the same name of the field - either left or right).Bitemporal visual field defects occur in patients with lesions in the optic chiasm the fibers (eg, when the chiasm lesion onyxoj and pituitary).Homonymous defects in the visual field occur at a lesion of the optic tract, optic radiation or visual cortex, that is, with the defeat of the visual pathway above the optic chiasm (these defects occur in opposite lesions fields of view: if the focus is in the left hemisphere, fall right visual field in both eyes, andon the contrary).The defeat of the temporal lobe leads to the appearance of defects in the upper homonymous quadrants of the visual field (contralateral upper quadrant anopsia), and defeat the parietal lobe - the appearance of defects in the lower homonymous quadrants of the visual field (contralateral lower quadrant anopsia).

Conductor visual field defects are rarely combined with the visual acuity changes.Even with significant peripheral visual field defects, central vision may persist.Patients with defects of fields of vision caused by optic tract lesion above the optic chiasm, may not be aware of the presence of these defects, especially with respect to cases of lesions of the parietal lobe.

fundus and his research

fundus examined with the ophthalmoscope.Assess the status of the disk (nipple) of the optic nerve (visible at the initial ophthalmoscopy, intraocular portion of the optic nerve), retinal, retinal vessels.The most important characteristics of the state of the fundus - the color of the optic nerve, the clarity of its borders, the number of arteries and veins (usually 16-22), the presence of venous pulsations, any anomalies or pathological changes: hemorrhages, exudates, change of vessel walls in the yellow spot (macula) and on the periphery of the retina.

Signs violations.Papilledema is characterized by its bulging (disc will stand above the level of the retina and juts into the cavity of the eyeball), redness (vessels on the disc rapidly expanded and filled with blood);disk boundaries become indistinct, the number of vessels in the retina increases (more than 22), the veins do not pulsate, there hemorrhage.Bilateral papilledema (stagnant nipples optic nerve) was observed with an increase in intracranial pressure (volumetric process in the cranial cavity, hypertensive encephalopathy, and others.).Visual acuity originally usually suffers.If time does not eliminate the increased intracranial pressure is gradually reduced visual acuity and blindness develops as a result of secondary optic atrophy.

stagnant optic disc must be differentiated from inflammatory changes (papillomas, optic neuritis) and ischemic optic neuropathy.In these cases, the disc changes often unilateral, typical pain in the eyeball, and decreased visual acuity.Pallor of the optic disc in conjunction with a decrease in visual acuity, visual field loss, decreased pupillary reactions characterized by atrophy of the optic nerve, which develops in many diseases affecting the nerve (inflammatory, dismetabolic, hereditary).Primary optic atrophy develops in lesions of the optic nerve or chiasm, and the pale disk, but has clear boundaries.Secondary optic atrophy develops after papilledema, fuzzy boundary of the disc first.Selective pallor of the temporal half of the optic nerve can occur in multiple sclerosis, but this pathology is easily confused with an embodiment of the normal state of the optic nerve.Retinitis pigmentosa degenerative possible or inflammatory diseases of the nervous system.Other important neurologist for abnormal findings on examination, fundus include arteriovenous angiomu retina and symptom of cherry pits, which is possible in many gangliosidosis and is characterized by white or gray circular hearth in the macula, the center of which is located cherry-red spot.Its origin is associated with atrophy of the retinal ganglion cells and translucence through it choroid.