Psychology

The Optic Nerve
The optic nerve is the second cranial nerve. It is a purely sensory nerve containing nasal and temporal fibers subserving the temporal and nasal fields of the eyes respectively. It is a very important nerve responsible for vision. Lesions in the nerve can result into a variety of visual abnormalities. However, such abnormalities which include total blindness, heteronymous hemianopea, homonymous hemianopea, etc. can be detected using appropriate tests.

Sensory Tests for Optic Nerve
Test of visual field - This is a very common and important test of assessing the function of the second cranial nerve. Various methods exist for carrying out this test, all of which have their merits and elements (Swash and Hutchison 249).

Confrontation test using a finger - This method maps the whole visual field. It compares the examiner s visual field with that of the client assuming the examiner s own visual fields are normal. The patient sits comfortably facing the examiner at a distance of 1 meter. Each failure is tested separately. The patient is instructed to cover the left eye with the left hand while the examiner covers his own right eye with the right hand.

The patient is further constructed to focus his gaze at the examiner s left eye while the examiner also looks on steadily at the patient s right eye. The examiner holds up the left index finger in a plane midway between the patient s face and the examiner s face, initially at full arm s length to the left side and subsequently from up down.

The index finger is gradually moved towards the midline while ensuring that the patient s eye is fixed on the examiners left eye. The 4 quadrants right, left, downward, and upwards are tested separately while the patient signifies when he first observes the moving finger in his field of vision. This is hence compared with when the examiner observes the moving finger in his field of vision taking the examiner s visual field as the standard (Swash and Hutchison 325).

The same process is repeated for the right eye. Its advantages include being rapidly executed fairly accurate, being reproducible, and requiring no sophistication. Its demerits include the fact that taking the examiner s own visual field as the standard may be misleading because the examiner may have an undiagnosed visual field defects. Similar methods for assessing visual field include the red pin confrontation test in which a red head pin mounted on a eraser base of a pencil replaces the use of the inhere finger. It is a very sensitive test of the central tailed of vision, and it allows the patents visit field inclusions the physiological blind sport to be prcising compared with that if the examiner (Swash and Hutchison 325).

Other methods of visual field assessment include perimetry and test of visual acuity. In perimetry, the visual field is quantitatively mapped using different kinds of perimeters from the simple mechanical perimeter to the more sophistical automated ones. The range of visual field is measured in  degrees and each examination is tested separately. The accuracy of the method is very high (Swash and Hutchison 252). Test of visual acuity is another very important test of the second cranial nerve, though it can also be used in detecting refractive errors of the eyes such as short sightedness, long sightedness, etc. This test is useful in grading blindness which is the gravest outcome at all disease of the second cranial never (optic nerve) (Swash and Hutchison 252).

The test of visual acuity is carried out using the Snellens chart in a well-illuminated room with the patient standing at a distance of 6m (20 feet) in front of the chart. The Snellen s chart is a plastic table containing rows of progressively reducing alphabets. Each eye is tested separately with the untested eye covered with a cardboard paper to enhance the sensitivity of the test. Visual acuity is recorded as dD in which d   distance of patient from the Snellen s chart and D is the arbitrary distance awarded for each of the 8 rows. From rows 1   8, the D is respectively given as 60, 36, 24, 18, 12, 9, 6, and 5. Normal eye will see that row of alphabet that is seen at 6m. For example, VA  612 means that the row of alphabet that is being seen by the patient at 6m will be seen by a normal eye at 12m. The patient stands at 6cm in front of the chart with one eye covered, and then reads out the rows of alphabet as far as possible and the visual (VA) is recorded. If the VA is 65, it suggests that the individual can see at 5 meters what normal eyes can see at 6m. If the individual cannot see the topmost row at 6m, he is moved gradually forward, i.e., 3, 2, 1 cm towards the chart. If the individual cannot still see the topmost row at 1m (VA  160), this means that the individual cannot see at 1 meter what a normal eye can see at 60m. The next step will be for the examiner to stand at 1m in front of the patient with one finger raised. If patient can then see the fingers, this is thus represented as  counting fingers  (CF). If the patient cannot see the fingers, the examiner moves the hand several times at the same distances in front of the client, and this is represented as hand movement (HM). If the individual cannot still see the movement of the hand, the examiner shines bright light from a pen touch still at the same 1 meter from the examiner and this is represented as light perception (LP). Visual acuity below 360 is regarded as blindness according to the World Health Organization (WHO).

Other methods for testing visual acuity include  illiterate E chart  for people who cannot read and the Sheridan Gardiner chart for illiterates and pre-school age children.


Clinical Anatomy (Ellis 385)
Seventh Cranial Nerve (Facial Nerve)
The seventh cranial nerve is the facial nerve, the embryonic nerve of the second pharyngeal arch which gives rise to the muscles and deep structures of the face. The facial nerve is hence the nerve of facial expression in its supply of motor nerve fibers to innervate these muscles. The facial nerve also subserves the sense of taste on the anterior 23 of the tongue via group nerves fibers called the  Special Visceral Efferent  fibers. Invariably, the facial nerve contains both sensory and motor fibers. The various tests available for assessing the state of the seventh cranial nerve are fashioned towards their sensory and motor functions. Taste sensation on the posterior 3rd the tongue is subserved by the glossophargngeal nerve (CNIX) (Ellis 379) .

Sensory test for facial nerve - Test for sense of taste in the ant 23 of the tongue is done using strong solutions such as sugar, common salt, citric acid, and quinine to respectively test for sweet, salty, sour, and bitter taste. A small quantity of the solution is added to the surface of the protruded tongue with the aid of a small swab on a spatula. The solution is now spread on the tongue to test other parts of the tongue. The patient is instructed to identity the type of taste sensation on the tongue. Having identified the taste, the mouth is properly rinsed so that other solutions can be tested and subsequently assessed (Ellis 379).

Motor test for facial nerve   The facial nerve has numerous methods of evaluating its motor functions.
The patient is instructed to shut the eyes as tight as possible while the examiner tries to open them. If the eye opens without any resistance, then there is facial nerve abnormality of lower motor type (intramuscular facial paralysis) (Ellis 379).

The patient is encouraged to open the mouth and the mouth is deviated to the healthy side if there is abnormality of the facial nerve (Ellis 379).

The patient can also be instructed to inflate his mouth with air, thus blowing out the cheek. Air can be made easier to escape while applying pressure on the cheek with the tip of the index finger when there is facial nerve abnormality causing paralysis of the Buccinator muscle (Ellis 379).

The patient is asked to whistle with the mouth, but this is impossible to do as a result of paralysis of the orbicularis oris, one of the muscles of facial expression supplied by the 7th cranial nerve (Ellis 379).

Fifth Cranial Nerve (Trigeminal Nerve)
The fifth cranial nerve is the trigeminal nerve which arises from the brainstem via a small motor nucleus and a bigger main sensory nucleus. It is therefore a mixed nerve containing both motor and sensory fibers. It is the embryonic nerve of the first branchial arch, the biggest cranial nerve in the body. It is the major sensory nerve of the face and the motor nerve to the muscles of mastication (chewing of food) (Ellis 379).

Sensory Test for the Fifth Cranial Nerve
Test of corneal reflex   This is one of the various tests that exist for assessing the sensory state of the fifth cranial nerve. It is a very sensitive but equally dangerous test, so the test should be carefully carried out. With the patient comfortably seated in front of the examiner, having explained what the test entails to him or her, a light wisp of soft cotton wool is twisted into a fine strand and lightly used to touch the lateral edge of the cornea, having initially instructed the patient to fix his or her gaze at a distant midline object or at the ceiling. If the corneal reflex is intact, the patient blinks and will not allow the wisp of cotton wool to touch the cornea. If the reflex is absent, there will be no blinking and the cotton wool can be used repeatedly to touch the cornea. This is however dangerous because of the risk of corneal ulceration with its accompanying complications. In view of the above, this test is sometimes carried out by gently blowing a puff of air into each eye. In turn, there will be blinking of the eyes if the corneal reflex if intact if not, there will be no blinking (Ellis 379).

Test of motor function of the fifth cranial nerve
The motor function of the fifth cranial nerve is usually assessed using the state of the muscles of mastication. The patient is instructed to clench the teeth the bulk and contraction of the muscles of mastication are subsequently assessed through palpation. With an intact motor function on both sides, the massetter muscles below the ear on each side and the temporal muscle (on the side of the head) become prominent and can be palpated. If there is an abnormality with the nerve on any side, the massetter and temporal muscles on both sides will not be prominent. Subsequently, if the patient is instructed to open the mouth, there is deviation of the jaw to the affected side. This is due to the pushing effect of the lateral pterygold muscle of the normal side on that of the paralyzed side, since these muscles on each side are supposed to be pushing each other with equal force such that any reduction in the pushing power on any side tilts the direction of push to the relatively weak side. It is worth to note, however, that the fifth cranial nerve paralysis is not the only condition that can elicit this test (Ellis 379).

Eighth Cranial Nerve
The eight cranial nerve is vestibulocochlear nerve, a purely sensory nerve which subserves hearing and balancing. It is a two-in-one nerve consisting of the cochlear component which mediates the hearing pathway and the vestibular component which is involved with body balance, equilibration, and sensations of bodily displacement.

Test of hearing
There are many methods for testing the state of hearing of an individual which can be a reflection of the state of the cochlear component of the 8th cranial nerve or the whole nerve itself. Such tests include Webers Test, Rinne s test, and Schwabach s test. Weber s and Schwabach s tests are particularly important in evaluating an individual for sensorineural hearing impairment which is a direct reflection of the state of the cochlear component of the eight cranial nerve.

Webers test is carried out using a tuning fork with a frequency of 512 Hz. The patient is comfortably seated after the whole test has been explained to him or her. The tuning fork is set into vibration and its base is subsequently placed on the patient s forehead in the midline (Swash and Hutchison 308). The patient is then asked to identify on which side the vibration is louder. Normally, the vibration is supposed to be heard in the midline and should not be louder in any of the two ears. However, in a lesion of the 8th cranial nerve damaging the cochlear component and hence the hearing pathway, the vibration is louder in the normal ear. Hearing is thus said to be lateralized to the normal side in the absence of a conductive hearing impairment in which the vibration of the turning fork will be louder in the affected ear. This is due to abnormality of the middle or external ear (pus, wax, foreign bodies like bean seed, pencil, etc.) causing obstruction to the passage of sound generated by the vibration and hence prolonging its stay in the affected ear. The setback to this test is that it cannot distinguish two normally functioning right and left ears from a case of symmetrical bilateral affectation of the two hearing pathways.

Schwabach s test of hearing compares the patient s hearing state with that of the examiner s with the use of vibrating turning forks with frequencies ranging from 128Hz, 512Hz, to 2048Hz. The tuning fork is set into vibration and then placed close to both the examiner and the patient at the same distance. If the total duration of hearing the tuning fork vibration by the patient is shorter than that of the examiner, the patient is said to have a sensorineural hearing impairment, and this points to impairment in the hearing pathway subserved by the cochlear component of the 8th cranial nerve. If the duration of hearing the vibration by the patient is longer than that of the examiner, the patient is said to have a conductive hearing impairment which is usually due to obstruction to the transmission of sound.

Other methods of assessing the state of the hearing pathway subserved by the cochlear component is the use of special investigation such as pure tone audiometry which measures the threshold for pure tone sounds introduced into each ear at different frequencies.

Test of Vestibular Component of the Eight Cranial Nerve
Caloric test   This test of vestibular function is performed with the patient lying comfortably on a couch at 300 to the horizontal. The patient is encouraged to fix his or her gaze upon a midline object and the ear is irrigated with cold water at 300C and subsequently at a temperature of 440C for about 40 seconds. This causes a conventional current within the endolymph of the inner ear (Swash and Hutchison 305).

In normal individuals, the cold water in the left ear causes a jerky movement of the eyeball with the fast movement to the right. Warm water in the left ear causes jerky eyeball movement with the fast movement towards the left. The right ear gives a response which is opposite to that on the left ear.

In diseases or damage to the vestibular apparatus, there is decreased or absence of jerky eye movement. This is a very sensitive test and should be done under specialist supervision.

Romberg s test   This is also a sensory test of the 8th cranial nerve that tests the vestibular function by assessing body balancing and equilibration. The individual is instructed to stand up with the two feet brought together and with the arms stretched out. The  patient s eyes are initially open but later on, the patient would be instructed to close them. In abnormality of the vestibular component of the vestibulocochlear nerve, the patient sways (shows postural instability) to the side affected, i.e., if the left vestibular component is affected, the patient shows instability to the left. The same applies to the right (Swash and Hutchison 237). It is worthy to note that the postural instability is more with the eyes shut and that this test can also be positive for some other central nervous system abnormalities.