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COMMISSIONED ARTICLE
Year : 2013  |  Volume : 1  |  Issue : 1  |  Page : 37-44

Work up of neuro-ophthalmological cases - Examination – Investigations


Department of Neuro Ophthalmology, Snakara Nethralaya, A unit of Medical Research Foundation, 18, College Road, Chennai, Tamil Nadu, India

Date of Submission21-Sep-2012
Date of Acceptance07-Nov-2012
Date of Web Publication22-Jan-2013

Correspondence Address:
Rashmin A Gandhi
Sankara Nethralaya, A unit of Medical Research Foundation, 18, College Road, Chennai, Tamil Nadu - 600006
India
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Source of Support: None, Conflict of Interest: None


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  Abstract 

Importance of thorough history-taking, meticulous examination and tailored investigations cannot be underestimated in any branch in medicine, and the same goes for neuro-ophthalmology too. In patients presenting with visual loss, ocular motility disturbances, or simply headache, the ophthalmologist may be the first one to diagnose life-threatening conditions. Thus, before referring the patient to other services, it is essential to arrive systematically and rationally at a conclusive, problem-oriented diagnosis. This article gives a stepwise approach to work up patients with a potential neuro-ophthalmic condition. It gives a brief and helpful overview about history-taking in these patients and clears most ambiguities regarding examination techniques and the choice and timing of investigations. It may especially prove to be very useful and of special interest for training ophthalmologists.

Keywords: Clinical examination, cranial nerve palsy, neuro ophthalmological investigations, neuro ophthalmology


How to cite this article:
Shrirao N, Gandhi RA. Work up of neuro-ophthalmological cases - Examination – Investigations. J Clin Ophthalmol Res 2013;1:37-44

How to cite this URL:
Shrirao N, Gandhi RA. Work up of neuro-ophthalmological cases - Examination – Investigations. J Clin Ophthalmol Res [serial online] 2013 [cited 2022 Jul 4];1:37-44. Available from: https://www.jcor.in/text.asp?2013/1/1/37/106285

Neuro-ophthalmological disorders are like a puzzle that unfolds at every step of the work up. Patients with ocular motility disturbances, headache, transient visual obscuration, head injury, sudden visual loss, and also gradual progressive visual loss are the patients who require a systematic neuro-ophthalmic examination, and if required, investigations. In many of these conditions, it may not be possible to do much for the involved eye, but it is essential to safeguard and monitor the other eye. Also, correct and timely diagnosis and intervention may prove to be not only sight-saving but also life-saving in some situations. This article covers, in short, the complete work up of commonly presenting neuro-ophthalmological cases; outlining the history-taking, clinical examination, and tailored investigations.


  History Top


Like in every medical case, a detailed history regarding onset [Figure 1], duration, and progress of the complaints must be taken. Sudden visual loss needs to be elaborated further; an exampleis given in the following table:

When a patient complains of gradual progressive visual loss, we may be dealing with a toxic neuropathy or - a compressive lesion [Figure 2]. History-taking becomes even more crucial in this scenario.
Figure 1: Onset of visual loss[3]

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Figure 2: History in Compressive optic neuropathy[3]

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[Figure 3]: TRON: Traumatic optic Neuropathy; NA-AION: Non-ArteriticAnterior Ischemic Optic Neuropathy; A-AION: Arteritic Anterior Ischemic Optic Neuropathy; PION: Posterior Ischemic Optic Neuropathy.
Figure 3: Course of visual loss

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  Visual Function Top


Visual acuity (Distance and near)

Color vision


Color vision deficit indicates an optic nerve involvement. Ishihara pseudo-isochromatic tests plates are most commonly used tests in the daily clinics. Inability to identify less than 13 out of 26 plates is considered as defective color vision. [1],[2] Defective color vision maybe due to optic nerve damage of congenital color blindness. This can be distinguished by simply asking the patient with the help of a red filter. Total improvement would indicate a congenital disorder; while in optic nerve damage, there may be no or partial improvement. [1],[2],[3] The D 15 color vision test is based on a set of colored plates or discs, which have to be arranged in the correct order. Tests like Farnsworth-Munsell 100 hue test and Hardy-Rand-Ritter (HRR) charts are more accurate and detailed. Though these tests can identify very early or fine changes, they are very time-consuming and very difficult to carry out in the outpatient department (OPD). Worse color vision in dim lighting and more red green color defects go in favor of optic nerve involvement. [1],[2]

Color saturation

Since patients with optic nerve disease perceive colors less bright and faded than normal people; this test gives a clue about presence of optic nerve diseases. A red stimulus (brightly colored stimulus preferred) is presented to each eye, and patient is asked if to one eye, the color appears 'brighter' or 'richer' than the other. If the patient clearly says yes, it is taken as a positive response. To the eye with defective optic nerve function, the red color may appear as a faded color such as orange, pink or faded red (indicating decreased saturation) or brown, gray (indicating decreased brightness). [3]

Brightness sensitivity testing

Bright torchlight is shone in both eyes, and patient is asked which one is brighter. Then, considering the brighter one as 100%, he is asked to rate the brightness in the other eye. This is also called subjective relative afferent pupillary defect (RAPD) testing. This test detects subtle and early optic nerve defects. [1],[2],[4]

Confrontation field testing

Confrontation testing grossly evaluates the visual field of a patient, examining one eye at a time. The obvious advantages of confrontation visual field testing include its simplicity, flexibility, speed of administration, and ability to be performed in any setting, including at the bedside. The disadvantages of confrontation visual field testing include the lack of standardization, the qualitative nature of the results, and the limited ability to detect subtle deficits and monitor progression or remission of visual loss. Because it is quick and easy to perform, confrontation visual field should be performed on all patients, regardless of their visual complaints. [1] Obviously, it should never replace formal visual field testing.

Confrontation testing [Figure 4] involves a series of stepwise tests, which are performed mono-ocularly. The examiner sits at the level of the patient, and the test is performed at the distance of one meter. Patient is asked to fixate on the bridge of the examiner's nose. While testing patient's right eye, his left eye should be occluded.
Figure 4: Confrontation testing

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Ask the patient if he can see the examiner's full face clearly. If not, then ask him to elaborate which parts are missing or not clearly visible to him. This will tell us about any gross defects in the field of vision.

There are different components of confrontation field testing-Testing of single quadrants[2],[4] : Stationary fingers are presented randomly in each quadrant of the right eye, taking care that the stimulus remains well within 30 degrees of the visual field; and the patient is asked to count the fingers. For ease of understanding of the patient, numbers of fingers shown are restricted to 1, 2, and 5. Children can be asked to simulate the number of fingers seen and at the same time, the examiner looks for the eye movements brought forth by the stimulus.

Delineating the scotoma[2],[4] : If the patient is not able to see the fingers - move the finger from the defective quadrant slowly towards the vertical meridian. Patient is asked to identify as soon as he sees the stimulus. This is to map the border of the defect; identify whether it is aligned to the vertical meridian. Same procedure should be repeated to if there is presence of a defect respecting the horizontal meridian.

Above steps are repeated in the left eye.

If a scotoma is present in either of the eye, the following tests are performed after occluding the other eye.

Testing double quadrants[2],[4] : This is performed if the patient correctly identifies stimuli in single quadrant testing, but the clinician suspects presence of defect in a certain quadrant. One or two fingers of both the hands are simultaneously presented in two different quadrants, and the patient is asked to count the total number of fingers seen. This makes it possible to detect homonymous defects.

Brightness comparison[3],[4] : If the patient responds correctly to the above tests, he may be asked to compare the clarity or brightness of fingerssimultaneously presented in two different quadrants and if there is any reduction in brightness of one of them.

If there is no obvious scotoma, a red desaturation test is performed to reveal any subtle field loss.

Red desaturation test[3] : After occluding the other eye, two identical bright-colored objects (preferably red) are presented to the patient in two different quadrants in front of the eye to be tested and asked if there is any difference in the brightness of the color in any of the quadrant [Figure 5]. If yes, the object is moved slowly from the defective quadrant towards the vertical meridian, and the patient is asked if the object becomes brighter or duller in the course. If there is marked difference, a hemianopic defect exists. Same maneuver is repeated with the horizontal meridian.
Figure 5: (a) In normal subjects (b) In patients with optic nerve disease[3]

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Amsler's grid

This test helps to evaluate the central vision of the patient. It helps delineates any central or centrocecalscotomas in the visual field, but is not specific to neurological diseases. The 4 questions to ask the patients are [3],[4] :

  • Is the central dot visible?
  • While looking at the central dot, are the 4 corners of the square visible?
  • Are any squares missing? If yes, ask the patient to mark out the scotomas.
  • Are any lines wavy or distorted? If yes, ask the patient to mark them out.


Presence of metamorphopsia is a sign of macular disease. Of all the types of Amsler's charts, the one with red squares on a black background with a central red dot helps to diagnose optic nerve, chiasmal, or toxic amblyopia related problems.

Contrast sensitivity measurement

Measurement of contrast sensitivity checks the responses of visual system to different sizes and contrasts. It is a useful adjunct to reveal the deficit in patients with normal visual acuity but who may have a visual pathway lesion. It is usually determined by measuring the contrast thresholds for sinusoidal gratings, an alternating pattern of light and dark bars, the luminance of which varies sinusiodally in a direction perpendicular to the orientation of the grating. The size of the grating is specified according to the spatial frequency, which is the number of cycles of the grating pattern (i.e. the pair of dark n light bars) per degree of visual angle. The contrast sensitivity function measures between 3 and 10 spatial frequencies from 0.5 to 30 cycles per degree. [1],[4]

Other tests that can be also used are Pelli-Robson contrast sensitivity chart, Vistech contrast sensitivity chart, and a low contrast version of the Bailey Lovie visual acuity chart. However, contrast sensitivity testing is not very specific for neuro-ophthalmological diseases.


  Pupillary Examination Top


The room lights should essentially be dimmed while examining pupils. The components of pupillary examination are:

Size (in Millimeters)

Should be measured in bright and dim illumination. A scale or pupil gauge is used for the measurement of size. To measure the pupil in dim illumination a dim, diffuse torch can be used to illuminate both eyes equally from below the chin of the patient.

Any difference in pupil size more than 2 mm is considered as pathological anisocoria. This indicates the integrity of the efferent pathway. [2],[4]

Shape

Any variation from the normal round shape is noted. Remember, the patient may have traumatic mydriasis or posterior synechiae; and inability to react due to this maybe mistaken for a poorly reacting pupil. [2],[4]

Direct reflex

After asking the patient to fixate on a distant target, light is shone on the pupil with a pen torch (most preferred), and pupillary reaction is observed. Remember to shine the light from the inferotemporal part and not directly from the front of the pupil, to avoid stimulating a near reflex. The speed and sustaining of constriction is noted. A BRISKLY REACTING PUPIL RULES OUT ANY PATHOLOGY OF THE IPSILATERAL OPTIC NERVE. [1],[2],[4]

Consensual reflex

While a dim torch is kept below the eye to be tested, a bright torchlight is shone onto the other eye, and reaction of the pupil is observed. Again, note the speed and sustaining of pupillary constriction. [1],[2],[4]

Swinging flashlight test

This is to look for RAPD or a Marcus gunn pupil. Direct reflex is observed, and the light is quickly moved across the bridge of the nose and directed into the opposite eye. If the light is moved too slowly, the pupil is seen to constrict when finally the light falls on it and thus, gives a wrong impression of a normal reaction. The pupillary reaction of the other eye is observed and compared in amplitude and speed to the first eye. This same test is repeated at least five times. [2],[4]

Normal response (RAPD absent): When light is shone into one eye, the pupil constricts. When moved to the other eye, its pupil is either remains constricted (due to consensual reflex) or constricts further. When it is shone back into the first eye, the same response takes place.

Abnormal response (RAPD present): When light is shone into the normal eye, its pupil constricts. When light is moved to the other abnormal eye, it will either consistently constrict more weakly compared to the normal eye or does not react, or actually dilates on light stimulation (phenomenon called as pupillary escape); RAPD is said to be present. When light is shone back into the first eye, the pupil constricts from a dilated state. [2],[4]

In individuals with essentially only one normal pupil: These may be situations where there is a poor visualization of pupil, sphincter damage, or an efferent defect. Use a dim torch to illuminate the normal eye and perform the swinging flashlight test, observing only the normal pupil. If there is an optic nerve disease in either eye, the normal pupil will show Marcus gunn features when light is shone into the affected eye. The eye with a RAPD is the eye, which is being stimulated by the bright light. [4]

Grades of RAPD[5]

Grade I: Weak initial constriction and greater re-dilatation

Grade II: Initial stall and greater re-dilatation.

Grade III: Immediate pupil dilatation following prolonged illumination of the good eye for 6 seconds.

Grade IV: Immediate pupil dilatation with no secondary constriction.

Neutral density filters can be used to quantify a RAPD. The filters grade the intensity of stimulus in the normal eye, thus simulating an afferent defect in that eye. When this apparent defect balances the actual defect in the affected eye, the RAPD disappears. [4],[5]

Near reflex

In a well-lit room, patient is asked to look at a distance target and then, a near accommodative target (e.g. Near vision chart) is brought about 30 cm in front of and between the patient's eyes. Patient is then asked to look at the near target, and the pupillary constriction is observed. Remember, there is no clinical condition where the light reflex is normal and near reflex is absent. [1],[2],[4]


  Cranial Nerve Examination Top


Optic nerve (Cranial nerve II)

Optic nerve function tests are covered above (1, 2, 3).

Oculomotor nerve (Cranial nerve III)

When testing the range of ocular movement, the examiner should ask the patient to follow a target through the full range of movement, including the cardinal (or diagnostic) positions of gaze. The eyes are tested individually with one eye covered (ductions) and together with both eyes open (versions).

Since the oculomotor nerve supplies all the extraocular muscles, except superior oblique and lateral rectus, the nerve can be tested by testing the range of adduction, elevation, and depression along with the elevation of eyelid (levatorpalpebraesuperioris-LPS). Contralateral elevation deficit and ptosis must be looked for to rule out nuclear lesion.

Incomplete limitation of movements may indicate a compressive lesion; at thesame time,it may be a sign of resolving isolated 3 rd nerve palsy. Signs of aberrant regeneration indicate either a traumatic or a compressive etiology and have to be looked for. [1] These are:

  • Inverse Duanne's sign - widening of palpebral fissure on attempted abduction. This is also known as lid-gazedyskinesis
  • Light near dissociation - constriction of pupil on adduction
  • Pseudo VonGraefe's sign - elevation of the lid on downgaze


The importance of pupillary examination in these cases cannot be underestimated. The pupil on affected side is dilated due to increased parasympathetic input from 3 rd nerve. The pupillomotorfibers being situated peripherally,pupillary involvement indicates a compressive lesion and requires urgent attention!

Further localization of the lesion can be simply done by ruling out any focal neurological deficits to exclude involvement of corticospinal tracts. This can be done by checking deep tendon reflexes and motor function. Also, look for cerebellar signs. [3]

Trochlear nerve (Cranial nerve IV)

Trochlear or the 4 th cranial nerve supplies the superior oblique muscle. Its palsy causes vertical or oblique diplopia. Do not overlook the head posture of the patient as it can give invaluable clues. Chin up with ipsilateral head turn, and contralateral head tilt is the classical head posture of patient with superior oblique palsy. A chin-up position is adopted by the patient to avoid the diplopia, which is worse on downgaze and is classical in cases of bilateral trochlear nerve palsy.

Extraocular motility examination reveals a subtle depression limitation in the affected eye. This may not be apparent if the examination is done with the head tilt, and it is, therefore, essential that all examination is performed with the patient's head erect. Hypertropia of the affected eye is evident on cover test. In cases of multiple cranial nerve involvement, a conjunctival vessel or pterygium is used as a landmark to assesintorsionduring attempted abduction, which can be examined on a slit lamp. [2],[3],[4]

The confirmatory test for an isolated unilateral 4 th nerve palsy is the Park's three step test,[2] which can be outlined as follows:

STEP I:

To determine which eye is hypertropic - This can be done easily by a cover test. The eye that comes down to fix is the hypertropic eye. Even if the other eye is suspected to be the affected eye, the eye that comes down to fix should be selected for evaluation. For ease of understanding, let us assume that the right eye is hypertropic. This brings us down to four muscles: Weak depressors of right eye (superior oblique, inferior rectus) or weak elevators of left eye (superior rectus, inferior oblique).

STEP II:

To determine in which gaze the diplopia is worse - The obliques act in adduction, whereas the recti act in abduction. Let us assume the double vision is worse on left gaze. This means either the adductor in right eye or abductor in left eye is defective. Now, this brings us down to right superior oblique and left inferior rectus.

STEP III:

To determine in which gaze the diplopia is worse - Bielschowsky head tilt is performed for the determination of the torsional malfunction of the muscle. It is based on Herring's law of equal innervations to yoke muscles. When the head is tilted to the left, the left eye intorts and right eye extorts. When the head is tilted to the right, the left eye extorts and right eye intorts. With this knowledge, let us assume that the double vision in our case worsens on right head tilt. This means fusion is disrupted in right head tilt, pointing to a fault in right intorter i.e. superior oblique.

In short, a 4 th nerve palsy would reveal hypertropia, worsening on horizontal gaze in the direction contralateral to the hypertropic eye, and worsening on head tilt ipsilateral to the hypertropic eye.

A long-standing head tilt evident on old photographs, facial asymmetry on the side of the head tilt, and macular torsion on fundus examination reveals a congenital superior oblique palsy.

Trigeminal nerve (Cranial nerve V)

Intact corneal sensations indicate a normal ophthalmic division of the 5 th nerve. With the patient looking straight, the examiner stands at the side and touches the cornea with a thin wisp of cotton. [1] Be careful not to touch the lids, and be sure that the patient is unaware of your actions.

Abducens nerve (Cranial nerve VI)

This nerve supplies the lateral rectus muscle and hence, checking its function tests the nerve. Abduction limitation along with slow abduction saccades in the affected eye is a feature of 6 th nerve involvement. A patient with horizontal diplopia and esodeviation more for distance than near most likely has an abducens palsy. [4]

Facial nerve (Cranial nerve VII)

The temporal and zygomatic branches of facial nerve supply the orbicularis oculi and can be checked by the strength of lid closure. Patient is asked to close his lids as tightly as he can while the examiner tries to open them and assess the tone of the muscle. In obvious paralysis, there will be evident lagophthalmos. By asking the patient to puff his cheeks, the buccal branch is examined, and by asking him to blow a whistle or purse his lips, we check the integrity of mandibular branch. Diminution of taste sensations and hyperacusis is also a sign of dysfunction of branches arising in the facial canal. [3]

Golden Rule [Figure 6] : Always check the function of all the above cranial nerves, and do full pupillary evaluation; even more carefully if any one of the nerves seem involved. It is unpardonable if limitation of abduction or intorsion is not checked in an apparently isolated 3 rd nerve palsy (cavernous sinus involvement) or the function of facial nerve is not checked in cases of limited abduction (cerebellopontine angle tumors). Multiple cranial nerve involvement spells danger and requires neuro-imaging without doubt.
Figure 6: Multiple cranial nerve palsies

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Restrictive Vs. Paralytic: When the range of motion is limited, it is necessary to determine whether the limitation is mechanical or paralytic.

Differential intraocular pressure (IOP)[1] is a simple method that can be used to distinguish between the two. When measured in the restricted gaze, the IOP tends to be higher. Although controversies exist, usually a differential IOP of >4 mm of hg is considered significant.

Forced duction testing[1] can be used more reliably in this scenario.The cornea is anesthetized using several drops of a topical anesthetic such as proparacaine. The conjunctiva is further anesthetized by holding a cotton swab or cotton-tipped applicator-soaked anesthetic against it for about 30 seconds. The conjunctiva is then grasped with a fine-toothed forceps near the limbus on the side opposite to the direction, in which the eye is to be moved. The patient is instructed to try to look into the direction of limitation, and an attempt is made to move the eye in that direction (i.e., opposite that in which mechanical restriction is suspected). If no resistance is encountered, the motility defect is not restrictive; however, if resistance is encountered, then mechanical restrictions exist.

Saccades,[1] if intact, in a case of limited ocular motility, points towards a restrictive cause and rules out a paralytic one.


  Saccades Top
[Figure 7]

Saccadesare fast eye movements (upto 800°/ sec) and appear as (1) volitionalrefixationmovements (changing objects of regard), (2) involuntary gaze movements without a specific target, and (3) spontaneous eye movements. In addition, they participate in optokineticand vestibular nystagmus as recovery movements (fast phases). [3]
Figure 7: Testing saccades[1]

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The patient is asked to change gaze back and forth between one object and another. The fixation objects should be presented at a separation of not more than 30°, because larger angles require more than one saccade. Refixation saccades should be tested between fixed points arranged symmetrically to either side of the mid-position; one of them 15° to therightandthe other 15° to the left. Similarly, vertical saccades should be tested betweenpoints15°aboveandbelowthemid-position. Notice the initiation, speed, and accuracy of the saccades while testing. [1],[2],[4]

Slowing of saccades is a non-specific finding present in many neuro-ophthalmic conditions. It is a feature of various supranuclear disorders and cerebellar lesions. When associated with head thrusting in a child, it is due to ocular motor apraxia.


  Pursuits Top


Pursuit movements are the motor response of the eye to a continuously moving object of regard (upto 50°/sec). The smoothness of the pursuit movements is of the greatest diagnostic importance. Over taxing of the smooth pursuit movements results in the generation of saccadic corrective movements (saccadic pursuit). [3]

Patient is asked to fix and follow a target; for example an object fastened on a rigid wand or examiner's finger. This is moved at a slow and constant rate, back and for thup and down, while the examiner watches the eye movements of the patient. The target object should not be moved very quickly to avoid inducing saccadic pursuit movements. [3]

The movement of the test object should cover an amplitude of 10° to either side of the mid-position (total motility angle of 20°) for both horizontal and vertical movements.Smooth pursuit movements should be seen for speeds of the target up to about 30°/s. [3],[4]

Lesions of the ipsilateral deep parietal lobe and ipsilateralparieto-occipital temporal junction cause defects of smooth pursuit movements.


  Ocular Examination Top


Without thorough structural examination of the eyes and ocular adnexa, this work up isincomplete.Presence of proptosis, lid retraction, ptosis, ocular misalignment is checked for, and this is coupled with slit lamp examination of anterior segment and ophthalmoscopic examination of the retina and optic nerve head almost completes the clinical evaluation of the patient with neuro-ophthalmic disease.

While examining the optic nerve head, special attention should be given to any pallor, hyperemia, and edema. Optic nerve head edema is manifested asblurring and elevation of disc margins, hyperemia, and surrounding nerve fiber layer edema.

The differential diagnoses of optic disc edema can be outlined as follows:

[Figure 8]: D/D of optic disc edema [1]

To reach the diagnosis, the co-relation of clinical findings and most importantly, history is the key. Remember, the diagnosis is essentially putting together of history, demography, clinical findings, and investigations.
Figure 8: D/D of optic disc edema[1]

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Papilledema is bilateral disc edema due to raised intracranial pressure. It is a neuro-ophthalmic emergency and needs immediate attention.

Optic atrophy manifests as a pale disc with attenuated vessels. This is due to the lesions anterior to the optic chiasm. It usually indicates poor visual prognosis in that eye. However, it isimportant to find out the etiology of optic atrophy for the presence of any underlying treatable and more dangerous lesions (e.g., intracranial space occupying lesion causing compressive optic atrophy), genetic counseling (in cases of hereditary optic atrophies), and to prognosticate the visual course in the other eye (e.g. optic atrophy after ischemic optic neuropathy).

[Figure 9]: Types of optic atrophy [1]

Apart from thorough history-taking and examination, these patients need the following investigations:

  1. Visual field examination
  2. Magnetic resonance imaging (CT scan if h/o trauma)
  3. Visual evoked potentials
  4. Electro-retinogram
  5. Optical coherence tomography
Figure 9: Causes of optic atrophy[1,3]

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  Investigations Top


After finishing the thorough clinical examination and formulating the differential diagnoses, we need the support of appropriate investigation to clinch the diagnosis.


  Visual Field Testing Top


This should be considered in all suspected optic nerve or visual pathway disorders and irrespective of the results of confrontation field testing. There are 2 types of field testing methods [1]

Kinetic - marks the contours of the 'Island of vision' at different levels; so, you get one isopter for each level.

Static - marks the contours vertically along a selected meridian.

For most practical purposes, central 30 degrees of visual field examination is sufficient. Manual Goldmann's kinetic perimetrycan be called a thing of the past, and most centers have now resorted to the SITA standard software for static perimetry testing. Measurements of the increment threshold are obtained at a variety of visual field locations that are usually arranged in a grid pattern or along meridians. A bracketing or staircase procedure may be used to measure threshold sensitivity. The SITA-FAST algorithms interrupt the threshold even earlier, resulting in a shorter test time. However, this reduction in test time is at the expense of accuracy and variability.

The major advantages of automated static perimetry are standardization of test conditions, quantitative visual field measurements, a normative database, statistical analysis procedures, and automatic calibration. Despite latest advanced algorithms, the time required for testing is still long, there is limited flexibility and high variability in areas of visual field damage. [2],[4]

Reading of fields should never be done in isolation; it must always be co-related with the clinical findings. In general, homonemoushemianopic defects go in the favor of retrochiasmal lesion, and bitemporal defects point towards chiasmal lesion. Unilateral altitudinal defects are seen in optic neuritis, and altitudinal defect are seen in anterior ischemic optic neuropathy. Nonetheless, visual field interpretation is a vast topic and beyond the scope of this article.


  Neuroimaging Top


A timely decision to image a patient cannot only be sight-saving but also life-saving in some conditions. As we already know, magnetic resonance imaging (MRI) is far more superior for the study of soft tissue and thus, for most neuro-ophthalmic conditions, MRI is the investigation of choice. The indications for neuroimaging are [4],[6] :

In cases of cranial nerve involvement,

  • Pupil involving 3 rd nerve palsy
  • Pupil sparing 3 rd nerve palsy in a young patient
  • Pupil sparing 3 rd nerve palsy in an old patient without vasculopathic risk factors (Diabetes, hypertension, other atherosclerotic factors)
  • History of trauma
  • Incomplete 3 rd nerve palsy
  • Signs of aberrant regeneration
  • All children presenting with a 4 th nerve palsy
  • Failure of a presumed vasculopathic 4 th nerve palsy to resolve in 3 months
  • Worsening of ocular mis-alignment and/or appearance of new symptoms and signs
  • Multiple cranial nerve palsies
  • Signs of raised intracranial pressure such as headache or papilledema
  • Any isolated cranial nerve involvement with focal neurological deficit


In cases of visual loss[3],[4],

  • Acute loss of vision; unilateral (suspicion of hemorrhagic, ischemic, embolic phenomenon) or bilateral (suspecting a lesion above the level of chiasm)
  • Hemianopic field defects on visual field analysis indicating chiasmal/ retro-chiasmal lesion
  • Suspicion of compressive pathology
  • Any signs of increased intracranial pressure
  • Suspicion of craniovertebral anomalies


A Computed Tomography (CT) scan is preferred in the following conditions [3],[4],[6] :

  • Trauma
  • Bony lesions
  • Evaluation of paranasal sinuses
  • Suspicion of an ONH drusen (e/o calcification on CT scan)
  • Contraindications for MRI (cardiac pacemakers, magnetic foreign bodies, shrapnel wounds, aneurysm clips of uncertain origin)


In other cases, an MRI can be safely ordered. MRI with Gadolinium contrast enhances the blood vessels, extra-ocular muscles, and active lesions and is preferred in this setting. [6]

In cases of suspected optic nerve lesions and involvement of extra-ocular muscles, as in thyroid eye disease, fat suppression techniques such as STIR (Short T1 Inversion Recovery) can be used. In FLAIR (Fluid Attenuation Inversion Recovery) sequence, the CSF signals are strongly attenuated. This causes accentuation of peri-ventricular and extra axial disease of the brain surface and can be considered if these lesions are suspected. [6]


  Electrodiagnostics Top
[Figure 10]

A. Electroretinogram (ERG) [1],[3],[4]: In the Standard full field (Ganzfield) ERG, the potentials are excited by short flashes of light and detected by recording electrodes on the anterior surface of the eye. The stimulus covers the entire retina, and the recorded responses are a summation of the electrical potentials generatedby the entire retina. It can thus provide information about a number of retinal diseases that simulate neuro-ophthalmic conditions. This can be used to investigate a case of visual loss when there are no visible ophthalmoscopic findings. These are especially useful in toxic and nutritional optic neuropathy. Multifocal ERG (Mf ERG) is the type of ERG, which includes topographic mapping of the retina and highlights the localized pathologies.
Figure 10: Electrodiagnostics in neuro ophthalmogy[1,3]

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B. Visual evoked potentials (VEP)[1],[2],[3],[4]: The VEP is simply a gross electric potential of the visual cortex in response to visual stimulation. Flash VEPis elicited by a flash that subtends a visual field of at least 20 deg. In Pattern VEP, black and white checks that change phase abruptly and repeatedly at a specified number of reversals per second. The parameters of VEP are altered in optic neuritis, ischemic optic neuropathies, multiple sclerosis, cortical blindness, and compressive lesions. It also can be used as a rough measure of visual acuity in children and uncooperative patients.


  Optical Coherence Tomography Top


In neuro-ophthalmology, OCT can be used for objective assessment of optic nerve head (ONH) and peripapillaryretinal nerve fiberlayer (PRNFL) thickness. The indications of OCT in neuro-ophthalmology can be outlined as follows:

  1. In disc edema - OCT is of specific use in cases of subtle disc edema where clinically the edema of PRNFL is not clear. Differentiation between true disc edemaand pseudo disc edema can be done in serial OCTs. In congenitally crowded discs, the PRNFL thickness remains stable, whereas in true disc edema, it may increase or decrease.
  2. In optic atrophy - PRNFL thickness is an objective measure of optic atrophy. It takes atleast 6-8 weeks for the optic atrophy to develop, so OCT inacute cases for example immediately post-trauma is not very helpful. OCT can be used for monitoring progression in chronic optic neuropathies andidiopathic intracranial hypertension (IIH) in conjunction with visual acuity, color vision, and visual field examinations. However, it must be kept in mind that OCT is unable to differentiate between resolving disc edema and early optic atrophy. Also, OCT is unable to distinguish between consecutive and primary optic atrophy and thus, the results of OCT have to always be interpreted in conjunction with the history and clinical picture.
  3. Use of OCT in specific conditions like NA-AION, Leber's optic neuropathy, and optic neuritis has been described.


While asking for this investigation, it must be kept in mind that the objective assessment of the optic nerve head and PRNFL has to be done in conjunction with subjective assessment, viz.pupillary reactions, visual acuity, color vision, visual fields to complete the picture.


  Other Investigations Top


These are additional tests; most of them performed for the systemic evaluation of the patient, which helps in formulating a diagnosis and hence management of the patient's condition. Following is a list of investigations with related common disorders:

Case of disc edema

  • Blood pressure : NA-AION, hypertensive retinopathy
  • Blood sugar levels : To rule out diabetic papillopathy
  • Serum Lipid profile : Non-Arteritic-AION
  • Serum Homocysteine levels : NA-AION
  • Erythrocyte sedimentation rate : Marker of inflammation; Arteritic AION
  • C-reactive protein : A-AION
  • Temporal artery biopsy : A-AION
  • Aquaporin 4 Antibodies : if suspecting neuromyelitisoptica
  • Cerebrospinal fluid examination : If bilateral; for pressure (Idiopathic intracranial hypertension), microscopic examination (Multiple sclerosis)


Case of isolated cranial nerve palsies

  • Blood sugar level
  • Tests to rule out Ischemic heart disease
  • Carotid Doppler studies


Others

  • For Myasthenia gravis
  • Edrophonium test
  • Neostigmine test
  • Repeated nerve stimulation
  • Single muscle electromyography


 
  References Top

1.Miller NR, Newman NJ, Biousse V, Kerrison JB. Walsh and Hoyt's clinical neuro ophthalmology. 6 th ed. 2005, Lippincott Williams & Wilkins.  Back to cited text no. 1
    
2.Walsh TJ. Neuro ophthalmology - clinical signs and symtopms. 4 th ed. 1983. Mosby, Williams & Wilkins.  Back to cited text no. 2
    
3.Schiefer U, Wilhelm H, Hart WM. Clinical Neuro ophthalmology, a practical guide. 2007, Springer.  Back to cited text no. 3
    
4.Burde RM, Savino PJ, Trobe JD. Clinical decisions in Neuro ophthalmology. 3 rd ed. 2002, Mosby.  Back to cited text no. 4
    
5.Bell RA, Waggoner PM, Boyed WM, Akers RE, Yee CE. Clinical grading of relative afferent pupillary defect. Arch Ophthalmol 1993;111:938-42.  Back to cited text no. 5
    
6.Lee AG, Johnson MC, Policeni BA, Smoker WR. Imaging for neuro-ophthalmic and orbital disease - a review. Clin Experiment Ophthalmol 2009;37:30-53.  Back to cited text no. 6
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]



 

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  In this article
Abstract
History
Visual Function
Pupillary Examin...
Cranial Nerve Ex...
Pursuits
Ocular Examination
Investigations
Visual Field Testing
Neuroimaging
Optical Coherenc...
Other Investigations
Electrodiagnostics
Saccades
References
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