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Neuro-Ophthalmic Examination Techniques

Denise Goodwin, OD, FAAO

College of Optometry, Pacific University

2043 College Way

Forest Grove, OR 97116

 

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Contents

Introduction

Examination of the afferent visual system is necessary to determine the cause of vision loss.   Likewise, examination of the efferent visual system gives valuable information regarding symptoms such as eyelid abnormalities, extraocular muscle problems, and pupillary disorders.  Here, we will cover examination of the afferent system first, followed by examination of the efferent system.  We will conclude by covering methods to examine other cranial nerves and basic neurologic disorders.

 

Vision Loss

-Subjective Examination

A thorough history is the most important part of a neuro-ophthalmic examination.  It helps to determine differential diagnoses and leads you down the proper path when choosing ancillary tests. 

Unexplained vision loss is a common reason for a neuro-ophthalmic referral.  Table 1 lists associated symptoms that help to differentiate causes of transient vision loss.  It is also critical to determine if medications are linked to the symptoms.  Table 2 lists common medications that can cause vision changes.

 

Table 1:  Associated symptoms that aid in distinguishing the cause of transient vision loss.

Characteristic

Possible Diagnoses

Duration of seconds

Dry eye; increased intracranial pressure

Duration of minutes

Amaurosis fugax

Gaze evoked

Tumor at orbital apex

Scintillations lasting 20-30 minutes

Migraine

Complete recovery over 4-6 weeks

Typical demyelinating optic neuritis

Slowly progressive

Compressive optic neuropathy

Pain with eye movements

Typical demyelinating optic neuritis

Headache in an elderly patient

Giant cell arteritis

 

Table 2:  Common medications that are associated with vision loss.

Tetracycline

Vitamin A

Pseudotumor cerebri

Ethambutol

Rifampin

Isoniazid

Amiodarone

Toxic optic neuropathy

Hydroxychloroquine

Maculopathy

Sildenafil, tadalafil, vardenafil

NAION, blue vision

Aspirin

Vitamin E

Ginseng

Ginkgo biloba

Increased bleeding

 

A careful review of the patient’s family history can help differentiate optic neuropathies such as glaucoma, optic neuritis secondary to multiple sclerosis, Leber hereditary optic neuropathy, and autosomal dominant optic atrophy.  A social history that includes alcoholism increases the likelihood of nutritional optic neuropathy.  Sexual habits, use of intravenous drugs, and a history of transfusion can also aid in finding causes of vision loss. 

 

-Objective Examination

VISUAL ACUITY:  Visual acuity is one of the most important tests in evaluating patients with neuro-ophthalmic disease.  A proper refraction and pinhole acuities are helpful in ruling out optical causes of vision loss (Figure 1).  In addition to loss of visual acuity, look for asymmetry between the two eyes.  Acuities of 20/20 in one eye and 20/15 in the other may indicate damage to the afferent visual pathway.  Near acuities can give an indication of accommodative ability.

 

Figure 1:  Pinhole acuities are important in determining the cause of vision loss.

 

CONTRAST SENSITIVITY:  Detection of contrast allows processing of complex visual scenes.  Patients with decreased contrast sensitivity often report trouble reading road signs, recognizing faces, and seeing distant objects.  Contrast sensitivity is often reduced in patients with optic nerve dysfunction, especially from optic neuritis and multiple sclerosis.  This can be tested with a standard contrast sensitivity chart or with the use of neutral density filters (Figure 2). 

Neutral density filters can aid in differentiating optic nerve disorders from amblyopia.  Patients with amblyopia will not have a large change in acuity when looking through a neutral density filter, whereas patients with optic nerve abnormalities often demonstrate profound loss of acuity. 

 

Figure 2:  Contrast sensitivity can be measured with the use of a contrast sensitivity chart (A) or neutral density filters (B).

A.  B.      

 

COLOR VISION:  Color vision testing can help detect subtle optic nerve disorders.  Congenital color vision defects are generally red-green deficiencies, much more common in males, and are symmetric between the two eyes.  Loss of color vision due to optic nerve disorders can be either red-green or blue-yellow, occur with any gender, and are often worse in one eye compared to the other or worse in different quadrants. 

VISUAL FIELD:  There are number of different ways to evaluate the visual field.  These include confrontation visual fields, Amsler grid, Goldmann perimetry, and automated perimetry.  No one type of visual field is good for all situations.  Despite the type of test, perimetry is valuable because it aids in localizing neurologic disease.  It also aids in detection and monitoring progression of visual defects.    

Confrontation visual fields are particularly helpful in patients that are unable to perform automated perimetry, such as those who are cognitively impaired.  Grossly evaluate the monocular visual field by having the patient tell you how many fingers you hold up in each of four quadrants.  If the patient is not able to count fingers, the visual field can be tested with hand motion or light perception in each quadrant.  The central visual field can then be tested by asking the patient to report any defects in your facial features while they look toward your nose.  An alternative, and perhaps more sensitive, way to test the visual field is to have the patient compare the color of two red objects, each held in different visual quadrants (Figure 3).1

 

Figure 3:  Visual fields loss can be detected by asking the patient to compare the appearance two red objects presented simultaneously in different visual quadrants.

 

Showing targets simultaneously in different quadrants is useful in detecting visual extinction.  With visual extinction, the patient, despite having no visual field loss, will be unaware of objects in areas of their visual field when a target is simultaneously presented in the opposite hemifield. 

Areas of missing, blurred, or distorted lines on the Amsler grid can give useful information regarding central scotomas seen with optic neuropathies.  It is sensitive to small scotomas.  The test is also useful for differentiating neuro-ophthalmic and macular disease.   

Advantages of Goldmann perimetry (Figure 4) include the ability to directly monitor patient attention, present custom test points, and test the complete visual field.  This type of visual field testing requires more training to do properly and can be more time consuming. 

 

Figure 4:  Central scotoma seen with Goldmann perimetry.

 

Automated visual field machines allows standardized testing and statistical analysis (Figure 5).  However, it requires increased patient cognitive skills and is more likely to produce fatigue.  Perhaps the biggest disadvantage of automated perimetry is the lack of flexibility in evaluating difficult patients.  Despite this, a central 30˚ threshold test will pick up the majority of neuro-ophthalmic lesions.       

 

Figure 5:  An advantage of automated perimetry is the standardized testing and the ability to statistically analyze the data.

 

Visual fields are very helpful in localizing a lesion (Figure 6).  If a visual field defect is present in only one eye, the causative lesion is anterior to the chiasm.  If visual field defects are present in both eyes, the lesion is either at or behind the chiasm, or there are bilateral optic nerve or globe lesions. 

 

Figure 6:  Visual field testing is helpful in localizing a lesion.2

 

 


After establishing laterality, determine the general location of the visual field defect.  A homonymous hemianopsia that respects the vertical midline is typically retrochiasmal (Figure 7).  If the patient has normal visual acuity, a relative afferent pupillary defect (RAPD) ipsilateral to the visual field defect, and pale discs, the lesion localizes to the optic tract.  A homonymous hemianopia with normal visual acuity, pupil responses, and optic disc appearance is due to a lesion of the optic radiations or visual cortex. 

 

Figure 7:  Appearance of visual fields with retrochiasmal damage.  The right eye is shown on the right, and the left eye is shown on the left.  A (top left).  Right homonymous hemianopsia.  B (bottom left).  Right superior quadrantanopia.  C (Top right).  Right homonymous hemianopia involving the macular region.  D (bottom right).  Right inferior quadrantanopia.

         

 

Lesions of the visual cortex and optic radiations can be further localized using associated symptoms, as well as characteristics of the visual field loss.  Occipital cortex lesions tend to be more congruous, and patients are aware of the defect.  A stroke involving the occipital lobe either above or below the calcarine fissure can cause a visual field defect that respects the horizontal meridian.  Involvement above the calcarine fissure causes an inferior quadrantanopia, and damage below the calcarine fissure results in a superior quadrantanopia. 

Injury to the temporal lobe can result in an incongruous superior quadrantanopia.  However, these patients often have memory impairment and seizures.  If the dominant lobe is involved, aphasia may be present; whereas damage to the nondominant lobe will cause impaired recognition of facial emotions and problems recognizing emotional overtones in spoken language.  These patients are often not aware of the visual field deficit. 

Parietal lobe lesions result in an inferior quadrantanopia, as well as contralateral sensory impairment.  Other deficits may be present depending on whether the dominant or non-dominant lobe is involved (Table 3). 

 

Table 3:  Associated symptoms of parietal lobe damage.

Dominant lobe involvement

Non-dominant lobe involvement

Apraxia

Finger agnosia

Acalculia

Right-left disorientation

Alexia

Aphasia

Denial of neurologic impairment

Failure to recognize hemiplegic limbs as belonging to self

Spatial disorientation

Hemispatial neglect

Abnormal drawing and copying

Dressing apraxia

Bitemporal loss that respects the vertical midline is suggestive of chiasmal damage (Figure 8).  Causes, such as pituitary tumors or aneurysms, can also result in a junctional scotoma (Figure 9).  Here, there is a superior temporal visual field defect in one eye and any other visual field defect in the other eye.  This occurs due to the inferior nasal fibers crossing and the looping anteriorly into the opposite optic nerve before continuing posteriorly.

Figure 8:  Various characteristics of visual field loss due to a lesion involving the chiasm. The right eye is shown on the right, and the left eye is shown on the left.  A (top left).  Bitemporal hemianopsia.  B (bottom left).  Bitemporal hemianopsia involving the macular fibers.  C (top right).  Superior temporal hemianopsia.  D (bottom right).  Inferior temporal hemianopsia.

       

 

Figure 9:  Three examples of junctional scotomas. The right eye is shown on the right, and the left eye is shown on the left. 

 

Visual field defects involving one or both eyes can be caused by optic nerve disorders or lesions affecting orbital structures.  Optic nerve lesions often demonstrate an RAPD if unilateral or asymmetric, as well as a swollen, pale, or cupped optic disc.  However, the optic disc can appear normal.  Unilateral or bilateral nasal defects are most indicative of glaucoma, but may occur with other optic neuropathies or retinal disease.  A bitemporal hemianopsia that does not respect the vertical meridian is indicative of congenital optic nerve problems or retinal lesions.  Visual field defects that respect the horizontal midline, including arcuate or altitudinal defects, indicate glaucoma, optic neuropathies such as ischemic optic neuropathy or optic nerve head drusen, or occlusion of a retinal vessel.  Generalized depression of the visual field can occur with media opacities and some optic neuropathies.

PUPIL REACTION:  Pupil testing is important to differentiate causes of vision loss.  This is one of the only objective signs of visual function.  Pupil testing is discussed in depth below. 

OTHER OPHTHALMIC TESTING:  Additional testing may be useful to differentiate retinal from optic nerve disease.  The photo stress test, which measures the time it takes for visual acuity to return to within 1 line of the best correct acuity level after a bright light is shined in the eye for 10 seconds, is prolonged with diseases that affect the photoreceptors or RPE.  Keratometry or topography can be useful in ruling out corneal distortion as a cause of vision loss. 

Of course biomicroscopy, tonometry, and fundus examination are critical in finding a cause of vision loss.  The use of red-free light will help in the evaluation of the nerve fiber layer as well as in the detection of sectoral nerve pallor.  Direct ophthalmoscopy may be useful to detect the presence of spontaneous venous pulsation.

Additional testing may be necessary to determine the cause of vision loss.  Fluorescein angiography; focal, pattern, or multifocal electroretinogram (ERG); or visual evoked potential (VEP) may be helpful.  Neuroimaging and laboratory work may also be necessary to establish a cause of vision loss.

 

 

 

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