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‘Doc, Part of My Vision is Gone!’

‘Doc, Part of My Vision is Gone!’

What conditions cause patients to present at your practice complaining first and foremost of vision loss? What can you do for these patients?

Kimberly Reed, O.D.



Few things provoke more anxiety (for both the patient and the doctor) than noticeable visual field loss. The underlying diagnosis is often serious and can threaten long-term vision and even the patient’s well-being. Glaucoma is the leading cause of visual field loss across all age groups.1 However, glaucoma patients often don’t present with an initial chief complaint of visual field loss, unless the disease is quite advanced.


This review discusses conditions (other than glaucoma) that can cause symptomatic visual field loss, and it includes a practical guide to ancillary testing and referral of these patients.

 

The Visual Pathway

To fully appreciate the potential underlying causes for various visual field defects, it is important to have a working knowledge of the anatomy of the visual system (figure 1).


Remember: Nearly half of the nerve fibers cross at the optic chiasm, so the loss of visual field on one side is quite different than loss of vision in one eye. Patients are often unable to accurately determine the location of field loss. So, if the patient says, “I can’t see on the left side,” you need more clarification before you develop a short list of differential diagnoses.


Also, defects that respect the vertical midline are nearly always located at the chiasm or farther back in the visual pathway. Causes of a visual field defect that respects the horizontal midline (altitudinal visual field defects) are more frequently located anteriorly in the pathway (near the optic nerve or retina).

1. The visual pathway. Note that half of the optic nerves cross at the optic chiasm, causing vision loss “on one side” to be quite different than that “in one eye.”

Demographics of VF Defects

Nearly one out of every 20 people past age 55 has visual field loss that is significant enough to impair daily functioning.1 Difficulties experienced by these patients include a higher risk of falling, reduction in physical mobility, disability, diminished quality of life, and diminished ability to watch television or read.1-7 The incidence of visual field loss increases with age. One study found a five-fold increase of visual field loss between ages 55 and 80.8


An even more surprising finding: In one study of 61 post-stroke patients suffering from homonymous visual field loss (as determined by Humphrey visual field analysis), none were aware of the visual field loss.9 Also, only two of those 61 patients were identified as having field loss using the National Institutes of Health Stroke Scale (NIHSS) technique, which is a finger-counting confrontation visual field screening. To further complicate matters, 30% of those subjects with significant visual field loss were still driving.9

 

Red Eye, Red Herring

A 49-year-old Hispanic male presented with complaints of a red, irritated left eye with significantly reduced vision in the same eye. He was alert and oriented, had a normal gait and displayed no affective abnormalities. Vision was 20/30 O.D. and 20/200 O.S.


Color vision, visual fields and extraocular motilities were normal in both eyes. A trace relative afferent pupillary defect was seen O.S., but both pupils were of normal size. Visual fields are below.
Ultimately, this patient was diagnosed with neurosyphilis, and was treated with penicillin. His visual acuity recovered fully, but his visual fields only partially recovered.

 

 

O.S. left, O.D. right. Note the bilateral involvement despite unilateral (O.S.) complaints.

Causes of Visual Field Loss

Glaucoma is the leading cause of field loss across all adult age groups when tested using automated threshold or supra-threshold perimetry.8


Other leading causes of visual field loss in patients past age 55 are non-glaucomatous optic nerve disease, stroke, age-related macular degeneration (AMD) and retinal vascular occlusive disease.1,8 Stroke is the leading cause of homonymous hemianopias, followed by trauma, tumor, brain surgery and demyelination.10


In younger age groups, prevalence of visual field loss is much lower, and causes are more varied and may be functional or psychogenic in nature. Tumors; drug-related; hereditary disease of the macula, retina or optic nerve; demyelination; and intracranial hypertension are among the more common causes.11-15

 

Patient Evaluation

When a patient presents complaining of loss of some or all of the vision in one eye or in a particular part of the field of vision, the most critical step is to determine if this is a neurological emergency. Is the patient alert and oriented? Are there any other sudden-onset neurological changes?


If the patient displays disturbances in speech, gait, memory, facial symmetry or behavior, an immediate referral to the ER is essential. Such changes, among others, may indicate a cerebrovascular accident (stroke). Time is critical! Don’t waste precious minutes before sending the patient for evaluation and care.


If the patient is alone, calling an EMT ensures safe transport to the ER, but if the patient is accompanied by a family member or caregiver, instruct this person to take the patient to the ER with written instructions from you. Alert the triage personnel at the hospital that a potentially time-critical patient is on the way.


Aside from these rare but critical cases, the most important test—one that must not be skipped—is automated perimetry.


Before formal visual field testing, however, you must determine several things. Besides your normal history and examination sequence, ask:


• Is the field loss in one eye, or is it on one side of the field? Confrontation visual field testing is not 100% reliable, even when done properly and carefully. You can enhance the reliability of standard finger-counting testing by adding a “facial Amsler” test (have the patient fixate on your eyes and ask him or her if your other facial features appear distorted or are missing) and by performing double simultaneous stimulation confrontation fields.


• Did the loss occur suddenly or gradually? When did you first notice it?
Vision “flickering off and on” is a common symptom of patients with giant cell arteritis. It occurs in the days or hours leading up to profound vision loss.


Often, patients first notice visual symptoms accidentally, even if the problem has been long-standing. Ask what the patient was doing when he or she first noticed the loss. A patient who experiences a large “hole” in the vision of the right eye immediately upon awakening may be quite different than the patient who noticed vision loss in one eye when the fellow eye was covered after a minor injury.


• Has this ever happened before? Recurrent and transient “holes” in the visual field may indicate a vascular perfusion deficit. Very low blood pressure and/or low blood sugar can cause this type of symptom. It’s not uncommon during pregnancy and puberty for patients to experience transient scotomas of this sort. Consultation with the appropriate medical caregiver is prudent.


When to do Automated Field Testing:

• Any complaint of headaches not explained by the exam.

• Any complaint of a fixed missing spot in the visual field (monocular or binocular).

• Identification of field loss using screening techniques.

• History of cerebrovascular accident.

• History of head trauma.

• Unexplained visual acuity loss.

• Optic nerve abnormalities.

• Any other clinical finding (subjective or objective) that does not correlate with other examination findings.

In many cases, attention to proper hydration and caloric intake, along with awareness of the effects of postural changes (e.g., standing up quickly from a seated or reclined position) is sufficient for managing the symptoms. In other cases, medical evaluation and treatment are necessary; vertebrobasilar insufficiency (VBI) and ocular ischemic syndrome (OIS) secondary to internal carotid artery insufficiency are far more serious potential causes of transient binocular (caused by VBI) and monocular (caused by OIS) scotomas.


• Does the missing area or spot remain the same size, or does it change? Scotomas that change can be considered transient, so they are more likely vascular in origin. Fixed scotomas usually signal retinal, optic nerve, or neurological involvement.16


• Are there any other unassociated symptoms? The presence or absence of coincident flashing lights, floaters, dyschromatopsia, eye pain, headache, vertigo, diplopia, metamorphopsia or other seemingly unrelated symptoms will often direct your management. A referral to a retinologist, neurologist or internist may be required.


• Is there a relative afferent pupillary defect (RAPD)? Compare the afferent anterior pupillary pathway of one eye vs. the fellow eye. Slightly more than half the nasal pupil pathway fibers cross at the chiasm, so significant defects anterior to the chiasm cause an RAPD. Lesions in the optic tract can also cause an RAPD in certain instances.17


The bottom line: From a clinical standpoint, a right positive RAPD means that you should be looking for a problem in the right retina and/or optic nerve. If you find nothing, neuroimaging is essential; place emphasis on the retro-orbital space, the optic nerves, chiasm and optic tracts.


If you think you see an RAPD but you aren’t sure, verify your findings. After the patient has a chance to recover from the transilluminator’s bleaching effects, do a “white light comparison” test. Occlude the abnormal eye and shine the light in the normal eye. Ask the patient to assign a brightness value of 100 points to that light. Quickly switch the occluder to the normal eye, and shine the light in the abnormal eye. A value of 80% or less is considered clinically significant. Of course, this test should be interpreted relative to other potential findings, such as corneal edema, cataracts, or other conditions that can affect the patient’s perception of brightness.


Another way to help confirm subtle RAPDs is to purchase an inexpensive 0.3 log unit neutral density (ND) filter. This enhances subtle pupillary defects. Hold the ND filter over the normal eye, and shine the light through the filter. Depending upon the degree of the RAPD in the other eye, this may appear to “even out” the signals being carried in both afferent systems. This simulates a normal swinging flashlight test; in effect, the pupils appear to respond equally. Next, hold the ND filter over the suspect eye and repeat the test. If an APD is present, it will nearly always become much more obvious with the addition of the ND filter.18


Understand that the presence of anisocoria doesn’t create a clinically observable “pseudo-APD” until anisocoria of 2mm or more is present.19 So, don’t dismiss subtle or trace RAPD responses to a 0.5mm anisocoria.


• Is there a color vision defect? In general, you can link the findings from color vision and pupil testing together. Optic nerve and significant retinal disease in one eye can create color vision disturbances and positive RAPD results in that eye. Whether you perform the dilated fundus examination before or after automated visual fields is your choice; you can find support for both sides of the issue.20-22 As long as the patient’s pupils are at least 3mm in diameter, you can probably evaluate the visual fields in these non-glaucoma cases regardless of the state of pupillary dilation. Just consider the cycloplegic effects of the dilating drops when determining which trial lens to use in patients who are not yet absolute presbyopes.


• Are there other neurological signs? Depending upon your level of comfort, you may also want to perform a cranial nerve screening, or even a gait, balance and symmetry screening. If you are not comfortable performing such tests, you can refer this patient to a neurologist for them.


• What does the rest of the ocular examination reveal? Carefully evaluate the anterior and posterior segments. Findings of ocular disease will dictate appropriate management strategies based upon the condition.


Common and/or Classic Visual Field Patterns and Their Causes

Type of field defect Sample visual field* Common cause(s) 
Altitudinal. These respect
the horizontal raphe, eithersuperior or inferior (unilateral or bilateral).

Glaucoma, branch retinal artery occlusion, anterior ischemic optic neuropathy.

Total monocular field loss. Prechiasmal lesion on the same side as the eye with the visual field defect.
Bitemporal field loss. Lesion at or near the optic chiasm (not always a pituitary adenoma).

Ring scotoma (usually bilateral).

Retinitis pigmentosa.
Superior quadrantanopia. Temporal lobe lesion (infarct, hemorrhagic stroke, trauma) on the side opposite the visual field defect.
Inferior quadrantanopia. Parietal lobe lesion (infarct, hemorrhagic stroke, trauma) on the side opposite the visual field defect.

Temporal defect in one
eye, central defect in the fellow eye.




*Images generated.
Anterior chiasmal syndrome, or a lesion just anterior to the chiasm on the same side as the eye with the central field defect.
 

Patient Management

What if there is no ocular cause for the field loss? In such cases, refer the patient to a neurologist—or better yet, a neuro-ophthalmologist.


The History Makes the Diagnosis

A 46-year-old white male complained of blurry vision and a “missing spot of vision” in his left eye for approximately eight months. Vision was 20/20 O.D. and 20/80 O.S. At a visit in our clinic several months prior, vision O.S. had been recorded at 20/25. 


There was a pronounced RAPD in the left eye with reduced color vision (1/14 plates) in the left eye only. White light comparison testing showed a 25% sensitivity in the left eye as compared to the right. A significant visual field defect was present in not only the left eye, consistent with the patient’s case history, but also in the right eye. The patient underwent neuroradiological evaluation, and a craniopharyngioma was found.


Unfortunately, during resection of the tumor, the right optic nerve was damaged, and the patient was left with partial visual field loss in both eyes.
 

O.S. left, O.D. right. Note that the defect in the right (asymptomatic) eye strongly respects the vertical midline. This is considered a bitemporal visual field defect despite the extension into the superior nasal quadrant in the left field.

How quickly does the referral need to be made? When patients display other neurological symptoms, an immediate referral is required. Otherwise, many of these cases are considered to be urgencies rather than emergencies, and require referral within a few days to a week. How the actual referral is carried out will vary based on the patient’s insurance, availability of neurologists in your area and other factors.


The decision to order radiological testing or wait for the neurologist to do it will also vary, depending upon your working relationship with the neurologist and the imaging centers in your area. If you do order neuroradiology studies for your patient, it’s a good idea to work with the neurologist the first few times so that you don’t end up with equivocal results. For example, I have had patients require a repeat scan because I didn’t specify thin enough sections through a particular region. A “normal” scan sometimes turns out to be not so normal when re-evaluated with more critical parameters!


One exception to neurology referral is a patient with visual field loss that you suspect is psychogenic in origin. If you can confirm that the visual field is not organic in nature, careful consideration for a referral to a psychologist or psychiatrist is indicated.

 

Patients who present with an awareness of a loss of visual field need prompt and accurate diagnosis, as management often involves immediate further evaluation and intervention. Knowledge of the functional anatomy of neurological pathways is essential in the interpretation of examination results. Such knowledge will enhance proper triage of these often-critical patients.

Dr. Reed is an associate professor at Nova Southeastern University, where she teaches ocular disease and primary clinical care.

 

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Vol. No: 145:10Issue: 10/15/2008

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