Ординатура / Офтальмология / Английские материалы / Field of Vision A Manual and Atlas of Perimetry_Barton, Benatar_2003

DISCUSSION

Field description: Bilateral cecocentral scotomata.

Localization: Bilateral optic neuropathy.

Pathology: B12 deficiency.

Confrontration testing was normal OU.

Although Humphrey 30-2 perimetry clearly shows the central defects in both eyes, Goldmann perimetry showed only the cecocentral scotoma on the right (The ‘x’ in the central field OS indicate that a flashed O2e target was seen at those locations.) This indicates the superiority of static threshold measurements in the highly sensitive central field (see Chapter 1). Although asymmetric, the slow progression of bilateral central defects over many years is most in keeping with a metabolic or degenerative condition of either

the optic nerves or maculae. The absence of a history of acute/subacute visual loss argues against old (bilateral) inflammatory or ischemic optic neuropathy. This patient had a lownormal serum B12 level and elevated homocysteine and methylmalonic acid (MMA), indicating a mild B12 deficiency.

The characteristic clinical features of toxic and nutritional optic neuropathies include slowly progressive, symmetric central visual loss, with dyschromatopsia, cecocentral scotomata, and eventual temporal optic disc pallor, reflecting loss of the papillomacular bundle (64). As in this patient, acuity can remain surprisingly good, but in many it is reduced to 20/200 or less (see Case 39). Apart from B12 deficiency, drugs such as ethambutol and isoniazid can cause a similar disorder. Visual loss may be reversible if the offending toxin is removed or the deficient nutrient replaced.

HISTORY AND EXAM

This 40-yr-old woman presented with bilateral visual loss of about 4 months’ duration. She reported having suddenly become aware of the visual loss, which had subsequently progressed gradually to the point where she could not read and struggled to watch television. In addition to heroin addiction, she had smoked a pack of cigarettes each day for

more than 20 years, and although she denied alcohol consumption, her breath smelled of alcohol in the clinic. Visual acuity was 20/200 OU and Ishihara color plates were 10/14 OD and 8/14 OS. There was no RAPD, and fundoscopy demonstrated mild temporal pallor OU. The remainder of the examination was normal.

DISCUSSION

Field description: Bilateral central scotomata OU.

Localization: Optic nerves.

Pathology: Tobacco/alcohol and B12 deficiency optic neuropathy.

Confrontation testing showed defects to red targets and face comparison, mainly in the temporal side of central vision OU.

The patient’s fields show a classic bilateral central depression. Her confrontation testing suggested bitemporal central defects, which is not an uncommon pattern for cecocentral scotomata of nutritional optic neuropathy to mimic.

MRI did not show a compressive lesion of the optic nerves. Genetic testing for the mitochondrial mutations of Leber’s hereditary optic neuropathy (LHON) were negative.

A toxic-metabolic optic neuropathy was considered most likely. She had low serum B12 and elevated homocysteine and methylmalonic acid.

Although B12 deficiency is a recognized cause of optic neuropathy (64), it may also represent a contributing factor in tobacco–alcohol ambylopia, a slowly progressive bilateral optic neuropathy that develops in the context of heavy tobacco and alcohol consumption. The mechanisms involved in tobacco/alcohol optic neuropathy are unclear. Cyanide moieties in tobacco may impair oxidative phosphorylation and lead to demyelination (65). Vitamin B12 binds to and detoxifies cyanide, and its deficiency, aggravated by chronic alcoholism, thus contributes to the pathophysiology of this disorder.

HISTORY AND EXAM

This 35-yr-old woman presented with rapid visual loss in the left eye, accompanied by disc edema. The next year she had blurred vision in the right eye and more visual loss in the left eye. She was diagnosed with Leber’s hereditary optic neuropathy (LHON) and placed on Coenzyme Q10 and vitamins. She noted gradual mild improvement in the vision of her left eye over the following months. Approximately 1 year later she developed tingling in her fingers as well as a sensation of tightness and swelling in her knees,

ankles, and back. MRI demonstrated periventricular T2-hyperintensities. She was diagnosed with MS and started on β-interferon treatment. On examination 3 years after onset, visual acuity was 20/200 OD and 20/30 OS. Ishihara color plates were 0/14 OD and 7/14 OS. There was an RAPD OD and fundoscopy revealed temporal pallor OU, but worse OD. She had impaired vibration and position sense at the ankles and knees and hyperreflexia in the legs with bilateral extensor plantar responses.

DISCUSSION

Field description: Bilateral cecocentral scotomata, worse on the right. Localization: Bilateral optic nerve.

Pathology: LHON.

Confrontation testing showed left superior perifoveal scotomata OU to red targets and face comparisons.

The patient’s fields show fairly large central depressions, slightly larger OD (deeper shade is an area where even the V4e target cannot be seen). In each eye, the area of highest remaining sensitivity is a small oval-shaped peak in the inferior field, just below the central valleys.

LHON is a maternally inherited optic neuropathy that typically affects men more often than women, usually in young adulthood. The presentation is usually subacute visual loss,

first in one eye and then the second within 6–12 months. The optic disc may appear normal or hyperemic with circumpapillary telangiectasias, as shown in the disc photo from another patient. It is the result of a point mutation in the mitochondrial genome, with mutations at positions 3460, 11778, 14484, and 14459 most frequently reported. The 11778 mutation, which this patient has, accounts for more than 50% of cases. The prognosis for visual recovery is particularly poor for patients with this mutation. Treatment is not effective, but many use Coenzyme Q10.

The patient’s other neurologic history and MRI findings (see FLAIR images) are reminiscent of MS. Indeed, others have described patients with LHON who presented with an MS-like illness and periventricular white matter changes on MRI (66,67). Similarly, a study of a large number of patients with a diagnosis of MS found three patients with either the 11778 or 3460 mutation, all with severe bilateral optic neuropathy (68).

HISTORY AND EXAM

This 30-yr-old woman had severe diffuse headaches constantly for a few weeks. Over the 3 days prior to her visit, she noted horizontal diplopia on right gaze and pulsatile tinnitus. Her examination in the emergency room showed papilledema. Computed tomography (CT) scan of her head was normal but the opening pressure on lumbar puncture was

50 cmH2O, with otherwise normal CSF. Visual acuity was 20/20 OU and color vision was normal. Both optic discs were swollen but more so on the right, which also had peripapillary flame hemorrhages. There was a mild right VI nerve palsy. She weighed 252 lb, with a height of 5 ft., 5 in.

DISCUSSION

Field description: Mild enlargement of blind spot OD.

Localization: Optic disc.

Pathology: Idiopathic intracranial hypertension (IIH), or pseudotumor cerebri.

Confrontation testing was normal.

Automated perimetry shows better reliability on the left than the right eye. This may be because in this, her first perimetric examination ever, the right eye was tested first (note in the upper right corners the time of 04:18, compared with 04:31 for the left eye). The right eye shows a high-responder criterion bias, with a false positive rate of 2/5. Despite this, she shows a depression at a location adjacent and superonasal to the blind

spot (see black square in pattern deviation). There may also be a slight depression just inferonasal to the blind spot on the other eye, but this is less significant, and there are other scattered reductions of a similar magnitude elsewhere in this field.

The diagnosis of IIH requires evidence of increased intracranial pressure with normal brain imaging and normal CSF contents. CSF opening pressure is under 25 cmH2O in normal and obese subjects (69). The pathogenesis of IIH is unclear but may involve impairment of CSF reabsorption at the level of the arachnoid granulations (70). Weight gain and obesity are the only risk factors convincingly demonstrated in case-control studies (71,72). Vitamin A ingestion and tetracycline-related drugs may exacerbate the condition (73,74).

HISTORY AND EXAM

This 26-yr-old woman had intractable headaches and was diagnosed with IIH. The headaches persisted despite repeated lumbar punctures and acetazolamide, and a lumboperitoneal shunt was inserted. She was referred because of persistent occipital headaches and episodes during which her vision would become hazy or black for 2–5 seconds. These

episodes were precipitated by bending over or standing up. She had gained 60–70 lb, to her current weight of 290 lb, over the preceding few years. On examination, visual acuity and color vision were normal OU. Fundoscopy demonstrated moderately severe chronic papilledema in both eyes.

DISCUSSION

Field description: Bilaterally enlarged blind spots.

Localization: Optic disk.

Pathology: IIH.

Confrontation fields were normal.

The patient’s blind spots are two to three times the size of normal. She was restarted on acetazolamide but defaulted on treatment and returned almost 2 years later, at which time her perimetry was repeated, showing a superonasal step defect on the right (shown here).

Transient visual obscurations (TVOs) occur in 68% of patients with papilledema (71). They are episodes of monocular or binocular visual grayout or blackout lasting a second

or so, rarely minutes, unlike amaurosis fugax, which lasts minutes or more and is monocular. TVOs are likely a manifestation of transient ischemia of an edematous optic disk and are provoked by a postural change half of the time; the temporary drop in blood pressure exacerbates a marginal perfusion situation. TVOs do not occur with congenitally anomalous disk elevations (pseudopapilledema).

If untreated, chronic intracranial hypertension may cause a compressive optic neuropathy, not unlike the situation in glaucoma, in which it is intraocular pressure rather than transmitted intracranial pressure that is affecting the optic disk. The result is similar, with nerve fiber bundle defects developing, most commonly arcuate defects. The aim of treatment in IIH is the prevention of this visual loss, which can be permanent.

HISTORY AND EXAM

This 42-yr-old woman had 3 weeks of episodes of visual loss in the right eye, lasting 2 to 3 seconds, precipitated by standing up. The visual loss involved either the entire field or just the nasal aspect. She also had pulsatile tinnitus and more frequent headaches. Visual acuity was 20/20 OU and Ishihara color scores 13/14 OD and 14/14 OS. There was

no RAPD. Fundoscopy (next page) showed papilledema OD with circumpapillary hyperemia and vessel obscuration and a milder degree of disk elevation OS. Weight was 139 lb and height 4 ft, 11 in. The remainder of the neurologic examination was normal. An overview and change analysis OD are shown. The fields OS remained normal throughout.