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

DISCUSSION

Field description: Mildly incongruous homonymous left inferior quadrantanopia involving the macula.

Localization: Right parietal lobe.

Pathology: GBM.

Other features: left hemineglect, topographagnosia, dressing apraxia. Confrontation testing showed a relative left inferior quadrantic defect, with slower

responses to targets here and extinction of stimuli in this quadrant when counting fingers.

The incongruity is seen mainly in the largest (V4e) isopter inferiorly, where it extends to 30° OS but only to 20° OD. The slight incongruity suggests that the pathology is more likely in the optic radiations than in the striate cortex, and involvement of the inferior

quadrant implies dysfunction of parietal rather than temporal optic radiations. The hemineglect, dressing apraxia, and topographagnosia all indicate dysfunction of the right parietal lobe. Axial and coronal gadolinium-enhanced T1-weighted MRI (shown) demonstrated a complex and irregularly enhancing space-occupying lesion involving the parietal optic radiation, and also extending toward the superior striate cortex.

Patients with topographagnosia get lost in familiar environments (190). There are two forms. In one, associated with lesions of the medial occipitotemporal cortex, patients cannot identify familiar landmarks, a problem that is often part of a broader visual agnosia, including prosopagnosia. In the other, associated with right parietal dysfunction, topographagnosia is a function of impaired spatial processing and patients are unable to describe, follow, or memorize a route.

HISTORY AND EXAM

This 20-yr-old man had horizontal diplopia in left gaze, left facial weakness, and left arm ataxia. MRI showed multiple periventricular white matter lesions, consistent with MS. He was treated with iv methylprednisolone. Two weeks later he noted darker vision

in the right eye, with blurring and decreased color vision worsening over the next 2 days. Visual acuity was 20/10 OD and 20/15 OS. Ishihara color plates were 13/14 OD and 12/14 OS. There was no RAPD.

DISCUSSION

Field description: Mild relative cecocentral depression OD.

Localization: Macula.

Pathology: Central serous retinopathy.

Confrontation testing was full OU.

In view of the recent diagnosis of MS, the patient was thought to have optic neuritis even though there was no definitive evidence of an optic neuropathy. The differential diagnosis, however, included a central serous retinopathy, and therefore he underwent a fluorescein angiogram, which confirmed the diagnosis.

Central serous retinopathy (or choroidopathy) is an idiopathic disorder characterized by the accumulation of serous fluid between the sensory retina and the retinal pigment epithelium. The serous fluid originates from a breakdown of the blood-retina barrier because of inflammation of the choroidal capillaries. The effect is a focal retinal detachment at the macula. Clinically, central serous retinopathy manifests with mildly reduced visual acuity (blurred vision), micropsia, and metamorphopsia (5). It is a disorder that typically affects young men. Spontaneous recovery is the norm. Fluorescein angiography, as shown in this example from another patient (courtesy of Tim Murtha), shows early a minute area of hyperfluorescence at the level of the retinal pigment epithelium where dye begins to leak into the subretinal space (between the sensory retina and the retinal pigment epithelium), eventually delineating the area of detachment in the ‘late’ image.

HISTORY AND EXAM

While driving to work one morning, this 35-yr-old woman became aware of a brown rectangle just temporal to fixation in the right eye. This central hole became darker and larger over the following week. She also reported that 6 weeks earlier, for a few days,

objects pressed against the back of her thigh felt hot, after which she had a persistent coldness and numbness over the front of the left thigh. Visual acuity was count fingers OD and 20/15 OS. There was a large RAPD OD. Optic disks were normal.

DISCUSSION

Field description: Large cecocentral scotoma OD.

Localization: Optic nerve.

Pathology: Retrobulbar optic neuritis.

Confrontation testing showed the large central defect OD with only light perception within it.

The patient’s MRI showed many T2-hyperintense lesions in the periventricular white matter bilaterally and in the inferior cerebellar peduncle. She was treated with steroids and her vision gradually improved over 7 weeks to 20/20 OD. Humphrey visual fields at this time demonstrated a residual central scotoma OD (shown here). Although the gray-scale plot does not show the defect well, both the deviation plots show that the central field is depressed nevertheless. This is consistent with a subtle central scotoma, despite her excellent acuity.

Acute visual loss in a 35-yr-old with a cecocentral scotoma and normal fundus is most consistent with optic neuritis. The prognosis for visual recovery is good. Approximately

95% of patients are at least 20/40 and 70% are 20/20 12 months later (191). Intravenous methylprednisolone hastens visual recovery but has no effect on ultimate visual function. Apart from visual prognosis, this patient will wish to know her risk of developing MS. Independent of MRI findings (see Case 28), a history of prior nonspecific neurologic symptoms (predominantly paresthesiae, as she had) is also associated with an increased risk of MS (192). Among the patients with optic neuritis and no lesions on brain MRI, the risk of subsequent MS over 5 yr was 44% in those with such symptoms and 15% in those without. The combination of earlier neurologic symptoms and three or more white matter lesions on MRI increases the risk even further to 66%. Should she start on β-interferon or wait until a second episode confirms the diagnosis of MS? The CHAMPS (193) and ETOMS (194) studies indicate that early treatment with β-interferon of patients with MRI scans indicating a high risk of MS (as in this patient) delays the onset of a second neurologic event. What is unclear, however, is whether early treatment has any effect on the more important outcome measure of later disability.

HISTORY AND EXAM

A 32-yr-old woman developed her typical migraine aura of zigzag lines followed by headache, but on this occasion she also had right-sided numbness and weakness. The latter resolved within a few hours but she was left with a permanent hazy area in the upper

quadrant of the left eye. She had had a myocardial infarction at age 29, suffered from Raynaud’s phenomenon, and smoked 1.5 packs of cigarettes per day. Three months later visual acuity and color vision were normal, as were the fundi.

DISCUSSION

Field description: Highly congruous homonymous peripheral scotomata in left upper quadrant.

Localization: Right inferior calcarine cortex, midzone. Pathology: Migrainous infarction.

Tangent screen perimetry showed a homonymous small defect in the upper left quadrant approaching the horizontal but not the vertical meridian.

Axial and sagittal T1 MRI showed an infarct in the midportion of the inferior calcarine cortex. Even though the scotomata are not aligned along the vertical meridians, they are highly congruous, indicating cerebral disease. Damage to optic radiations is also possible.

Ischemic stroke is a rare complication of migraine with aura (195,196). The International Headache Society (197) suggests that the diagnosis of migrainous stroke requires a history of migraine with aura and that the attack in question is typical of prior attacks with the exception that the neurologic deficit fails to resolve. Other possible causes of infarction must be excluded. Migraine may increase the risk for stroke in general in women under age 45 (198), especially if they smoke or use oral contraceptives.

HISTORY AND EXAM

This 74-yr-old woman had slowly progressive bilateral visual loss over about 9 years. She had a 15-year history of diabetes mellitus and hypertension. She was also a lifelong vegan, although she had recently started eating meat at the prompting of her daughter. On examination her visual acuity was 20/100 OD and 20/60 OS. Ishihara color plates were

7.5/14 OD and 4/14 OS. There was a small RAPD OS. Fundoscopy revealed bilateral temporal pallor of the optic disks and no diabetic retinopathy. The remainder of the examination was normal.

DISCUSSION

Field description: Bilateral shallow relative central scotomata.

Localization: Optic nerve.

Pathology: B12 deficiency optic neuropathy.

Confrontation fields were full OU.

The two sausage-shaped zones surrounding each central area are peaks of sensitivity, indicating that there is a relative depression between them, affecting central vision. The gradually progressive visual decline with evidence of bilateral optic neuropathy (decreased color vision, optic atrophy, and central scotomata) is most consistent with a toxic-metabolic optic neuropathy. The long-standing history of veganism without vitamin

supplementation makes vitamin B12 deficiency most likely. Serum B12 was normal (note that she recently started eating meat), but homocysteine was elevated at 14 (normal: <12.4) and methylmalonic acid (MMA) markedly elevated at 430 (normal: <279 nmol/L).

Cobalamin (B12) is a cofactor for a number of enzymatic reactions, including the conversion of homocysteine to methionine (in which a methyl group is donated from methyltetrahydrofolate) by methionine synthase, and the conversion of methylmalonic-CoA to succinyl-CoA. B12 deficiency, therefore, results in the accumulation of both homocysteine and MMA. Elevated serum concentrations of homocysteine and MMA are thus useful markers of more subtle vitamin B12 deficiency.