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

DISCUSSION

Field description: Superior arcuate defect with nasal step OD.

Localization: Optic nerve.

Pathology: Primary Open Angle Glaucoma (POAG).

The overview shows gradual progression of the severity of the superonasal defect, with worsening of thresholds within the depths of the defect. The first and second fields show one arcuate defect at about 10° eccentricity, within the Bjerrum area, as well as a more peripheral superonasal depression. These merge by the time of the third field. The change analysis is drawn from many fields over a longer time span. The linear regression of the mean deviation against time (MD SLOPE, at bottom) shows a declining slope of

– 0.03 dB/yr, which is not significant because of the scatter of the points and the reduced reliability of some data points. Despite this, inspection of the plot of MD against time does suggest a slow decline over this 8-year period, even though the patient’s intraocular pressures have been reasonably controlled.

The visual field of his left eye has remained normal over this period. His optic discs show an asymmetry that corresponds with his visual fields. The left disc has a normal cup and a healthy rim, whereas the right eye has a larger cup with more disc pallor.

Intraocular pressure normally ranges from 10 to 22 mmHg. Glaucoma is often defined as a triad of elevated intraocular pressure, optic atrophy with cupping, and nerve fiber bundle defects in the visual field. Increased intraocular pressure alone is variably labeled “glaucoma suspect” or “ocular hypertension.” Acute angle-closure glaucoma is a dramatic form attributable to impaired outflow of the aqueous humor through Schlemm’s canal (24). It presents with high intraocular pressures, ocular inflammation, and corneal edema. POAG, which accounts for 70% of glaucoma (25), is more insiduous. As many as 17% of patients with POAG never have high intraocular pressures, despite typical glaucomatous discs and field loss, suggesting that the definition should not include elevated intraocular pressure (25). The pathophysiology of “normal tension” POAG is unclear. The optic nerves of these patients may have a vulnerability, perhaps of a vascular nature, that makes normal ranges of intraocular pressure damaging.

HISTORY AND EXAM

This 69-yr-old African-American man noted poor vision in his peripheral field for about a year, which had not progressed much. He was unsure of the tempo of onset. Visual acuity was 20/20 OU, Ishihara color scores were 12/14 OD and 7/14 OS, and there was

an RAPD OS. Optic discs showed significant cupping OU, with mild superior disc pallor OS. Intraocular pressures were monitored and found to be consistently elevated, in the range of 24–26 mmHg. Other investigations for optic neuropathy were negative.

DISCUSSION

Field description: Bilateral inferior arcuate defects. Localization: Bilateral optic nerve.

Pathology: Primary Open Angle Glaucoma (POAG).

Confrontation testing showed an inferonasal step defect OS to red targets and finger counting.

The patient has bilateral arcuate defects, more extensive OS, where the defect marches from the blind spot to the nasal meridian. Glaucoma is among the most common causes of bilateral arcuate defects. However, many other bilateral optic neuropathies could cause similar loss, particularly ischemic or inflammatory conditions (but not toxic/metabolic ones, which cause central scotomata almost exclusively). Without clearer information about the onset, it is difficult to definitively exclude these.

Automated perimetry has assumed the dominant role in the evaluation of glaucomatous visual field defects. Nevertheless, in up to 25% of patients with glaucoma, Goldmann

perimetry of the more peripheral field can show defects when automated assessments of the central 24° are normal or equivocal (26). Generalized constriction, a nasal step, or a temporal sector (wedge) defect are the most frequent findings. General constriction may be an early finding, but it is hard to differentiate from other nonspecific causes of constriction. A more focal constriction of nasal isopters is helpful, even if no nasal step is evident. This may represent equivalent damage to both upper and lower arcuate fibers, whereas a step defect always means more severe damage to one arcuate bundle or the other. One last interesting defect is the “hemianopic offset,” a peripheral wedge in the nasal field adjacent to the vertical meridian. This can be confused with a retrochiasmal hemifield defect, except that it is seldom bilateral or homonymous.

The three major risk factors for POAG are age over 70, being African American, and elevated intraocular pressures. Several genetic loci have also been identified recently for POAG (24).

HISTORY AND EXAM

This 56-yr-old woman presented with a painful right IV nerve palsy. Two months later she developed a fluctuating partial right III nerve palsy with tingling in the right forehead and vertex. Over the next month her right lid swelled and the eye reddened. Acuity was 20/25 OD and 20/15 OS. Ishihara color scores were 11/14 OU and there was no RAPD.

Optic discs were normal. There was a mild anisocoria, with the right pupil larger in light, and periorbital and lid swelling OD. There was 4-mm proptosis OD, and scleral and conjunctival vessels were dilated. There were partial right III and VI nerve palsies.

HISTORY AND EXAM

A 27-yr-old woman had a few weeks of vague blurred vision OD, which she attributed to dirty contact lenses. However, this developed into a “cloudy” spot just superotemporal to center. An optometrist documented acuity at 20/200 OD, and she had an MRI of the

orbit and brain that was normal. By the time she saw us 6 weeks after onset, vision had started to improve 4 days earlier. Visual acuity was 20/40 OD and 20/15 OS. Ishihara color scores were 12/14 OD and 14/14 OS. There was a mild RAPD OD. Optic discs and maculae were normal OU.

DISCUSSION

Field description: Cecocentral scotoma OD. Localization: Retrobulbar optic nerve.

Pathology: Retrobulbar optic neuritis, demyelinating.

Confrontation fields showed a blurry region just temporal to fixation, when viewing the examiner’s face. On Amsler grid there was a fading of lines in the same region.

Central defects have traditionally been considered the classic field defect of optic neuritis (27). If the abnormal central area is large enough to merge with the normal blind spot, this is termed a cecocentral scotoma. If not, it is just a central scotoma. Because central vision is so heavily used in daily life, virtually all patients notice their loss. Testing almost always shows reduced acuity and/or color vision. Sometimes with very subtle loss, or more frequently as a residue of earlier optic neuritis, there might be a central scotoma with normal acuity. In such cases, contrast sensitivity testing may reveal impaired vision for faint gray stimuli on white backgrounds (i.e., low contrast), compared to the typical Snellen letters, which are black symbols on white backgrounds (i.e., high contrast) (28).

Why might central vision be vulnerable to optic neuritis? Some argue that it is simply

the odds. Since so many retinal ganglion axons are devoted to central vision, even a random pattern of pathologic hits would tend to create a large proportion of central defects. Others claim that the papillomacular bundle (see Chapter 2) that serves the cecocentral zone has some special, still undefined Achilles heel to demyelination. Yet others suggest that since there are so many parvocellular (P-cells, see Chapter 2) retinal ganglion cells in central vision, where color vision and spatial acuity are at their peak, optic neuritis might be a P-cell disease (29). However, while this issue was being debated, it became clear that small, isolated central scotomata actually comprise only about 15% of the focal field patterns in optic neuritis (30,31). Perhaps the “random hit” answer is the correct one after all.

This patient’s vision returned to normal 2 months later. Her normal MRI and negative neurologic examination and earlier history place her in a low-risk group for developing future attacks of multiple sclerosis (MS) over the next 5 years (see Case 22). However, she developed leg numbness and bladder incontinence 1 year later, with white matter lesions on MRI of her cervical cord and brain (axial FLAIR image shown, see arrow). She started β-interferon treatment at this point.

HISTORY AND EXAM

This 26-yr-old woman noticed a small white area in the center of vision of the left eye, which grew over 5–6 day into a dense “faded” central region, with frontal headache and pain with eye movements. Visual acuity was 20/20 OD and count fingers at 4′ OS. There was a large RAPD OS, but fundoscopy was normal OU. The remainder of the neurologic examination was normal. The initial visual field is shown in field A. Over the next month

her vision improved to 20/25 OS. About 6 months later, however, she returned with blurred vision OS, imbalance, and vertical diplopia. Visual acuity was 20/30 OD and 20/60 OS, with Ishihara color scores of 14/14 OD and 7/14 OS. She had an RAPD OS and normal optic discs. She had a skew deviation and mild gait ataxia. Visual fields from this next visit are shown in field B (next page).

DISCUSSION

Field description: (A) Large cecocentral scotoma OS; (B) inferior arcuate defect OD and superior paracentral scotoma OS.

Localization: Retrobulbar optic nerve. Pathology: Retrobulbar optic neuritis.

Confrontation testing with hand motions easily showed the large central defect at first examination.

In field A, there is a large hole OD in which the patient cannot see even the largest V4e target. This defect also eliminates most vision for the I4e target superiorly, so that it is mainly seen inferiorly, because vision is normally more sensitive eccentrically in the inferior field. In field B, there are more subtle bilateral defects that conform to nerve fiber layer defects around the central zone.

The patient’s initial presentation is a more severe version of Case 21, with a larger cen-

tral defect yet still normal-appearing disc. Isolated retrobulbar optic neuritis without antecedent neurologic history is the scenario, proven by the anticipated recovery of vision a few weeks later. The key question in this setting is, What is her risk of MS? The single most informative prognostic tool during an attack is MRI of the brain (not the orbit, since we already know that she has optic neuritis and numerous studies have shown that imaging the orbit in typical cases is a waste of time). In the Optic Neuritis Treatment Trial (ONTT), the cumulative probability of a second demyelinative attack over the next 5 years increased from 16% in those with no white matter lesions to 51% in those with three or more lesions of 3 mm or more in diameter (32). Unfortunately, her MRI showed numerous lesions, illustrated on a T2 axial slice, and within 6 months she had the second attack mentioned, involving not just both eyes but also her brain stem and cerebellar pathways. (Of note, bilateral sequential optic neuritis, as she has, is itself a high risk factor for MS, in contrast to bilateral simultaneous optic neuritis, as in Case 30.)

HISTORY AND EXAM

This 44-yr-old woman had 1 week of blurred vision nasally in the left eye, which worsened slightly 6 days after onset, when there was also some pain with eye movement.

Acuity was 20/20 OU, and Ishihara color scores were 14/14 OU. There was an RAPD OS. There was also mild disc edema OS.