10Chapter 1: Ocular disease or neurologic disease?

Its pale color is misleading. What the viewer is seeing is exposed lamina cribrosa, which, being a continuation of the sclera, is normally white. Based on this optic disc appearance, ophthalmic consultation was obtained. His intraocular pressures (IOPs) were asymmetric, measuring 13 mm OD and 26 mm OS. Gonioscopy revealed angle recession in the left eye, presumed due to his past history of eye injury. He was treated with topical medications to lower the IOP in his left eye, and subsequent serial examinations showed that his visual field defect was stable.

Discussion: The optic disc has a limited repertoire of expression. Processes that interfere with axonal transport cause disc swelling, whereas those that reflect axonal loss manifest as pallor and/or excavation. Acquired excavation of the optic nerve head, or disc cupping, is traditionally divided into glaucomatous and non-glaucomatous forms. The large majority of cases of disc cupping are glaucomatous in origin.

Glaucomatous optic nerve damage has a characteristic appearance. The disease has a predilection for the arcuate fibers, which produces progressive loss of the neural rim starting at the superior and inferior poles of the optic disc, and causes vertical elongation of the cup. If both eyes are equally affected, this early stage of the disease may be difficult to recognize. In other cases, asymmetry of the C/D ratio in the two eyes may be the first sign of the condition (Figure 1.9A). An interocular C/D asymmetry of 0.1 or more is found in only 10% of the normal population, and thus raises suspicion of glaucoma. Another helpful finding is the presence of a single splinter hemorrhage on the disc margin, termed a Drance hemorrhage (Figure 1.9B). While similar hemorrhages are seen in a variety of conditions that cause disc edema, in the absence of disc swelling this finding is strongly suggestive of glaucoma. Focal damage to the nerve fiber layer, appearing as a notch in the neural rim, is also characteristic of glaucomatous optic neuropathy and sometimes follows a Drance hemorrhage (Figure 1.9C).

Uncommonly, causes of optic nerve damage other than glaucoma produce optic disc excavation.

These mechanisms include compression, disc infarction due to giant cell arteritis, trauma and radiation necrosis. The fundus feature that is most helpful for distinguishing glaucomatous from non-glaucomatous cupping is the status of the remaining neural rim. In glaucomatous discs, the rim generally maintains a more normal hue. Even in advanced cases of glaucoma in which nerve fiber loss is severe, the degree of disc excavation is disproportionately greater than the severity of rim pallor (Figure 1.10). In contrast, rim pallor is a prominent feature of non-glaucomatous cupping. Other fundus features may also be helpful in making this distinction. Focal thinning of the temporal retinal rim is more characteristic of nonglaucomatous damage, whereas diffuse obliteration of the neural rim and peri-papillary atrophy usually reflect glaucomatous change.

In addition to optic disc appearance, measures of optic nerve function are also important. In keeping with the predilection for superior and inferior nerve fiber bundles, field defects in glaucoma are typically arcuate, particularly affecting the superior field. Central vision is spared until late in the course of the disease. In contrast, compressive causes of acquired disc excavation are often associated with visual field loss that respects the vertical meridian. The clinical challenge in cases such as the above is to distinguish optic disc excavation from disc atrophy. Despite advances in optic disc imaging techniques such as ocular coherence tomography (OCT), careful fundus examination is usually the key to making this diagnosis.

Diagnosis: Glaucomatous optic neuropathy

Tip: Glaucoma should be included in the differential diagnosis for any patient with unexplained optic neuropathy.

Painful mydriasis

Case: A 62-year-old librarian periodically noted a dull pain around her right eye when she worked nights in the archives section. At times, along with

12Chapter 1: Ocular disease or neurologic disease?

the pain she experienced fuzziness of vision and halos around lights in her right eye. Her symptoms always resolved by the following morning so she did not seek medical advice until one evening when her dull pain rapidly escalated to a severe right-sided headache. She felt weak and nauseated and could not see well. In the emergency room, visual acuity

was 20/60 OD and 20/20 OS. There was mild anisocoria in room light (right pupil 4.5 mm compared to left pupil 3.5 mm), and the right pupil was nonreactive to light and near stimulation. Eye movements were full and there was no ptosis. Before any further examination could be performed, she became bradycardic and hypotensive and vomited. Acute third nerve palsy due to ruptured posterior communicating artery (pCOM) aneurysm was suspected, and she was sent for immediate brain MRI and magnetic resonance angiography (MRA). These imaging studies, however, were normal.

What clues suggest an alternative diagnosis?

The first clue is the unilateral pupillary unreactivity in the absence of other neurologic deficits. When the pupil is dysfunctional due to a pCOM aneurysm, it is virtually always associated with other elements of a third nerve palsy (NP). In the setting of transtentorial herniation, a dilated pupil is occasionally the earliest sign of third nerve compression, but in such cases there is also alteration of consciousness and, in most cases, other focal neurologic deficits. The presence of an isolated, non-reactive pupil in an awake patient should be considered an indication of ocular rather than intracranial disease. The second and more specific clue that helps to further narrow the differential is the patient’s description of seeing halos in the eye with the mydriasis. This symptom is not due to the pupillary unresponsiveness but indicates, in addition, an aberration of the ocular media. In this patient, the most likely cause is corneal edema secondary to acute angle closure glaucoma.

After her negative neuro-imaging, an ophthalmic consultant confirmed an elevated intraocular pressure of 55 mmHg in the right eye and closure of the

angle. Examination also revealed mild conjunctival injection and corneal haze (Figure 1.11). The patient was treated with acetazolamide, timolol and pilocarpine followed by anterior chamber paracentesis, which brought dramatic relief of pain. She subsequently underwent bilateral peripheral laser iridotomies and has had no further attacks of pain.

Discussion: Angle closure glaucoma can be categorized as primary (due to a structurally narrow angle) or secondary (due to inflammation, trauma, ischemia or other ocular disorders). In secondary glaucoma the examination typically shows evidence of the condition that produced the changes in the drainage system. In contrast, in patients with primary angle closure the examination between episodes may be entirely normal and thus the diagnosis may be more challenging.

The clinical manifestations of angle closure glaucoma are variable with some patients hardly symptomatic and others nearly prostrate with pain. Many patients have repeated self-limited episodes of subacute angle closure before a full attack. Such prodromal attacks generally consist of unilateral face or head pain accompanied by blurred vision and halos around lights, typically lasting 30–60 minutes. Pain is usually localized around the eye but may extend to the maxillary region and mimic dental pathology. In occasional patients, headache rather than eye pain is the presenting symptom. Because there is often conjunctival injection during an attack, these painful episodes may be mistaken for cluster headache or other hemi-cranial headache syndromes. It is important that neurologists keep the possibility of angle closure attacks in the differential diagnosis for these patients and consider ophthalmic referral to evaluate this possibility in selected patients.

Factors that may precipitate an attack in predisposed individuals include prone position, a dark or dim light environment, prolonged near-work, stress, sneezing, pharmacologic mydriasis and certain anesthetic agents. Patients with a high degree of hyperopia are particularly prone to such attacks. During an attack of angle closure, the IOP increases