by David S. Greenfield, M.D.

Clinical Assistant Professor of Ophthalmology

The New York Eye & Ear Infirmary

New York, N.Y.

The phenomenon of cupping associated with normal intraocular pressure has long been a difficult diagnostic and therapeutic problem for both the physician and patient alike. The essential issue to address in these individuals is whether the patient has a glaucomatous or non-glaucomatous optic neuropathy. There are a variety of compressive and non-compressive optic neuropathies that may produce atrophic cupping simulating normal tension glaucoma.

Intraorbital and intracranial mass lesions may be associated with cupping of the optic nerve head. Some of these lesions include meningiomas, pituitary adenomas (Figure 1), craniopharyngiomas, gliomas, and dolichoectasia (fusiform aneurysms) of the intracranial carotid artery. Anterior ischemic optic neuropathy, particularly when associated with giant cell arteritis, may cause visual field disturbances and changes in the morphology of the optic nerve that resemble normal tension glaucoma. In addition, previous episodes of optic neuritis (Figure 2), resolved infectious processes such as luetic optic neuropathy (Figure 3), hereditary diseases of the optic nerve such as dominant optic atrophy, toxic effects of heavy tobacco and alcohol abuse associated with malnutrition, and trauma to the optic nerve may produce similar changes in the optic nerve that resemble normal tension glaucoma . With a careful history and complete ocular examination, arriving at the correct diagnosis is made less difficult and may obviate the need for expensive neurodiagnostic imaging procedures.

Paramount in the clinical evaluation of individuals with normal tension glaucoma is a careful history with attention to the presence of a family history of glaucoma, vasospastic symptoms such as Raynaud's phenomenon or migraine headache, or history of hypotension or significant blood loss. The chronicity and pattern of visual loss (e.g., darkening or blurring of acuity) is critical. Patients with non-glaucomatous cupping may report a history of ocular trauma, ocular pain (particularly associated with eye movements) or prior episodes of visual loss, concurrent neurologic symptoms (such as headache or cranial arteritis symptomatology), or history of syphilis. In addition, it is important to inquire about a history of prior cortictosteroid use which may suggest previous intraocular pressure elevation.

During the ocular examination, attention should be directed towards a number of specific tests. Perhaps one of the most useful and simplest clinical tests that may help distinguish glaucomatous from non-glaucomatous optic neuropathy is one of color vision testing. Although advanced age, cataract, refractive error, pupillary miosis and glaucoma may reduce color acuity, a significant dyschromatopsia is generally associated with a non-glaucomatous processes. It is important to perform a careful ocular motility examination, to rule out the presence of nystagmus or limited ductions, in addition to Hertel exophthalmometry to exclude proptosis from a retrobulbar mass lesion.

During examination of the optic nerve head the clinician should assess for the presence of splinter hemorrhages, typically located inferotemporally (Figure 4). This is a commonly observed phenomenon in patients with normal tension glaucoma and appears in as many as 20-40% of these individuals. Additional clinical signs suggestive of normal tension glaucoma include peripapillary atrophy and acquired pits of the optic nerve head (frequently referred to as "the 5:15 or 6:45 syndrome" based upon the location of these lesions). This often produces a moth-eaten appearance to the optic nerve.

Clinical inspection of the neuroretinal rim is critical. Perhaps the most specific indicator of a non-glaucomatous process is that of neuroretinal rim pallor in excess of cupping. Similarly, focal notching or thinning of the neuroretinal rim represents a highly specific sign of glaucomatous optic neuropathy. Emphasis should be always be placed on the correlation between the pattern of cupping and the location of the field disturbance when "topographically" evaluating visual field defects.

An effective, albeit non-flawless, rule of thumb generally dictates that individuals with retention of central acuity, absence of a dyschromatopsia, and vertical elongation of the optic cup corresponding with a specific nerve fiber bundle visual field defect, is characteristic of a glaucomatous process. These findings, particularly when associated with a history of splinter hemorrhages of the optic nerve head and minimal neuroretinal rim pallor, are consistent with pre-chiasmal disease and strongly suggest normal tension glaucoma. Although a number of entities should be considered when evaluating a patient with cupping associated with normal intraocular pressure, a careful history and ocular examination may help distinguish glaucomatous from non-glaucomatous mechanisms of optic nerve head injury .

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