Visual Field Testing

Visual field testing can help to localize a lesion affecting the anterior visual pathway. Optic nerve related defects may be central, cecocentral, arcuate, or altitudinal (Figure 7.1). Most lesions causing an optic neuropathy in the orbit will produce ipsilateral visual field loss consistent with optic nerve related field loss. Some orbital lesions, however, involve the intracra-nial optic nerve and chiasm, and combination visual field defects may occur. Lesions that involve the anterior chiasm may cause optic nerve related field loss in one eye and temporal field loss in the fellow eye from compression of the junction of the optic nerve

FIGURE 7.1. Goldmann visual field of the right eye shows a central scotoma and inferior arcuate visual field loss due to an optic neuropathy.

and chiasm. Lesions of the body of the optic chiasm produce a bitemporal hemianopsia. Lesions of the optic tract and other retrochiasmal diseases produce a contralateral homonymous hemianopsia.

Confrontation visual testing can easily be performed in the clinic. The clinician sits facing the patient and tests each eye separately, using his or her own eye as a control. The field can be tested with static or kinetic targets of various sizes or with the examiner's fingers or hand as the target. Formal visual field testing provides more information than confrontation field testing. Kinetic manual perimetry (e.g., Goldmann perimetry) offers the ability to vary the test object size and brightness and the ability to test the peripheral visual field; another advantage is that the technician can monitor the testing. Goldmann perimetry also provides excellent information about the shape of visual field defects. The disadvantages of Goldmann perimetry are that the test is time-consuming, requires a trained technician, and is not universally available. Automated computed perimetry (e.g., Humphrey visual field) has the advantage of re-producibility, and the depth of field loss can be quantified in decibels. The disadvantages of automated perimetry are the need for a reliable patient, who is able to follow instructions and pay attention to the testing stimuli. Elderly, very young, inattentive, or acutely ill patients may perform better on the Goldmann perimetry than automated testing. The Humphrey automated perimetry strategies can test the central 10 (e.g., 10-2 strategy), 24, 30, or 60 degrees. Patients with poor visual acuity (e.g., 20/200 or worse) may not be able to perform automated perime-try using the default stimulus size (e.g., Goldmann III test object size in Humphrey perimetry). The size of the stimulus can be increased (i.e., to Goldmann V) to improve reliability in patients with impaired central acuity.

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