Visual Pathway: Examination Methods

Examination Methods

Visual field testing (perimetry): 

This is the most important test for visualpathway lesions. Because it permits one to diagnose the location of the lesion, it is also of interest from a neurologic standpoint. The “visual field” is defined as the field of perception of the eye at rest with the gaze directed straight ahead. It includes all points (objects and surfaces) in space that are simultaneously visible when the eye focuses on one point.

The examination is performed on one eye at a time. The principle of the test is to have the patient focus on a central point in the device while the eye is in a defined state of adaptation with controlled ambient lighting (see below). Light markers appear in the hemisphere of the device. The patient signals that he or she perceives the markers by pressing a button that triggers an acoustic signal.

There are two types of perimetry.

1. Kinetic perimetry.

Hemispheric GoldmannorRodenstockperimeters areused for this test (Fig. 14.2). Kinetic perimetry involves moving points of light that travel into the hemisphere from the periphery. Light markers of identical size and intensity produce concentric rings of identical perception referred to as isopters. The points of light decrease in size and light intensity as they move toward the center of the visual field, and the isopters become correspond-ingly smaller (Fig. 14.2b). This corresponds with the sensitivity of the retina, which increases from the periphery to the center.

The advantage of kinetic perimetry is the personal interaction between physician and patient. This method is especially suitable for older patients who may have difficulties with a stereotyped interaction required by a com-puter program. Specific indications for kinetic perimetry include visual field defects due to neurologic causes and examinations to establish a disability (such as hemianopsia or quadrantic anopsia).

2. Static perimetry.

This is usually performed with computerized equipmentsuch as the Humphrey field analyzer (Fig. 14.3) or Octopus 2000, although a Goldmann or Rodenstock hemispheric perimeter can also be used for static testing of the visual field. In static perimetry, the light intensity of immobile light markers is increased until they are perceived. The intensity threshold continuously increases from the macula, with the highest sensitivity, to the periphery. A variety of different computer programs can be selected depend-ing on the specific clinical setting. These include the outer margins or the 30 degree visual field in glaucoma (Fig. 14.3b).

Other examination methods:

❖Pupillary findings.

❖Pupillary light reflex.

❖  Visual evoked potential.

❖ CT or MRI to diagnose causes.