Figure 5. .

Gazing 20° into bilateral 20Δ sector prisms. (A) Simulated Goldmann diagram with the prism configuration of Figure 4 and the patient facing the fixation target, but gazing left into the prisms by 20°, for a total gaze shift of 26°. The arrow is rotated counterclockwise at the gaze point into the prism to indicate the 26° angle of incidence (from perpendicular) of the gaze. A 20°-wide region of field from 17° into the blind hemifield is visible (6° to the prism apex plus 11° of prism shift), but the 11° just left of the prism apex is missing due to the apical scotomas. Since the gaze is shifted left, some of the right far periphery has been lost from view. (B) The corresponding percept diagram shows that the patient sees 20° of field shifted from 11° farther left, but there is a discontinuity where 11° of pericentral view has been lost to the apical scotomas. The triangle is also shown here to indicate the location of the prism apex. Fixation is at the lower intersection of the triangle and the hemifield margin. (C) In order to provide a fixation reference when gazing into the prism, it is necessary to perform Goldmann perimetry with the patient's head turned right so that the gaze falls on the shifted view of the perimeter's fixation target. A simulation of a field diagram taken that way is shown in (C). We have rotated the prism symbol clockwise about the gaze point to indicate the magnitude of head rotation to the right needed to see the fixation target with a 20° gaze into the prism (37°; 6° to the prism, plus 20° into the prism, plus 11° of prism shift). The arrow rotation indicates the gaze incidence at the prism. (D) An actual Goldmann visual field diagram taken this way. This patient has overall restricted peripheral fields on the seeing side in addition to the hemianopia. The measured apical scotoma is highlighted in dark gray.