The vertical field border in hemianopia and its significance for fixation and reading

The existence of macular sparing, a central seeing area of several degrees within the hemianopic field defect, has been controversial for a long time, because inaccurate fixation during perimetry can produce ambiguous results. The visual field border in hemianopia was studied to examine whether a vertical strip of hemifield overlap described in monkeys exists in humans and whether additional macular sparing could be found.

Vertical triplets of dots were scanned on the retinas of eight patients (13 eyes) with hemianopia at different eccentricity from the vertical meridian during strict simultaneous fixation control using a scanning laser ophthalmoscope (SLO). Additionally, eye movements were measured by SLO and by an infrared reflection system while subjects read texts.

Macular sparing of 2 degrees to 5 degrees and absence of sparing were observed. The presence and amount of sparing influenced fixation behavior, reading performance, and reliability of conventional perimetry. The smaller the macular sparing, the less stable the fixation. In the absence of sparing, either central unstable fixation with frequent saccades toward the hemianopic side or eccentric fixation occurred, resulting in a shift of the field defect toward the hemianopic side. A vertical strip of sometimes partial perception was found in 12 eyes at 0.5 degrees from the midline.

Macular sparing and a slight vertical strip of hemifield overlap exists in humans. Adaptive strategies like eccentric fixation and predictive saccades improve reading performance and can augment rehabilitation.