Homonymous hemianopia is a very severe visual deficit that effectively hides whatever lies to the left or right of the line of sight, depending on the laterality of damage. For example, when sitting in front of a computer display, a subject with a left homonymous hemianopia usually only sees the right-hand portion of the display: the left-hand portion is not only not seen but its invisibility may go unnoticed. This handicap can at least partially be compensated by learning to look in an unaccustomed way, namely, to actively cast gaze to the blind side . Unfortunately, the required eye movements, so-called "blind saccades", do not come natural but have to be learned. Furthermore, for maximum utility in daily life, blind saccades need to be actively executed more or less constantly.
It is important to note that gaze casting cannot restore any lost vision: its objective is to use remaining vision in a maximally efficient way. Actual restoration of lost vision currently appears unrealistic .
A suitably programmed computer display should prove useful to teach and train the active casting of gaze. Indeed, several avenues have been explored, in both free and commercial formats. Examples of the former category include Eye-Search and Read-Right from the University College of London (no affiliation). Both require registration. In contrast, the Pest Control display presented here can be used directly. It features
The Pest Control display is best used on a PC, which offers a much larger test area than smaller devices like smartphones or tablets. Users of touch-screen devices need to note that the cross-shaped screen cursor must be touched quite precisely to record a response. There are no specific rules for test distance or illumination: just arrange for a comfortable setting. Use the same setting for repeated use. Scoring may be inconsistent across different settings.
Learning to execute blind saccades may initially be quite tiring. It is better to use multiple brief sessions than a few exhausting ones. There are no side effects except exhaustion and perhaps frustration. Begin with the largest test target. Writing down successive test scores, it is possible to monitor the improvement in the ability to make blind saccades. Once test scores stabilize with the largest test target switch to training with the next smaller one, and then the smallest one. To maintain skill, the Pest Control display may have to be run repeatedly over long periods of time.