Abstract
Purpose :
Field of view (FoV) through prisms (shifted view) brings the view from the blind field into the residual seeing field. This “shift” has been illustrated in the literature as a lateral shift on a flat screen orthogonal to the primary position of gaze. It is not a linear shift in the distance domain but should be interpreted as an angular shift (a rotation of the viewpoint). The apparent viewpoint of the shifted view through the prisms may be located outside of the eye. To understand the viewpoint changes in the shifted view and further investigate the impact on detection, we analyzed and demonstrated the apparent viewpoint of the shifted view.
Methods :
We modeled peripheral 57Δ Fresnel (30° power and FoV) and our 100Δ distortion-free multi-periscopic prisms (MPPs; 45° power and FoV) as prescribed for homonymous hemianopia (HH). Rays originating from the eye and deflected through the prisms were traced and extended back by optical ray-tracing simulation (LightTools), which formed an apparent viewpoint. To verify the viewpoint changes, the scene through the prism and the scene without the prism were photographically captured by the camera at the location of the eye and the apparent viewpoint, respectively.
Results :
The apparent viewpoint of the shifted view was formed outside of the eye (not only rotated but also translated from the eye). While the apparent viewpoint of the shifted view through 57Δ Fresnel prisms was slightly diverged due to prism distortion, MPP provides a focused apparent shifted viewpoint. The rotation of the viewpoint (toward the prism base) was the same as the nominal prism power. The translation was close to the width of the prism when the prism power and the angular span of the prism are the same (the preferred fitting for HH). The photographic depictions of the shifted view through MPP and the scene without MPP at the translated and rotated camera confirmed the same scene and perspective. However, the scene through the Fresnel prism was further distorted and thus different from the scene captured at the apparent viewpoint.
Conclusions :
We demonstrated that the shifted view through the prism is the same as the scene observed by the rotated eye with slight head translation. However, the prism distortion (stronger in higher power refractive prisms) further deteriorates the viewpoint changes.
This is a 2021 ARVO Annual Meeting abstract.