Introduction: Background: The first approach to a frequency-selective visual training in amblyopia had been proposed in the sixties by the physiologist Fergus Campbell. During the stimulation, his grating was moving very slowly, i.e., only once a minute around its axis. Therefore, the CAM-stimulator was based exclusively on the proposed influence of spatial frequency selectivity, however there was no significant contribution of the temporal frequency of the stimulus. Accordingly, we are convinced that this was one of the main reasons for the failure of Campbell's approach after the evaluation by a multiple of placebo-controlled studies. The aim of the present work, therefore, was to investigate in the influence of visual exercises, which contained moving circular gratings as compared to such of stationary gratings implemented into computer games on the development of visual acuity. Especially we were interested in the effects of such type of visual exercises using a circular sinusoidal grating on the visual acuity development in patients with meridonal amblyopia. We assume, in particular, that such a ring-shaped stimulus can reach all angular positions equally, and thus excite the most ametropic meridians, as compared to the least ametropic meridians, in a particular way. Methods: Overall, we investigated in two groups of patients with meridional amblyopia who had been selected according to the age structure and to their type of disturbance. Using a cross-over design, the first group was alternately exercised 10 days with the moving followed by 10 days with the stationary grating stimulus, and the second group was alternately exercised 10 days with the stationary followed by 10 days with the moving grating stimulus, i.e. in reverse order. For the treatment, a sinusoidally modulated drifting grating had been implemented as a background stimulus into simple computer games. These games served for the attraction of attention of the children. For the present study these exercises were provided by the telemedical portal of the Amblyocation ltd. in the following two versions. The first version contained a concentric outward-moving ring-shaped sinusoidal grating behind of the computer games during the process of visual stimulation. The grating was fixed at a spatial frequency of 0.3 cyc/deg with the time frequency of 1 cyc/sec, which gave an angular velocity of 3.33 deg/sec. The second version of the program contained the same grating, but in a non-moving presentation. In order to additionally distinguish between the envisaged meridional stimulus effects, we examined our patients with regard to their corrected visual acuity using a directionally sensitive set of optical characters developed at the Kharkevich Institute. The monocular corrected visual acuity was tested in all patients at 4 meridians: 0, 45, 90 and 135 degrees. Additionally, in all patients of the first group and all patients of the second group, the binocular visual acuity was examined too. Results: In the measurements of the corrected visual acuity along four meridians, a statistically significant improvement was found with alignment of the directional optical characters close to the meridian with maximal ametropia, and the minimal improvement in the orientation perpendicular thereto. In the patients of the both groups, the corrected visual acuity had significantly increased as a result of the treatment performed in the stage with a series of exercises with the moving circular sinusoidal grating. After the stage of treatment using the stationary grating, however, there was found no statistically significant improvement. Conclusions: Telemedical exercises using special computer games that contained a moving circular sinusoidal grating resulted in a statistically significant positive dynamics of visual acuity development in the most ametropic meridian as compared to the least ametropic meridian. No statistically significant improvement was observed after exercises with the stationary grating.

When stereoscopic images are presented alternately to the two eyes, stereopsis occurs at F ≥ 1 Hz full-cycle frequencies for very simple stimuli, and F ≥ 3 Hz full-cycle frequencies for random-dot stereograms (eg Ludwig I, Pieper W, Lachnit H, 2007 “Temporal integration of monocular images separated in time: stereopsis, stereoacuity, and binocular luster” Perception & Psychophysics 69 92–102). Using twenty different stereograms presented through liquid crystal shutters, we studied the transition to stereopsis with fifteen subjects. The onset of stereopsis was observed during a stepwise increase of the alternation frequency, and its disappearance was observed during a stepwise decrease in frequency. The lowest F values (around 2.5 Hz) were observed with stimuli involving two to four simple disjoint elements (circles, arcs, rectangles). Higher F values were needed for stimuli containing slanted elements or curved surfaces (about 1 Hz increment), overlapping elements at two different depths (about 2.5 Hz increment), or camouflaged overlapping surfaces (> 7 Hz increment). A textured cylindrical surface with a horizontal axis appeared easier to interpret (5.7 Hz) than a pair of slanted segments separated in depth but forming a cross in projection (8 Hz). Training effects were minimal, and F usually increased as disparities were reduced. The hierarchy of difficulties revealed in the study may shed light on various problems that the brain needs to solve during stereoscopic interpretation. During the construction of the three-dimensional percept, the loss of information due to natural decay of the stimuli traces must be compensated by refreshes of visual input. In the discussion an attempt is made to link our results with recent advances in the comprehension of visual scene memory.

Communicated by Ivars Lâcis

Some strabismic patients with inconstant squint can fuse two images in a single eye, and experience lustre and depth. One of these images is foveal and the other extrafoveal. Depth perception was tested on 30 such subjects. Relief was perceived mostly on the fixated image. Camouflaged continuous surfaces (hemispheres, cylinders) were perceived as bumps or hollows, without detail. Camouflaged rectangles could not be separated in depth from the background, while their explicit counterparts could. Slanted bars were mostly interpreted as frontoparallel near or remote bars. Depth responses were more frequent with stimuli involving inward rather than outward disparities, and were then heavily biased towards "near" judgements. All monocular fusion effects were markedly reduced after the recovery of normal stereoscopic vision following an orthoptic treatment. The depth effects reported here may provide clues on what stereoscopic pathways may or may not accomplish with incomplete retinal and misleading vergence information.