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Rapid monocular adaptation of saccade amplitude in constant strabismus
Published in Jan-Tjeerd de Faber, 28th European Strabismological Association Meeting, 2020
H.J. Griffiths, D. Buckley, J.P. Whittle
This present study found anomalous disconjugacy in two subjects with small angled strabismus. Bucci et al. (1997) found anomalous disconjugacy only in subjects with large angle strabismus and no fusion. They proposed that this might be driven by monocular visual inputs occurring to improve fixation of each eye and not to reduce binocular disparity. They suggest that the movements of the two eyes are controlled independently, so-called utrocular vision (or vision with each eye separately), as described by Schor (1991). This is a primitive form of binocular vision found in vertebrates with complete decussation of the visual pathways. Bucci et al. (1997) suggested that this form of independent eye control could allow avoidance of diplopia, but not establishment of a true binocular linkage.
Phoria Adaptation: The Ghost in the Machine
Published in Journal of Binocular Vision and Ocular Motility, 2020
Binocular disparity does not generate phoria adaptation. There is always binocular disparity in a complex world (in different planes even when the eyes are aligned), and this binocular disparity is a necessary stimulus for stereopsis. While binocular retinal image disparity provides the stimulus for the fast fusional vergence system, it is the motor signal from the fast fusional vergence system that serves as the error signal for phoria adaptation.5 The input to the slow neural integrator for phoria adaptation is generated by the output or effort of fast fusional vergence. Because there has to be an effort to fuse for phoria adaptation to be recruited, fixation disparity induced by a conflict in vergence and accommodation may provide a driving stimulus for prism-induced phoria adaptation9 (Figure 1). The fast vergence system has a neural integrator with a short half-life of 10–15 s.7,14 By contrast, phoria adaptation consists of a more stable neural integrator that leaks with a much longer time constant (varying from minutes to several days).5,9 The output of the slow neural integrator allows for a reciprocal reduction of the output of fast fusional vergence by means of the negative feedback loop in which the system is trying to adapt until the phoria is controlling the entire response.9 As the slow fusional vergence system charges up, the fast fusional vergence system decays to maintain a constant total output.6,7 This feedback loop presumably reduces the fatigue and eyestrain that would result from the prolonged use of the fast vergence system.7–9
Comparative analysis of the Lang Stereopad in a non-clinic population
Published in Strabismus, 2019
Fiona J. Rowe, Lauren R. Hepworth, Claire Howard, Chung Shen Chean, Meera Mistry
Stereoacuity is the angular measurement of the minimal resolvable binocular disparity which is necessary for the appreciation of stereopsis. The ability to demonstrate stereopsis indicates the presence of retinal correspondence, the normal average level of stereopsis varies dependent on the test being used but typically the threshold stereoacuity ranges from 30 to 60 seconds of arc in the presence of normal equal visual acuity in each eye.1 The level of stereoacuity decreases with a reduction in visual acuity2 and there is an age-related deterioration in stereoacuity with a linear correlation between age and stereopsis threshold.3
Stereopsis: are we assessing it in enough depth?
Published in Clinical and Experimental Optometry, 2018
Anna R O'connor, Laurence P Tidbury
Stereoacuity is traditionally considered as the threshold measure of how well an individual can interpret binocular disparity as perceived depth, by determining the spatial correlation of points projected onto the retina. As a physical object moves toward or away from an individual, a number of factors change, including monocular cues, and the two binocular cues to depth. Any point forward of where the eyes are fixated provides crossed disparity, that is, these points are projected on the temporal retina of both eyes. This is binocular disparity, as the corresponding point to the temporal retina of one eye, is the nasal point of the other eye.