Beyond Rehabilitation of Acuity, Ocular Alignment, and Binocularity in Infantile Strabismus.

Chantal Milleret,Emmanuel Bui Quoc

doi:10.3389/fnsys.2018.00029

Abstract

Infantile strabismus impairs the perception of all attributes of the visual scene. High spatial frequency components are no longer visible, leading to amblyopia. Binocularity is altered, leading to the loss of stereopsis. Spatial perception is impaired as well as detection of vertical orientation, the fastest movements, directions of movement, the highest contrasts and colors. Infantile strabismus also affects other vision-dependent processes such as control of postural stability. But presently, rehabilitative therapies for infantile strabismus by ophthalmologists, orthoptists and optometrists are restricted to preventing or curing amblyopia of the deviated eye, aligning the eyes and, whenever possible, preserving or restoring binocular vision during the critical period of development, i.e., before ~10 years of age. All the other impairments are thus ignored; whether they may recover after strabismus treatment even remains unknown. We argue here that medical and paramedical professionals may extend their present treatments of the perceptual losses associated with infantile strabismus. This hypothesis is based on findings from fundamental research on visual system organization of higher mammals in particular at the cortical level. In strabismic subjects (as in normal-seeing ones), information about all of the visual attributes converge, interact and are thus inter-dependent at multiple levels of encoding ranging from the single neuron to neuronal assemblies in visual cortex. Thus if the perception of one attribute is restored this may help to rehabilitate the perception of other attributes. Concomitantly, vision-dependent processes may also improve. This could occur spontaneously, but still should be assessed and validated. If not, medical and paramedical staff, in collaboration with neuroscientists, will have to break new ground in the field of therapies to help reorganize brain circuitry and promote more comprehensive functional recovery. Findings from fundamental research studies in both young and adult patients already support our hypothesis and are reviewed here. For example, presenting different contrasts to each eye of a strabismic patient during training sessions facilitates recovery of acuity in the amblyopic eye as well as of 3D perception. Recent data also demonstrate that visual recoveries in strabismic subjects improve postural stability. These findings form the basis for a roadmap for future research and clinical development to extend presently applied rehabilitative therapies for infantile strabismus.

Highlights

AND OVERVIEWThe visual scene may be decomposed into what are referred to as visual attributes, i.e., image location, orientations, spatial frequencies, velocities/directions of movement, binocularity, contrasts and colors (Figure 1A)
Not included yet in the current treatments of amblyopia after infantile strabismus by medical and paramedical professionals, at least the data obtained by Hess and his group obtained through the “binocular therapy” strengthen the hypothesis we have developed here since modifying the contrast of patterns presented to each eye may have a positive impact on the perception of the high spatial frequencies, i.e., acuity
It has been demonstrated that the speed and accuracy of saccades, the vergence and the combined eye movements are generally poor before eye surgery and much better after eye surgery (Bucci et al, 2002, 2009). From this example, in agreement with our hypothesis, we demonstrate that rehabilitation after surgery for infantile strabismus may take place in domains other than acuity, ocular alignment and binocularity, and even far beyond the visual system itself

Summary

INTRODUCTION

The visual scene may be decomposed into what are referred to as visual attributes, i.e., image location, orientations (horizontal, vertical, oblique), spatial frequencies (ranked from low to high, corresponding to gross to fine details respectively), velocities/directions of movement, binocularity (subtending 2D and 3D perception), contrasts and colors (Figure 1A). Experimental approaches in animals have allowed to establish that in case of infantile strabismus: (a) the more the central vision is concerned, the more the impairment is marked; (b) the more the deviation of the eyes develops near the peak of the critical period of a given attribute, the more the impairment is substantial (e.g., ocular dominance: Yinon, 1978; see Figure 2); (c) there is no discernible relation between the degree of alteration of the neural bases for visual perception and the amplitude of the angle of deviation of the ocular axes after infantile strabismus (Yinon, 1978; Kalil et al, 1984); (d) M, P and K channels are all affected; (e) Among the above reported abnormalities, some at least likely result from the maintenance of functional immaturity in V1 because of the misalignment of the eyes (for example large receptive fields, lack of orientation selectivity, poor ability to detect fast motions, etc...) Note that such observations were primarily made in experimental models of “early onset” strabismus in animals.

Summary of data

Findings

CONCLUSION