Restoration Of Binocular Vision Research Articles

Experience-dependent structural plasticity at pre- and postsynaptic sites of layer 2/3 cells in developing visual cortex

The developing brain can respond quickly to altered sensory experience by circuit reorganization. During a critical period in early life, neurons in the primary visual cortex rapidly lose responsiveness to an occluded eye and come to respond better to the open eye. While physiological and some of the molecular mechanisms of this process have been characterized, its structural basis, except for the well-known changes in the thalamocortical projection, remains obscure. To elucidate the relationship between synaptic remodeling and functional changes during this experience-dependent process, we used 2-photon microscopy to image synaptic structures of sparsely labeled layer 2/3 neurons in the binocular zone of mouse primary visual cortex. Anatomical changes at presynaptic and postsynaptic sites in mice undergoing monocular visual deprivation (MD) were compared to those in control mice with normal visual experience. We found that postsynaptic spines remodeled quickly in response to MD, with neurons more strongly dominated by the deprived eye losing more spines. These postsynaptic changes parallel changes in visual responses during MD and their recovery after restoration of binocular vision. In control animals with normal visual experience, the formation of presynaptic boutons increased during the critical period and then declined. MD affected bouton formation, but with a delay, blocking it after 3 d. These findings reveal intracortical anatomical changes in cellular layers of the cortex that can account for rapid activity-dependent plasticity.

Амблиопия и бинокулярное зрение

The review presents new insights into the mechanisms of development of amblyopia. There is objective evidence that amblyopia develops simultaneously as the monocular and as the binocular deficit of visual processing and that decrease in monocular visual acuity and disorders of binocular and stereoscopic vision take place. Given the ever-increasing evidence of fundamental and clinical studies, it is most likely that the binocular dysfunction is primary, and the decrease of monocular visual acuity is secondary in this disease. Amblyopia is a binocular pathology, and binocular interaction plays a critical role in the pathogenesis of strabismic, anisometropic and combined amblyopia. Accordingly, it seems appropriate to start the treatment with the restoration of binocular vision, which also leads to the recovery of the amblyopic eye. Visual dysfunction in amblyopia is often associated with the emergence of powerful suppression while watching with both eyes. Suppression converts the structurally binocular system into a functionally monocular one. Therefore, the elimination of suppression should be considered the first and the most necessary step to restore binocular vision. Quantification of suppression is a critically significant step for the development of new methods of treatment of amblyopia, including those based on the perception of global motion, associated with the function of the extrastriate dorsal visual cortex. The new understanding of amblyopia becomes the basis for a large amount of diverse research targeted to the development of more effective treatment methods, which will focus primarily on the elimination of suppression and restoration of binocular vision // Russian ophthalmological journal. 2017; 10 (2): 97-102. (in Russian). doi: 10.21516/2072-0076-2017-10-2-97-102.

Parental perspectives on surgical fees of pediatric squint surgeries

Aim: To report the parental feedback on the 'squint surgery fees' of their ward in an urban private practice. Design: Prospective cohort study. Subjects and Methods: Three months after the surgery, a 10 item questionnaire was administered on the parents of the children who underwent a squint surgery. Multivariate analysis was performed. Results: The parents of 46 children were included. Thirty-three respondents were fathers. The educational status ranged from 6 th grade to postgraduates including doctors. Four respondents refused to disclose the income. The mean total and per capita monthly income of the families were 59,590/- INR (Indian Rupees) and 14,670/- INR, respectively. Thirteen parents found the surgical charges inappropriate. Concession was demanded when the total cost of surgery (28,417/- INR) exceeded the per capita income of the family (10,149/- INR) by three times. The most appropriate cost of the surgery adjudged by the parents was two times the per capita income. The appropriateness of the fees had no correlation with the outcome (P = 0.4). All the parents recommended heavy concession in the fees for the reoperations. The quality of the medical expertise was considered the most important determinant of the surgical fees. Of 18 children with mediclaim, 12 had rejection due to 'congenital' nature of the disease. Two were considered cosmetic. Conclusions: In a private practice, the parental feedback on fees is desirable to make surgical services demand sensitive. Clinician should avoid the term congenital in the medical records and loudly express, restoration of binocular vision as the indication of squint surgery in children.

Strabismus in Cerebral Palsy: When and why to Operate

Cerebral palsy (CP) is the most common physical disability in children. Orthoptists and ophthalmologists who care for children with CP know that strabismus is a common feature. This paper reviews the literature on strabismus in patients with CP, and then provides summary data and recommendations for management of these patients. The incidence of strabismus in patients with CP, especially in patients with spastic diplegia, is much higher than in neurologically normal children. Esotropia is the most common ocular misalignment. CP patients with strabismus benefit from nonsurgical treatment and should be treated promptly. Strabismus surgery should be considered in CP patients for psychosocial reasons as well as for potential successful ocular realignment and restoration of binocular vision. The literature is lacking in a long-term natural history study, prospective strabismus surgery studies, and long-term outcome studies of strabismus management in patients with CP.

The impact of binocular vision disorders on 3D display viewing

AbstractPurpose Recent advances in display technology have led to 3D display viewing becoming a commonplace activity. This exciting development has a number of implications for the vision science community. From a scientific point of view 3D displays allow us the opportunity to develop new types of tests to examine binocular function, while clinically a number of issues arise relating to visual symptoms and treatment.Methods Here we review the range of methods employed to create a 3D viewing environment and discuss the advantages and disadvantages of these technologies from a binocular vision perspective.Results We will summarise the recent research findings relating to the influence of 3D viewing on visual measures such as the AC/A and CA/C ratio and discuss how these changes may induce visual symptoms in certain patient groups. The impact of 3D viewing upon the visual system during the earlier stages of visual development will also be considered.Conclusion Findings suggest that in the mature visual system 3D display technology may induce visual symptoms in patients with normally insignificant binocular anomalies. In the immature binocular vision system, consideration should be given to the possibility of developmental problems arising from prolonged 3D display viewing. However, continued advances in 3D display technology also offer great potential for the assessment and restoration of binocular vision in patients with binocular vision anomalies such as amblyopia and strabismus.

Restoration of Binocular Vision in Amblyopia

Purpose: To develop a treatment for amblyopia based on re-establishing binocular vision.Methods: A novel procedure is outlined for measuring and reducing the extent to which the fixing eye suppresses the fellow amblyopic eye in adults with amblyopia. We hypothesize that suppression renders a structurally binocular system, functionally monocular.Results: We demonstrate that strabismic amblyopes can combine information normally between their eyes under viewing conditions where suppression is reduced by presenting stimuli of different contrast to each eye. Furthermore we show that prolonged periods of binocular combination leads to a strengthening of binocular vision in strabismic amblyopes and eventual combination of binocular information under natural viewing conditions (stimuli of the same contrast in each eye). Concomitant improvement in monocular acuity of the amblyopic eye occurs with this reduction in suppression and strengthening of binocular fusion. Additionally, stereoscopic function was established in the majority of patients tested. We have implemented this approach on a headmounted device as well as on a handheld iPod.Conclusion: This provides the basis for a new treatment of amblyopia, one that is purely binocular and aimed at reducing suppression as a first step.

Functional Benefits of Adult Strabismus Surgery

The most common functional benefits from strabismus surgery in the adult patient are restoration of binocular vision and elimination of diplopia and/or a compensatory head posture. Adult patients with chronic strabismus have been thought to have the potential to achieve only a cosmetic result from surgery. On the contrary, several studies have shown that unexpected sensory fusion is possible after excellent postoperative motor alignment in these patients. Other functional benefits of strabismus surgery in the adult patient include the expansion of binocular visual fields in patients with esotropia and the psychosocial and economic benefits from restoration of ocular alignment. This paper will explore the impact of untreated strabismus in the adult patient and what changes occur in the patient's quality of life once strabismus has been successfully treated.

The functional significance of stereopsis.

Purpose. Development or restoration of binocular vision is one of the key goals of strabismus management; however, the functional impact of stereoacuity has largely been neglected. Methods. Subjects aged 10 to 30 years with normal, reduced, or nil stereoacuity performed three tasks: Purdue pegboard (measured how many pegs placed in 30 seconds), bead threading (with two sizes of bead, to increase the difficulty; measured time taken to thread a number of beads), and water pouring (measured both accuracy and time). All tests were undertaken both with and without occlusion of one eye. Results. One hundred forty-three subjects were recruited, 32.9% (n = 47) with a manifest deviation. Performances on the pegboard and bead tasks were significantly worse in the nil stereoacuity group when compared with that of the normal stereoacuity group. On the large and small bead tasks, those with reduced stereoacuity were better than those with nil stereoacuity (when the Preschool Randot Stereoacuity Test [Stereo Optical Co, Inc., Chicago, IL] results were used to determine stereoacuity levels). Comparison of the short-term monocular conditions (those with normal stereoacuity but occluded) with nil stereoacuity showed that, on all measures, the performance was best in the nil stereoacuity group and was statistically significant for the large and small beads task, irrespective of which test result was used to define the stereoacuity levels. Conclusions. Performance on motor skills tasks was related to stereoacuity, with subjects with normal stereoacuity performing best on all tests. This quantifiable degradation in performance on some motor skill tasks supports the need to implement management strategies to maximize development of high-grade stereoacuity.

Adult visual experience promotes recovery of primary visual cortex from long-term monocular deprivation

Prolonged visual deprivation from early childhood to maturity is believed to cause permanent visual impairment. However, there have been case reports of substantial improvement of binocular vision in human adults following lifelong visual impairment or deprivation. These observations, together with recent findings of adult ocular dominance plasticity in rodents, led us to re-examine whether adult primary visual cortex (V1) is capable of any recovery following long-term monocular deprivation starting in development. Using mice as a model, we find that monocular deprivation from early development to mature ages (well past the critical period) severely impaired binocular vision by reducing the amplitude of responses elicited by stimulation of the deprived eye. Surprisingly, we find little effect on nondeprived eye responses. Restoration of binocular vision in mature adults yields modest but significant improvement of visual responses in V1. Remarkably, we find that when binocular vision is followed by occlusion of the nondeprived eye, visual responses in V1 recover almost fully, as measured by visual evoked potential amplitude, spatial frequency threshold, and single-unit activity. We conclude that adult V1 can recover from long-term deprivation when provided with an optimal regimen of visual experience.

Protein Synthesis-Independent Plasticity Mediates Rapid and Precise Recovery of Deprived Eye Responses

Monocular deprivation (MD) for a few days during a critical period of development leads to loss of cortical responses to stimulation of the deprived eye. Despite the profound effects of MD on cortical function, optical imaging of intrinsic signals and single-unit recordings revealed that deprived eye responses and orientation selectivity recovered a few hours after restoration of normal binocular vision. Moreover, recovery of deprived eye responses was not dependent upon mRNA translation, but required cortical activity. Interestingly, this fast recovery and protein synthesis independence was restricted to the hemisphere contralateral to the previously deprived eye. Collectively, these results implicate a relatively simple mechanistic process in the reactivation of a latent set of connections following restoration of binocular vision and provide new insight into how recovery of cortical function can rapidly occur in response to changes in sensory experience.

Different Mechanisms for Loss and Recovery of Binocularity in the Visual Cortex

Diverse molecular mechanisms have been discovered that mediate the loss of responses to the deprived eye during monocular deprivation. cAMP/Ca2+ response element-binding protein (CREB) function, in particular, is thought to be essential for ocular dominance plasticity during monocular deprivation. In contrast, we have very little information concerning the molecular mechanisms of recovery from the effects of monocular deprivation, even though this information is highly relevant for understanding cortical plasticity. To test the involvement of CREB activation in recovery of responses to the deprived eye, we used herpes simplex virus (HSV) to express in the primary visual cortex a dominant-negative form of CREB (HSV-mCREB) containing a single point mutation that prevents its activation. This mutant was used to suppress CREB function intracortically during the period when normal vision was restored in two protocols for recovery from monocular deprivation: reverse deprivation and binocular vision. In the reverse deprivation model, inhibition of CREB function prevented loss of responses to the newly deprived eye but did not prevent simultaneous recovery of responses to the previously deprived eye. Full recovery of cortical binocularity after restoration of binocular vision was similarly unaffected by HSV-mCREB treatment. The HSV-mCREB injections produced strong suppression of CREB function in the visual cortex, as ascertained by both DNA binding assays and immunoblot analysis showing a decrease in the expression of the transcription factor C/EBPbeta, which is regulated by CREB. These results show a mechanistic dichotomy between loss and recovery of neural function in visual cortex; CREB function is essential for loss but not for recovery of deprived eye responses.

The role of afferent activity in the maintenance of primate neocortical function

The major neuronal populations of the primate cerebral cortex can be classified immunocytochemically according to their transmitters and in terms of the differential expression of certain other molecules such as neuropeptides, calcium-binding proteins and protein kinases. We have been able to chart the time course of developmental expression of these molecules and to show that gene expression for many of them is regulated in adult and infant animals by afferent activity entering the cortex. In the visual cortex of adult monkeys, levels of immunocytochemically detectable gamma aminobutyric acid (GABA), of its synthesizing enzyme glutamic acid decarboxylase (GAD) and of the tachykinins are greatly reduced in deprived ocular dominance columns within 24 h of blocking impulse activity in the optic nerve by intraocular injection of tetrodotoxin (TTX). Conversely, levels of immunocytochemically detectable calcium-calmodulin-dependent protein kinase (CAMII kinase) are increased in deprived eye dominance columns. These effects are quickly reversible on restoration of binocular vision, and experiments involving in situ hybridization and S1 nuclease protection assays show that the changes are associated with parallel changes in mRNA levels for preprotachykinin and CAM II kinase, but not for GAD, which appears to be regulated by post-transcriptional mechanisms. Experiments in the primate somatic sensory cortex suggest comparable activity-dependent effects on gene expression there also. It is proposed that effects of this type underlie the establishment of cortical maps during development and their activity-dependent mutability in adulthood.

Contact lens correction of post-traumatic unilateral aphakia. Late visual and orthoptic results

From 1978 to 1981 total of 122 perforating eye injuries were treated in the eye department of the Salzburg provincial clinic. In 25% of the cases treated the opacified lens had to be removed. The authors followed up 35 patients with unilateral post-traumatic aphakia. Of these, 27 proved suitable candidates for contact lenses. Visual function was good in 15 patients, but reduced in 12 due to post-traumatic changes. Ten patients achieved binocular vision, while in 12 it was possible to restore binocular vision by appropriate measures. The paper deals particular with the restoration of binocular vision and maintenance of binocular function in cases of unilateral post-traumatic aphakia.

Restoration of Binocular Vision

Numerous studies have shown that pseudophakic surgery is a better (because it is a more natural) method of restoring binocularity than contact lenses or aphakic spectacles provided that the potential for binocular vision was present before the onset of the cataract(s). However, this restoration is achieved more easily in some groups of patients than others. Unilateral: Excellent prognosis for binocularity is retained for many years--even 50-60 years--in adult unilateral traumatic cataract/aphakia. At the other extreme are patients born with one normal eye and the other containing a well-marked cataract. In unilateral traumatic cataract/aphakia in children the potential for restoration of binocularity is related to age--the older the child, the better the chances. To achieve binocularity central vision must not fall below 20/70 in each eye. Bilateral: There is not much to choose between pseudophakia and contact lenses; both are effective in restoring binocularity, and both are superior in this respect to cataract spectacles of keratophakia.

Aftereffects of short-term monocular deprivation on critical flicker frequency of the non-occluded eye.

Ten subjects were monocularly deprived for a period of 6 hr. The CFF of the non-occluded eye was determined just before deprivation, at 3 and 6 hr. of deprivation and at 1, 3, 5, and 18 hr. following restoration of binocular vision. Results indicated a large depression in CFF at 6 hr. of deprivation followed by a gradual return to baseline that was virtually complete 18 hr. afterr binocular vision was restored. The results were discussed in terms of previous research and theory.

Case study: restoration of binocular vision to functionally monocular sighted adult.

Binocular vision was restored to a 26-yr.-old woman who had had, functionally, monocular vision since infancy. Testing was carried out a few hours and 2 wk. after restoration. The normative, data obtained from testing on such items as color vision, visual illusions, depth perception, and recognition thresholds are discussed.

DIAGNOSTIC VALUE OF MONOCULAR OCCLUSION

The ophthalmologist frequently fails to give his patient comfortable binocular vision in spite of the fact that he has adequately corrected errors of refraction and motility and has eliminated the possibility of ocular disease and inflammation. The reason for this may be that some disorder of binocular vision is at fault. Of interest, therefore, is a report of the results obtained in a series of cases studied at the Dartmouth Eye Institute in which monocular occlusion was used for the purpose of determining whether binocular anomalous vision was at fault. The chief disorders affecting the comfortable and efficient cooperation of the two eyes in binocular vision are heterophoria, accommodation-convergence imbalance and aniseikonia. Binocular single vision is not present in cases of strabismus, and symptoms in such cases cannot be due to disorders of the binocular processes. On the contrary, correction of the deviation and restoration of binocular vision may result