The changing face of Amblyopia (original) (raw)

Treatment of amblyopia in the adult: insights from a new rodent model of visual perceptual learning

Frontiers in neural circuits, 2014

Amblyopia is the most common form of impairment of visual function affecting one eye, with a prevalence of about 1-5% of the total world population. Amblyopia usually derives from conditions of early functional imbalance between the two eyes, owing to anisometropia, strabismus, or congenital cataract, and results in a pronounced reduction of visual acuity and severe deficits in contrast sensitivity and stereopsis. It is widely accepted that, due to a lack of sufficient plasticity in the adult brain, amblyopia becomes untreatable after the closure of the critical period in the primary visual cortex. However, recent results obtained both in animal models and in clinical trials have challenged this view, unmasking a previously unsuspected potential for promoting recovery even in adulthood. In this context, non invasive procedures based on visual perceptual learning, i.e., the improvement in visual performance on a variety of simple visual tasks following practice, emerge as particularl...

The Pathophysiology of Amblyopia: Electrophysiological Studies

Annals of the New York Academy of Sciences, 1980

Functional amblyopia may be defined as a loss of visual acuity caused by form deprivation and/or abnormal binocular interaction, for which no organic cause can be detected by the physical examination of the eye.' Amblyopia is usually associated with strabismus (turned eye), anisometropia (unequal refractive error), or form deprivation early in life, and thus represents a developmental disorder. There appears to be a critical period for the development of amblyopia in humans and it may be preventable if the causative factors are discovered and eliminated within this critical period.' Interestingly, amblyopia may also be reversible much later in life.* Over the past 15 to 20 years, there has been a renewed interest in the study of amblyopia, which is in large part attributable to the single-unit studies in cats and monkeys reared with experimentally induced amblyopia. These studies have shown that normal visual experience is essential for the development and maintenance of the physiological characteristics of cells in the visual cortex, and that disruption of the normal visual process during an early period of susceptibility by light or form deprivation, strabismus, or anisometropia, may result in a marked disturbance of the physiological organization of the visual cortex, cell shrinkage in the LGN, and severe a m b l y~p i a .~-~ However, it is not clear whether strabismus and form deprivation (due to lid suture or occlusion) affect similar cell populations in the visual pathway. There is evidence that the effects of monocular lid suture are selective for the Y or transient cells," while in kittens reared with unilateral strabismus, the X or sustained cells appear to be most affected."-" Although such methods of investigation are valuable in dealing with experimental animals, studies of human amblyopia have, for the most part been restricted to psychophysics and visual evoked potentials (VEP). In humans, with naturally occurring amblyopia, the VEP is generally the only direct method available for studying cortical responses to visual stimuli and may provide a valuable tool for the assessment of visual function in amblyopia for several reasons: (1) it provides an objective measure of function which may be useful in infants and nonverbal patients; (2) it may aid in localizing function and dysfunction; (3) it may be of value in assessing prognosis and monitoring therapy; and (4) it may be helpful in bridging the gap between psychophysics and physiology. Over the past few years we have been studying the VEP of observers with naturally occurring amblyopia using luminance and pattern stimuli. The present paper reviews some of the results. LUMINANCE EVOKED POTENTIALS There have been a large number of studies of the VEP in amblyopia using unpatterned stimuli; however, the results are quite equivocal. Some investigators

Structural and functional deficits in human amblyopia

Neuroscience letters, 2008

Many neuroimaging tools have been used to assess the site of the cortical deficits in human amblyopia. In this paper, we aimed at detecting the structural and functional deficits in humans with amblyopia, with the aid of anatomic magnetic resonance imaging (aMRI) and functional MRI (fMRI). We designed the visual stimulus to investigate the functional deficits, and delineated the V1/V2 areas by retinotopic mapping. Then we performed the brain parcellation to calculate the volume of the subcortical structure on each individual, and reconstructed the cortical surfaces to measure the cortical thickness. At last, the statistical comparison was carried out to find the structural abnormities and their relationship to the functional deficits. Compared with the normal controls, it is found that the hemisphere difference existed on the unilateral amblyopia subjects, and the functional deficit might come along with the changes in the cortical volume, especially in the occipital lobe. The examined results may provide insight to the study of the neural substrates of amblyopia.

Amblyopia: New molecular/pharmacological and environmental approaches

Visual neuroscience, 2018

Emerging technologies are now giving us unprecedented access to manipulate brain circuits, shedding new light on treatments for amblyopia. This research is identifying key circuit elements that control brain plasticity and highlight potential therapeutic targets to promote rewiring in the visual system during and beyond early life. Here, we explore how such recent advancements may guide future pharmacological, genetic, and behavioral approaches to treat amblyopia. We will discuss how animal research, which allows us to probe and tap into the underlying circuit and synaptic mechanisms, should best be used to guide therapeutic strategies. Uncovering cellular and molecular pathways that can be safely targeted to promote recovery may pave the way for effective new amblyopia treatments across the lifespan.

Perceptual learning in adults with amblyopia: A reevaluation of critical periods in human vision

Developmental Psychobiology, 2005

Critical periods for experience-dependent plasticity are ubiquitous. The idea that experience-dependent plasticity is closely linked with the development of sensory function is still widely held; however, there also is growing evidence for plasticity in the adult nervous system. This article reviews the notion of a critical period for the treatment of amblyopia in light of recent experimental and clinical evidence for neural plasticity. Specifically, adults with amblyopia can improve their perceptual performance via extensive practice on a challenging visual task, and this improvement may transfer to improved visual acuity. Amblyopes achieve this improvement via the mechanisms that have been shown to explain perceptual learning in the normal visual system. It is hypothesized that these same mechanisms account for at least some of the improvement that occurs in the treatment of amblyopia.

Global processing in amblyopia: a review

Frontiers in Psychology, 2014

Amblyopia is a neurodevelopmental disorder of the visual system that is associated with disrupted binocular vision during early childhood. There is evidence that the effects of amblyopia extend beyond the primary visual cortex to regions of the dorsal and ventral extrastriate visual cortex involved in visual integration. Here, we review the current literature on global processing deficits in observers with either strabismic, anisometropic, or deprivation amblyopia. A range of global processing tasks have been used to investigate the extent of the cortical deficit in amblyopia including: global motion perception, global form perception, face perception, and biological motion. These tasks appear to be differentially affected by amblyopia. In general, observers with unilateral amblyopia appear to show deficits for local spatial processing and global tasks that require the segregation of signal from noise. In bilateral cases, the global processing deficits are exaggerated, and appear to extend to specialized perceptual systems such as those involved in face processing.

Tackling amblyopia in human infants

Eye, 1996

Amblyopia can possibly be avoided if it is detected early and treated appropriately. It remains to be decided whether the general population should be screened or whether a subpopulation of infants likely to develop this pathology can be isolated. A population study using the odds ratio was performed on a group of unselected infants (n = 2143) aged 5-15 months who attended a surveillance programme. Results show that a family history of visual defect has a 'protective' effect on individual infants, most probably because more of these infants are brought in for a checkup at an early age on the parents' initiative. The risk factor with the highest predisposition for amblyopia was found to be anisometropia. These results indicate the necessity for screening of refraction and resolution defects in the whole popUlation. The French health authorities have recently decided to provide for a visual assessment visit to all infants at the age of 9 months. Amblyopia is a reduction in visual capacity in one or both eyes that is not improved by refractive correction and occurs in the absence of detectable ocular pathology. Only developmental unilateral amblyopia is considered here. Detailed studies have shown that several aspects of visual function may be affected besides acuity. Usually the reduction in visual acuity, or a reduced contrast sensitivity for high spatial frequencies, is used to diagnose amblyo pia on the grounds that it is the visual function most accessible to commonly used tests (for a review see Levi and Carkeet l). However, it is now clear that the concept of unilateral amblyopia not only affects binocular processes 2 but also includes deficits of contrast sensitivity?-S spatial discrimination and skills, 6 , 7 visual field and the temporal processing of visual signals affecting motion perception 8 , 9 (see From: l Cerveau et Vision,

Amblyopia affects the ON visual pathway more than the OFF

The Journal of Neuroscience, 2019

Visual information reaches the cerebral cortex through parallel ON and OFF pathways that signal the presence of light and dark stimuli in visual scenes. We have previously demonstrated that optical blur reduces visual salience more for light than dark stimuli because it removes the high spatial frequencies from the stimulus, and low spatial frequencies drive weaker ON than OFF cortical responses. Therefore, we hypothesized that sustained optical blur during brain development should weaken ON cortical pathways more than OFF, increasing the dominance of darks in visual perception. Here we provide support for this hypothesis in humans with anisometropic amblyopia who suffered sustained optical blur early after birth in one of the eyes. In addition, we show that the dark dominance in visual perception also increases in strabismic amblyopes that have their vision to high spatial frequencies reduced by mechanisms not associated with optical blur. Together, we show that amblyopia increases visual dark dominance by 3-10 times and that the increase in dark dominance is strongly correlated with amblyopia severity. These results can be replicated with a computational model that uses greater luminance/response saturation in ON than OFF pathways and, as a consequence, reduces more ON than OFF cortical responses to stimuli with low spatial frequencies. We conclude that amblyopia affects the ON cortical pathway more than the OFF, a finding that could have implications for future amblyopia treatments.