Insidious 2 wikipedia full#
This is usually done by prescribing the cyclopegic refraction to the child for full time wear. Treatment of anisometropic amblyopia starts with eliminating the competitive advantage of the dominant eye. Conversely, vertical grating resolution is asymmetric in patients with strabismic amblyopia and is dependent on their type of eye-misalignment. Patients with anisometropic amblyopia do not show any visual field asymmetry when testing vertical grating resolution. However, patients with amblyopia secondary to strabismus show a greater loss of Vernier acuity than grating acuity. Grating acuity and Vernier acuity have been shown to be equally decreased in patients with anisometropic amblopia. found that contrast sensitivity was reduced in anisometropic amblyopia, however these contrast deficits were not apparent in bilateral refractive amblyopia. Conversely, contrast sensitivity was only decreased in the central visual field in patients with strabismic amblyopia. demonstrated that patients with anisometropia amblyopia have decreased contrast sensitivity across the entire visual field (central and peripheral field). The decrease in contrast sensitivity for patients with anisometropic amblyopia is more pronounced at mid and high spatial frequencies. Many studies have shown that contrast sensitivity is decreased in patients with amblyopia. This may explain why patients with amblyopia have difficulty resolving surrounding characters of similar size when testing their amblyopic eye. Studies using spatial summation have shown that neuronal receptive fields are larger in the amblyopic visual system. This is recognized as the crowding phenomenon and is speculated to be caused by contour interaction. It is well known that patients with amblyopia show better visual acuity with isolated or single letter visual acuity than linear acuity. These areas of the visual system may be affected differently depending on the type of amblyopia (deprivation, strabismus, anisometropia). Deficits from amblyopia affect neuronal receptive fields, contrast sensitivity, and grating acuity. However, the ocular dominance columns do not appear to shrink in size in patients with strabismic or anisometropic amblyopia Diagnostic TestingĪlthough amblyopia is most commonly detected by a difference in optotype visual acuity, studies have shown that changes occur in different areas of the visual system. Recent studies using PET, FMRI and VEP have verified that there is significant loss of neural activity in the visual cortex. Subsequent amblyopia studies in animals have shown neurological changes in layer IVc of V1 and the lateral geniculate nucleus. Experiments by Hubel and Wiesel were the first to demonstrate neuronal loss in the primary cortex (V1) using experimental deprivation amblyopia in kittens. It is generally accepted that pathological changes from amblyopia occur primarily in the primary visual cortex and lateral geniculate nucleus. Īs previously discussed, anisometropic amblyopia can occur when there is a difference in refractive error between the two eyes. However, other authors have reported that 50% of cases with amblyopia are caused by anisometropia. According to Hess et al., one third of amblyopia cases are caused by anisometropia, one third by strabismus and one third from a combination of the two. The prevalence of amblyopia is reported as 2-4% in North America and is the primary cause of unilateral vision loss in children.