Maria Fronius

Naso-temporal asymmetries in human amblyopia consequence of long-term interocular suppression.

Abstract The resolution for vertical gratings was tested at different eccentricities in the visual field of 9 strabismic and 2 anisometric amblyopes. It has been found that, within the central 20° of the visual field of esotropic amblyopes, the acuity of the nasal retina was much more reduced than that of the temporal retina. Outside this region, acuity was practically identical to that of the non-amblyopic eye. This asymmetric loss of acuity was well correlated with the interocular suppression as determined by a method of interocular perimetry. For anisometropic amblyopes, the acuity loss was symmetric, diminishing gradually towards the periphery. The interocular suppression was also symmetric, uniformly affecting all tested positions in the visual field of the amblyopic eye.

Binocular interaction in the peripheral visual field of humans with strabismic and anisometropic amblyopia

Abstract Residual binocular interaction was tested across the visual field of 9 strabismic and 2 anisometropic amblyopes in threshold and suprathreshold conditions. Binocular summation and interocular transfer of adaptation after-effects, both absent or very much reduced in the central region of the visual field of squint amblyopes, were highly significant in the periphery. The regions of preserved binocularity were well correlated with the areas for which there was no acuity loss and no interocular suppression. In anisometropic amblyopes, both binocular summation and interocular transfer of adaptation were lost at all tested eccentricities. Dynamic local stereopsis was also present in the periphery, but not in the central field of both squint and anisometropic amblyopes.

The development of visual acuity in the peripheral visual field of human infants: binocular and monocular measurements

We measured binocular and monocular grating acuity in the peripheral visual field of infants, using a modified preferential looking procedure. Both binocular and monocular peripheral acuity increased between 2 and 11 months of age, but had not reached adult levels at the end of the first year of life. Binocular acuity was always higher than monocular acuity. At all ages tested, acuity was higher in the temporal than in the nasal visual field. We conclude that, in spite of the relative morphological maturity of the peripheral retina, visual acuity develops in the peripheral visual field.

Pointing Errors in strabismics: Complex patterns of distorted visuomotor coordination

Monocular eye-hand coordination was tested in a pointing experiment in the central and peripheral visual field of each eye of strabismic and anisometropic amblyopes, strabismic alternators and normal controls. In the normal controls, pointing was accurate in the central visual field. Towards the periphery, normal observers showed a varying amount of undershoot as well as increasing uncertainty. The pointing pattern was similar in the two eyes of these subjects. Increased uncertainty of pointing responses was found in most amblyopic eyes as compared to the dominant eyes. Three strabismic amblyopes and one strabismic alternator also had systematic pointing errors (i.e. systematic differences between pointing under the control of the dominant as compared to the nondominant eye). The pointing pattern was not uniform across the visual field in some of the strabismics, but was composed of areas of larger and smaller pointing errors. Larger pointing errors (i.e. larger differences between the dominant and nondominant eyes) were usually found in the central visual field. These errors were not closely related to the angle of squint. The clinical history of the strabismics seems to be an important factor for the occurrence of pointing errors.

Deficits of spatial localization in children with strabismic amblyopia

BackgroundBesides loss of visual acuity and binocularity, spatial localization deficits (comprising both increased spatial uncertainty and spatial distortions) are an important feature of strabismic amblyopia. Although they have been extensively investigated in adult amblyopes, there are still many open questions concerning their substrate and relationship to clinical parameters. Our aim was to develop a procedure for assessing vertical alignment, which enabled us to find out whether children with strabismic amblyopia had similar spatial localization deficits, and their relation to the children’s clinical condition.MethodsVertical alignment was assessed in children by comparing the visual direction in space of three loci along the vertical meridian, separated by 5xa0deg of visual angle. We tested alignment in the amblyopic and dominant eyes of 32 strabismic and in both eyes of 35 control children from 4.5 to 10 years, together with a careful orthoptic examination.ResultsIn the amblyopic eyes, increased uncertainty and systematic distortions outside the normal range occurred. Large angles of deviation and pathological fixation patterns were necessary, but not sufficient conditions for gross spatial deficits to occur. The fellow dominant eyes showed spatial localization similar to normal eyes.ConclusionsChildren with strabismic amblyopia exhibited localization deficits and relationship to clinical data similar to those in adult amblyopes. These data are important for further investigations about the substrate, plasticity and the clinical relevance of perceptual distortions.

Eye alignment and cortical binocularity in strabismic kittens: A comparison between tenotomy and recession

Interocular alignment was assessed by corneal light reflex photography in 15 normal and 26 strabismic kittens. Strabismus was induced at 3-4 weeks of age by severing one extraocular muscle (tenotomy), by cutting and reinserting the muscle at another position on the ocular globe (recession), or by combining recession of the medial rectus muscle with resection of the lateral rectus muscle of the same eye. Nineteen strabismic and five normal kittens were followed longitudinally from 12 days to about 6 months of age. Three out of six longitudinally followed tenotomized cats and six out of the 13 recessed cats conserved their postoperative ocular deviation throughout the testing period (large-angle strabismics). Three tenotomized and seven recessed cats showed a transient deviation for 1-2 weeks after surgery, after which the interocular deviation diminished to values found in normal cats (microstrabismic cats). Both recessed-resected cats showed a transient interocular deviation. In spite of their different developmental histories, all cats showed a clear breakdown of binocularity in area 17. Large-angle strabismics showed a dominance of the non-operated eye, while in microstrabismic cats, both eyes were equally effective in driving cortical cells. It thus appears that a transient strabismus is sufficient to produce a reduction of binocularity in area 17.

Preliminary report: Monocular spatial localization in children with strabismic amblyopia

Defective spatial localization is an important feature of strabismic amblyopia. Based on our experience from testing adult strabismics under various test conditions, we developed a test for assessing vertical alignment in strabismic children. Patients had to align a vertical test line with the apices of two vertically arranged reference triangles, under the control of both the dominant eye and the amblyopic eye. Means and standard deviations of several judgements represent systematic errors and uncertainty of alignment. We tested 27 strabismic and 34 age-matched control children aged 4.5-10 years. Control children showed a scatter of mean systematic alignment around the correct position of up to 7 minarc. In the amblyopic eyes of strabismic children, uncertainty was consistently higher than in the eyes of the control children. Systematic errors outside the normal range frequently occurred. In children tested repeatedly during occlusion therapy, uncertainty decreased as visual acuity improved. In several cases we observed changes of systematic vertical alignment during therapy, sometimes unexpectedly in the sense of a change in the direction of mislocalization or an initial increase and later decrease of errors. Thus, children with strabismic amblyopia show spatial localization deficits which are similar to those of adult strabismic amblyopes. Both spatial uncertainty and systematic distortions are susceptible to change due to enforced use of the amblyopic eye during occlusion therapy.

A perspective on psychophysical testing in children

In this paper, we show that the development of acuity in infancy is not due solely to foveal maturation, since there is a clear development of acuity in the peripheral visual field.The development of peripheral acuity, and the naso-temporal asymmetry during early development reinforce the idea that the visual loss in adult strabismic amblyopes is not due to an arrest of development, but rather to the chronic interocular suppression of the deviated eye.The Teller Acuity Card Test does not reliably detect strabismic amblyopia, and therefore should not be recommended as a screening test. However, the test is adequate for diagnosing visual losses in children with organic eye disorders and possibly anisometropia.