George Amigo

Bio: George Amigo is an academic researcher from University of New South Wales. The author has contributed to research in topics: Horopter & Binocular vision. The author has an hindex of 7, co-authored 21 publications receiving 128 citations.

Variation of stereoscopic acuity with observation distance.

Abstract: The stereoscopic acuity of five subjects was investigated in two consecutive and related studies. In the first one a modified horopter apparatus was used and the stereoscopic acuity was determined, at a mean retinal locus of 4° to the left of the fovea, at the 333- and 1000-mm observation distances. Two types of fixations were used, and the exposure time was kept above 1 sec. The results indicated a significant variation of the stereoscopic acuity with observation distance. In the second investigation a haploscopic apparatus was used to study the stereoscopic acuity at a mean retinal locus of 4° and 12° to the left of the fovea, at 500, 750, 1000, 1500, and 2000 mm for the 4° and at 500, 750, and 1000 mm for the 12° locations. The duration of the stimulus was accurately controlled by a mirror-shutter. The exposure times used were 0.05, 0.10, 1.00, and 2.00 sec. Fixation was central and all known physical variables were kept constant. The results again indicated a significant variation of the stereoscopic acuity with the observation distance. The possible implications of this finding are discussed.

A Vertical Horopter

Abstract: When a perpendicularly stretched thread is fixated at its centre with the eyes in symmetrical convergence, the thread has to be tilted around the fixated point with its top away from the observer for it to appear perpendicular. This fact was recognized by a number of investigators as early as the 1850's. For this reason both Hering and Helmholtz described the horopter as an ‘upside-down’ cone. The present investigation employs a twin point-light source apparatus to estimate the orientation and the shape of a subjective equidistant line that lies in the median plane of the observer. Since the method of measurement depends on retinal disparity clues, this locus corresponds to the stereoscopic frame of reference in the median plane. The results are in qualitative agreement with previous findings. Quantitatively, however, they show a much smaller tilt of the reference plane than the ones reported by Helmholtz and others. The stereoscopic sensitivities of the retinal regions at the various elevations above and...

The Mathematical Treatment of Horopter Data Obtained with the Eyes in Asymmetric Convergence

Abstract: The conic section approximation designed to fit the experimental points of the longitudinal horopter in symmetrical convergence is extended to satisfy conditions during longitudinal horopter settings with the eyes in asymmetric convergence. The special case of the straight line horopter is re-examined and the theoretical general formula obtained. The implications of these theoretical results are discussed and the relevant findings of an extensive investigation of the horopter in asymmetric convergence are presented. The variation of the empirical H (the Hering-Hillebrand deviation) with the angle of asymmetric convergence is compared to the variation of H with observation distance. Whilst evidence is insufficient to refute the “stability of corresponding points” hypothesis, these results suggest a tendency of the visual apparatus to maintain a constant individual shape of the horopter.

Visual Characteristics of an Underprivileged Croup of Australian Children

Abstract: Stewart House, at one of the seaside suburbs of Sydney, provides a unique service for the needy families of the state. Every three weeks it welcomes 70 to 80 schoolchildren and during this period it looks after them in a lavish way. Foremost amongst the services are entertainment, education and health. Our team provides comprehensive optometrical care. During the first week all children are screened with the aid of a well-established test battery that probes key aspects of the visuo-sensory and visuo-motor mechanism. Children who fail this screening receive a full refraction during the second week. Based on these two examinations the type of treatment is decided upon, which includes referral to the appropriate educational, psychological or health authorities. During the third week optical appliances are fitted and final check-ups are made on borderline cases. The aim of this paper is to report on the results obtained from 1166 consecutive cases. These results indicate a statistically significant difference both in the visuo-sensory and the visuo-motor characteristics of this group when compared to available figures obtained from children of similar age distribution.

The neuropsychology of 3-D space

Abstract: The neuropsychological literature on 3-D spatial interactions is integrated using a model of 4 major behavioral realms: (a) peripersonal (visuomotor operations in near-body space), (b) focal extrapersonal (visual search and object recognition), (c) action extrapersonal (orienting in topographically defined space), and (d) ambient extrapersonal (orienting in earth-fixed space). Each is associated with a distinct cortical network: dorsolateral peripersonal, predominantly ventrolateral focal-extrapersonal, predominantly ventromedial action-extrapersonal, and predominantly dorsomedial ambient-extrapersonal systems. Interactions in 3-D space are also regulated neurochemically with dopaminergic and cholinergic excitation associated with extrapersonal activation and noradrenergic and serotonergic excitation associated with peripersonal activation. This model can help explain the 3-D imbalances in prominant neuropsychological disorders.

Learning to read: An unnatural act.

Abstract: The six-year-old's sight is as good as the adult's (Amigo 1972), and his hearing is nearly so (Elliott and Katz 1980). The child has an excellent memory (Mandler, in press), and his learning ability is remarkable. Even a conservative estimate of the size of his vocabulary will show that he must have learned, on average, more than four new words every day since his first birthday (Carey 1978). He has already learned to speak and understand his native language with remarkable fluency. The average American six-year-old can already produce and recognize more than a dozen vowels and nearly 30 consonants of English. He can produce and understand literally thousands of different words, and he can comprehend virtually any sentence that one can form with those words. To be sure, his language acquisition is not complete. Over the next decade he may have to smoothe out some rough spots in his phonology (Templin 1953), his vocabulary will grow by many more thousands of words (Oldfield 1963), and he must capture a few syntactic niceties which still escape him (Chomsky 1969). But his mastery of English would be the envy of any college graduate learning English as a second language. Yet for all his cognitive and linguistic talents, the child has one peculiar linguistic shortcoming: he cannot read a word. Indeed, that is one of the primary reasons why we now send him to elementary school. His teacher

Prevalence of Refractive Error in Singaporean Chinese Children: The Strabismus, Amblyopia, and Refractive Error in Young Singaporean Children (STARS) Study

Abstract: Refractive error, and myopia in particular, is one of the five leading causes of visual impairment in the world.1 It is estimated that, by 2020, approximately one third of the world's population (2.5 billion) will be affected by myopia alone.2 The prevalence of refractive error in children, particularly before the typical school commencement age of 6 to 7 years, has been assessed in only a limited number of population-based studies. Pediatric studies exploring refractive error have provided useful insights into the early development of refractive error.3–5 Studies in Western populations have collectively shown that the prevalence of myopia is low (<5%) in children aged 8 years or younger.6–11 However, studies in Southeast Asian children suggest a significantly higher prevalence of myopia than that in Western populations. A study of 10,000 Taiwanese school children found that the prevalence of myopia was 6% in 6-year-olds.12 By comparison, myopia was reported in less than 2% of Australian school students (mean age, 6.7 years),13 6.6% of African-American children (age range, 6–72 months), 3.7% of Hispanic children (age range, 6–72 months) (Tarczy-Hornoch K, et al. IOVS 2008;49:ARVO E-Abstract 3130), and only 0.7% of Caucasian children (age range, 6–71 months) (Katz J, et al. IOVS 2008;49:ARVO E-Abstract 1549). In this study, we determined the prevalence of refractive error, including myopia, astigmatism, and hyperopia, in a large population-based study of young Singaporean Chinese children aged 6 to 72 months who were recruited through the Strabismus, Amblyopia and Refractive Error in Singaporean Children (STARS) study.

Nearpoint of convergence: test procedure, target selection, and normative data.

Abstract: Background. The purpose of this study was to help determine the most appropriate target to be used for the assessment of the nearpoint of convergence, normative data for the break and recovery in adults, and the diagnostic value of the red-glass modification and repetition of the nearpoint of convergence. Methods. A total of 175 subjects with normal binocular vision and 38 subjects with convergence insufficiency were evaluated. The nearpoint of convergence was measured three ways, with an accommodative target, a penlight, and a penlight with red and green glasses. The nearpoint of convergence was also measured using a penlight for 10 repetitions. Results. Results suggest a clinical cutoff value of 5 cm for the nearpoint of convergence break and 7 cm for the nearpoint of convergence recovery with either an accommodative target or a penlight with red and green glasses. Conclusion. This study establishes normative data for the nearpoint of convergence break and recovery in the adult population and supports the value of various test modifications when other testing is equivocal. (Optom Vis Sci 2003;80:214-225)