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SKILL Assess vision: acuity in adults
Published in Sam Evans, Patrick Watts, Ophthalmic DOPS and OSATS, 2014
Acuity measurements are based on the assumption that the foveal cone photoreceptors are able to resolve (differentiate) light subtending an angle of 10 arc minutes (spatial resolution). In fact, significantly higher orders of resolution (greater than 0.5 arc minutes) can be made by the human eye (vernier acuity). This is a product both of intraretinal processing of relative stimulation of neighbouring cones and, to a greater extent, of higher (post-retinal) centres. Vernier acuity is measured using offset gratings, whereas gross acuity is measured by optotype charts.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
The ability to partition space may also be assessed by measures of the smallest discriminable difference in the position of stimuli. The prime exemplar of this is VERNIER ACUITY that measures the minimum displacement that permits perception of misalignment. This amazing ability (5 sec of arc or better) is exploited practically in vernier scales or in slide-rules. Other measures that probe the ability to assign location include the ability to perceive differences in width, length or orientation of two stimuli. In principle, the location of a stimulus requires only the detection of the centroid of the distribution of the RETINAL IMAGE of that feature, a task that can be achieved with arbitrary precision provided that sufficient quanta are available. As such, location acuities (collectively referred to as HYPERACUITIES) are not limited by the sampling densities of receptors as is the case for resolution acuity.
Normal and Abnormal Development of the Neuronal Response Properties in Primate Visual Cortex
Published in Jon H. Kaas, Christine E. Collins, The Primate Visual System, 2003
Yuzo M. Chino, Hua Bi, Bin Zhang
Despite relatively good optical quality, the monocularly measured visual acuity of infant monkeys is very poor (about 1 to 2 cycles/degree) compared to that in adults (30 to 50 cycles/degree).12,13 Although the shape of an infant monkey's contrast sensitivity function is qualitatively adultlike near birth,14,15 the peak spatial frequency, peak contrast sensitivity, and spatial resolution continue to improve over the first 12 months of a monkey's life. Similarly, vernier acuity is very low soon after birth, much worse than grating acuity, but improves by a factor of 50 to 60 over the same time period.12
A pragmatic approach to amblyopia diagnosis: evidence into practice
Published in Clinical and Experimental Optometry, 2018
Ann L Webber, Jayne E Camuglia
The normal development of the visual system has ‘critical periods’ during which normal visual input is necessary for normal visual development. Neural plasticity peaks during early childhood (less than six-years of age), and then diminishes.1998 This critical period does not have an abrupt end, but rather tapers off and if there is some visual interruption after that time, permanent damage is less likely.2005 Three sensitive periods within acuity have been described, each with different time courses, namely, the period of visually driven normal development, the sensitive period for damage, and sensitive period for recovery.2005 Further, different sensitive periods can be mapped out for visual functions other than acuity, such as contrast sensitivity, vernier acuity and stereoacuity.1998
The functional impact of amblyopia
Published in Clinical and Experimental Optometry, 2018
Amblyopia principally affects one eye; nonetheless, the non‐amblyopic eye often has an array of small but measurable deficits of spatial, positional and motion sensitivity.2005 Clinically, high contrast recognition visual acuity is the predominant measure that leads to a diagnosis of amblyopia, based on two or more lines difference in visual acuity measured between eyes. The amblyopic eye may also have poorer grating acuity, poorer vernier acuity, poorer contrast detection thresholds and altered contrast sensitivity function, the pattern of which varies between aetiology groups.2003 In addition to deficits determined at threshold, amblyopic vision has disturbance at supra‐threshold levels, including perceived spatial distortion, such as misperception of orientation and positional uncertainty.2003
The Role of Binocularity in Anisometropic Amblyopia
Published in Journal of Binocular Vision and Ocular Motility, 2019
Sarah J. Murray, Charlotte J. Codina
A linear correlation between visual acuity and stereopsis has been reported18, especially when stereoblind anisometropes (with central fixation and no strabismus) were removed from analyses.50 This is not a universal finding, however.15,46 For anisometropic amblyopes, the absence of any demonstrable binocular function leads to an “extra deficit” that is disproportional to their reduction in grating and Vernier acuity. In a study of 495 participants (ages 8–40), pure anisometropes with no demonstrable central binocular function demonstrated similar defects to strabismic amblyopes in the absence of eccentric fixation or manifest strabismus.53