Lalor_2018.pdf (45.85 MB)
Measures of visual acuity, contour interaction and crowding with contrast-modulated optotypes in adults and children
thesis
posted on 2023-08-30, 15:48 authored by Sarah J. H. LalorThe presence of ‘crowding’ features on visual acuity tests for young children are
considered important for detecting amblyopia, early treatment of which is key to success.
The optimum placement of ‘crowding’ features has not previously been investigated, nor
has the change in magnitude of crowding with age been measured with such stimuli.
Recently, contrast-modulated noise (CM) stimuli have been suggested to be potentially
more sensitive to amblyopia, than standard black on white, or luminance (L) stimuli.
CM stimuli also result in larger magnitudes of crowding in normal adults, but this has
not been tested in children, or in adults with child-friendly CM optotypes. The first
study of this thesis shows that placement of features surrounding the target optotype
provide more consistent crowding across symbols, pictures and letters, when separation
is specified in units of stroke width, as opposed to units of optotype width. Steeper slopes
of the underlying psychometric functions, and thereby increased sensitivity, are produced
by placing contour interaction or crowding features near to 1 (one) stroke width away.
This separation also maximises contour interaction and crowding. In normal adults, the
magnitude of contour interaction is smaller than that of crowding with L and LM, but
not with CM, stimuli. The second study of this thesis shows that visual acuity develops
more slowly, and becomes adult-like later with CM, compared to L and LM (luminancemodulated
noise) stimuli. The magnitude of contour interaction is similar for L, LM and
CM stimuli and varies very little across age group (3 to 16 years old and adults). Crowding
is larger than contour interaction with L and LM, but not CM stimuli in binocularly normal
participants; this is not the pattern of results found in very young children or in binocularly
anomalous adults. A comparison of ‘equivalent ages’ for binocularly abnormal adults
finds that CM crowded acuity predicts an earlier arrest of normal development, than do L
or LM crowded, or any of the isolated optotype acuities.
History
Institution
Anglia Ruskin UniversityFile version
- Accepted version
Language
- eng
Thesis name
- PhD
Thesis type
- Doctoral