Development of visual acuity and spatial interactions for luminance- and contrast-modulated symbols, pictures and letters

Visual acuity (VA) measured with contrast-modulated noise (CM) optotypes has potential to improve detection of amblyopia in children, however normal VA development and spatial interaction effects with CM optotypes in children, is not known. VA was measured in 11 adults and 84 children (3–16 yr) with single-optotypes from Kay Picture, Lea Symbol and HOTV tests, with and without a surrounding box. VA with HOTV letters surrounded by letters was also measured. Luminance (L), luminance-modulated noise (LM) and contrast-modulated noise (CM) optotypes/boxes were created. Surrounds were 1 stroke-width from the target. VA for isolated optotypes is adult-like at 6.40 ± 0.36 yr (L = 6.13 ± 0.76, LM = 5.96 ± 1.54 and CM = 7.11 ± 1.61 yr). VA is worse with CM than LM optotypes (by 0.49 ± 0.01 logMAR), consistent across age. VA is degraded with a box surround but not different across type (L, LM and CM: 0.10 ± 0.00 logMAR) or age. For L/LM letters, letter surrounds degrade VA more than a box for 3–4 year-olds (by 0.34 ± 0.01 logMAR) but flanking CM letters are less effective (by 0.04 ± 0.05). Adding noise to L (to create LM) letters does not worsen VA in 3–7 year-olds (0.00 ± 0.03 logMAR) but does in older participants (0.08 ± 0.01 logMAR). A surrounding box degrades VA in children and adults proportionately. With L/LM letters, surrounding letters degrade VA more in young children, which is likely due to increased crowding. A lack of VA developmental differences and reduced crowding for CM versus L/LM stimuli, suggests that they will not enhance amblyopia detection, although amblyopic children still need to be tested.