Table 3

Type of study and outcome for observational studies
Reference Type of study Number of participants, group (and age). Method Outcome
Fern 198624 Cross-sectional N = 105 Children NV (2-7y)
    Stimulus:
Isolated Landolt C/Landolt C with flanking bars at 3 m.
Contour interaction area
Children showed the same contour interaction effects as adults at 2.5 × MAR.
N = 16 Adults NV
    Threshold symbol size:
75%
    Flanker spacing:
2.5 MAR
    Foveal/Eccentric:
foveal
Manny 198721 Cross-sectional N = 13 Children NV (3-4y)
    Stimulus:
Isolated Landolt C/Landolt C with flanking bars at 3 m.
Contour interaction area (see Figure 2).
N = 5 Adults NV
    Threshold symbol size:
90-95%
    Flanker spacing:
0–8.52 MAR
    Foveal/Eccentric:
foveal
Chung 19959 Case- control N = 4 Adults CN
    Stimulus:
Isolated Landolt C/Landolt C with flanking bars at 4.1 m.
Contour interaction area (see Figure 3).
N = 6 Adults NV
    Threshold symbol size:
50%
    Flanker spacing:
1, 2, 5, or 10 MAR
    Foveal/eccentric:
foveal
Pascal 19948 Case- control N = 6 Adults NV
    Stimulus:
Isolated Landolt C/Landolt C with flanking bars (3 m or 6 m).
Contour interaction area (see Figure 3).
N = 6 Adults idiopathic CN
    Threshold optotype size:
50%
N = 6 Adults with albinism
    Flanker spacing:
1, 5 MAR
    Foveal /eccentric:
foveal
Semenov 200020 Cross- sectional N = 140 Children NV (3-9y)
    Stimulus:
Isolated Landolt C/Landolt C with flanking bars at 4.3 m.
Contour interaction area (see Figure 2).
N = 4 Adults NV
    Threshold optotype size:
75%
    Flanker spacing:
3.75-10 MAR
    Foveal/eccentric:
foveal.
Bondarko 200522 Cross- sectional N = 292 Children NV (8-17y)
    Stimulus:
Isolated Landolt C, E-letters, Gratings/Landolt C with flanking bars, E-letters with E-letters, Gratings by Gratings at 4.3 m.
Contour interaction
The maximum inhibition separation significantly decreased from approximately 2 MAR to 1.5MAR from age 8 to age 17.
    Threshold optotype size:
75%
    Flanker spacing:
0–7 MAR.
    Foveal/eccentric:
foveal
Jeon 20107 Cross- sectional N = 59 Children NV (5-, 8-, 11y)
    Stimuli:
Single Sloan E/Sloan E with gratings at 4.2 m.
Contour interaction area (see Figure 2).
    Threshold optotype size:
79.1%
N = 19 Adults NV
    Flanker spacing:
started at 20MAR (10 reversals)
    Foveal/eccentric:
foveal
Atkinson198526 Cross- sectional
    Study 1:
N = 14 Children NV (5;3–6;2y) N = 9 Mothers
    Study 2:
N = 13 Children NV (3;1–4;1y) N = 8 Mothers
    Stimulus:
Single Landolt C/Landolt C surrounded by Os and Cs at 1.5-8.3 m.
    Interoptotype spacing:
50% (line/circular configuration)
    Foveal/eccentric:
foveal
Crowding ratio (see Figure 5).
Atkinson 198827 Cross- sectional N = 47 Children NV (3-4y) N = 12 Adults NVN = 12 Children NV (5-7y)
    Stimulus:
Single Sheridan Gardener card/5-letter Sheridan Gardener card at 3 m and 6 m.
    Interoptotype spacing:
50%
    Foveal/eccentric:
foveal
Crowding ratio (see Figure 5).
Kothe 199023 Cross-sectional N = 90 Children NV (4-11y)
    Stimulus:
Isolated acuity/Regan Repeat Letter acuity/Snellen acuity at 6 m.
    Interoptotype size:
100%
    Foveal/eccentric:
foveal.
Crowding ratio (see Figure 4).
Jacobson 19966 Cross-sectional N = 13 Children CVI (5-14y)
    Stimulus
: LH single /LH line at 3 m.
    Interoptotype spacing
 = :100%
    Foveal/eccentric
 =: foveal
Crowding ratio (see Figure 4).
Pike 199411 Cross-sectional N = 42 Children CVI (2-9y)
    Stimulus:
Single Sheridan Gardener /7-letter Sheridan Gardener at 6 m.
    Interoptotype spacing
:50%
    Foveal/eccentric:
foveal
Crowding ratio (see Figure 5).
Pardhan 199710 Case–control N = 18VI Adults (42-85y)N = 25 Adults NV (42-85y)
    Stimulus:
Isolated visual /Regan Repeat Letter Chart, Snellen Line chart at 6 m.
    Interoptotype spacing:
100%
    Foveal/eccentric:
foveal
Crowding ratio (see Figure 4).
Norgett 201125 Cross-sectional N = 103 Children NV (4-9y)
    Stimulus:
Single: Kay Picture Single, Single Sheridan Gardiner. 50%: Log MAR crowded acuity, Kay Picture Crowded Log MAR100%: Sonkson Log MAR at 6 m.
    Interoptotype spacing:
see above.
    Foveal/eccentric:
foveal
Crowding ratio (see Figure 4 and 5)
Huurneman 201215 Case–control N = 75 Children NV (4-8y) N = 20VI children without CNN = 38 VI children with CN
    Stimulus:
C-test, LH-version C-test, LH line test with 25%, 50% and 100% spacing at 40 cm.C-test at 5 m.
    Interoptotype spacing:
see above.
    Foveal/eccentric:
foveal
Crowding ratio
C2.6′ C (LH)2.6′ C2.6′ far (5m) LH25% LH50% LH100%
NV 1.39 1.38 1.22 1.19 1.12 1.12
VI without CN 1.52 1.56 1.17 1.12 1.12 1.11
VI with CN 1.76 1.78 1.53 1.25 1.22 1.11

Huurneman et al.

Huurneman et al. BMC Ophthalmology 2012 12:27   doi:10.1186/1471-2415-12-27

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