Table 3 Type of study and outcome for observational studies

Fern 1986 ²⁴

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 1987 ²¹

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 1995 ⁹

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 1994 ⁸

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 2000 ²⁰

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 2005 ²²

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 2010 ⁷

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

Atkinson 1985 ²⁶

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 1988 ²⁷

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 1990 ²³

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 1996 ⁶

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 1994 ¹¹

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 1997 ¹⁰

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 2011 ²⁵

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 2012 ¹⁵

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

C^2.6′

C (LH)^2.6′

C^{2.6′ far (5m)}

LH^25%

LH^50%

LH^100%

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