Table 3 Type of study and outcome for quantitative studies on near visual acuity in 0–3 year olds

Dayton 1964 [11]

Cross sectional

n = 39

Group = NV

Age = 0–8 days

Procedure: Binocular OKN + electro-oculography

Range stimuli: 20/150, 20/290, 20/440 (5 mm/s)

Threshold used: 50%

Viewing distance: 37 cm from center

% Successful: 45%

See Fig. 2.

Mayer 1980 [12]

Cross sectional

n = 6

Group = NV

Age = 6–24 months

Procedure: Binocular Operant Preferential Looking (OPL)

Range stimuli: 20/5 to 20/640 (octave steps), stimuli were selected for each child 4/5 widths per child.

Threshold used: 60% + 75% (psychometric curve)

Viewing distance: 57 ± 3 cm from target

% Successful: 100%

Test duration: 45–60 minutes

See Fig. 2.

McDonald 1985 [13]

Cross sectional

n = 8

Group = NV

Age = 4w-6 months

Procedure: Binocular acuity card procedure

Range stimuli: 0.4–24 cpd (octave steps)

Threshold used: Finest grating that infant can see

Viewing distance: 36 ± 3 cm from center

% Successful: 100%

Test duration: 3–5 minutes

See Fig. 2.

Sokol 1985 [14]

Cross sectional

n = 26

Group = NV

Age = 3 months

Procedure: Binocular VEP and FPL

Range stimuli: 0.31,0.62,1.25, 2.5 cpd

Threshold used: 55% and 70% FPL and VEP lat + amp

% successful: 65%

See Fig. 2.

Preston 1987 [15]

Cross sectional

n = 20

Group = VI

Age = 2–8 months

Procedure: Mono- and binocular acuity card procedure and FPL

Range stimuli: 0.2–2.0 cpd (half octave steps)

Threshold used: Finest grating that infant can see

Viewing distance: 33 ± 3 cm

%Successful: 100% (mono- and binocular) 83% monocular FPL

Test duration: 8 minutes

10/20 subjects were identified as having subnormal acuity on at least one test (binocular, left or right eye). Acuity card procedure is validated for use in patients.

Kohl 1988 [16]

Longitudinal study

n = 18

Group = NV

Age = 12–24 months

Procedure: Mono- and binocular acuity card procedure

Range stimuli: 20/25-20/3200 (octave steps)

Threshold used: Finest grating that infant can see.

Viewing distance: 34 cm

%Successful: Mean testable 12–24 month group 79.6% lower than 90% testable for the 0–12 month old group.

See Fig. 2.

Salomao 1995 [17]

Cross sectional

n = 646

Group = NV

Age = 0–36 months

Procedure: Monocular and binocular TAC

Range stimuli: 0.23–38 cpd (half-octave steps). Start card 0.44 cpd 1–6 months, 1.3 cpd 10–18 months, 2.4 cpd >20 months

Threshold used: Staircase. Last card with 2 correct responses.

Viewing distance: 0–6 m: 38 cm; >6 months 57 cm.

% Successful: 99.3% (binocular) 96.2% (monocular)

Duration: 13 min. for one binocular and two monocular measurements

See Fig. 2.

Neu 1997

Cross sectional

n = 210

Group = NV

Age = 1–6 years

Procedure: Monocular TAC, KAC (resolution acuity) and C-test (recognition acuity)

Range stimuli: TAC: 0.32–0.38c/cm (half-octave steps), KAC: 0.40–49.2 c/cm, C-test: 0.1–1.4 (decimal)

Distance: TAC and KAC: 38, 55 and 84 cm; C-test: 40 cm

Threshold used: TAC as above (Salomao); C-test (3/4) 75%

% Successful: TAC 40% < 2y; 96% 2-4y;

See Fig. 2.

C-test gives lower acuity estimates than TAC and KAC and has higher sensitivity of the C-test for detecting uncorrected refractive errors.

Jones 2014 [19]

Cross sectional

n = 30

Group = NV

Age = 2.6–12.7 months

Procedure: Binocular validation of computerized acuity card procedure using an eye tracker (ACTIVE)

Range stimuli: 0.18–12.5 cpd (KIAC), ACTIVE started at 0.36 cpd and used the same staircase procedure as TIAC

Distance: 38 cm (KIAC) and 84 cm (ACTIVE)

Threshold used: ACTIVE 33.3% (up2-down 1 staircase)

% Successful: 100%

ACTIVE acuities fell within the 90% range of TAC acuity norms.

In 101 s a reliable VA could be obtained. Test-retest data showed difference of 0.04 octaves, which is very small. Larger study needed to collect norms.

Jones 2015 [20]

Cross sectional

n = 55

Group = NV

Age = 2.6–12.7 months

Procedure: Binocular ACTIVE (see above)

Range stimuli: see above

Threshold used: 33.3% and 70.7%

This paper stresses the importance of using a low threshold (<50%) in infants or max correct response to assess perceptual sensitivity.