Related Experiment Video
Updated: Jun 18, 2026
An Automated Method for Assessing Visual Acuity in Infants and Toddlers Using an Eye-Tracking System
Published on: March 17, 2023
The 'mirror test' for estimating visual acuity in infants
Richard Bowman1, Daphne L McCulloch, Elizabeth Law
1Royal Hospital for Sick Children, Yorkhill, Glasgow, UK. richardandruthbowman@gmail.com
Insights
Infant fixation distance to their own reflection increases with age and correlates with visual acuity card tests. This simple method could aid in detecting visual impairments in infants.
Area of Science:
- Ophthalmology
- Developmental Pediatrics
- Infant Vision Research
Background:
- Assessing visual function in infants is crucial for early detection of potential impairments.
- Traditional visual acuity testing in infants can be challenging and requires specialized equipment.
Purpose of the Study:
- To investigate the relationship between the distance infants fixate on their own reflections and standard visual acuity card testing.
- To explore the potential of using mirror fixation distance as a novel clinical test for infant visual function.
Main Methods:
- 78 healthy infants under 9 months were observed fixating their reflections in a mirror.
- The distance at which fixation was lost was recorded.
- Binocular visual acuities were assessed using the Teller acuity card procedure.
Main Results:
- Mirror fixation distance showed a strong positive correlation with infant age (R²=0.73, p<0.0005) and Teller acuity (R²=0.69, p<0.0005).
- Using logarithmic scales and logistic growth functions, correlations improved (log mirror distance vs log Teller acuity, R²=0.86; log mirror distance vs log age, R²=0.88).
- Both age and Teller acuity independently predicted mirror fixation distance in multivariate analysis.
Conclusions:
- Infant mirror fixation distance increases with age and correlates well with visual acuity card results.
- The simplicity and portability of this method suggest its utility as an additional tool for screening infant visual function.
- This technique offers a promising, non-invasive approach for assessing visual development in infants.
Objective:
The authors aimed to investigate the association between the distance at which infants fixate their own reflections and visual acuity card testing, and to determine whether this could form the basis of a new clinical test of visual function in infants.
Methods:
78 healthy infants under 9 months of age (range 1-266 days, mean 56.5+/-64SD) were recruited and held close to a mirror such that they attended their own reflections. The distance from the mirror was increased until they no longer held fixation. Binocular acuities were tested with the Teller acuity card procedure.
Results:
Reliability was rated 'good' in 58 and 60 infants respectively, for mirror distances and for the acuity cards. Data were also included for moderate reliability (n=20 and 14 respectively). The mean mirror distance was 54.9 cm (range 13.5-178, SD=42.8). The mean Teller acuity was 2.19 cycles per degree (range 0.2-14.5, SD=2.8). (Snellen equivalent 6/82, range 6/900-6/12). Mirror distance showed linear correlation with both Teller acuity (R(2)=0.69, p<0.0005) and with age (R(2)=0.73, p<0.0005) by univariate analysis. Using multivariate analysis, only age retained significance. Using logarithmic scales and a logistic growth function for age, correlations were stronger (log mirror distance vs log Teller acuity, R(2)=0.86, p<0.0005; logistic regression of log mirror distance vs log age, R(2)=0.88, p<0.0005), and both retained independent significance in a multivariate model.
Conclusion:
Mirror fixation distance increases with age in infants and has a good correlation with acuity card results. The portability and ease of use would make it a useful additional tool for detecting impaired visual function in infants.
