The 'Mirror Test' for Estimating Visual Acuity in Infants
The 'Mirror Test' for Estimating Visual Acuity 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=0.69, p<0.0005) and with age (R=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=0.86, p<0.0005; logistic regression of log mirror distance vs log age, R=0.88, p<0.0005), and both retained independent significance in a multivariate model.
Assessing visual acuity in infants may be important in early detection of treatable conditions that may cause irreversible amblyopia if missed, such as cataract or high refractive error. Such an assessment is challenging, since infants cannot communicate what they are seeing. Face recognition is not routinely ascertained, even in those who can communicate, and its relationships with standard metrics of vision are not well understood.
Acuity card techniques, which are widely used, depend on infants' preference to look at patterns rather than homogeneous fields. These tests require specialist equipment and skills. Infants make differential responses to faces or face-like patterns compared with similarly detailed non-face stimuli. It seems logical to utilise this preference to facilitate rapid acuity assessment in this age group.
We have observed that infants will attend to the reflection of their own faces in a mirror and that attention is lost at progressively greater distances with increasing age. Using only a mirror and the infants' interest in their own reflections, we designed a simple test for infants and compared this with a standard acuity card test.
Abstract and Introduction
Abstract
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=0.69, p<0.0005) and with age (R=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=0.86, p<0.0005; logistic regression of log mirror distance vs log age, R=0.88, p<0.0005), and both retained independent significance in a multivariate model.
Introduction
Assessing visual acuity in infants may be important in early detection of treatable conditions that may cause irreversible amblyopia if missed, such as cataract or high refractive error. Such an assessment is challenging, since infants cannot communicate what they are seeing. Face recognition is not routinely ascertained, even in those who can communicate, and its relationships with standard metrics of vision are not well understood.
Acuity card techniques, which are widely used, depend on infants' preference to look at patterns rather than homogeneous fields. These tests require specialist equipment and skills. Infants make differential responses to faces or face-like patterns compared with similarly detailed non-face stimuli. It seems logical to utilise this preference to facilitate rapid acuity assessment in this age group.
We have observed that infants will attend to the reflection of their own faces in a mirror and that attention is lost at progressively greater distances with increasing age. Using only a mirror and the infants' interest in their own reflections, we designed a simple test for infants and compared this with a standard acuity card test.
