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Published on: March 14, 2013
Calibration of the Hirschberg test in human infants
P M Riddell1, L Hainline, I Abramov
1Department of Psychology, Brooklyn College, University of New York 11210.
Insights
The Hirschberg ratio, used to estimate strabismus, remains consistent from infancy through adulthood. This finding supports using the standard adult Hirschberg ratio for all age groups in clinical assessments.
Area of Science:
- Ophthalmology
- Pediatric Ophthalmology
- Strabismus Research
Background:
- The Hirschberg ratio quantifies the relationship between eye alignment and corneal light reflex position.
- The adult Hirschberg ratio (approx. 22 prism diopters/mm) is commonly used, but its applicability across all ages, especially infants, is not well-established.
- Infant eye structures undergo significant growth, potentially influencing the Hirschberg ratio during the first year of life.
Purpose of the Study:
- To empirically determine if the adult Hirschberg ratio is suitable for all age groups.
- To investigate potential age-related changes in the Hirschberg ratio during infancy.
- To measure angle lambda in infants and adults to understand its relationship with eye growth.
Main Methods:
- Photographic techniques were employed to calculate the Hirschberg ratio in 323 infants (27-365 days old) and 10 adults.
- Angle lambda, the angle between the visual axis and the pupillary axis, was also measured in both infant and adult cohorts.
- Statistical analysis was performed to compare Hirschberg ratios and angle lambda values across different age groups.
Main Results:
- The Hirschberg ratio showed no significant change with age during infancy and was comparable to adult values in both magnitude and variance.
- Angle lambda exhibited a rapid decline from an extrapolated birth value of approximately 8.4 degrees to around 5 degrees by 5 months.
- The observed decrease in angle lambda is presumed to be a consequence of axial eye growth during infancy.
Conclusions:
- The findings support the use of a single, average Hirschberg ratio for estimating the angle of strabismus across all ages.
- The study highlights the importance of considering the dynamic changes in angle lambda during infancy when interpreting Hirschberg test measurements.
- This research provides valuable empirical data for the clinical assessment of strabismus in pediatric populations.
Purpose:
The Hirschberg ratio has been defined as the ratio of the change in angular position of the line of sight to the change in location of the first Purkinje image relative to the pupil center. This study was designed to determine empirically whether the adult value of the Hirschberg ratio (approximately 22 prism diopters/mm) is a suitable value to use for all ages. Because many structures in the eye are growing during the 1st year, it is possible that there could be some change in the Hirschberg ratio during this period.
Methods:
A photographic technique was used to calculate the Hirschberg ratio for 323 infants between the ages of 27 and 365 days and for ten adult subjects. The study also measured angle lambda, the angle between the line of sight and the pupillary axis, in these populations.
Results:
The Hirschberg ratio did not change with age during infancy and was similar for adults and infants both in value and in variance. Angle lambda, however, declined rapidly, from an extrapolated value of about 8.4 degrees at birth to near 5 degrees at 5 months, a change that is assumed to reflect axial growth of the eye.
Conclusions:
The results suggest that the same average Hirschberg ratio can be used to estimate angle of strabismus across age. The change in angle lambda is important to consider when evaluating angle of deviation from measures using the Hirschberg test.
