Semi-Automatic Measurement of Horizontal Angle of Strabismus Using Digital Pictures
Chloé C. Couret; Pierre P. Lebranchu; Guylène G. Le Meur; Alain A. Pechereau
CHU de Nantes
Introduction: To assess the validity of an objective and reproducible method for the measurement of the horizontal angle of deviation of strabismus with a new computer-assisted photographic method in adults and children.
Methods: The method proposed was first validated in patients without strabismus and then in patients with strabismus in a prospective study. It consisted of 3 steps: (1) acquisition of 3 pictures (binocular – monocular right eye and left eye), (2) tracking the nasal limbus, the corneal reflect and the temporal limbus with the mouse on each picture, (3) automatic measurement of the horizontal angle of deviation using innovative software. Each picture was taken twice in primary position at a “conversational distance (approximately 1 meter) with glasses but without any other equipment, and analyzed twice by two independent orthoptists.
Results: 2 populations were studied. 34 adults without strabismus were first included. Then 79 adults and children with strabismus were prospectively included. 4 were excluded because of non-analyzable pictures. The angle of deviation of 4 patients with deep amblyopia was analyzed separately with success using partial data of the non-amblyopic eye. The method provided quick semi-automatic data of the horizontal angle of deviation for both populations with no statistical difference between the two pictures and between the two computer-assisted measurements. The accuracy of the method was between 2 and 5 prism Diopters for both populations.
Discussion: This semi-automatic photographic method is simple, objective, reproducible and reliable for the measurement of the horizontal angle of deviation of strabismus. It is easily used for adults or very young children, for small and large angles, and for patients with deep amblyopia. It can also be used for measuring strabismus under general anesthesia. It provides new data of the angle of deviation of strabismus at a ‘conversational distance’ and has to be considered as a complementary method for measuring strabismus.
Conclusion: This semi-automatic photographic method of measurement of the horizontal angle of deviation of strabismus using digital pictures is an easy, quick and cheap way to measure strabismus in ‘everyday life conditions’ and should be used to standardize measurements for future studies.
References: Barry JC1, Backes A. Limbus versus pupil center for ocular alignment measurement with corneal reflexes. Invest Ophthalmol Vis Sci. 1997 Nov;38(12):2597-607.
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1:307–10.
Group PEDI. Inter-observer reliability of the prism and alternate cover test in children with esotropia. Arch Ophthalmol. 2009;127:59.