The Calibration of the Corneal Light Reflex to Estimate the Degree of an Angle of Deviation

Supaporn Tengtrisorn MD*, Sitthi Tangkijwongpaisarn MD*, Somporn Burachokvivat BSc*

Affiliation : * Department of Ophthalmology, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla, Thailand

Objective : To measure the conversion factor for the size of an angle of deviation from the clinical photographs of the corneal light reflex. Material and Method: In this cross-sectional study, 19 normal subjects with 20/20 visual acuity were photographed with a digital camera while staring at targets placed five prism diopters (PD) apart from one another on a screen. The subjects were tested at a distance of 1 meter (m) and 4 m from a screen. Measurement of the corneal light reflex displacement for each fixed target was obtained from the photographs. The calibration of the corneal light reflex displacement in millimeters (mm) against the angle of deviation in PD was then analyzed with repeated measure linear regression analysis.
Results : At 1 m, the values of 0.047 mm/PD and 0.058 mm/PD were obtained as the conversion factor from reflex displacement to deviated angle for the nasal side and temporal side respectively. At 4 m, the values were 0.050 mm/PD and 0.064 mm/PD for the nasal side and the temporal side respectively. There were significant differences between the values obtained at the different distances, regardless of nasal or temporal side.
Conclusion : Conversion factors were presented for estimating the strabismic angle at different distances and gazes. For clinical practice, the use of photographs to estimate the strabismic angle should use different values for different distances and strabismic types.

Keywords : Corneal light reflex, Hirschberg, Photograph, Angle deviation

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