Calibration of Hirschber Test Photographs under Clinical Conditions

Quantitative measurement of horizontal strabismus with digital photography

“…Applying the deviation angle to an automated and computerized system has been investigated for years. [2][3][4][5][10][11][12] Usually the Hirschberg ratio (HR) is used, but high errors have been reported, especially with increased strabismus angles. 4,11,13,14,17 Scholarly work has reported substantial variation in Hirschberg ratio values.…”

“…This study demonstrates that the best-fit function of the relation between them is in fact not linear, but sigmoid, as shown in Figure 3. Brodie 2,19 and DeRespinis and colleagues 10 have also discussed the nonlinearity of that function. We therefore suggest using the term Hirschberg function in this context.…”

Hemispherotomy can cause post-operative strabismus

“…The examiner held a pen light at a position about 50 cm away from both eyes and took a picture from the front side [15]. The examiner measured the corneal reflex positions and divided them into three levels [16]. Levels 1-3 were approximately 15 degrees, 30 degrees, and 45 degrees, respectively [17].…”

Assessment of binocular alignment using the three-dimensional Strabismus Photo Analyzer

“…However, according to previous studies, the Hirschberg ratio varies from 7 to 16° (12 to 28 prism dioptres (PD))/mm and is subject to inter-individual variability of more than ±20% 2–10. The major limitations of the Hirschberg ratio are that the true angle of deviation has a non-linear correlation with the reflex displacement, the measurements of reflex displacement are valid only along a true frontal plane, which is examiner-dependent,3 and the angle κ has to be adjusted 8 9…”