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Fixation-free assessment of the Hirschberg ratio


Model, D; Eizenman, M; Sturm, V (2010). Fixation-free assessment of the Hirschberg ratio. Investigative Ophthalmology and Visual Science, 51(8):4035-4039.

Abstract

PURPOSE: To describe a novel methodology by which to measure the Hirschberg ratio (HR) in infants. The methodology does not require fixation on specific points, and measurements are made while infants look naturally at a display.

METHODS: The HR is calculated automatically from measurements of the direction of the optical axis, the position of the pupil center, and corneal reflexes in video images from an advanced two-camera eye-tracking system. The performance of the novel fixation-free procedure (FFP) was evaluated in 43 adults by measuring the average difference and the 95% limits of agreement with the standard fixation-based procedure (FBP). Repeatability of the HR measurements was evaluated by assessing the 95% limits of agreement between two independent measurements. Performance of the FFP was also evaluated in five infants.

RESULTS: In adults, the average HR was 12.89 +/- 1.22 degrees/mm for FFP and 12.81 +/- 1.22 degrees/mm for FBP. FFP and FBP measurements were highly correlated (r = 0.95; P < 0.001). The 95% limits of agreement between FFP and FBP were +/-0.86 degrees/mm. The 95% limits of agreement of repeated measurements were +/-0.66 degrees/mm for FFP and +/-0.77 degrees/mm for FBP. In infants, the 95% limits of agreement of repeated measurements by FFP were +/-0.63 degrees/mm.

CONCLUSIONS: In adults, the FFP provides accurate measurements of the HR that are in excellent agreement with measurements by FBP. In infants, measurements of HR by FFP show the same repeatability and consistency.

PURPOSE: To describe a novel methodology by which to measure the Hirschberg ratio (HR) in infants. The methodology does not require fixation on specific points, and measurements are made while infants look naturally at a display.

METHODS: The HR is calculated automatically from measurements of the direction of the optical axis, the position of the pupil center, and corneal reflexes in video images from an advanced two-camera eye-tracking system. The performance of the novel fixation-free procedure (FFP) was evaluated in 43 adults by measuring the average difference and the 95% limits of agreement with the standard fixation-based procedure (FBP). Repeatability of the HR measurements was evaluated by assessing the 95% limits of agreement between two independent measurements. Performance of the FFP was also evaluated in five infants.

RESULTS: In adults, the average HR was 12.89 +/- 1.22 degrees/mm for FFP and 12.81 +/- 1.22 degrees/mm for FBP. FFP and FBP measurements were highly correlated (r = 0.95; P < 0.001). The 95% limits of agreement between FFP and FBP were +/-0.86 degrees/mm. The 95% limits of agreement of repeated measurements were +/-0.66 degrees/mm for FFP and +/-0.77 degrees/mm for FBP. In infants, the 95% limits of agreement of repeated measurements by FFP were +/-0.63 degrees/mm.

CONCLUSIONS: In adults, the FFP provides accurate measurements of the HR that are in excellent agreement with measurements by FBP. In infants, measurements of HR by FFP show the same repeatability and consistency.

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7 citations in Web of Science®
10 citations in Scopus®
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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Hospital Zurich > Ophthalmology Clinic
Dewey Decimal Classification:610 Medicine & health
Language:English
Date:2010
Deposited On:16 Nov 2010 08:43
Last Modified:05 Apr 2016 14:24
Publisher:Association for Research in Vision and Ophthalmology
ISSN:0146-0404
Publisher DOI:10.1167/iovs.09-5014
PubMed ID:20375328
Permanent URL: http://doi.org/10.5167/uzh-38394

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