Fixation target position for increased limbus measurement accuracy with AS-OCT
Reviewed by Fiona Rowe

The authors intended to determine the optimal gaze fixation points for lateral rectus and medial rectus muscle insertions using anterior segment - optical coherence tomography (AS-OCT) compared with intraoperative measurements. They recorded 46 lateral and 36 medial rectus muscles from 44 patients (22 male; 22 female) aged 5-83 years. Average intraoperative distance from the limbus to lateral rectus insertion was 6.3 ±0.7mm. With AS-OCT, this was 5.8 ±0.7mm for an inner gaze fixation target and 6.4 ±0.5mm for an outer gaze fixation target. Comparison of intraoperative and OCT measurements showed <1mm difference for 73.9% who fixated their gaze on an inner target and 89.1% for an outer gaze target. Average intraoperative distance from the limbus to medial rectus insertion was 4.9 ±0.6mm. With AS-OCT, this was 4.9 ±0.6mm for an inner gaze fixation target and 5.7 ±0.9mm for an outer gaze fixation target. Comparison of intraoperative and OCT measurements showed <1mm difference for 80.6% who fixated their gaze on an inner target and 58.3% for an outer gaze target. Inner and outer fixation targets were calculated at 30 and 36 degrees respectively. The authors conclude there is better consistency for measurements with outer gaze fixation for lateral rectus, and inner gaze fixation for medial rectus, as appropriate techniques to assess limbus and extraocular muscle insertion distances with AS-OCT.

Effects of the gaze fixation position on AS-OCT measurements of the limbus and extraocular muscle insertion site distance.
Inagaki R, Suzuki H, Haseoka T, et al.
JOURNAL OF PEDIATRIC OPHTHALMOLOGY AND STRABISMUS
2021;58:28-33.