Synchronization of a Removable Optical Element with an Eye Tracker: Test Case for Heterophoria Measurement

Abstract

Heterophoria describes the deviation of the optical axes in the absence of binocular fusion. Eye trackers (ET) can provide an objective assessment but are not broadly used clinically. We examined the feasibility of combining an infrared (IR) passfilter, IR detector, and an off-the-shelf ET. The proposed setup was validated against the broadly used cover test (CT). Furthermore, the setup was used to examine whether testing conditions can affect the measurements. Methods: An IR detector was attached to a handheld IR-pass filter that blocks visible light to provide occlusion while passing IR light for eye tracking. The detector senses the IR illumination of the eye tracker, creating a recordable signal of the occluder position synchronized with eye positions acquired by the SMI Red250 tracker. The mean of three measurements of each condition, three versus ten seconds occlusion, the occluded eye, and ET versus CT results were compared using the Wilcoxon test, correlation and Bland and Altman plots. Differences between measurements that were within 2 were considered clinically insignificant. Results: Thirty normally-sighted subjects (mean age 24.50 ± 2.20, range 20-28) with heterophoria ranging between 14 exophoria and 4 esophoria were recruited. There was no significant difference between the occluded eyes. However, there was a difference between 3 and 10 seconds' cover duration. The CT data were more similar to the 10 seconds cover duration, although differences were less than the clinical resolution of 2. Conclusions: An inexpensive off-the-shelf ET can be used to measure heterophoria with controlled testing parameters. Translational Relevance: Our study demonstrated a robust technique for synchronization of an optical element such as an IR cover, with an off-the-shelf commercial eye tracker. The synchronization of optical elements with eye tracking, which has been described here for heterophoria, can be adapted for other clinical measurements.

Eye tracking in optometry: A systematic review

“…Eye movement data were collected when taking measurements at the near-point of convergence or vergence ( 38 ; 63 ; 86 ; 97 ). Some studies even used technology to perform automated measurements of phorias and heterophorias and determine the influence of age on adaptation to disparity ( 8 ; 41 ; 78 , 77 , 76 ).…”

“…Eye movement data were collected when taking measurements at the near-point of convergence or vergence (Feil et al, 2017;Kim et al, 2022;Namaeh et al, 2020;Ramakrishnan & Stevenson, 2020). Some studies even used technology to perform automated measurements of phorias and heterophorias and determine the influence of age on adaptation to disparity (Alvarez et al, 2017;Gantz & Caspi, 2020;Mestre et al, 2017Mestre et al, , 2018Mestre et al, , 2021.…”

Comparative Analysis of Strabismus Measurement Using a Video Oculagraphy System and Alternate Prism Cover Test

“…ET and VOG are currently used in various areas associated with visual functioning, including nystagmus, 6–8 oculomotricity, 9–14 contrast sensitivity, 15 visual acuity, 15 pupillography, 16 cyclotorsion, 17,18 and primarily for detecting and/or quantifying ocular misalignment, whether it be heterophoria 19–24 or heterotropia 25–52 …”

“…ET and VOG are currently used in various areas associated with visual functioning, including nystagmus, [6][7][8] oculomotricity, [9][10][11][12][13][14] contrast sensitivity, 15 visual acuity, 15 pupillography, 16 cyclotorsion, 17,18 and primarily for detecting and/or quantifying ocular misalignment, whether it be heterophoria [19][20][21][22][23][24] or heterotropia. In recent years, various investigations have compared the measurement of strabismus using APCT and VOG, showing that both measurements are interchangeable due to the high precision of the technology.…”

Do standard optometric measures predict binocular coordination during reading?

“…Technical instrumentation allows for very precise objective measurement of the individual oculomotor behavior (Gantz & Caspi, 2020;Jainta & Joss, 2019;Kim, Vicci, Granger-Donetti, & Alvarez, 2011). In clinical optometric and ophthalmologic settings, however, methods that need charts, an experienced examiner and which rely mostly on the answers and perceptions of the patient are usually applied to assess individual binocular status (Howarth & Heron, 2000;Hussaindeen et al, 2015;Schroth, 2012;Wajuihian, 2018).…”