Name: using an automated hirschberg test app to evaluate ocular alignment
Uploaded: 2020-03-24T15:00:00
Description: Watch this Scientific Journal Video about Using an Automated Hirschberg Test App to Evaluate Ocular Alignment at JoVE.com

This work was supported in part by NIH grant R44EY025902 and by the Mass Eye &#38; Ear Curing Kids Grant.

This study was conducted in accordance with the tenets of the Declaration of Helsinki, at Schepens Eye Research Institute (Boston, MA) and Spaulding Rehabilitation Hospital (Boston, MA). Informed consent was obtained from all the participants. The study was approved by the local institutional review boards of Mass Eye and Ear (Boston, MA).
NOTE: Patient inclusion criteria were prior diagnosis of horizontal strabismus (constant or intermittent exotropia or esotropia) and no other visual impairm...

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A person without professional training can use the EyeTurn app to capture pictures of the eyes and obtain ocular alignment measurements, which might be interpreted by an eye care specialist onsite or remotely. The app only provides magnitude of the misalignment, rather than any interpretation or diagnosis. Eye care professionals such as optometrists or ophthalmologists should determine if the misalignment is significant or not, and make a diagnosis after considering other factors including the conditions under which the ...

Measurement of eye alignment is frequently performed in vision care clinics. Cover test with prism neutralization is the commonly used clinical method for quantifying the degree of eye misalignment (strabismus). This method requires a high degree of training and experience. Accurate measurement becomes more challenging when patients cannot fully engage in the exam such as young children1, individuals with brain injuries or stroke2, or developmental disabilities3. Furthermore, there is a need for ocular alignment testing in school screening, because strabismus develops during childhood in an estimated 5&#8722;8% of the US population4, and is a substantial risk factor for amblyopia with about 30&#8722;40% of cases of amblyopia attributed to strabismus5,6,7. However, school nurses are normally not trained to conduct the standard cover test with prism neutralization for such screening. For non-eye care professionals, an additional challenge in strabismus screening is that intermittent strabismus (misalignment is not always manifested) and smaller magnitudes of misalignment are not visually obvious (&#60;15 prism diopters [&#916;])8.
In an attempt to address the challenges in the detection and measurement of strabismus, we have developed a smartphone app (EyeTurn) that implements and automates the photographic Hirschberg method9 by comparing the displacement of corneal reflections between the eyes. While conventional photographic Hirschberg method has been shown to have good reproducibility in clinics10,11, the cost for dedicated, standalone devices is a barrier for wide adoption. By providing an easy-to-use tool to measure eye alignment with standard smartphones, we hypothesize it will be widely adopted in school vision screening and used by non-eye care professionals. Our previous evaluation studies have shown that the app measurement is consistent with the current clinical standard of prism and alternate cover test12, for strabismus magnitudes of esotropia and exotropia up to 60&#916;. In a pilot school screening study, we also showed that the app can help the school nurse detect children with intermittent exotropia who were missed by standard school vision screening protocols13.
The iOS version of the app is currently available to researchers and clinicians upon request for research purposes. The requesters have thus far included school nurses, pediatric ophthalmologists, optometrists, neuro-ophthalmologists, and strabismus specialists. The purpose of this article is to share the detailed app protocols for using the app to evaluate ocular alignment under different viewing conditions, namely, near and far fixation distance; with and without eye covering to break binocular fusion.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>EyeTurn</td>
			<td>EyeNexo</td>
			<td></td>
			<td>Smartphone app for measureing eye misalignment</td>
		</tr>
	</tbody>
</table>

using an automated hirschberg test app to evaluate ocular alignment

A smartphone app has been developed to perform the automated photographic Hirschberg test for objective measurement of ocular misalignment. By computing the difference in corneal reflection generated by the phone camera flash relative to the iris center based on high resolution images, the app can measure misalignment with a much higher precision than the naked eye performing the Hirschberg test. It has been validated in a previous clinical evaluation study by comparing to the clinical gold standard-prism and alternate cover test. The goal of this article is to describe the testing techniques regarding how to use the app to measure ocular alignment for different fixation distances, without or with cover to break fusion, as well as angle kappa, so that users can use the app to perform equivalent tests typically done in clinic using prisms.

In this work, we describe the protocols to evaluate ocular alignment using a smartphone app that performs the photographic Hirschberg test. The interface of the app is shown in Figure 1. The users can choose to perform cover test or measure a patient with both eyes fixating at a target simultaneously, either at near or far fixation distances. Once the viewing conditions are determined depending on the test purposes, the users can follow the protocols and take...

Watch this Scientific Journal Video about Using an Automated Hirschberg Test App to Evaluate Ocular Alignment at JoVE.com

Using an Automated Hirschberg Test App to Evaluate Ocular Alignment

We present a protocol of using a smartphone app to perform Hirschberg test for measuring manifest and intermittent ocular misalignment (strabismus) under near and far fixation conditions.

A smartphone app has been developed to perform the automated photographic Hirschberg test for objective measurement of ocular misalignment. By computing ...

The mobile app that we have developed can be used to measure strabismus for research or for clinical use. This method, facilitates an easy strabismus measurement, which currently requires extensive training and experience to be performed using only a standard phone camera and the app software. In the app interface, users can choose to perform a cover test or to measure a patient with both eyes fixated at a target simultaneously, at either a near or far fixation distance.To measure tropia, with a single snapshot in with a near fixation, launch the app and set the mode to No Cover. Select Near and position the phone in a landscape orientation about 40 centimeters from the patient at eye level, with the rear camera facing the patient. Instruct the patient to fixate on the flashlight, which should be off at this point.For tests requiring a precise accommodation, paste a fixation target on the back of the phone directly below or above the flashlight. When the patient confirms they are fixating, press the round button to take a snapshot to be analyzed by the app. When the analysis is complete, the app will show the detected limbus boundary, the center of the eye, and the location of the corneal reflection.After verifying that these features have been detected without obvious errors, observe the measurements related to the eye alignment. Then, press the Save button to save the current test in the phone, or press the back arrow button to retest. To measure intermittent ocular misalignment for far fixation in the app, set the mode to Cover Test and select Far.Hold the phone in a landscape orientation, about 40 centimeters from the patient at eye level with the flash camera positioned between the patient's eyes. Instruct the patient to look just above the phone, to a target about six meters away. Have the patient cover one eye and press the round button, the app will begin the detection.While making sure that the patient is fixating properly, have them quickly remove the occlusion. The app will automatically take a picture as soon as the occlusion is removed. When the analysis is complete, the app will show the detected limbus boundary, the center of the eye, and the location of the corneal reflection.After verifying that these features are detected without obvious errors, review the measurement outcomes for the eye alignment in prism diopters, before saving the data or repeating the test. For Angle Kappa measurement in the app, select measure Kappa angle. Position the phone in a landscape orientation about 40 centimeters from the patient at eye level, and instruct the patient to use the eye to be tested to fixate on the flashlight while covering the other eye.While making sure the patient is fixating properly, tap the round button to take a snapshot, which will be analyzed by the app. When the analysis is complete, the app will show the detected limbus boundary, the center of the eye, and location of the corneal reflection. After verifying that these features are detected without obvious errors, view the measurement outcomes for Kappa angle in degrees.In this representative analysis, the limbus boundaries of the two eyes and the corneal reflection of the flashlight, were detected correctly, suggesting that the ocular alignment measure is not subject to Image Analysis error. In this particular case, the patient had left exotropia as is obvious from the larger corneal reflection offset in the left eye. The app did not report which eye was deviated however, because in cases of a small strabismus angle and unknown Kappa angle, it would be unreliable for the app to determine the deviated eye.For comparison, here an example without strabismus is shown. In this analysis, erroneous limbus detection can be observed. While the detection of the corneal reflection is correct, the green circle clearly does not match the limbus boundary, indicating that the test should be repeated.In this analysis of 14 subjects, 10 subjects exhibited exotropia and four subjects presented with exotropia. Linear regression analysis, revealed that the eye measurements of the strabismus angles, were consistent with clinical cover test measurements. When using the app, there are two important things to keep in mind.One, set the cover test and the fixation mode correctly for each specific test. Two, check if the eye feature detection is correct. The app only allows strabismus measurement and it doesn't give a diagnosis.Clinicians will need to combine the ocular measurement with other vision measurements to make a diagnosis.

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