This article is from the RightEye Whitepaper: Automated Sensorimotor System for Testing Binocular Vision Issues.
Symptoms associated with Binocular Vision Disorder are numerous and varied. Common symptoms include headache, blurry vision, visual fatigue and tearing eyes. Binocular vision is also important for the ability to perceive depth and relationships between objects, such as seeing which object is closer than another.
Secondary symptoms may include overall fatigue, and inability to concentrate, irritability, short attention span, burning of the eyes, motion sickness, vertigo and a general “poor performance” on tasks.
While a basic sensorimotor exam, such as “follow the finger, is typically part of an eye exam, eye care providers many times do not perform additional exams, such as vergence testing. Since approximately 30% of patients display vergence problems not present in basic H-pattern or follow and fix testing, many times ECPs are overlooking these conditions. Convergence insufficiency is one of the most prevalent conditions clinicians find, and it is highly treatable.
With an automated Binocular Vision test, such as the RightEye Sensorimotor exam, eye care providers have a quantifiable, reliable, step-by-step test and process that provides easy-to-understand results to guide towards next steps.
The process takes approximately 30 seconds for the basic exam and approximately 2 to 3 minutes for the full exam. The exam process can be conducted by a technician under the assignment of “general guidance” by The Centers for Medicare and Medicaid Services.
What Tests Clinicians Use with an Automated Binocular Vision Test
Screening Mode (Average Test Duration: 30-60 seconds)
- 9-Point Motor Function Test
- Near Point of Convergence Test
Exam Mode (Average Test Duration: 5-10 minutes)
- 9-Point Motor Function test
- Cardinal Gaze Test
- Four-Dot Test
- Fixation Stability Test
- Horizontal Smooth Pursuits Test
The following section will describe each test in the sensorimotor exam along with its purpose, how it works, and what the test measures.
9-Point Motor Function Test
This test measures ocular alignment in multiple fields of gaze by measuring each eye’s location as they look at a red dot placed in all 9 cardinal gaze positions. The test takes approximately 18 seconds and provides information on oculomotor behavior and binocular vision.
The points of gaze are located throughout the screen to measure the six muscles of the eye as they move around the three axis. Using the RightEye eye-tracking technology, a clinician can precisely see, record and quantify where the patient is looking.
Various oculomotor calculations are derived from the 9-Point motor function test, including: Distance between the eyes, measured in millimeters, also referred to as interpupillary distance is measured from the center of the left and right pupils. Pupil diameter is the average, standard deviation, and range of the pupil size, measured in millimeters.
Of particular interest for examination of binocular vision testing and oculomotor function is both the disparity and displacement metrics. Disparity is a measure of the distance between the left eye gaze point (light blue dot) and the right eye gaze point (dark blue dot) at each of the gaze locations and reported in diopters. Finally, horizontal, and vertical displacement for each eye (left and right), at each target point, is conveniently reported in diopters.
The 9-Point Motor Function Test has been evaluated for its reliability, that is the consistency of results, which according to gold standards (the Cronbach Alpha; Fleiss, 1986) has passed with a rating of “very good” (CA = .831). The test has also been examined to ensure it provides similar results to the Cover test at near. When comparing the Cover test results to 9-Point Motor Function test results there are no statistically significant differences in either the left or right eye results. Therefore, the output can be used inform doctors as to alignment, or misalignment of the eyes. Furthermore, the test quantifies the misalignment in each point of cardinal gaze for each eye. Hence a doctor can see and quantify the extend of alignment and determine if the patient has orthophoric (normal) or non-orthophoric (abnormal) alignment.
To determine if a patient has a binocular vision issue the doctor looks to see if:
- On any of the targets BOTH eyes appear outside of the target or,
- If one eye appears outside of the target on 2 or more targets
If either or both results occur, then the doctor can reliably recommend the full exam (if this was done during the screener).
If this was part of the full exam (as the 9-Point motor function is included in both examination steps) then the doctor can use the results to assist in their conclusion.
Near Point of Vergence Ruler Test
This test is used to determine the ability of the patient’s eyes to converge on an object that is near. Then to compare those values to normative standards, resulting in either normal convergence, or convergence insufficiency or (with other tests) divergence excess if abnormal
The Consists of a measurement for a “break point” and a “recovery point.” Break point refers to when the eyes no longer maintain a fusion on the target and effectively move apart, or “break” away from each other. Recovery refers to the person’s ability to voluntarily converge back on the target point and “recover” fusion. The break point occurs when the target is moving towards the patient. The recovery point occurs after the break point and when the target is moving away from the patient.
The break and recovery points can be reported in centimeters or inches. According to research by Cooper and Jamal (2012), the typical break in convergence ruler test is greater than 4 inches (or 10 centimeters). The typical recovery point is less than 5 inches or (12 centimeters).
The Vergence Ruler Test has been evaluated for its reliability that is the consistency of results, which according to gold standards (the Cronbach Alpha; Fleiss, 1986) has passed with a rating of “very good” (CA = .850 for break point; 0.851 for recovery point).
As the Vergence Ruler is a current gold standard for testing vergence there is no need for validity testing. There is however a need for testing the consistency of results from one practitioner to another. This testing is referred to as “generalizability” testing. Therefore, a sample of 50 persons were tested three times by three different optometry doctors. Results revealed no significant differences between the testers (p > 0.05). Therefore, the tool is deemed generalizable in that, with proper training, it generates the same results on a patient, by different testers.
It is important to note that the results of the Convergence Ruler Test are not the only factor in considering convergence problems. The test is however, one piece of a puzzle that the doctor can use to assist in their conclusion. More on this in the diagnosis section.
Cardinal Gaze Test
This test uses one eye at a time, to examine the oculomotor movements in each of the cardinal gaze positions. The test, which takes about 10 seconds, begins with the patient looking at the central point of gaze and the, when directed by an arrow, moving their eyes quickly and accurately to one of the eight cardinal gaze positions.
Similar to the 9-Point Motor Function test, the Cardinal Gaze Position Test measures the cardinal positions of gaze, at near. The points of gaze are located throughout the screen to measure the six muscles of the eye as they move around the three axes. It differs from the 9-Point test in that it assesses one eye at a time, therefore being a monocular test. It also differs in that it tests the movement of the eyes from a central point of gaze each time. Furthermore, different calculations are made to provide additional insights into the dynamic movement of the eyes during the Cardinal Gaze Position Test compared to the 9-Point Motor Function test.
There are five different calculations for the Cardinal Gaze Position Test, these include saccadic latency, visual reaction speed, cardinal gaze position, disparity, and accuracy. Saccadic latency is measured in millisecond and refers to the time it took for the individual’s eye to move off the central position once the arrow is (randomly) generated. Visual Reaction Speed is also measured in milliseconds and refers to the time it took for the eye to travel the distance from the central position of gaze to the peripheral position of gaze. Cardinal Gaze Position is a measure from 1 to 8 and refers to the rank order of each peripheral gaze position in terms of speed. The fastest position is labeled as 1 and the slowest is 8. Accuracy is a non-directional metric that measures the distance the eye is from the target, in diopters.
The Cardinal Gaze Position Test has been evaluated for its reliability, that is the consistency of results, which according to gold standards (the Cronbach Alpha; Fleiss, 1986) has passed with a rating of “very good” (CA = .812). The test has also been examined to ensure it provides similar results to the Cover test at near. When comparing the Cover test results to Cardinal Gaze Position test results there are no statistically significant differences in either the left or right eye results. Therefore, the output can be used inform doctors as to dynamic movement of the eye to assess alignment, or misalignment. Furthermore, the test quantifies the misalignment in each point of cardinal gaze for each eye. Hence a doctor can see and quantify the extend of alignment and determine if the patient has orthophoric (normal) or non-orthophoric (abnormal) alignment.
To determine if a patient has a binocular vision issue the doctor looks to see if:
- The eye extends well beyond the age based normative data
- If the accuracy of the eye shows large numbers of diopters, indicating the eye was far from the target
RELATED POST: Top 7 Reasons to Automate Sensorimotor Eye Exams
4-Dot Fusion Test
Consists of four dots, a red dot positioned at the top, a green dot on the horizontal left and right and a white dot at the bottom. When using red/green glasses, the colors should remain the same except for the bottom white color that will turn either green or red. If this is what the patient identifies then they have normal binocular single vision.
The purpose of the 4-Dot Fusion test is to assess a patient’s degree of binocular vision, that is when assessing the function of the eyes to work in coordination. More specifically, it tests for fusion, suppression, and anomalous retinal correspondence (ARC).
The 4-Dot fusion test has been evaluated for its reliability, that is the consistency of results, which according to gold standards (the Cronbach Alpha; Fleiss, 1986) has passed with a rating of “excellent” (CA = .929)
The Four Dot Fusion Test has also been examined for validity. When comparing the RightEye Four Dot Fusion (digital) Test to the clinical gold standard, Worth Four Dot Fusion test, results revealed no significant differences (p > 0.05). Therefore, these results indicate that the two tests are equivalent in their output and the Four Dot Fusion test can be used in replacement of the Worth Four Dot test.
Fixation Stability Test
This test measures how stable the eye(s) remain(s) in fixed target locations over a short period of time. Testing the neurological stability of fixation gaze given “fixation is an afferent and motor process: retinal sensory afferents produce efferent signals towards the extraocular muscles in order to maintain eye position. This can imply visual impairment, or eye diseases such as macular degeneration or scatoma.
The test presents a one-degree cross for 7-seconds in the center of the screen. The user is instructed to press a key to begin the test once they are looking at the target.
This test was added to the Sensorimotor suite of tests as it provides additional information on the alignment of the eyes when they are still (fixating) at middle distance. The report also provides head tilt in relation to eyes which illustrates compensatory behaviors that may develop from Binocular Vision Disorders. Furthermore, eye dominance, indicating which eye is “stronger” and horizontal and vertical deviations for ocular alignment issues are reported.
Horizontal Smooth Pursuit Test
This test measures a user’s ability to track an object in a horizontal straight line. This can provide further information about the degree of damage of the frontal white matter and the dorsolateral prefrontal cortex – areas that are critical to assess in concussion and TBI individuals (Bloom, 2013; Contreras et al., 2008; Contreras et al., 2011). Again, these tests determine if the user has a normal or an abnormal response.
In these tests, the user follows a horizontal target in each for approximately 10 seconds (back and forth to starting position). This is a digitized version of the Vestibular Ocular Motor Screening (VOMS) a clinical protocol used as part of a series of tests to assess for neurological deficits. The RightEye test for horizontal and vertical smooth pursuit is highly quantifiable, measurable, repeatable and specific.
This test was added to the Sensorimotor suite of tests as it provides additional information on the movement of the eyes in the horizontal plane. Specifically, if the eyes deviate up or down from the target when moving from central gaze (hyper/hypo) and if the eyes are tracking on-target, behind or in front of the target, indicating tracking issues associated with eso or exo gaze. As most deviations are found on the horizontal plane a horizontal test was deemed an appropriate add-on for the Sensorimotor suite of full-exam tests.
Convergence Insufficiency Symptom Survey (CISS)
While technically not a “test”, the CISS was developed to identify convergence insufficiency and has been used in several treatment trials such as the Convergence Insufficiency Treatment Trial (Borsting, et al., 2003). The CISS consists of 14 questions where patients answer on a scale of “never,” “infrequently,” “sometimes,” “fairly often,” and “always.” These responses are numbered and from 0 to 4 respectively. A person can score a minimum score of zero and a maximum of fifty-six.
The CISS has been tested for reliability and has found to be highly reliable (intraclass correlation = 0.77,95% confidence interval). The CISS has also been tested for discriminate validity, or the ability to “discriminate” between those who have convergence insufficiency problems and those who do not. The results of discriminate validity show that it is highly discriminatory using the score of equal to or greater than 16. In other words, if a person scores below 16 on the CISS they are highly likely to have normal range of convergence. Those who score at or above 16 are likely to have convergence insufficiency. These results were significantly different (p < 0.0001), and 96% sensitivity and 88% specificity.
Therefore, the results of Borsting et al. (2003), show that the CISS is a valid and reliable instrument to use as an outcome measure concerning convergence insufficiency. In the same manner as all prior tests, the CISS is one piece of the puzzle and when taken with other information can help the doctor assess a patient’s binocular vision status. Should a convergence insufficiency result be found there is a solution, and this is discussed in the diagnosis section.
The RightEye Research and Development (R&D) Department in collaboration with external research university partners have tested and validated the RightEye Sensorimotor product. Various optometry practices across the United States, have been involved in testing, to include clinical examinations such as cover tests and RightEye Sensorimotor tests. Product testing was conducted at three sites from June 30th to September 9th, 2021. Analysis of the data was conducted independently of RightEye with external university partners.