The authors have declared that no competing interests exist.
This study investigated the feasibility of using three-dimensional (3D) technology as a multi-functional visual stimulus to assist the clinical eye exam. Specifically, we examined: (1) whether the receding movement of a 3D fixation target into distance could relax the accommodation of non-cycloplegic hyperopic subjects so that accurate refraction measurements could be achieved; (2) the feasibility of using the left-eye and right-eye images from the 3D monitor as the light source to perform swinging-flashlight pupil tests; and (3) the implementation of 3D technology to interrupt the binocular visual/motor fusion as required for the clinical cover test to identify strabismus.
Using a 3D TV to provide visual stimuli and a photoscreening (PS) device, near-infrared (NIR) eye images were acquired and analyzed for each of the three objectives. The result of accommodation test showed that with visual stimuli, the maximal hyperopic refractions could more accurately suggest the patients’ true refractions and the more hyperopic patients responded more to the 3D projected distance. However the very mild hyperopia did not show significant response. The pilot tests also showed distinguishable normal and abnormal pupillary responses with 3D image illumination and also the difference in phoria and tropia in the ocular alignment test using 3D stimuli.
In recent years virtual reality (VR), augmented reality (AR), and various types of 3D-imaging technology have blossomed. Stereoscopic technology provides more realistic perception to viewers. In medical practices, it allows more accurate analyses of the morphology, and therefore, helps to improve surgical accuracy, reduce operation times, and enhance patient safety
Children with ocular diseases are often unaware of their impairment until a later stage when treatment is less effective. The importance of regular vision screening is indisputable, but comprehensive examinations for all children would put a significant strain on limited clinical health-care resources. The growing popularity with children in VR and 3D-video games has provided a potentially effective treatment for amblyopia
This pilot study investigated the feasibility of using 3D technology as a multi-functional visual stimulus. A NIR video camera captured eye images of retinal reflex and thereby observed ocular activities as the patient viewed 3D animations. We examined whether the recession of a 3D cartoon character into far distances could relax accommodation in hyperopic patients. We demonstrated the approach of using 3D monitor to perform the swinging flashlight pupil test. Also examined was the application of 3D technology to interrupt the binocular visual/motor fusion as the cover test requires.
The human subjects of this pilot study were 155 volunteers with an age range of 4 to 81 years old who were recruited in their visit at Walmart vision center
All subjects received comprehensive eye exams in the same visiting period.
The first of the three tests in this study is to check the feasibility of relaxing visual accommodation by 3D stimuli. Although the ocular accommodation driven by 3D displays were discussed in many studies
In the clinical testing cohort, we included only hyperopic subjects younger than 35 years of age who had healthy accommodation. Both eyes of the subjects must be hyperopic, their cylinder-refractive error must be less than 1.5 diopters, and the best corrected visual acuity (BCVA) obtained from phorometry or un-corrected distant VA must equal or better than 20/30. Strabismic, amblyopic, and dilated patients were excluded. Only 16 subjects, all between the ages of 5 and 20 years, fulfilled these inclusion requirements.
The 3D animation for this test used a cartoon character dressed in a doctor’s white gown. On the 3D screen the character was presented which then attempted to walk slowly from its location to three farther distances. To capture the attention of the patient, at each of the four standing distances, the cartoon figure stood still for 3 seconds with a flashing or spinning object on his hands. The first standing position was at the screen distance of 75-cm, which corresponds to 1.3 diopters. The farthest distance was 6 m calculated by assuming a 60-mm inter-pupillary distance (IPD). The fixation target size at furthest distances, was equivalent to the letter size in 20/400 lines of the eye chart.
To determine the patient’s accommodation activity, we used a NIR photoscreening (PS) device, the Dynamic Ocular Evaluation System (DOES)
The second test simulates the clinical swinging-flashlight pupil-function test. Since 3D technology can deliver independent left- and right-eye images to produce stereoscopic perception, this feature was used to illuminate each pupil independently with different levels of visible light while the pupil sizes of both the direct-illuminated and the consensual eyes were recorded with infrared camera in 20 frames per second.
The 3D screen first presented a dark screen for three seconds for spontaneous dilation. Then a bright and large cartoon figure of about 1/3 of the screen area, popped up, and the image on the screen illuminated the eyes for half of a second. Three seconds later this cartoon figure reappeared visible for only the right eye. Another three seconds later the pop-up happening was repeated for only the left eye. The illumination timing is illustrated in
Strabismus is one of the important screening targets that link to amblyopia development. The Hirschberg method is a simple and objective test to identify the binocular mis-alignment. It measures the locations of corneal light reflections. Any asymmetry between the two eyes or significant deviation from the pupil centers indicates a potential ocular mis-alignment. Although this method is easy to implement, the diagnostics is not as reliable when compared to the subjective cover-uncover test, which actively disturbs the binocular vision to stimulate and reveal the abnormality
In subjects with very mild hyperopia (<+1 diopter) including J, L, M, N, and O, the 3D figure and its distance did not appear to be affective to their accommodation. They appeared to accommodate with small magnitude constantly.
For healthy eyes, both the muscle and stroma of the iris and the afferent and efferent neurological pathways of either eye are well, if either eye is illuminated, the pupillary response is such that both pupils contract equally. The pupil-test results are shown as the pupillograms in
Cover and uncover effects took place when the target moved across the boundaries between monocular and binocular viewing regions. These are indicated with small arrows in the plots. For the results of a typical normal case, both cover and uncover of either eyes’ should not result to any significant re-alignment (deviation) from the track. Both eyes followed the target smoothly without being disturbed by the cover and uncover destructions.
Phoria is a deviation that occurs when fusional stimuli are absent. For binocular viewing, both eyes’ foveas are aligned to the fixation target. When one eye is suddenly covered, the (relative) alignment is assumed appropriately by the covered eye. However, the eye will gradually relax and drift away from the initial projection. When a covered-eye was uncovered, this eye would quickly re-align (its fovea) to the visual stimulus to form motor fusion and reclaim binocular vision. Therefore, the uncover shifting is more noticeable than the cover drifting.
One thing to be addressed is that the clinic cover test is commonly performed for both near-fixation (~40cm) and distant- fixation. Since this particular experiment was performed only at a fixed distance of 50 cm, the demanded vergence for binocular viewing was equivalent to ~6 prisms of angle for eyes with inter-pupillary distance (IPD) of 6 cm. If the cover test was performed with a distant fixation, the degree of phoria is likely reduced. Generally, if patient’s binocular vision is not compromised, a small degree of phoria is still considered normal.
For a tropia, the binocular viewing motor fusion is not present. When a viewing target is presented to a tropia, only one eye is aligned to the target whether it is a right-eye, left-eye, or alternating between the two eyes.
The ability of 3D technology to deliver independent binocular visual stimuli was investigated as a versatile clinical tool for evaluating binocular vision health. Of the large number of potential applications, three specific tests were conferred in this study.
We first examined the prospect of using the 3D images to relax hyperopia’s accommodation so that the accurate refraction status can be assessed objectively without using sedation eye drops. Our result with a small number of subjects shows that stereoscopic images appeared to relax the accommodation in patients with hyperopia greater than 1 diopter. Though the result is promising, the experiment requires a larger number of participants with more extensive hyperopic range to gain more solid data. During a typical cartoon viewing, children are usually much engaged in the story, and their eyes follow the main character intensively. The refraction measurement could be performed multiple times to study the optimal stimulation to assess the maximal hyperopic refraction and reduce the error due to accommodation.
We also investigated the swinging-flashlight pupil-function test by delivering non-synchronous pulses of bright image to the eyes. We showed the pupillogram results of typical normal cases, an anisocoria case, and a case of +RAPD. The typical 3D TV screen was sufficient to provide proper illumination levels for pupil test, and the pupillogram result provided clear indication of the abnormalities. This demonstration showed the use of 3D display to obtain dynamic pupil response to light stimuli, which could also possibly be applied to the assessment of pain, alertness, study of pharmacodynamics, and psychiatry.
Lastly, the cover test was performed with an objective 3D moving-bull-eye-target. We demonstrated a new automatic method of cover-uncover test with the self-calibrated individual’s HR and kappa angle. Results of the normal eyes, the phoria, and the tropia were compared.
There are many advantages in the 3D visual stimuli eye assessment. In additional to having a playful and close-to-natural viewing and testing atmosphere, the use of NIR video prevent the difficulty of observing patients directly in typically dimmed clinic room illumination. Digital results from such applications can be easily stored and evaluated by clinicians at convenient times in high resolution and slow motion if desired, which could reduce stress for both patient and clinician. Digital recording helps to improve quantitative assessment and therefore, diagnostic accuracy. Furthermore, digital data make automatic Computer Aided Diagnosis (CAD) possible to develop and allows establishing database and promoting advance in the Big Data era.
The authors would like to acknowledge the UTRF maturation funding support, the support and consultation from Dr. Palmer and Walmart Vision Center at Tullahoma, Tennessee, and the support of Center for Laser Applications of the University of Tennessee Space Institute.