The overall goal of this procedure is to quantify interocular suppression in patients with amblyopia and treat this suppression where appropriate. This is accomplished by first familiarizing the observer with the psychophysical task used to assess interocular suppression and providing careful instructions to ensure that the test is completed correctly. Next, ensure that the images shown separately to each eye through the goggle apparatus are correctly aligned so that they are perceived as superimposed by the observer.
The observer then completes a series of trials during which they judge the direction of groups of moving dots presented separately to each eye. This provides a measure of interocular suppression. The final step is to use a portable iPod device to systematically reduce interocular suppression using a video game training paradigm.
This step can improve a range of visual functions in some observers, but should only be undertaken with the supervision of a qualified clinician. Ultimately, this technique provides a new approach to the measurement of suppression and may provide the basis for a novel treatment of amblyopia in both adults and children. The main advantage of this technique over existing methods for assessing suppression such as the W four Lights test and the bagi lenses, is that it allows for the level of suppression to be accurately quantified.
Whereas existing tests often only indicate whether suppression is present or absent. This technique can also be used to treat amblyopia in certain patients by reducing the level of interocular suppression over time. Demonstrating the procedure will be Victor Borges, a PhD student from my laboratory Before beginning the measurement of suppression familiarize the patient with the visual stimuli to be used by displaying them on a laptop screen.
Next, fit the goggles to the patient over their spectacles or contact lenses. The screens should sit parallel to the ocular surface and can be adjusted to account for each patient's inter pupillary distance. To begin the suppression assessment, first align the patient's eyes.
The screens will display a black half cross in each eye against a gray screen. Ask the patient to move the half of the cross seen by the amblyopic eye until it lines up with the half seen by the fellow eye using the keyboard. Once the patient reports that the half crosses are aligned, begin the binocular threshold measurement by first giving verbal instructions.
Here, the same visual stimuli are shown to both eyes and the minimum number of signal dots required to accurately judge the direction of the dot movement is measured. Five measurements using the binocular staircase paradigm are now made repeating ocular alignment before each new measurement is started. The results obtained from each measurement is the threshold number of signal dots required to correctly judge the direction of signal dot motion when both eyes see the same stimuli, as well as the range of responses as a standard error of the measurement.
Next, begin the contrast imbalance measurement by averaging the five binocular threshold results to define the number of signal dots to be presented to the amblyopic eye. The remaining noise dots are presented to the non amblyopic eye at varying contrast. To assess suppression at the start of the measurement, the threshold number of signal dots are shown to the amblyopic eye at 100%contrast, and the remaining number of noise dots are shown to the fellow eye at 0%Contrast, meaning that only the signal dots are visible correct.
Identification of the signal dot direction results in an increase in the contrast of the noise dots shown to the fellow eye according to the three down one up staircase algorithm. After making five measurements, the average contrast threshold will inform the examiner about the level of contrast imbalance that is necessary to overcome suppression and allow the amblyopic eye and fellow eye to see the dots simultaneously. The contrast imbalance value found in the previous steps can be used as a starting point for a training regime that is presented in video game format.
The video game involves a series of falling blocks, which are fitted together to form complete lines. The amblyopic eye sees full contrast blocks shown here in the right panel, and the fellow eye sees reduced contrast images shown here in the left panel. Information presented to each eye must be perceived simultaneously for successful play over time as the training regime continues, the contrast imbalance is reduced by increasing the contrast to the fellow eye, making it more difficult for the visual system to overcome the suppression caused by more similar dichotic images.
The treatment can be provided using video goggles or a portable device such as an iPod touch using anaglyph or auto stereoscopic rendering. The training duration should be one to two hours a day and should be continued until no further improvement in contrast imbalance is observed. Shown here are clinical and psychophysical data obtained from one adult participant with strabismus amblyopia who completed the training procedure.
This graph demonstrates the change in visual acuity measured with a logarithmic style chart in log MAR units. Over four weeks of training for both the amblyopic eye and fellow eye as seen here training improved visual acuity in the amblyopic eye, resulting in lower log mar values. The cumulative number of hours of gameplay is shown in brackets on the X axis here, the change in contrast imbalance over four weeks of training is shown.
The Y axis shows the contrast that could be tolerated in the fellow eye. Therefore, larger values indicate less suppression at the start of training only 30%contrast could be tolerated in the fellow eye before the amblyopic eye became suppressed. However, as training progressed, more contrast could be tolerated indicating a reduction in suppression.
Stereo acuity also improves over the training period for some patients as measured with the RAND dot stereo test here. Zero on the Y axis indicates no stereo vision and increasing values indicate improving stereo sensitivity. Once mastered, this technique can be performed in under 30 minutes if it's performed properly.
After watching this video, you should have a good understanding of how to measure and treat interocular suppression in patients with amblyopia. Don't forget they've been working with this group of patients. It is important to have a suitably qualified clinician involved to provide information about diagnosis and training outcomes.
Precautions, such as continued clinical testing should be taken during the training procedure to ensure that double vision does not occur.
