A recent study published in the Journal of Neuro-Ophthalmology tested the efficacy of a prototype software for commercially available mixed reality glasses (MRG) to help patients with homonymous hemianopia (HH) better navigate their visual environment.
Give me some background on HH.
HH is a visual field (VF) loss in the same halves of the VF of each eye; for example, in right HH, the VF loss is on the right side of both the right and left eye.
This condition is most commonly caused by stroke and trauma in adults.
- Note: The prevalence of stroke in the United States is > 7 million patients, with up to 28% of patients with acute stroke experiencing VF loss.
And its negative effects?
As one would expect, HH adversely impacts functional ability, quality of life, mental health, and independence due to the significant VF loss.
- Moreover: Prisms, eye movement training, and visual restoration have been applied for HH rehabilitation—but have demonstrated limited efficacy.
Now bring in mixed reality technology.
Unlike virtual reality, mixed reality allows users to see the actual environment with superimposed holograms.
In fact: Previous studies have suggested MRG for HH rehabilitation due to its ability to provide supplemental visual information and widen patients’ available VF in a variety of settings.
Talk about this new software.
A research team from the University of Alberta developed software on the Unity platform for the Microsoft HoloLens 2 (HL2) MRG to enable real-time picture-in-picture navigation (PIPN).
- How PIPN works: A miniaturized view of the visual environment is transposed into the intact VF in HH patients.
And why use HL2?
Investigators chose to use the HL2 because it:
- Is one of the most widely-available MRG (cost: $3,500)
- Can be programmed with user-friendly, cross-platform software
- Has an optical see-through lens and can be worn over spectacles
- Doesn’t have a wire computer tether
Now onto the study.
In this crossover study, five patients with HH (average age: 59 years, 80% men) were tested on a timed 50-meter course with four soft obstacles with and without MRG and then rated the utility of PIPN on a linear analog scale.
- Note: All patients had strokes with occipital lobe involvement of median 11-month duration before testing with the HL2.
Investigators transposed 52 diagonal degrees of the full field as a picture-in-picture into the intact hemifield of patients with HH.
Findings?
In total, five patients with HH were tested and on average rated the HL2 as 19.7% more helpful for ambulation (p = 0.028).
Three of the participants without the HL2 hit four of the obstacles; however, only one participant ran into one of the objects while wearing the HL2.
Anything else?
The average rating of the HL2 as a navigation aid was 69.7±13.1 out of 100, with a median of 74.3.
The average walk time using the HL2 was 90±59 seconds and 84±59 seconds without HL2, though this 6-second difference was not statistically significant.
- For comparison: An able-bodied 50–59-year-old walking at a leisurely pace would finish a 50-meter course without obstacles in 41 seconds.
Limitations?
These included:
- The small number of participants led to insufficient statistical power to show that patients with complete HH perceived the MRG as more beneficial than those with quadrantopsia
- All participants had strokes with occipital involvement, so it is unknown whether HH patients with neglect would benefit from the MRG
- While some obstacles were rearranged, the same ambulation path was used for a second run with some learning effect
- The position of the holograms from the HL2 varies with the pantoscopic tilt of its screen and patients with head tremor may have difficulty using the HL2
- The system does not work in a completely dark room
- PIPN MRG was not useful for reading 12-font print because of the approximate 4.5x minification
- The HL2’s maximal field of view is 44° horizontal field of view and 28° vertical field of view make it suboptimal for navigating stairs
- Walk time should not be the primary consideration in future MRG studies as two participants noted that they purposely walked slower because the HL2 allowed them to examine more visual detail
Take home.
These results demonstrate the feasibility of a prototype software for PIPN on a commercially available MRG.
Plus: PIPN should be considered a viable rehabilitation option to improve ambulatory navigation for patients with HH—and will continue improving with advancements in hardware and software.
Next steps?
Using MRG to find solutions to other visual issues stroke and brain trauma patients face, including torsional diplopia and nystagmus.
Future studies could involve applying an MRG with:
- Wider field of view
- More user-friendly controls
- Possible incorporation of obstacle alert software