In 2018, Tom Finn took his father, Nigel, to a physiotherapy appointment. Nigel was living with vascular dementia, which can present with symptoms similar to Parkinson’s disease, a progressive neurological disorder characterized by motor symptoms such as tremors, stiffness, and trouble balancing. He was losing the ability to walk.

The physiotherapist told Finn about cue markers—colored lines laid on the floor that can help Parkinson’s patients overcome difficulty walking. Finn was unconvinced. He couldn’t see how some lines on the floor would help his father. But when they got home, he laid some colored exercise bands down in the kitchen and watched in amazement as his dad easily marched back and forth across them.

The technique, called external cueing, works by using visual, auditory, or tactile prompts—colored tape on the ground, playing a metronome, or physical vibrations—to engage neural pathways not affected by the disease. “It can help people focus their attention and help them take that first step and overcome the freeze,” says Claire Bale, associate director of research at Parkinson’s UK, a research and support charity in the UK.

While Finn—who worked in marketing and video production in London—was struck by the effectiveness of this simple intervention, he thought it too basic to actually be helpful. But augmented reality glasses from the likes of Magic Leap had just started coming to market, and he wondered whether they might be able to project virtual lines onto the ground to act as cues. He founded a startup, Strolll, to try to make that vision a reality.

Two years later, Strolll had no staff and about £50 in the bank, according to Jorgen Ellis. Ellis, a New Zealander with a background in furniture startups, had come to the UK looking for his next venture and wanted to get involved with something he felt passionate about. His grandfather had lived with Parkinson’s for over a decade, and when he met Finn through a mutual contact, he immediately saw the promise of the technology. He came onboard as CEO and started by trying to demonstrate that AR-based cueing was scientifically valid.

Ellis and Finn soon found a group of academics at VU University in Amsterdam, led by Melvyn Roerdink, who were working on something similar. Strolll acquired their ...