In a move that is sure to stoke rumors about Apple’s future work in augmented and virtual reality technologies, Apple has acquired SensoMotoric Instruments (SMI), an eye-tracking firm, MacRumors is reporting.

The German company, which was founded in 1991, has done significant work in eye-tracking research with proprietary eyeglass hardware while also working on consumer-focused applications like eye-tracking for virtual reality. Last year, the company announced it had created an eye-tracking development kit for the HTC Vive VR headset.

We don’t know any details on how much Apple paid for the company or whether it will operate independently, but we’re keeping an eye out.

Apple’s acquisitions have historically presented one of the clearest possible looks into the company’s future product roadmap, this acquisition marks the strongest indication yet that Apple is working on its own head-mounted display

One of the primary use cases for eye-tracking technology in headsets is called “foveated rendering,” which tracks a user’s gaze on a display and renders the focal area at full resolution while blurring out the extraneous areas, lessening processing loads significantly. The technology is seen as essential by many experts to bring ultra high-resolution screens to VR and AR headsets.

Eye-tracking technology also has a number of use cases for headset-based AR and VR input. In October, Google acquired Eyefluence, an eye-tracking startup that uses eye movements to make interface selections.

Last month, Apple introduced ARKit, a set of APIs for developers interested in building augmented reality experiences. The company also brought VR development support to the company’s highest-end desktop, the iMac Pro.

We reached out to Apple for confirmation of the acquisition and they gave us their classic line: “Apple buys smaller technology companies from time to time, and we generally do not discuss our purpose or plans.”