Tai Jarkum, Preetirupa Devi, Shrikant Bharadwaj and colleagues from LVPEI in collaboration with City St George's, University of London report that the type of optical blur and whether it affects one or both eyes influences performance on depth-based visuomotor tasks.
Imagine a ball soaring towards you. You track its arc, move into position, and stretch out your hand to catch it. In those few seconds, your brain has judged distance, speed, and depth by combining the slightly disparate images received from each eye to achieve binocular vision (using images from both eyes to perceive a single image). This combination of dissimilar binocular inputs allows the brain to build a three-dimensional understanding of space. The ability to judge how near or far objects are is called depth perception and is essential for binocular vision. We rely on clear but distinct visual inputs from our two eyes to perform everyday tasks like pouring out a glass of water or inserting a key into the keyhole.
Blurred vision can interfere with this process. It can result from a need for glasses, cataract, or aberrations on the corneal surface. And not all blurs are the same. Spherical blur reduces clarity equally in all directions while irregular or ‘astigmatic’ blur can lead to a more complex haze. The blur may be equal in both eyes (isometropic) or unequal between the eyes (anisometropic). Different levels of blur can impact depth perception, making it less accurate. While we know blur affects what we see, how much does it affect our ability to perceive depth or build an accurate 3D mental map?
In a new study published in Investigative Opthalmology and Visual Science researchers from LVPEI examined this through a wire-loop (a ‘buzz-wire’) task. Fifteen people with normal vision were asked to guide a metal loop along a curved wire without touching the loop to the wire. The wire consisted of 24 different patterns, preventing participants from memorizing its shape. The researchers used lenses to induce spherical and astigmatic blur, in one or both eyes. They measured how often participants made errors (touched the wire), how long they took to correct the errors, and how fast they completed the task.
Astigmatic blur caused more errors than spherical blur of similar strength. When only one eye was blurred (spherical or astigmatic), participants performed almost as well as when using one clear eye, suggesting that the brain relied on the better eye to perform the task. But when both eyes were equally blurred, performance dropped. The study found that performance declined as blur increased. Additionally, when different blur patterns were induced in each eye, the effect was severe than when the blur was similar across both eyes. The team noted that participants did not reduce their speed even under high blur conditions, instead they made more errors (accuracy decreased) and spent longer correcting them. It is not just the amount of blur that matters, but how that blur alters depth perception and binocular vision, impacting our ability to perform everyday tasks. For clinicians, this means considering a patient’s daily activities while planning to correct their blurred vision.
‘This study demonstrates that everyday depth judgement visuomotor tasks can be affected by optical blur and its pattern. High levels of blur and asymmetrical blur create the most challenging conditions. Clear vision and equal image quality in both eyes are the ultimate requirement for optimal binocular vision that supports perception and action,’ says Tai Jarkum, Project Optometrist at LV Prasad Eye Institute and first author of the paper.
Citation
Jarkum T, Devi P, Solomon JA, Tyler CW, Bharadwaj SR. The Impact of Induced Optical Blur on Monocular and Binocular Depth-Related Visuomotor Task Performance. Invest Ophthalmol Vis Sci. 2025 Dec 1;66(15):8. doi: 10.1167/iovs.66.15.8. PMID: 41328991; PMCID: PMC12697702.
Photo credit: Srinivas Marmamula
