Brain fog. Headaches that won’t quit. Difficulty reading. Light sensitivity that makes screens and fluorescent lighting unbearable. Blurry or double vision.

These are among the most common — and most frustrating — symptoms of post-concussion syndrome. And for many patients, they have a common root cause that goes unaddressed: visual dysfunction.

Why Concussion Affects Vision

This surprises many people: vision is not just a function of the eyes. It is a brain function.

An estimated 90% of the brain’s neural pathways are involved in processing visual information. The eyes capture light — but the brain does the actual work of interpreting it: tracking moving objects, coordinating both eyes to focus on a single point, judging depth and distance, and integrating visual information with spatial awareness and movement.

When a concussion disrupts the brain’s neural networks, the visual system is almost always affected. In fact, visual disturbances are among the most common symptoms reported by concussion patients — and yet they’re often the last thing evaluated and treated.

Common Visual Problems After Concussion

Convergence insufficiency

Convergence is the ability of both eyes to turn inward together to focus on a nearby object. After concussion, this coordination is frequently disrupted. When your eyes can’t converge properly, your brain receives two slightly misaligned images and has to work overtime to merge them — producing headaches, eye strain, blurry or double vision, and significant cognitive fatigue.

Saccadic dysfunction

Saccades are the rapid, precise eye movements your brain uses to scan text, track moving objects, and shift focus between different points in your visual field. Concussion often disrupts the brain’s ability to execute these movements accurately. Difficulty reading, losing your place on a page, and trouble following moving objects are all signs of saccadic dysfunction.

Visual processing speed

Beyond the mechanical movements of the eyes, the brain needs to rapidly interpret what it sees. Post-concussion patients often experience a dramatic slowdown in visual processing speed, contributing to the cognitive sluggishness and “brain fog” they report.

Light sensitivity (photophobia)

When the brain’s visual processing networks are dysregulated, bright light can trigger a cascade of neurological overload — producing headaches, dizziness, and worsening of nearly every other PCS symptom. Photophobia is one of the most disabling aspects of PCS for many patients.

Why Visual Dysfunction Drives So Many PCS Symptoms

Here’s something important to understand: unaddressed visual dysfunction doesn’t just cause eye symptoms — it drives cognitive symptoms.

When your visual system is working inefficiently, your brain is constantly burning energy compensating for it. Every time your eyes fail to converge properly, your brain has to work harder to create a single, stable image. Every saccade that’s slightly off-target requires correction. This constant low-level neurological effort depletes cognitive resources that would otherwise be available for attention, memory, and reasoning.

This is why many PCS patients report that their brain fog, difficulty concentrating, and mental fatigue improve significantly when their visual system is addressed — even though those symptoms didn’t seem “visual” at all.

What Is Vision Therapy?

Vision therapy is a structured program of exercises designed to retrain the visual system — specifically the brain’s control of eye movement, coordination, and processing. It’s distinct from correcting refractive errors (nearsightedness, farsightedness) with glasses; it addresses the functional performance of the visual system as a whole.

Vision therapy for concussion typically involves:

• Convergence exercises — training both eyes to work together at various distances
• Tracking and saccade exercises — improving the speed and accuracy of eye movements
• Visual-motor integration — combining visual tasks with physical movement
• Processing speed training — exercises that gradually increase the speed at which the visual system must respond

Ideally, vision therapy is overseen by an optometrist or ophthalmologist specializing in neuro-optometry. However, many of the foundational exercises can be performed at home, making them accessible to patients who can’t access specialist care regularly.

The Brock String: A Simple Tool with a Big Impact

One of the most well-established at-home vision therapy tools is the Brock string — a length of cord with colored beads spaced along it, held by one end and attached to a fixed point at the other.

Named after optometrist Frederick Brock, who developed it in the mid-20th century, the Brock string trains binocular vision — the ability of both eyes to work as a coordinated team.

How to use a Brock string

1. Attach one end to a fixed point (a doorknob or wall hook works well) and hold the other end to the tip of your nose, so the string extends away from you horizontally.
2. The beads are placed at varying distances along the string.
3. Focus on the nearest bead. When your eyes are properly converging, you should see the string form an “X” pattern crossing at the bead, with two strings appearing to converge on it from either side.
4. If one string disappears, your brain is suppressing the image from one eye — a sign of convergence difficulty.
5. Practice moving your focus from bead to bead, maintaining the “X” at each one, and gradually increase the time and distance as your convergence improves.

The exercise seems simple, but it directly trains the neural pathway coordination that concussion disrupts. Regular practice over weeks produces measurable improvement in convergence ability, and — for many patients — significant reduction in headaches, brain fog, and eye strain.

Visual Processing in MyndSpark’s Program

The MyndSpark Cognitive Efficiency Tool includes both a Brock string and a set of visual processing activities designed to rehabilitate the full spectrum of visual dysfunction common in PCS.

The visual processing section of the program addresses:

• Eye teaming and convergence (via the Brock string and related exercises)
• Visual perception and spatial processing (puzzle-based activities)
• Visual-motor integration (activities combining visual tasks with coordination)
• Processing speed and attention (timed visual scanning exercises)

Because MyndSpark is entirely screen-free, patients with light sensitivity and photophobia can engage with the visual exercises without the added burden of screen exposure — a critical design consideration for the PCS population.

The visual exercises are also designed to be combined with activities from other brain domains, creating the multisensory integration that accelerates neural recovery.

What to Expect from Visual Recovery

Visual dysfunction after concussion responds well to targeted therapy for most patients — but it requires consistency and patience.

Patients typically begin to notice improvement in eye strain and headaches within 4–6 weeks of consistent convergence practice. More significant improvements in processing speed and visual-cognitive integration often take 2–3 months of regular work.

The trajectory is rarely perfectly linear. Some weeks will feel like progress; others will feel like a setback. This is normal in neural recovery. The key is sustained, consistent engagement over the full course of the program.

For most PCS patients, addressing the visual system is not optional — it’s one of the highest-leverage interventions available, and it unlocks recovery in the cognitive and emotional domains as well.

When to Seek Professional Evaluation

If you’re experiencing significant visual symptoms after a concussion — especially double vision, severe light sensitivity, or balance problems triggered by visual input — seek evaluation from a neuro-optometrist or vision therapy specialist.

At-home exercises like the Brock string are valuable and evidence-supported, but a professional evaluation can identify specific deficits that benefit from tailored intervention, and can confirm that your symptoms don’t have a more serious underlying cause.

The MyndSpark Cognitive Efficiency Tool includes Brock string training and visual processing exercises as part of a complete at-home recovery program. Learn more at www.myndspark.com