Prisms in spectacles work like gentle tilts, redirecting light rays to the correct spot on the retina. This helps misaligned eyes see a single, clear image.

Correcting misalignment of the eyes: When the eyes are misaligned, the light rays from an object strike different spots on the retinas of each eye. This can cause double vision, blurred vision, and headaches, making it difficult to read comfortably. Prisms bend the light rays so that they fall on the same spot on each retina, allowing the brain to fuse the two images into a single, clear image. This can significantly improve reading comfort and clarity.

How do prisms help with strokes?

Yoke prisms are a type of prism used in vision therapy to help stroke patients with visual impairments, such as homonymous hemianopia (loss of vision in one half of the visual field) and unilateral spatial neglect (difficulty paying attention to one side of the body or environment).

Think of yoke prisms as special glasses that create a slight shift in the visual field. When stroke patients wear yoke prisms, they gradually adapt to this shift, causing the brain to rewire its visual processing pathways. This rewiring can help expand the visual field, improve attention to the neglected side, and enhance overall visual perception.

Imagine a patient with homonymous hemianopia who struggles to see objects on their left side. Yoke prisms can gently nudge the visual field to the right, allowing the patient to perceive objects they previously missed. This expansion of the visual field can significantly improve their daily activities, such as walking, eating, and dressing.

Similarly, for patients with unilateral spatial neglect, yoke prisms can help them recognize and attend to the neglected side. By shifting the visual field, they become more aware of their surroundings and can better navigate their environment.

Yoke prism therapy is typically prescribed by an optometrist or neuro-ophthalmologist and involves wearing the prisms for several hours each day. The therapy may continue for several weeks or months, depending on the patient’s progress.

In summary, yoke prisms help stroke patients by:

1. Expanding the visual field for those with homonymous hemianopia
2. Improving attention to the neglected side for those with unilateral spatial neglect
3. Enhancing overall visual perception and spatial awareness
4. Promoting brain plasticity and rewiring of visual processing pathways