Glasses containing prisms are a specialized type of lens correction designed to address specific visual challenges. Unlike standard lenses that correct for nearsightedness or farsightedness, prism lenses manipulate how light enters the eye. This article explores the reasons why someone might need prism glasses, how they function, and what to expect during the adjustment period.
What Prisms Accomplish
Prism lenses alleviate visual symptoms and improve comfort. They primarily correct double vision (diplopia), which occurs when the eyes do not align properly to form a single image. Wearing prism glasses can reduce or eliminate this symptom.
These specialized lenses also reduce eye strain and alleviate headaches caused by misaligned eyes. When the eyes struggle to work together, it can lead to visual fatigue and discomfort. Prisms help the eyes coordinate more effectively, leading to improved visual clarity and comfort during daily activities.
How Prisms Redirect Light
Prism lenses function by bending or “refracting” light before it reaches the eye. A prism is shaped like a wedge, with one side being thicker (the base) and the opposite side thinner (the apex). When light passes through this wedge, it is redirected towards the thicker base of the prism.
This manipulation of light shifts the image on the retina of each eye. When the images seen by both eyes are properly aligned on the retinas, the brain can more easily fuse them into a single, clear perception. This process reduces visual effort, allowing the brain to interpret a unified image.
Common Reasons for Prism Prescriptions
Prism prescriptions address underlying conditions causing eye misalignment or coordination difficulties. One common reason is strabismus, a condition where the eyes do not align correctly, sometimes appearing crossed or turned outward. This misalignment can lead to double vision, as each eye sends a different image to the brain.
Another condition benefiting from prisms is convergence insufficiency, where the eyes struggle to turn inward sufficiently for close-up tasks like reading, resulting in eye strain or double vision at near. Similarly, divergence excess or other phorias (tendencies for eyes to drift inward or outward) can cause discomfort and necessitate prism correction. Neurological conditions, such as those resulting from a stroke, head injury, multiple sclerosis, or certain cranial nerve palsies, can also disrupt eye movement and alignment. Prisms can help manage these conditions by compensating for the disrupted eye coordination.
Adapting to Your New Prism Glasses
When first wearing new prism glasses, an adjustment period is common as your eyes and brain learn to interpret the altered visual input. This transition typically lasts from a few days to several weeks, with individual experiences varying based on the prism strength and underlying condition. During this initial phase, some people may experience sensations such as spatial distortion, where objects appear shifted or closer than they are, or a slight feeling of dizziness or nausea. Changes in depth perception are also common, requiring extra caution, especially when navigating stairs or uneven surfaces.
To facilitate adaptation, wear the new glasses consistently throughout the day. Focusing on distant objects can help stabilize vision. Practicing conscious head movements, by pointing your nose towards what you are looking at rather than just moving your eyes, aids in adjusting to the new lens configuration. Patience is important, as your brain needs time for initial sensations to subside and visual comfort to improve.