How Your Eyes See Color
The human eye processes light to create the vibrant world we perceive. Light enters the eye and focuses onto the retina, a light-sensitive layer at the back of the eye. The retina contains millions of specialized cells called photoreceptors, which convert light into electrical signals that the brain interprets as images.
These photoreceptors are primarily of two types: rods and cones. Rods are responsible for vision in low light conditions and do not detect color, while cones are active in brighter light and enable color perception. Humans typically possess three types of cone cells, each sensitive to different ranges of light wavelengths.
These cone types are often referred to as L-cones, M-cones, and S-cones, corresponding to their sensitivity to long, medium, and short wavelengths of light, respectively. L-cones are most sensitive to longer wavelengths, which are perceived as red light. M-cones detect medium wavelengths, associated with green, and S-cones respond to shorter wavelengths, seen as blue. The brain combines signals from these three cone types to interpret a full spectrum of colors.
What Can Make You See Red
Experiencing a predominant perception of red can stem from various physiological issues within the eye. One cause is a vitreous hemorrhage, bleeding into the vitreous humor, the clear, gel-like substance that fills the space between the lens and the retina. When blood enters this space, it can absorb or scatter light, making vision appear red or causing a reddish tint across the visual field. This condition can result from weakened blood vessels, trauma, or underlying medical conditions like diabetic retinopathy.
Certain types of retinal detachment can also cause red vision, especially with bleeding. The disruption to the retina and associated hemorrhages can lead to altered light perception, sometimes appearing as a reddish hue or a “curtain” effect. Inflammation within the eye, such as uveitis, can lead to blurred vision, pain, and sometimes a reddish appearance due to blood vessel dilation or bleeding.
Beyond medical conditions, several non-medical optical phenomena can temporarily cause you to perceive red. Afterimages are a common experience, occurring due to temporary fatigue of cone cells in the retina. For example, staring at a bright green object then looking at a neutral surface can cause the green-sensitive M-cones to become desensitized. When these cones are less responsive, the L-cones (red-sensitive) become more active, leading to a perception of a red afterimage.
Lighting environments or optical aids can also induce a red tint to vision. Being in a darkroom illuminated solely by a red safelight makes everything appear red as only red wavelengths are present. Similarly, wearing red-tinted glasses or sunglasses will filter out other colors, causing the entire visual field to take on a reddish hue. This perception is a direct result of the light filtering properties of the lenses.
When to Consult a Doctor
Experiencing an unusual or persistent red perception in your vision warrants medical evaluation. This is concerning if the red vision appears suddenly or is accompanied by other symptoms. Symptoms include eye pain, a sudden decrease in overall vision, the appearance of new floaters (small specks or cobwebs drifting in your vision), or flashes of light.
Consultation with an ophthalmologist or eye care professional is advised for unexplained vision changes. A medical expert can diagnose the underlying cause of seeing red, whether it is a benign optical phenomenon or a serious condition requiring intervention. Self-diagnosis is not recommended, as many conditions that cause red vision can lead to permanent vision loss if left untreated.
If you notice a reddish tint to your vision, or if it is associated with any discomfort or visual disturbances, seeking medical advice is advisable. Early detection and appropriate treatment can help preserve your vision and eye health.