Jul. 21, 2025
Photoreceptors are a key part of how your eyes detect light and convert it into a form your brain can use. When you think about your eyes, it can be easy to think of them like cameras. But in reality, cameras — especially modern digital cameras — are technology based on how the human eye works.
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Inside a modern digital camera, there’s a special sensor, and that sensor works very much like the human retina. It detects light and converts it into computer code. A tiny computer chip inside the camera then processes that code into a picture or video.
That’s basically the same process that happens when your retinas and brain work together so you can see the world around you. Your retinas turn what they detect into coded nerve signals and then send those signals through your optic nerve to your brain. Your brain decodes the signals and uses them to “build” what you see. And the cells in your retinas that start this process are the photoreceptors.
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The human eye has two main types of photoreceptors, rods and cones, which get their names from their shapes.
These photoreceptors are tall and have a cylindrical (tubelike) shape. They’re extremely sensitive to even tiny amounts of light. About 95% of the photoreceptors in your eyes (about 100 - 125 million) are rods. They’re great at helping you see in dim places, but they aren’t as good at fine details, and they can’t see colors at all.
Rod photoreceptors are mainly responsible for low-light vision and night vision. When they help you see in dim light, that’s called scotopic (“sko-TOE-pick”) vision.
Cones are photoreceptors with a cone-like shape, meaning they’re circular at the bottom and have a pointed tip at the top. They need more light to activate than rods, but they can detect colors when they’re active. Most cones are in one place on your retina, the macula. They’re why the center of your visual field can see colors and other fine details.
Your eyes have three types of cones that work together as part of color vision. The cones don’t see the colors themselves. Instead, they see light wavelengths and tell your brain about them. Your brain turns that into your ability to see color.
When you look at a rainbow, you’re looking at a helpful way to understand the visible light spectrum. Red light has the longest wavelength, which is why it forms the outermost — and longest — part of the rainbow’s arc. Violet has the shortest wavelength, which is why it forms the inner — and shortest — part of the arc.
Most people have three types of cone photoreceptors. Having these three cone subtypes is called “trichromacy.”
The three subtypes are:
While the three cone types each specialize in a specific color, there’s a lot of overlap in sensitivity across the three types. Your brain can compare the differences in the signals from all three cone types to determine colors. That’s why the average healthy human eye can distinguish up to 1 million colors.
There’s a rare genetic mutation that can only happen in females that causes them to have four cone subtypes. That’s called “tetrachromacy” (tetra comes from the ancient Greek word for the number four). When tetrachromacy happens, it can be either weak or strong.
Weak tetrachromacy means the brain can’t fully process the input from the fourth cone. Strong tetrachromacy means the brain does process the fourth cone’s input. That fourth cone lets someone with tetrachromacy distinguish 100 million colors. But strong tetrachromacy is also very rare, which makes it hard for experts to tell how often it happens or do more research on it.
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Several conditions can affect your rods and cones. Some of them are more general and affect other parts of the retina or surrounding eye tissue, too. But some conditions can affect your photoreceptors very specifically.
Conditions that can affect your photoreceptors include:
When you have a condition that affects your photoreceptors, vision loss is the main symptom. But that vision loss can take different forms, depending on the photoreceptors affected.
Many photoreceptor-related conditions affect both cones and rods at the same time. That’s especially true with conditions that involve damage or displacement of retinal tissue. Macular degeneration is a key, common example of that.
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A standard eye exam is like an annual physical for your eye. It allows an eye care specialist to look at the back of your eye for any changes or other signs of tissue changes in your retina. Certain parts of the exam, especially eye dilation (mydriasis) and the slit lamp exam, can detect conditions that are otherwise invisible and don’t cause symptoms early on.
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Further reading:Other, more specific tests that might help include electroretinography (which measures electrical activity in your retinas) and visual evoked potentials (VEP). VEP is a brain test, but it can tell healthcare providers if signals from your retinas are reaching your brain.
And there are a few imaging tests that your eye care specialist may also recommend. These often involve seeing the different layers of the retina or mapping the blood vessels in and around your retinas. Doing that can help your eye care specialist see new blood vessel growth or other tissue changes that could lead to retinal damage or vision loss. Your eye care specialist can explain any additional testing options they recommend.
Many of us take color for granted. We know the particular shade of blue in the sky, the green in the trees, and the three colors of a stoplight. But these colors can be muddy. That’s the reality for those who have color deficiencies more commonly known as color blindness, a condition typically first diagnosed in children with an eye exam.
However, after conducting extensive research on the different wavelengths of light and how a color blind patient interprets their color, Enchroma glasses were developed. This development opens a new world of colors for those with color deficiencies. Enchroma lenses use special lenses to filter the wavelengths of light before they enter the eye, making colors easier to distinguish for people with certain types of color blindness.
Color vision deficiency or color blindness is a common condition that affects many people worldwide. In this condition, your eye does not see colors correctly. It’s usually genetic, but there is a slight chance that eye diseases or brain/eye damage can cause it. Risk factors for color blindness include:
Color blindness is often misunderstood and can be tricky to explain, but that’s why we’re here! Despite its name, people with color blindness often can still see color. They simply perceive color differently, and in a world where we use color as indicators, that can cause wide-reaching difficulties.
The way color blindness affects a person depends on the type of color blindness they have.
Color vision deficiency can be classified in a few different ways, but it all comes down to the cones in your eyes. Cones, along with rods, are one of the types of photoreceptors (light sensitive cells) in the retina at the back of your eyes. They give us our color vision, and there are 3 types that each detect one of the 3 primary colors: red, green, and blue.
For people with color blindness, 1 type of cone may see their designated color incorrectly or not see that color at all.
The most common type of color blindness is red-green, with 8% of men and 0.5% of women having it. In color blindness, the part of the light spectrum that ‘red’ and ‘green’ cones detect overlap significantly, so these cones tend to have similar responses to different wavelengths of light. People with red-green color blindness can have trouble distinguishing between reds, greens, browns, and oranges.
Types of red-green color blindness are based on what color of light is affected, such as:
Only about 10% of your cones see blue light, and it’s the less common type of color blindness. People with this type can have trouble seeing between shades of blue and green, and red and yellow.
Blue-yellow color blindness has 2 types:
The third and rarest type of color blindness is complete color blindness. Only about 1 in 33,000 people have this form of color blindness, and individuals with this condition can’t distinguish any colors and see the world in only shades of gray.
Enchroma glasses were first invented by researchers in California. These glasses use a special kind of lens that enhances the color perception of the wearer in an innovative way — by actually blocking certain colors of light out!
Enchroma glasses don’t just magically make colors appear; they work by selectively filtering specific wavelengths of light. The key is to filter out the wavelengths where the color cones overlap. Typically, these wavelengths cause confusion for those with color blindness. Filtering these wavelengths out enhances the other wavelengths to make colors more vibrant and distinguishable.
Enchroma glasses are designed for people with anomalous trichromacy. These are the 3 types of color blindness where your cones have a reduced ability to see color. They are:
Anomalous trichromacy accounts for color blindness in 4 out of 5 patients, most of which are deuteranomaly and protanomaly, typically called red-green color blindness. Enchroma glasses are designed to deal with the “confusion line” between red and green, allowing them to address red-green color blindness, so it’s very likely Enchroma glasses can give you a new world of color.
For people with severe red-green color blindness, they don’t have any cones that can see one of those colors. This is called deuteranopia or protanopia. They may see limited results when using Enchroma glasses since they totally cannot see the difference between red and green.
Take the color vision test to learn if Enchroma lenses may work for you.
Although the experience of wearing Enchroma glasses varies from person to person, users have reported an improvement in their color perception. For some, it’s an emotional experience as they see colors they’ve never seen before, bringing tears to their eyes. For others, it’s a practical tool that helps them distinguish between colors, making it easier to match clothes or perform certain tasks.
While they may not work for everyone, those with mild to moderate color blindness may benefit from wearing Enchroma glasses. Perry Eyecare & Morgan Eyecare proudly offer prescription and non-prescription Enchroma glasses for people with red-green color blindness.
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