Do you sometimes feel like you can't see things clearly when you're walking on the street at night, or when it's dark inside your house? Do you sometimes feel a little difficult in a movie hall, in a place with low lighting? So today, let's talk about what this "night vision " or (as it is called in English) is, how our eyes adapt to it, and why some people have reduced night vision. Since this is a problem that many people have, let's be aware of this.
What does it mean to see at night? Is that (Scotopic Vision)?
Simply put, night vision is the ability to see things in low light, or in the dark. In medical terms, this is also called Scotopic Vision . This is the exact opposite of seeing things in daylight, under good lighting conditions. We call it Photopic Vision .
Imagine, our eyes and brain work together to do this thing called seeing. It's like teamwork. In daylight, in artificial light, and in the dark, these two work together to convert electrical signals into images and show them to us. Isn't it amazing?
How do our eyes help us see in the dark?
Our eyes are very complex and very clever organs. Let's see what happens inside the eye at night.
Light enters the eye through the cornea, which is the membrane in front of the eye. This is like a lens. Then this light goes through a small black hole in the middle of the eye. This is called the pupil , or in Sinhala, the ' black eye '. The colored part around this pupil is called the iris , or the 'eye's iris'. This iris works like a muscle. When there is more light, the pupil shrinks, and when there is less light, that is, in the dark, the pupil enlarges. It works like a camera lens.
Next comes the most important part. Inside our eyes, specifically in the retina , there are two types of light-sensitive cells. These are called photoreceptors . They are:
- Rod cells
- Cone cells (Cones)
These cells are what capture the light particles, or photons , that enter the eye, convert them into electrical signals, and send them to the brain. Our eyes typically have about 6 million cone cells and about 120 million rod cells! That's an incredible number, isn't it?
What is the difference between rods and cones?
Okay, now let's see the difference between these two cells.
- Cones: These are the cells that help us see color. They work best in daylight and good light. They are mostly found in the center of the retina, in an area called the macula .
- Rods: They are the heroes of our story today! These rod cells are what help us see things in low light, that is, in the dark. They are mostly found on the outer edges of the retina . That is why we get peripheral vision. But there is a small thing, these rod cells cannot distinguish colors. That is why at night we only see black, white and gray.
What's more, these rod cells are about 500 to 1000 times more sensitive to light than cone cells! That means they can pick up even the tiniest bit of light.
Why can't people see as well at night as animals?
You've probably seen how well animals like cats and dogs see at night. Why can't we? There are several reasons for that.
- Some animals have larger eyes than humans.
- Also, their pupil , or black eye, can open larger than humans, allowing more light to enter the eye.
- Another special thing is that some animals have a membrane called the Tapetum Lucidum inside their eyes. This reflects the light that enters the eye back to the retina . It's like a mirror. That's why they can use light twice. Humans don't have this Tapetum Lucidum .
How does our vision change at night?
As we've said before, the rods are the ones that work the most at night. Because they can't see color, we can't see color at night. We only see black, white, and gray. Like an old black-and-white movie.
It is said that a person with 20/20 vision during the day can see about three miles away, although the curvature of the Earth limits our ability to see beyond that. However, we can see things like buildings and stars that are much farther away than that.
What is Night Blindness?
Some people have very poor night vision. This means that even in darkness, which is normal for others, they cannot see things clearly. For example, they have a hard time seeing in dimly lit places like restaurants or movie theaters. This condition is called Night Blindness , or in medical terms , Nyctalopia .
The important thing is that Nyctalopia is not a single disease. It can be a symptom of another underlying eye disease.
This is often related to the fact that when you go from a well-lit place to a dark place, your eyes cannot adjust quickly. People who are short-sighted, that is, those with myopia, may also sometimes have difficulty seeing at night. This is not due to a disease of the retina , but rather to a problem with the way light is focused inside the eye.
What are the main reasons for reduced visibility at night?
There are a number of possible causes of reduced night vision, or nyctalopia . Let's look at a few of them.
Glaucoma and its treatment
Glaucoma is a group of eye diseases that damage the optic nerve, which is the nerve that carries signals from the retina to the brain. Glaucoma can cause night vision loss. Also, some medications for glaucoma, such as pilocarpine, constrict the pupil . This can also cause night vision loss.
Cataracts
Cataracts are a condition in which the clear lens inside the eye becomes cloudy and cloudy. This prevents light from focusing properly. This is a very common condition, especially as we age. It is estimated that more than 50% of people over the age of 80 have or have had cataracts. The usual treatment for cataracts is to remove them surgically. When cataracts develop, vision at night becomes significantly reduced, especially when driving. They can appear as if lights are scattered.
Retinitis Pigmentosa (RP)
Retinitis Pigmentosa (RP) is a group of inherited eye diseases. It directly affects the retina . One of the first symptoms of RP is decreased night vision. This often affects both eyes. Many people with RP have reduced vision, and some may even go blind.
Vitamin A Deficiency
Vitamin A is essential for our eyes, especially for night vision. Vitamin A is needed to make a chemical called rhodopsin, which helps us see at night. A deficiency in vitamin A can lead to poor night vision. People who do not eat a balanced diet or who have had certain surgeries (such as intestinal bypass surgery) can develop a vitamin A deficiency. Not only does it affect the eyes, but it can also affect the skin, heart, lungs, and immune system.
Diabetes (Diabetes Mellitus)
Diabetes Mellitus is a condition in which the blood sugar level, or glucose, increases. Diabetes can cause various eye problems. Blurred vision and reduced night vision are some of them. Therefore, if you have diabetes, it is very important to control your blood sugar level. Also, it is essential to regularly see an ophthalmologist and have your eyes checked. This is because diabetes increases the risk of developing conditions such as glaucoma and cataracts.
Age-related Macular Degeneration (ARMD)
Age-related Macular Degeneration (ARMD) is also an eye disease that can be inherited. It mainly affects central vision . Peripheral vision is usually not affected. It most commonly occurs in people over the age of 50. It can affect one or both eyes.
There are two main forms of this: dry and wet.
- Dry ARMD: In this, yellow deposits called drusen form in the area of the eye called the macula . The macula then thins and becomes dry.
- Wet ARMD: In this, abnormal blood vessels form under the macula and leak fluid. The macula then swells.
In all of these situations, night vision can be affected.
What tests are done to find the cause of night vision?
If you tell a doctor that you have poor night vision, the first thing he or she will do is examine your eyes carefully. He or she will ask about your medical history and other symptoms. In addition, they may do a few other tests.
- Electroretinography: This test looks at how your retina responds to light.
- Pelli-Robson contrast sensitivity chart: This is similar to the chart we use to read letters when we go to the doctor. However, this one starts with black and gradually goes to gray. This measures how well you can distinguish different shades of gray.
- Blood tests: You may also have a blood test to check your vitamin A and glucose levels.
These tests are the only way to find out the exact cause.
Is it possible to have 20/20 vision during the day but not see at night?
Yes, it is entirely possible. Even if you have perfect daytime vision (20/20 vision), you may have difficulty seeing at night or in low light.
Your night vision may gradually decrease over time. However, if you experience this, it's important to talk to your healthcare team. This is especially important if you have other medical conditions, such as diabetes.
What to remember from what we talked about (Take-Home Message)
Okay, so we've talked a lot about night vision today. Here are some of the most important things you need to remember:
- Seeing at night, that is, night vision, is very important for our daily lives.
- If you notice any changes or loss in your night vision, don't ignore it. Be sure to seek medical advice.
- It is very important to have your eyes checked at regular intervals , especially if you have conditions like diabetes or glaucoma, or if someone in your family has these eye diseases.
- Eating a balanced diet and exercising can help maintain eye health.
Don't forget, our eyes are a very valuable asset. Therefore, it is our responsibility to take good care of them. If you have any problems, don't be afraid to talk to a doctor.
` Night vision, eyesight, night vision, night blindness, eye health, retina, glaucoma
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