People with great eyesight tend to take it for granted. The percentage of the U.S. population with vision problems is 50 percent and growing, according to data gathered by the National Institutes of Health.

In recent years, scientists and doctors have made miraculous headway in combatting eye problems. From improved contacts and glasses to corrective eye surgeries, a wide range of eye maladies are now correctable and curable. If you have eye issues, there has never been better treatment options, reports VSP Direct, a national family and individual vision insurance provider.

Among human organs, eyes are second only to brains in complexity. Here are facts about some of the amazing attributes of human eyesight.

Every human eye has a blind spot

Each of your eyes has a small blind spot where the optic nerve passes through the retina. People rarely notice this lack of visual information. Some experts believe our brains fill in the blind spot based on surrounding detail and information from the other eye, explains the American Academy of Ophthalmology. Others theorize that our brains simply ignore the blind spot.

Upside down and backward

Human retinas see everything upside down and backward. Your brain reorients the image. Because you have two eyes, your brain is also combining two separate images, Physics and Astronomy Online explains. Visual processing is a complex task which takes up a relatively large part of the brain compared to other senses.

“This is because your brain performs several tasks to make images 'easier' to see. One, of course, is combining the two images, which is helped by the corpus callosum, the tiny part of your brain which joins the two big hemispheres. The other part is handled in the optic part of your brain itself and part of its job is to make images right-side-up. It does this because your brain is so used to seeing things upside-down that it eventually adjusts to it.”

Understanding “red eye”

No doubt you’ve used a flash to take photos of your family or friends only to have them appear with fiery red eyes when you looked at the images. This red-eye phenomenon occurs in photos because, in the dark, our pupils open wide to allow extra light to help us see, notes yalescientific.org. When the flash fires, your eyes are unprepared for the burst of light and it bounces off the back of the eye. Behind the retina is a part of the eye called the choroid. It is loaded with blood vessels, which make it glow red in images taken with flash photography.

It takes seconds for our pupils to dilate in darkness, but our night vision continues to improve for several hours, according to Christopher Baird, assistant professor of physics at West Texas A&M University.

Peripheral vision is weak

Compared to our central vision, peripheral vision is weaker, especially when distinguishing color and shape, according to sciencedaily.com. This is because the density of receptor cells on the retina is greatest at the center and lowest at the edges. An area near the center of the retina, called the macula, has the highest concentration of cone cells and it produces the sharpest, clearest vision. Peripheral vision is good at detecting motion.

Eye security

You’ve probably seen movies where access to secure areas requires an eye scan. You might even work someplace where this technology is in place. Security checkpoints use two types of eye scans: iris scans and retinal scans. While a fingerprint has 40 unique characteristics, a human iris has 256 and an iris scan compares those unique features against a known database. Similarly, a retina scan compares the complex features of an individual’s network of retinal blood vessels.

Even though the technology is available and eye scans are almost impossible to fake, eye scanning is uncommon because of difficulties associated with image acquisition and false rejections, explains Fleming Companies.

No eye transplants — yet

While doctors can transplant hearts, livers, kidneys and even corneas, because of the complexity of human eyes, so far no eye transplant has been attempted. The biggest challenge is figuring out how to regenerate and regrow delicate optical nerves.

"When you switch out an eyeball you have to completely cut all connections between the optic nerve and the eye. So then you need to reconnect the donor eye's nerve fibers back to the recipient's brain in order to achieve vision restoration,” explains Dr. Jeffrey Goldberg, director of research at the Shiley Eye Center at University of California, San Diego, in an article for WebMD.com.

Many people fear losing their eyesight above any other health problem, according to a WebMD report about a survey published in JAMA Ophthalmology in 2016. Protecting your eyesight and that of your family should be high on the list of healthcare priorities. One way to do that is by having vision insurance like that available through VSP Direct.

Related topics