AP Biology class blog for discussing current research in Biology

Tag: Eyes

Do humans have night vision?

Can humans see in the dark?

If you said yes, you are correct! When I saw the title of Emily Underwood’s article, “How humans- and other mammals- might have gotten their night vision“, it immediately intrigued me. Sight is an amazing gift that we all take for granted. Our eyes are incredible organs, and scientists are now discovering how they work when we see in the dark naturally. That is pretty cool!

Underwood’s article describes a study that gives insight into how our eyes work in the dark. According to her, “On a moonless night, the light that reaches Earth is a trillion–fold less than on a sunny day. Yet most mammals still see well enough to get around just fine—even without the special light-boosting membranes in the eyes of cats and other nocturnal animals.

In broad daylight, mammalian retinas respond to photons, which activate rods, which then send an electrical signal to the brain through a ganglion cell. It was thought that this retinal circuit was the same when the sun went down, but a new study by Greg Field and his colleagues at Duke University proves that the retinal cells adapt when there is no light to create what we know was natural night vision. How?

To understand this new study, we first need to know about direction-selective ganglion cells.

Direction-selective ganglion cells (DSGCs) specialize in motion detection. Depending on the movement of an object, different cells get excited. For example, some DSGCs fire when an object moves up and down and other DSGCs fire when an object moves from left to right. These ganglion cells play an important role in telling the brain where an object is moving towards. By doing this, the brain can make a decision as to how your body should act.

However, in the dark DSGCs behave very differently. Field’s experiments aimed to see how the DSGCs adapt when there is no light. His team examined slices of mouse retinas on glass plates embedded with electrode arrays. In an oxygenated solution, the mouse retinas could still “see” while the arrays recorded the electrical activity of the neurons. They ran the experiment twice: once under a normal “office light” setting, and once by dimming the lights to a moonlight setting. Looking at the results, Field found that three of the four directional DSGCs did not have a response to motion when they dimmed the lights. The only cells that were responding were the ones that usually respond to the motion “up” in daylight. In fact, these cells compensated for the other DSGCs, and were now responding to motions like “down” and “sideways”.

Why were the “up” DSGCs were acting differently? To answer this question, Field genetically engineered mice without intracellular gap junctions to run the experiment again. Gap junctions have previously been associated with night vision, and the results in Field’s experiment confirmed their relationship. The mice lacking gap junctions were not able to adapt to the dark. This shows that gap junctions are critical in boosting motion detection in the “up” cells when there is limited light.

It is still not known why specifically the “up” cells contribute to natural night vision, what do you think?

Field’s findings will be helpful to artificial vision efforts. DSGCs make up 4% of ganglion cells in humans, a small amount compared to 20% in mice. Yet a large part of retinal prosthetics relies on electrically stimulated ganglion cells. Studies like this can fine-tune the technologies that will be able to help visually impaired people, which is why I love reading about them. These experiments are crucial in progressing the future of medicine and the treatment of all kinds of health issues.

Trust Your Eyes?

How do illusions deceive people into seeing false perceptions of what is actually in front of them? Illusions are caused from a misunderstanding between eyes and the brain. All illusions start with the eyes. The light that bounces off an object enters the cornea of the eye. The cornea refracts the light through the pupil. The light rays then go through the lens towards the retina where the nerve cells are present. The cells, commonly called rods or cones, which are the two types of cells that  send the light through the optic nerve for the brain to interpret. Illusions are set up in a particular way with patterns, images or colors that trick the brain.

Illusions sometimes occur due to familiarity of the situation we are falsely perceiving. The whole process of interpreting information takes fractions of a second, so often times the brain quickly notices a familiar situation and is hard wired into coming to a conclusion. The link below displays a picture providing an example of this phenomena. The second picture consists of what seems to be simply a nature photo, but with a closer look actually shows the outline of a women’s face. Naturally the brain quickly perceives just trees becasue it is the “normal” understanding of the photo.

Another type of illusion, called a physiological illusion, occurs from a certain type of light, color, and position. This type of illusion occurs when the stimuli that are sent to the brain are so intensive or repetitive that it causes some sort of jam that creates a misperception. The picture below seems to be moving side to side. The reason this illusion works is becasue the repetition that the eyes can’t fully digest and an over stimulation occurs.



Sometimes simply context can confuse the mind. The illusion below shows two groups of circles. The middle ones on both sides are surprisingly the same size. It is extremely shocking because the one on the left looks much bigger than the one on the right. This happens becasue the brain groups each part of the image separately and compares those circles. The circle on the left is big compared to the others while the one on the right is smaller than the others. This shows how the brain analyses some situations. The brain simply compares each circle to the other and gives it a general big or small association.


Essentially illusions come from the false information and trickery our eyes send to the brain. Our eyes and brain work to process information in fractions of a second. Because of this optimization and simplicity is key. Rather than fully grasping all of the information many comparisons and quick conclusions can be made. The brain is forced to take shortcuts with comparisons such as light and dark, big and small, and shape to quickly adapt and react to what the eyes see.

Brand New Species of Butterfly Discovered

Abstract Butterfly Vector Graphic

A new species of butterfly has been discovered in Texas, earlier this spring. Named after it’s founder’s wife, the Vicroy’s Ministreak (it’s scientific name is Ministrymon Janevicroy), went unnoticed as a “new” breed because it was mistaken for the Gray Ministreak, due to the similarity of appearance between the two butterfly species. The trademark difference of the Vicroy’s Ministreak, however, is it’s olive green eye. The Gray Ministreak is known for having a dark brown to black eye coloring. Other differences between he two species include the patterns on their wings as well as differences in genital structures. Some of these differences were noticed when both butterflies were examined when dead. The founder, Jeffrey Glassberg, mostly used a new method of study to differentiate between the two Vicroy and Gray Ministreaks; he used cameras and binoculars, instead of the standard net.

The Vicroy’s Ministreak can be found in greater population in southern America and even reaching down to Central America, in “dry deciduous forest and scrub.” They have also been spotted in fewer population some of the northern South American countries. This new species is thought to be among the last that will be discovered in North America.

For additional information about this new breed of butterfly, please check out the following websites:


Big News for Retina Pigmentosa Patients


Photo by luisar

In a recent article, it was revealed that patients with the rare disease retinitis pigmentosa, may be able to find treatment using the Argus II Retinal Prosthesis System. Retinitis Pigmentosa is a rare, only about 100,000 Americans have it, inherited retinal disease that “causes the breakdown of cells in the retina.”

Dr. Robert Greenberg, CEO of Second Sight (the company that created the Argus II Retinal Prosthesis System), stated that those with retinal pigmentosa are “looking down a tunnel that gradually narrows until it disappears entirely.”

The Argus II uses a “video camera and a transmitter mounted on a pair of glasses” to help the individual. “Images are then wirelessly transmitted to electrodes implanted into the patient’s retina.” While the Argus II will not restore vision completely, it will allow users to partially regain vision. Tests show that the Argus II helped patients perform daily activities with ease. These activities included “navigating sidewalks and curbs, matching different color socks, and recognizing large words in sentences.”

Personally, I think this is a great technological leap. This prosthesis system will hopefully reach out to those with retinal pigmentosa and others with macular degeneration.

Wait, Babies can be Born Without Eyes?

This picture displays a baby with healthy eyes!

This photo was found on through Google Advanced Search

I always knew individuals could lose eyes if a terrible accident occurs, but I never knew that babies can be born without eyes! Did you?

Recently, a condition called anophthalmia has been discovered. It is when there are complications with the development
of both copies of the STRA6 gene, one that is “responsible for transporting vitamin A into the cells.” In fact, vitamin A is needed for the development of every inch of our retina, a tissue lining the inside of the eye. In less scientific terms, anopthalmia is when an individual is born with the loss of one or both eyes. Microphthalmia, a condition where an individual has small eyes, and coloboma, which is a deformed eye, are two other eye conditions that develop in a baby while he or she is still in the womb. These three diseases make up eleven percent of all eye deformations. However, the Micro & Anophthalmic Children’s Society UK reported that microphthalmia and coloboma are much more common than anopthalmia.

Doctors like Dr. Sean Ennis from the UCD School of Medicine and Medical Science, University College Dublin, and the National Centre for Medical Research started researching the perplexing idea that babies can be born without eyes with “nine individuals from across several generations of an Irish ethnic minority family of nomadic descent who suffer with one or more of the three eye defects to varying degrees of severity.”
Dr. Ennis says,


“Using advanced gene sequencing technologies, we firstly scanned for regions of DNA shared by all patients before analysing a single common region for the disease gene. From this we pinpointed STRA6, a gene responsible for transporting vitamin A into cells.


In the past, doctors have found that alterations and complications of the STRA6 gene in DNA can cause Matthew-Wood syndrome. This is a disease that can cause irregular eye formation and hardships for development in general.
Scientists of the University College Dublin, Ireland, in addition to doctors such as Dr. Hui Sun and Dr. Riki Kawaguchi of the University of California, actually made this fascinating discovery recently. Now, they are attempting to make genetic testing to determine whether a baby in a mother’s womb will have anopthalmia early on. They would really like to develop a clinical practice, which would take place at the National Centre for Medical Genetics (NCMG) in Dublin. Professor Andrew Green of University College Dublin says,

“Accurate carrier testing and genetic counselling can be offered to those individuals planning to have children. And ultimately, this work may be used to develop preventive measures or possible treatments in the future,”

As of right now, babies born with small eyes, deformed eyes, or no eyes must get prosthetic eyes to help them see and help the development of other parts of their bodies, including the face and skull. Eye defects can also be associated with birth defects and deformations in the heart, lungs, and diaphragm. We must hope for progress in the research and clinical trials for anophthalmia, so that the malformation and lack of eye disorder disappears forever one day!

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