I. Intrauterine development of the embryonic eye – starting from the October conception
The development of the embryonic eye is closely related to the development of the nervous system of the brain. At 4 weeks of pregnancy, the eye starts to develop, and the anatomical structures of the eye start to develop and differentiate gradually.
At 27 weeks of pregnancy, the fetus can open and close its eyes, and at this time, when the mother’s abdominal wall is illuminated with light, the fetus will already turn its head to the light source, and at 30 weeks of pregnancy, the baby can already distinguish between light and darkness, and will even chase the light source back and forth. At birth, the structure of the eye has been basically developed, but the function still needs to gradually develop and mature, the baby’s vision at birth is very poor, only a dozen centimeters in front of the object can be seen.
Some eye diseases are caused by congenital anomalies, and there are two main causes of congenital anomalies of the eye.
1. genetic inheritance;
2. abnormal intrauterine development due to external causes.
For eugenics, the latter is relatively controllable and avoidable, and therefore is receiving more and more attention. Pregnant women need to do well in pregnancy health care including.
(1) Prevention of rubella and other viral infections in the first trimester to reduce the incidence of congenital cataracts;
(2) Keep away from radiation damage from various physical rays (such as X-rays) to avoid the occurrence of some eye malformations;
(3) Avoid abdominal trauma and abnormal development of the nerves and muscles of the eye caused by uterine pressure;
(4) Take various chemical drugs carefully to avoid various ocular malformations;
(5) Pay attention to nutrition, such as vitamin A deficiency, the fetus may develop night blindness or dry eye disease;
(6) Quit smoking and drinking alcohol, smoking is likely to cause fetal miscarriage, premature birth and various eye congenital anomalies, drinking alcohol is likely to cause abnormal development of the fetal nervous system.
From the “white eye” to the “black eye” – the structure of the eye
Our eye is a 2cm diameter sphere with a tip, which is the optic nerve that leads to the brain at the back surface of the eye. The sphere includes the wall of the eye and the contents of the eye, which are divided into three layers: outer, middle and inner.
The outer layer consists of the cornea and the sclera, with the cornea being the prominent transparent part in front, which can reveal the brown iris color behind it, commonly known as the “black eye”, and the white part around it being the sclera, commonly known as the “white eye”.
The middle layer consists of the iris, ciliary body, and choroid, all of which are rich in pigment and vascular tissue. The iris is located in front of the eye and forms a round pupil in the middle. The ciliary body is attached to the iris anteriorly and to the choroid posteriorly. The choroid is lined between the sclera and the retina and has abundant blood circulation to nourish the retina.
3. The inner layer is the retina, which is the key part for forming visual information.
If the eye is compared to an egg: the wall of the eye is similar to the egg shell, which plays the role of protection and support, the retina is like the egg membrane, located in the innermost layer of the egg shell, and the vitreous body is like the egg white clinging to the egg membrane, which can support the egg membrane from falling off and collapsing.
Third, the structure of the eye and the camera
The structure of our eyes is almost identical to the structure of a camera, so people used to compare the eyes to a fully automatic camera. Like the camera, our eyes also have “aperture”, “lens”, “dark box” and “negative”. It can take in all the colorful scenes of nature. Moreover, the eye is more sophisticated and automated than the most advanced cameras. The pupil of the human eye is equivalent to the aperture of the camera, as the light into the eye changes in intensity, the pupil can be narrowed or expanded to play a role in regulating the light.
The transparent cornea and lens are equivalent to the lens of a camera, which focuses light on the retina and plays the role of light convergence; the choroid has rich blood circulation and is lined between the sclera and retina, which is a brown pigmented film that blocks light and is equivalent to the camera’s dark box; and the retina, which is located in the innermost layer, has a light-sensitive role and is equivalent to the camera’s negative.
External light enters the eye through our transparent cornea and lens, and is accurately focused on the retina by the human eye after fine adjustment (mainly done by the lens), thus forming a clear image and achieving good vision. It is similar to getting a clear photo after we focus through a precision camera.
Fourth, the imaging of the human eye vs. the imaging of the brain
Light from natural objects or reflected light from objects entering the human eye will form an inverted image on the retina after refraction by the cornea, atrial fluid, lens and vitreous humor. But why do we see the object not upside down, but upright? Because the object image is processed and processed by the brain before it is perceived by the human eye.
Photoreceptors on the retina of the human eye, also known as photoreceptor cells (cone and rod cells) are stimulated by light, after a series of physical and chemical changes, converted into nerve impulses, and through the optic nerve of the human eye (the nerve that conducts the visual impulses of the human eye) to the visual center of the brain, after the integration and comprehensive analysis of the cerebral cortex, thus producing vision, we see the object, at this time to see the object as The orthogonal stereo image. Therefore, the imaging of the human eye has to go through the visual system and the brain center two processes to complete.
V. What is the advanced visual function of the human eye
People have two eyes, the position of the two eyes are different, so the object in the retina of both eyes will have a subtle difference in the imaging, it is due to the existence of this difference, the brain center for analysis, processing, integration, the formation of a three-dimensional sense of depth of the complete impression, this process is the formation of binocular vision, which is also the process of stereo vision.
Binocular vision is the highest level of human visual function, it is because of the formation of binocular vision, human can more accurately obtain the external object shape, orientation, distance and other concepts, and stereo vision is the highest level of binocular vision function. In daily life, such as driving, ball games, up and down stairs, etc. are inseparable from a good stereo vision function. Some delicate tasks especially require good stereo vision, such as using microscopes, painting, architectural design, etc.
When stereo vision is impaired, there is a risk of not being able to distinguish objects clearly, falling down stairs, tailgating in a car, etc. Stereo vision does not develop until the age of 5-6 years. The development of stereo vision may be affected by abnormal eye development, such as strabismus and amblyopia. Therefore, early detection and treatment of diseases in children is of immeasurable importance for the establishment of stereopsis.
Sixth, color vision – let you have a colorful world
There are two types of light-sensitive cells in the retina of the human eye – the cone cells and the rod cells. The reason why people can distinguish between colorful and colorful world is that the cone cells play a major role. There are three main types of cone cells, which are sensitive to red, green, and blue, respectively. Under different wavelengths of light stimulation, these three types of cells are excited in different proportions, thus enabling the human eye to see the many colorful colors in nature.
Most people have normal proportions and numbers of the above three types of visual cone cells and are able to accurately discriminate between different colors, but some people have abnormal color vision due to genetic or acquired eye diseases, and their ability to discriminate colors is poor or completely lost, which can be divided into color weakness and color blindness according to the severity. They can be divided into different types of color weakness and color blindness according to the severity of their weakness or loss of color discrimination.
Seven, the characteristics of children’s visual development – sensitive and critical period
Children’s vision goes through a long process from birth to maturity, and there are two important stages in this process, namely the critical period and the sensitive period of children’s visual development. The child’s vision is weak at birth, and he or she only has a sense of light and has not yet established binocular vision. Thereafter, visual acuity and binocular visual function gradually develop based on the continuous stimulation of the external environment and the normal development of the eye’s own tissues and structures.
It is generally believed that the visual development before the age of 3 is the most important, called the critical period, and 3-10 years old is the sensitive period, because in these two periods, the development of human eye vision is not yet mature, there is a lot of plasticity, and the younger the age, the greater the plasticity, once waiting until the visual development is mature and then intervention is irreversible. Therefore, all adverse factors affecting visual acuity and binocular vision development should be corrected within these two periods, in order to get the best corrective effect.
Eight, focus on newborn eye care to promote children’s visual development
Eye care for children should not be neglected after birth. Newborn babies’ eyelids are often covered with a layer of grayish-white fetal fat, which protects the skin and maintains body temperature, and generally does not require hard scrubbing. In addition, parents should pay attention to their child’s visual status. Although infants have poor visual function at this time and cannot clearly express their visual acuity, parents can generally determine the visual status through some details of daily life and should consult an ophthalmologist as soon as possible if abnormalities are found.
As infants grow, the visual function of the eyes gradually develops to perfection. The first is the effect of light intensity on visual function. Since babies are born with poor vision, they need light stimulation to develop gradually. Most of the time, newborn babies are in a sleeping state, and parents often like to turn off the lights in the bedroom, so when babies are awake, they should keep the room brightly lit to facilitate the development of vision. However, too much light entering the eyes can also cause damage to the infant’s retina, so try to avoid direct light exposure to the infant’s eyes, such as camera flashes, strong daylight, chandeliers, etc.
The second is the stimulation of visual development by objects, brightly colored toys help children’s visual development. When infants are young, they generally lie flat in bed, and parents like to hang some toys above their beds to amuse their children, but the position of the toys should be changed from time to time, when near and far is conducive to the flexibility of eye movements, in order to avoid prolonged gaze at the same position and collection fatigue or strabismus, toys should also be from large to small to adapt to the development process of the eye.