How pale eye mass were prevented

Interesting figures on the eye are listed on this page. For an explanation of the individual structures, see also components of the eye:

  • The See is the most meaningful sense we have. With no other sense organ can we absorb nearly as much information in such a short time. It is estimated that 70% of all information important for humans is absorbed by the visual system (everything that is necessary for vision: eye, optic nerve, visual center, etc.). In today's visually oriented society in particular, the importance tends to be set even higher. It is all the more dramatic when vision fails and visual impairment or even blindness occurs.

  • The eye weighs 7.5 grams, is hollow and spherical. In the adult it has a mean diameter of 2.3 cm (child 1.7 cm). The volume is 6.5 cm3

  • The Eyelids, are protection and "wipers" of the eye. They are 2mm thick. By blinking the eye - blinking - the tear film is distributed and foreign bodies are wiped away. People blink an average of 20,000 times a day. Women blink almost twice as often as men. The frequency of blinking on the screen drops by half to a third. By blinking, the eyes are closed for a total of about 15 minutes a day.

  • In the white area of ​​the eye (Dermis = sclera) the wall of the eye is 0.3 to 1.35mm thick. The Cornea - the window to the eye - is the clear area in the middle with the black area (the pupil) and the colored area (the iris) behind it. It has a diameter of approx. 11 mm, is approx. 0.5-0.6 mm thick and bundles the light together with the lens onto the retina in the back of the eye. The refractive power of the cornea, i.e. the ability to deflect and focus light, is 43 diopters. Together with the lens, it is, so to speak, the lens of the eye. The total refractive power of the cornea and lens is approx. 60 diopters.

  • The Choroid, the middle layer of the eye wall, which is well supplied with blood, is 0.1-0.3mm thick. Half a liter of blood is pumped through the eye every minute to meet the high demand for oxygen. 95% percent of this half a liter flows through the choroid.

  • The iris (Diameter 12mm and thickness 0.5-3.0mm) with its central opening of the pupil, regulates the incidence of light into the eye like the aperture on a photo camera and protects the retina from over-stimulation (glare). When the brightness is high, the pupil is smallest (1-2 mm) and largest in the dark (approx. 9 mm). This allows her to let through sixteen times as much light. Between a new moon night and glaring sunlight, however, there is a difference in brightness of 1 to a billion, all of which one eye must be able to regulate. The iris can only do a part here, the pre-filtering, so to speak. The rest is regulated in the retina, which can regulate its sensitivity up and down. However, this chemical process takes some time. Therefore, you can only see well in the dark after a certain amount of getting used to. The eye color is created by the bluish basic tint of the iris and the possible additional coating with brownish pigment cells (see eye color). 10% of the world's population are naive.

  • Overall, there are 11 more important ones on the eye Muscles. One lifts the lid, one is responsible for squeezing the eyes in a ring, one makes the pupil smaller, one makes the pupil larger, one is responsible for focusing and 6 muscles move it in different directions. If one of these 6 muscles fails, e.g. due to an injury to the muscle itself or the controlling nerve or due to malfunctions in the activation in the brain, strabismus occurs. These muscles have to work hard as they step into action 100,000 times a day to point the eyes in the right directions. Screen work, for example, represents an additional burden here.

  • The bony Eye socket contains the eye, muscles, padding fatty tissue, and nerves and blood vessels. Their volume is approximately 30ml.

  • The Retina is also differently efficient in the different areas. The maximum visual acuity (100%) only exists in the area of ​​0.35mm in diameter Foveola (Point of sharpest vision in the center of the retina), the center of the fovea. There are 147,000 cones (light-sensitive receptors) per square millimeter here. Compare that with the pixels on a monitor. When reading, the Foveola only captures 2 letters at the same time. The density of the receptors - and thus the visual acuity - decreases more and more towards the edge of the retina. There are a total of 7 million cones (color receptors) and 120 million rods (black and white receptors). The sensitivity to light of the rod is higher, so with increasing darkness one no longer sees colored but only gray and also not so sharp, because in the middle of the retina - the foveola - only Cones available. The frequency and distribution of color receptors (cones) in the retina varies. In the center (fovea) there are 2-3% blue cones. In total, there is approximately 9-12% blue cones, 33% red cones, and 55% green cones. The Macula is slightly larger (approx. 5 mm in diameter) than that Fovea (approx. 1.5 mm in diameter and 0.2 mm thick), with the fovea in the middle of the macula. Outside the macula, visual acuity is less than 30% (see field of vision below). If the macula fails due to a disease (macular edema, maculopathy), the center is missing when looking. Then, for example, the face of the person opposite is not recognizable. The percentages relate to so-called full visual acuity (visual acuity 1.0 or 100% for laypeople). Especially in younger patients without visual defects, there is an even higher visual acuity of up to 1.6 or 160% (see also the page on the eye test and there the term vision). In newborns and small children, however, the eyesight is not yet fully developed (see Development of Vision on the Child Examination page) The resolution of the human eye, i.e. the smallest distance between 2 seen points is 1/120 of a degree. Movement vision, i.e. the ability to recognize movement as such, begins at 1-2 angular minutes per second.Today's generally available high-resolution photo cameras have 47 megapixels, i.e. 47 million pixels that they can resolve. Some therefore wonder how many megapixels there are in an eye. Among other things, due to the uneven structure of the eye, you can't really say that. You can find more details and how to get the value of 576 megapixels for the eye HERE.

  • The one that fills the eye between the lens and the retina Vitreous (see also the Vitreous Diseases chapter) has a volume of 4ml. It consists of around 98 percent water. There is also about 2 percent hyaluronic acid and so-called collagen fibers. These fibers are very evenly distributed in youth and create the gel-like consistency. In old age there are structural changes and segregation with the result of vitreous opacities.

  • The field of vision (the area that can be seen with both eyes at the same time without eye movement) is 174 to 138 degrees, depending on age, with a tendency towards older age. In women it is a few degrees wider than in men (is genetic and is often included in “sexist” comparisons of the sexes). For figures see HERE

  • Color vision disorders are mostly hereditary. Due to inheritance via the sex chromosomes (x-linked recessive), 7.5% of men and only 0.25-0.5% of women are affected by a color weakness or color blindness for a color. Mostly it is a weakness of seeing green. A person with normal vision can distinguish between 100,000 and 1 million color nuances but cannot name that many. Usually 11 basic colors (white, black, red, green, yellow, blue, brown, orange, pink, purple and gray) are differentiated and possibly further specified by 150-200 additional color names based on appropriately colored objects (e.g. cherry red, copper red , Salmon red etc.), depending on how trained you are. However, there are also acquired color vision disorders (poisoning, illnesses, etc.) that can be detected in tests.

  • The Optic nerve, which transmits the image information to the brain is 3-4mm thick, 25mm long and has 1 million fibers in the eye socket. When entering the eye, the mouth is in the shape of the papilla in a healthy state 1.5 to 2.2 mm in diameter. The optic nerve goes through a bone canal into the cranial cavity and transmits its information to the brain. It is one of the so-called cranial nerves, i.e. nerves that emerge from the brain and are, so to speak, an "extension" or "appendage" of the brain. The visual impression, the actual image, only arises in the brain, the visual center (see also under visual process) in the back of the head. If this fails - e.g. due to a blow to the back of the head - one is blind, although the eye is still intact.

  • The optical system of the eye consists essentially of the cornea with a refractive power of 43 dioptres and the lens with a variable refractive power of 19-33 dioptres. Overall, there is an average refractive power of approx. 60 diopters. For comparison: If you have moderate myopia, you need glasses with 2-4 dioptres.

  • The human lens weighs an average of 0.174 grams (65mg at birth and up to 270mg in old age due to growth and hardening processes). It has a diameter of 6.5-9mm. Their shell (lens capsule) is between 2 and 15 micrometers (thousandths of a millimeter) thick, depending on the region. In the course of life their thickness increases due to aging processes from 3.5mm to about 5mm in the 80th year of life. It also becomes cloudy, the contrast vision is therefore reduced and "cataracts" occur. An eye without visual defects can only see far when relaxed. To see up close, the lens has to deform and thereby increase its refractive power (ability to “focus” nearby). This process is called accommodation. The maximum power of the lens decreases with age. This means that the next point that can be clearly seen moves further and further away. At 10-19 years of age it is 7cm in front of the eye, at 40-49 years it is 22cm and at 60-69 years it is 100 cm. One speaks of the so-called “presbyopia”. This is the reason for the reading glasses.

  • The Tear production begins in the 3rd week of life and amounts to about 1 gram per day. The individual tear weighs only 15 mg. In the whole of life there is an average of 80 liters of tear fluid, corresponding to 2 billion individual tears, that are formed. In adults, 38 mg / hour is excreted and in children 84 mg / hour. A basic production of 1.2 microliters (1.2 millionths of a liter) is differentiated from a stimulus secretion that is 100 times higher than what is known as crying or tears in the eyes. In addition, there are “annoying” things like cold, bright light, foreign bodies etc. but also for psychological reasons (see also reasons for watery eyes). The tears run over the surface of the eyes and moisten them, create optically ideal conditions, distribute nutrients, bring disinfecting substances and wash away foreign bodies. The tears form a protective layer against dehydration, the so-called tear film. It is 3 micrometers (3 thousandths of a millimeter) thick. The tears are distributed through the eyelids (the "windshield wipers" of the eye, wipe over the eye approx. Every 4-6 seconds) and then drain through the tubules into the nose. The tubules up to the tear sac are 10mm long. From the tear sac (10-14x5mm) it is then 12-18mm into the nose. Overall, the draining tear ducts are about 36mm long. Problems with drainage arise from lacrimal diseases. Problems with the production of tears, a suboptimal tear film or disorders of the lid function can lead to "dry eyes". The additional capacity of the conjunctival sac of the lower eyelid is 20-30 microliters of fluid. A normal therapeutic eye drop from a dosing bottle contains 25-55 microliters of liquid, i.e. some of the eye drops always run over the lower eyelid. The various psychological / emotional reasons for the so-called "Cry" include joy, sadness and anger. But "tactical" crying to get affection was also used not only in adults, but also in infants as early as six months old. So crying as manipulation. Evolutionary biologists (science of the development of living things) compare this to the "separation calls" that can be observed in many birds and mammals. A little interesting in the following statistics In addition: Up to the age of 13 boys and girls cry about equally often. That changes later. Men cry about once a month or 6-17 times a year and women about 3 times a month or 30-64 times a year. The frequency and reasons for crying, even in infants and even more so in adults, vary widely depending on the culture. In China, for example, women cry on average once a month and men only four times a year. German men let their tears run for two minutes on average and women for six minutes. With women there are around 50 tears and with men it is at most moist eyes. In 65 percent of women, crying turns into sobs, but only in six percent of men. Women are most likely to cry when they feel inadequate or face difficult-to-resolve conflicts, or when they remember past life episodes. Men cry more out of compassion or when their own relationship has failed. Adults are most likely to cry between 7 p.m. and 10 p.m. On average, every German sheds 70 liters of tears in the course of his life, enough to fill a bathtub. All Germans together cry 40 baths full every day. The actual benefit and the exact causal relationships of crying have not been finally clarified until today. Charles Darwin still believed that crying relieved stress and that tears served as a coolant for eyes that were overheated by emotions. Both later turned out to be wrong. Even only the current emotion, the automatic reflex on a situation as the basis for crying, does not quite hit it, because actors can produce tears by remembering emotions ("method acting") and it also comes in as a learned behavior in primitive peoples predefined situations. The special science that deals with tears is by the way Dacryology (from the Greek "dakryon" = tear).

  • The print inside the eye is 12-21mmHg (mmHg means "mm of mercury", an old unit for measuring pressure). For comparison: the blood pressure fluctuates between 80 and 140mmHg. If the intraocular pressure rises too high, glaucoma can occur.

  • The Precursors of the photoreceptor cells (Rods and cones) were found in front of the actual eye in the brain of a common ancestor of worms and humans. The eye has been around for around 538 million years (see also the history of the development of the eye)

  • Every quarter there are 7.5 million treatment cases in Germany Ophthalmological practices at. 6% of them are small children. The most common diagnoses are cataracts (20%), macular degeneration (15%), glaucoma (12%), sugar disease (10%), and inflammation and injury (18%).

  • Current statistics of the professional association of ophthalmologists (BVA) for Incidence and causes of eye diseases in general, see: the statistical information page of the BVA

Books about crying:

  • Jeffrey A. Kottler, "The Language of Tears", San Francisco, 1996
  • Tom Lutz: "Crying: The Natural and Cultural History of Tears", New York, 1999
  • Gisela Berkenbusch: "To Heulen", Berlin, 1985

(As of May 1st, 2021)

These pages were written by Dr. Become a man from Ochsenfurt.