Eye myopia and farsightedness physics. What's interesting in science: Myopia and physics

The human eye is an optical system. Light rays entering the eye are refracted at the surface of the cornea and lens.

The lens is a transparent body similar to a lens. A special muscle can change the shape of the lens, making it more or less convex.

Thanks to this, the lens either increases or decreases its curvature and, along with it, its focal length. The optical system of the eye can be considered as a converging lens with a variable focal length that projects an image onto the retina.

If the object is very far away, the image is obtained on the retina without straining the lens muscle (that is, when the eye looks into the distance, it is in a relaxed state). When an object located nearby is examined, the lens contracts and the focal length decreases so much that the plane of the resulting image again aligns with the retina.

In some people, the eyes, in a relaxed state, create an image of an object not on the retina, but in front of it. As a result, the image of the object “blurs”. Such people cannot clearly see distant objects, but they can see objects that are nearby well.

This is observed if the width of the eye is large or the lens is too convex (has a large curvature). In this case, a clear image of the object is formed not on the retina, but in front of it. This lack (defect) of vision is called myopia (otherwise known as myopia).

Myopic people need glasses with diverging lenses. Having passed through such a lens, the light rays are focused by the lens exactly onto the retina. Therefore, a nearsighted person wearing glasses can view distant objects, just like a person with normal vision.

Other people can see distant objects well, but cannot distinguish those that are close. In a relaxed state, a clear image of distant objects is obtained behind the retina. As a result, the image of the object “blurs”. This is possible when the width of the eye is not large enough or the lens of the eye is flat, then a person sees distant objects clearly, but close ones poorly. This lack of vision is called farsightedness.

A special form of farsightedness is senile farsightedness or presbyopia. It occurs because with age, the elasticity of the lens decreases, and it no longer contracts as well as in young people. Farsighted people can be helped by using glasses with converging lenses.

Glasses, being a simple optical device, bring great relief to people with visual impairments in everyday life.

5465 04/16/2019 5 min.

Our eyes allow us to receive the most full information about the world around us, but when myopia or farsightedness appears, then without vision correction we begin to feel uncomfortable and insecure.

Myopia (myopia) and farsightedness (hypermetropia) are the most common vision pathologies. We will talk in detail about what these two violations are below.

Physiological features of vision

Vision is understood as a psychophysiological function that gives a person the ability to perceive and distinguish the movement, location and colors of objects in the surrounding world. Thanks to work visual system, allowing the perception of light stimuli and objects, in conjunction with the higher parts of the central nervous system we can see.

ABOUT proper care read behind the lenses

The eye perceives an image due to the fact that a stream of light rays moves through its media. First of all, it passes through the cornea, then through the anterior and rear camera the eye, through the lens and vitreous body, and finally reaches the retina.

Thanks to the macula and the central fovea of ​​the retina, which are located opposite the pupil near the exit optic nerve, the image is focused.

The image appears on the retina in an inverted, reduced form. To see an object clearly, the lens changes its curvature. Curvature can change under the influence ciliary muscle, which can either tense or relax.

Normally, the rays should focus on the retina. This is called emmetropia. Ametropia– this is a deviation from the norm when the focus is in front of the retina (myopia) or behind it (farsightedness).

Myopia

Myopia or myopia is a vision pathology characterized by the fact that the focus of the image is in front of the retina. Therefore, a person sees poorly in the distance, but clearly sees up close. U myopic people the length of the eyes may be increased or the cornea may have greater refractive power. In the first case, myopia is called axial, and in the second - refractive.

Visual acuity with myopia may be less than one, so nearsighted people are prescribed.

As practice shows, in most cases, myopia occurs between the ages of six and twenty years. To this age group include schoolchildren and students.

Reasons for the development of myopia:

• Hereditary predisposition. If parents are myopic, then there is a high probability that their children will also have myopia.
Myopia is a common companion of those people who, due to their work, are forced to work with objects at close range. In addition, poor lighting and improper seating at the workplace can also cause myopia.
• Incorrectly selected vision correction or lack thereof. This leads to progression of the disease.

1. Glasses, contact lenses.

Farsightedness

Farsightedness or hypermetropia is a vision pathology characterized by the fact that the focus of the image is behind the retina. In this case, the length of the eye decreases, so the person sees close objects poorly, but at the same time sees well into the distance. With farsightedness, the refractive power is quite weak, therefore, in order for the focus to fall on the retina, the muscles that change the curvature of the lens are overstrained.

The degrees of farsightedness are described in.

With hypermetropia, it can also be observed in the distance (especially with a high degree of hypermetropia).

In addition, with excessive eye strain, headaches and burning sensations may occur, and various inflammatory diseases, for example, and so on. Children may experience amblyopia or strabismus.

How does a person see with and without glasses?

For the treatment of farsightedness methods such as:

1. Glasses, contact lenses.
2. Photorefractive keratectomy.
3. Laser thermokeratoplasty.
4. Lens replacement.
5. Lens implantation.

Methods for determining farsightedness and myopia

Generalizing factors (stages of disease)

Both farsightedness and nearsightedness can occur three stages:

1. Weak;
2. Average;
3. Heavy.

Regardless of whether a person has myopia or hyperopia, he needs to visit an ophthalmologist twice a year.

Regular check-ups will allow you to track the progression of the disease and promptly select new glasses or contact lenses. This will also allow you to detect in time dangerous diseases, for example, which are frequent companions of myopia and farsightedness.

Farsightedness

To determine farsightedness, there are the following methods:

• Checking visual acuity using tables. Allows you to determine the number of lines visible to the patient without correction.
• Computer vision diagnostics – autorefractometry. Using this method, the optical power of the eyes can be measured. Autorefractometry also allows you to diagnose astigmatism.
• Measuring the optical power of the cornea - .
• Cycloplegia - dilation of the pupils with eye drops. The drops block the work of the ciliary muscle, which makes it possible to detect hidden farsightedness.

Orlov's table for testing vision is located.

• Skiascopy and autorefractometry on a dilated pupil. Allows you to determine the true degree of hypermetropia. Skiascopy is usually performed on children because they may have difficulty focusing their eyes.
• Measuring the length of the eye using ultrasound. The length of the eye is determined to assess the degree of hypermetropia. The method is needed to carry out surgical interventions for the treatment of this disease.

Sometimes this is used additional method definition of farsightedness as the topography of the cornea. In farsighted people, the cornea is usually thicker. Another method that is used for people after forty years is gonioscopy. It allows you to determine the condition of the angle of the anterior chamber of the eye.

If you look closely at my photo on the blog, you will notice that I have quite severe myopia (depending on the eye and the direction from −12 to −14). In general, this is, of course, inconvenient, but myopic people nevertheless have some optical advantages over “ordinary” people - we can see some things that ordinary people don't see (or don't notice). So here is a short story with pictures about how I see. :)

Of course, I cannot attach photographs of how I see it in reality, so I will illustrate everything using photographic effects.

1. Vagueness. In a nearsighted person, the crystalline lens focuses light from a distant source not onto the retina, but in front of it, so the image on the retina itself is blurry. Everyone probably knows this, but not everyone knows what type of vagueness this is. This is not at all the “gaussian blur” that is found in Photoshop, but rather similar to the bokeh effect in photographs (which is not surprising, since the physics is essentially the same).

The easiest way to explain the difference is in a night shot with bright lights. Let's take this beautiful photo ():

Let's apply gaussian blur to it and get this image:

So, this is completely different from how I see without glasses! And I see something like this ():

The difference is that with regular smudging, light and dark areas are mixed into something in between. And with the bokeh effect bright dots blur into circles, quite clearly defined by the way, which simply creep into the dark areas. With the right lighting it can be very beautiful. :)

Addition. In the comments they also gave me a link to Philip Barlow’s paintings, written in the “myopic style”.

2. Diffraction. In a bokeh photograph, the circles look small and uniform. In fact, with my vision, these circles are large (about 4-5 degrees), and in each of them I see a rich “inner world”. Each circle has dots, spots, stripes, sometimes smooth, sometimes clearly defined. Something like this, only even richer ():

These are manifestations of microscopic dust particles and villi on the surface of the eye, as well as inhomogeneities at the interfaces somewhere deep in the eye (they give motionless “ripples”). [ As it was explained to me in the comments, floating villi, commonly called “floaters,” are physically located within the vitreous; see details.] I can see how these specks of dust float across the surface of the eye, how they twitch sharply when blinking, etc. And what’s most beautiful is that on all circles in the field of view the picture is approximately the same, all these smooth movements occur synchronously across the entire field of view. But the images in the two eyes are, of course, different.

Concentric rings and other patterns that surround dust particles and other boundaries are a manifestation of light diffraction. Yes, diffraction is indeed easily visible to the naked eye, at least to nearsighted people! Moreover, sometimes you can even see the Arago-Poisson spot (maximum brightness in the center of the geometric shadow) of very small dust particles (by the way, they are visible in this photo). All this “life” can sometimes be funny to watch.

3. Uneven illumination. The spot in the previous photo is still illuminated more or less evenly. But in reality I see spots, the brightness of which varies from edge to edge. Moreover, in the two eyes this brightness gradient does not coincide at all. I tried to roughly depict how I actually see a blurry speck without glasses:

This, by the way, creates additional problems: the two eyes “don’t know” how to combine these images, either along the contours of the circle, or along the center of brightness.

Where I get this from, I still don’t know.

4. Comfortable vision distance. With myopia, distant objects are difficult to see, but everything is clearly visible up close. Moreover, it looks much more comfortable than for ordinary person, because I don't need to strain my eyes. My comfortable vision distance is 7 cm. That is. I relax my eye, as if I were going to look into the distance, and I can perfectly see the smallest details of an object at a distance of 7 cm. Since I can look at objects so close without any problems and since there is nothing wrong with my retina, I have an advantage in “near vision” .

5. Spectral analysis. And finally, a superpower - I can arrange light into a spectrum! I look sideways at the light source and see individual emission lines, etc. Something like this, just not as clear:

This skill, of course, is achieved thanks to glasses, especially with high-index lenses (mine have a refractive index of 1.8). At the edge of the glass they act as a prism, which decomposes the light into a spectrum, and due to the fact that I have a large minus, this decomposition is quite strong. I have no problem distinguishing incandescent lamps from their continuous spectrum from gas lamps, I see individual narrow lines of radiation, I can easily distinguish, for example, a truly yellow light from a green + red one. Well, coupled with time sweep, which I also do, time-resolved spectroscopy becomes available to me! Within reasonable limits, of course. :)

By the way, another effect associated with the dispersion of light in strong glasses is lights different colors seem to me to be at different distances. At binocular vision(i.e. when looking with two eyes) this generally leads to wonderful illusions. Let's say, a blue LED on the surface of a device looks to me as if it is hanging in the air a few centimeters above the surface. And a multi-colored luminous neon sign for me looks mounted on several planes.

Lesson objectives:

• Educational: study the structure, optical system and basic properties of the eye; establish the causes of myopia and farsightedness; learn to distinguish between the lenses used in glasses to correct myopia and farsightedness.
• Educational: development of speech skills, theoretical thinking; the ability to express thoughts out loud; development of attention and curiosity; increasing interest in the subject being studied.
• Educational: formation of tolerant awareness in children; cultivating the ability to listen to a friend and respect the opponent’s opinion; development of the desire for knowledge.

Equipment and aids: table “Structure of the eye”; biology textbook for 8th grade “Man” (on each desk); slide projector; transparencies "eye. Visual defects and their correction"; educational memory cards (on each desk); portrait of I. Kepler; “Verification test” task cards, individual cards; visual posters; magnetic board, wall newspaper “These are the eyes!”; application .

Lesson Plan

No.	Stages	Time, min	Techniques and methods
	Organizational	1 I – 2 I	Greeting, checking readiness for the lesson, students’ favorable mood to perceive the lesson material, recording the topic of the lesson.
	Preparation for mastering new knowledge (updating knowledge).	5 I – 7 I	Frontal survey. At the same time, a written individual task is given to strong students, and a test is given to weak students.
	Explanation new topic.	23 I	Opening remarks teachers. Conversation. Student messages. Frontal student experiment. Teacher's explanation. Write on the board and in notebooks.
	Initial check of the material being studied	2 I – 3 I	Frontal survey.
	Consolidation of the studied material.	5 I	Short test.
	Summing up the lesson, grading.	2 I	Record homework in the diary.

I. Organizational moment

Greeting, checking readiness for the lesson, students' favorable mood to perceive the material, recording the topic of the lesson in workbooks.

II. Preparation for mastering new knowledge (knowledge updating)

Frontal survey(for middle class):

1. What is a lens called?
2. What is the difference between convex lenses and concave lenses? (use of a visual table).
3. What point is called the main focus of the lens?
4. What is the optical power of a lens? (write on the board)

At the same time, for strong students - individual cards(solving problems to determine the optical power of a lens or lens system), for weak students – test(on individual cards).

1. What is the optical power of a system of two lenses, one of which has a focal length F 1 = -20 cm, and the other has an optical power D 2 = 5 diopters?
2. The optical power of the lens system is D = 2.5 diopters. What is the focal length of the converging lens if the second lens has an optical power of D 2 = -4.5 diopters?
3. The optical power of the lens is 0.5 diopters. What kind of lens is this and what is the focal length of this lens?
4. Focal length 10 cm lens. What is the optical power of this lens? What kind of lens is this?
5. The optical power of the lens system is D = 4.5 diopters. What is the optical power of a collecting lens if the first lens has an optical power of D 1 = -1.5 diopters? Name the first lens?

1. What letter indicates the main focus of the lens?
   a) F; b) O; c) D.
2. In what units of measurement is the optical power of a lens given?
   a) mm; b) kg; c) diopter; d) A.
3. Lens focal length F = -20 cm. What kind of lens is this?
   
4. Lens optical power D = 2 diopters. What lens is this?
   a) collecting; b) scattering.

III. Explanation of a new topic

Teacher's opening remarks:

See eternity in one moment,
A huge world in a grain of sand,
In a single handful there is infinity,
And the sky is in the cup of a flower!

The person is surrounded amazing world, rich in colors, sounds, smells. We perceive it either with admiration or with fear.

Information about what is happening in environment We receive through the senses - sight, hearing, touch, taste and smell.

The topic of our lesson is “Eye and vision. Myopia and farsightedness. Glasses" (write on the board). Purpose of the lesson: to study the structure, optical system and basic properties of the eye; establish the causes of myopia and farsightedness; learn to distinguish between the lenses used in glasses to correct myopia and farsightedness.

Topic study plan(written on the board):

1. The importance of vision in life.
2. The structure of the organ of vision.
3. Optical system of the eye.
4. Myopia and farsightedness.
5. Ophthalmic devices (glasses and contact lenses).
6. Visual hygiene.
7. Kaleidoscope of facts.
8. Summing up.

During the lesson you will have to listen to pre-prepared short messages your classmates.

Message 1(student):

The eye is an organ that can be compared to a window into the world around us.

Can we always trust what we see? Do we all see?

We live in an amazing world of light. Light brings joy to everyone. We see the outside world thanks to vision. The organ of vision plays huge role in a person's life. Sunlight has always been and will remain a symbol of life and eternal youth. Light is an electromagnetic wave with a radiation length from 400 to 760 nm. Other waves do not cause visual sensations. Our eyes are sensitive only to a certain, relatively narrow range of wavelengths. We receive more than 90% of information about the world around us through vision.

The eye has adaptation properties - the ability to change its sensitivity depending on the amount of light flux. The eye is a very sensitive device. “Our eyes are capable of distinguishing the finest shades of colors - they perceive the blue of the sea wave and the glow of the sunset, the gold of the autumn leaf and the Levitan palette,” wrote I.B. in the book “Bionics”. Litinetsky. ( reproduction of Levitan).

Teacher: looking at the world and seeing its beauty is great happiness. And this happiness is given to a person by the eyes.

Let's get acquainted with the structure of the eye ( table “Structure of the eye”, terms written on the board). The human eye consists of an eyeball connected by the optic nerve to the brain, and auxiliary apparatus(eyelids, lacrimal organs and muscles that move eyeball).

The eyeball is protected by a dense membrane called the sclera. The front (transparent) part of the sclera is called the cornea. Behind the cornea is the iris, which in humans may have different color. IN iris there is a small hole - the pupil. The diameter of the pupil can vary from 2 to 8 mm, decreasing in the light and increasing in the dark. Behind the pupil there is a transparent body resembling a biconvex lens - the lens. The lens is surrounded by muscles that attach it to the sclera. Behind the lens is the vitreous body. The back of the sclera—the fundus of the eye—is covered by the retina (retina). It consists of the finest fibers covering the fundus of the eye and representing the branched endings of the optic nerve.

How do images of various objects appear and are perceived by the eye? ( slide projector, transparencies).

Light, refracted in the optical system of the eye, which is formed by the cornea, lens and vitreous body, gives real, reduced and inverse images of objects on the retina. Once at the endings of the optic nerve, light irritates these endings. These irritations are transmitted to the brain, and a person develops visual sensations: he sees objects.

The image of an object appearing on the retina of the eye is inverted. The first to prove this by constructing the path of rays in the optical system of the eye was the German astronomer I. Kepler ( Portrait of a scientist). This entire system is similar to the optical system of a converging lens (table “optical system of a lens” on the board).

But why then do we see objects not upside down? The process of vision is continuously corrected by the brain. ( Biology textbook “Man”, 8 class, illustration “Structure of the visual apparatus"). The English poet William Blake once remarked:

Through the eye, not with the eye
The mind knows how to look at the world.

The human eye is a device whose operating principle is repeated in the camera.

The eye is adapted to work in different conditions: with different distances of objects, both at close and further distances (due to accommodation) of different lighting intensities (thanks to adaptation). ( The terms “accommodation”, “adaptation” on a magnetic board). When viewing closely spaced objects, the lens becomes more convex, the radius of curvature of its surface decreases, and, consequently, the optical power increases ( D = 1/F on a magnetic board).

The eye's sensitivity to light can change billions of times due to changes in pupil diameter.

The adaptability of the eye can cause illusions - the observed object appears to us as it really is. ( The term "optical illusion" on magnetic board posters).

A person has two eyes. What is the benefit of seeing with both eyes?

Firstly, we can distinguish the distance between objects. This allows you to see the object as voluminous rather than flat. Secondly, it increases the field of view. ( Biology textbook "Man", 8th grade, pp. 76-77 – illustration).

During the development of the body, deviations from the norm may occur, as a result of which the basic conditions are violated best vision, since the lens loses elasticity and the ability to change its curvature. These deviations are called visual defects. The image of nearby objects blurs - farsightedness develops. Another vision defect is myopia, when people, on the contrary, have difficulty seeing distant objects. ( Slide projector, slide "Visual defects", table « Myopia. Farsightedness»).

Farsightedness and myopia can be caused by congenital changes eyeball. With myopia, the image of an object is fixed in front of the retina and is therefore perceived as blurry. With farsightedness, the image of an object is fixed behind the retina and is also perceived as blurry.

“According to the long-term trends of our days
The vision of weakened eyes becomes dull.
Great is the sorrow of my heart to be deprived of reading books:
More boring than eternal darkness, heavier than faith!
Then the day is disgusting, more joyful annoyance!
Glass alone is our only consolation in this poverty.
It is promoted by skillful hands
He knows how to give us vision through glasses!”
(M.V. Lomonosov)

Glasses were invented before Lomonosov, and we know that with their help a person corrects his vision, i.e. corrects myopia and farsightedness.

Message 2 (student):

“We spend a century working at home
And only on holidays we see the world through glasses.”
(I.V. Goethe “Faust”)

The depiction of optical glasses in the Middle Ages opened up enormous possibilities. Magnifying glasses have captured the imagination. Small objects were examined through them. It took a lot of effort for the simplest lenses to turn into modern binoculars, microscopes, telescopes and other optical instruments, and finally, just into glasses ( posters).

Glasses are the simplest medical device. Myopia and farsightedness are corrected (compensated) by using lenses. Nowadays, instead of glasses, contact lenses made of special transparent plastic are often used. They are applied directly to the eyelid, to the eyeball. Contact lenses do not require any frame, do not fog up, and are invisible. There are up to 80 types of glasses for various purposes.

Teacher: What lenses should be used in glasses?

In case of myopia, it is necessary to move the image of the object away from the lens and move it to the retina. For this, removed lenses are used - they scatter light with negative optical power.

In case of farsightedness, the image of an object behind the retina is moved using convex lenses that collect light. The optical power of such lenses is positive. ( Table “Lens used in glasses for correction myopia and farsightedness»).

IV. Initial check of the material being studied:

Answer the following questions:
An ophthalmologist prescribes glasses to a patient with an optical power of +2 diopters. What vision deficiency do these glasses correct? (farsightedness).

If a person is nearsighted, what kind of glasses does he need: +1.5 diopters or -1.5 diopters? (-1.5 diopters)

V. Explanation of a new topic (Continued):

The eye is alive optical instrument. During one school day, a student’s eye muscles experience the same load that the muscles of his arms and torso experience if he were trying to lift and hold a barbell over his head with a weight intended for an average professional athlete. To save your eyes from overstrain, you need special gymnastics that restores vision.

The simplest exercises can be used in any conditions, including at school, where the eyes get tired the most.

Let's do some of the exercises together:

1. Close your eyes as hard as you can, and then open them. Repeat this 4-6 times.
2. Stroke your eyelids for 30 seconds with your fingertips.
3. Do circular movements eyes: left - up - right - down - right - up - left - down.
4. Extend your hand forward. Follow your fingernail with your gaze, slowly bringing it closer to your nose, and then just as slowly moving it back. Repeat 3 times.

What if you wear glasses?

In this case, it is important to store them correctly and wash them regularly. warm water with soap. After all, your vision now depends on glasses!

And most importantly, if your vision is impaired, you must strictly follow the instructions of your ophthalmologist. A well-chosen frame of glasses decorates the face and makes it more attractive.

For the normal formation of vision and its preservation, you must follow simple rules:

1. read, write in a well-lit room;
2. you cannot read in transport, lying down, placing texts closer or further than 30-35 cm from your eyes;
3. very harmful to look at too bright light;
4. visit more often fresh air;
5. protect eyes from impacts;
6. Take vitamin A in your food.

The human eye is a delicate and valuable instrument. Take care of your eyesight from childhood!

Now let’s turn to the kaleidoscope of interesting factors:

Message 3. (student):

In many Slavic languages there is the word "eye". Once upon a time it was the only word for the name of the organ of vision. From him to different times new words were formed: glasses, perch.

Message 4. (student):

In the 16th century the word “eye” appeared. According to many scientists, this word was used in a figurative sense and meant: “pebble.”

Message 5. (student):

The human eye can distinguish 7 thousand shades of different colors.

And also the eyes do not freeze. This is because they do not have nerve endings that are sensitive to cold. On the contrary, there are a lot of these points in the tips of the fingers and nose, so these places first and most strongly feel the cold.

Message 6. (student):

The most water-rich fabric human body- the vitreous body of the eye contains 99% water. The poorest - tooth enamel– 0.2% water.

Message 7. (student):

Another vision defect is color blindness. The eye is unable to distinguish between red and green colors. This case was first described by the English chemist Dalton, hence the name color blindness. For many professions it is insignificant, but for a driver, machinist railway, it is extremely important for a pilot to distinguish red from green.

Teacher: Thank you for interesting messages. So, let's spend brief overview studied material. Today in class we talked about the importance of vision in our lives. We studied the structure of the optical system and the properties of the eye. We also learned with the help of which lenses can correct myopia and farsightedness.

We learned all this thanks to biology, history, literature, and of course physics.

VI. Consolidation of the studied material:

A short-term screening test will help us find out how we have mastered the new material we have learned.

1. Which part of the eyeball is a biconvex lens?
   a) lens; b) cornea
2. On what part of the eyeball is the image of an object formed?
   a) on the retina; b) on the cornea
3. The ability of the eye to adapt to vision, both at close and at a more distant distance:
   a) adaptation; b) accommodation; c) visual illusion
4. For myopia, glasses are used
   a) with diverging lenses; b) with converging lenses
5. For farsightedness, glasses are used
   a) with diverging lenses; b) with collecting lenses.

(The work is done on separate sheets of paper, which are handed over to the teacher for checking. At the same time, writing is done in the margins in workbook student in order to independently evaluate and analyze their work).

The work is carried out for the purpose of self-control by the students themselves of their work (This form of work is familiar to the children, as it is carried out regularly). Students’ primary knowledge on the topic studied is tested:

• five correct answers given – score “5”
• four correct answers given – score “4”
• three correct answers – score “3”
• two or fewer correct answers - score “2”

VII. Presentation of lesson results, grading.

Each student is given reminders “Gymnastics for the eyes” and “How to protect the eye from injury”

Homework: § 37.38 (for those interested, p. 148 of textbook No. 149)

References

1. Gromov S.V. Physics: Textbook for 9th grade of educational institutions / S.V. Gromov, N.A. Homeland. – M.: Education, 2002
2. Lukashik V.N. Collection of problems in physics for grades 7-9 of educational institutions / V.I. Lukashik, E.V. Ivanova. – M.: Education, 2002.
3. Demchenko E.A. Non-standard lessons physics grades 7-11. – Volgograd, 2002.
4. Kirik L.A. Physics – 9. Multi-level independent and tests. Ilexa, 2003
5. Young erudite. – M.: No. 2, 2003.
6. Physics at school. – M.: school – Press, No. 6/91, No. 2/97.
7. Encyclopedic Dictionary of the New Physicist / comp. V.A. Chuyanov. Pedagogy - Press, 1998.
8. Biology at school. – M.: School – Press, No. 8/93, No. 1/95.
9. Medical encyclopedia/ comp. M.P. Obramyan. – M.: Medicine, vol. 3 1983.

EYE AND VISION. Myopia and farsightedness. GLASSES

Integration of subjects: physics - biology.

Explanatory note:

1. During the lesson you will need: a model of the human eye; poster “Structure of the eye and camera”; glasses for myopia and farsightedness, converging and diverging lenses.

Lesson progress

Physics teacher. Guys, today in the lesson we will study the human eye, find out why we see, find out what eye defects there are and how they are eliminated.

The eye is sometimes rightly called a living camera (poster “Structure of the eye and camera”), since the optical system of the eye, which produces the image, is similar to the lens of a camera.

What does the human eye (not just a human) represent?

Biology teacher. The eye of humans and many animals has an almost spherical shape (Fig. 1).

Rice. 1. Structure of the human eye

The human eyeball has a diameter of approximately 25 mm. The eye is protected by a tough membrane called the sclera (1). Anterior part of the sclera - cornea, or cornea (10), transparent. Behind the cornea is the iris (7), which varies from person to person. different color. Between the cornea and the iris is an aqueous fluid (5) or anterior chamber.

Physics teacher. The cornea has the shape of a spherical cup with a diameter of about 12 mm and a thickness of 1 mm. Its radius of curvature is on average 8 mm. Refractive index 1.38.

Biology teacher. In the center of the iris there is a hole - the pupil (6), the size of which can change with the help of muscle fibers controlled from the central nervous system.

Physics teacher. The pupil changes from 2-3 mm in bright light to 6-8 mm in low light. This regulates the amount of light passing into the eye.

Biology teacher: Directly behind the pupil is the lens (5), a transparent and elastic body.

Physics teacher: The shape of the lens is close to a biconvex lens. Its diameter is 8-10 mm. The radius of curvature of the front surface is on average 10 mm, and the rear one is 6 mm. The refractive index of the lens substance is 1.44.

Biology teacher. The lens is surrounded by muscles that attach it to the sclera (9). Behind the lens is the vitreous body (4). It is transparent and fills the rest of the eye.

The fundus of the eye is covered by the retina (retina) (3), which is adjacent to choroid(2). The retina is about 0.5 mm thick and consists of several layers containing optic nerve fibers. The retina consists of rods and cones and nerve cells, from which excitation goes to the brain. Total number cones ≈ 7 · 10 6, and rods ≈ 100 · 10 6. Cones are concentrated in the central part of the retina, in the macula, and especially in its central fovea. The rods are located mainly in the peripheral parts of the retina.

Rods have high light sensitivity, but do not provide color discrimination.

Rice. 2. Schematic representation of the structure of the human eye

Cones have lower light sensitivity and produce the sensation of color.

Physics teacher. The optical system of the eye is the cornea, lens, and vitreous body. The main optical axis of the 00 system passes through the geometric centers of the cornea, pupil and lens.

Biology teacher. In the eye, there is also a visual axis 00", passing through the center of the lens and yellow spot. In this direction the eye has little light sensitivity.

Physics teacher. The optical and visual axes form a small angle of ≈ 5°.

How is the image of an object obtained and perceived by the eye?

Light falling into the eye is refracted at the front surface of the eye (cornea) at its border with the air. Therefore, of all refractive media, the cornea has the greatest optical power (40 diopters). Then the light, passing through the lens, is further refracted. The optical power of the lens is 16-20 diopters. The light is still refracted in the anterior chamber and vitreous body, the optical power of which is 3-5 diopters. So, the optical power of the eye = 63 diopters, due to which a real, reduced and inverted image of the objects in question is formed on the retina of the eye.

Biology teacher. Light falling on the endings of the optic nerve, which make up the retina, irritates these endings. Irritations are transmitted along nerve fibers to the brain, and a person receives a visual impression, that is, he sees objects. The process of vision is corrected by the brain, so we perceive objects not upside down.

Physics teacher. Now let's find out how a clear image is created on the retina when we move our gaze from a distant object to a close one and vice versa. This happens because the curvature of the lens changes. When we look at distant objects, the curvature of the lens is relatively small.

Biology teacher. In this case, the muscles supporting the lens will be relaxed and the lens will be stretched. And when they look at nearby objects, the muscles compress the lens (Fig. 3).

Rice. 3. Accommodation of the eye

Physics teacher. Then the curvature of the lens and optical power increase.

Biology teacher. The ability of the eye to adapt to vision at both near and far distances is called eye accommodation. The limit of accommodation of the eye occurs when the object is at a distance of 12 cm from the eye. Move the textbook page to a distance of 12 cm, what do you observe? The best vision distance (move the page away from your eyes), at which the details of objects can be seen without strain for a normal eye, is 25 cm. This should be taken into account when writing, reading, sewing, etc.

Physics teacher. But what advantage does seeing with two eyes give?

Biology teacher. Firstly, we see more space, that is, the field of view increases. Secondly, vision with two eyes allows us to distinguish which object is closer and which is further from us. The fact is that different images are obtained on the retina of the left and right eyes; we seem to see objects on the left and on the right. And the closer the object, the more noticeable this difference is; it creates the impression of a difference in distance, although the images merge in our minds into one. Thanks to vision with two eyes, we see objects not flat, but three-dimensional.

Physics teacher. Only thanks to the accommodation of the eye, the image of objects is obtained on the retina.

This occurs if the eye is normal. An eye is called normal if, in a relaxed state, it collects parallel rays at a point lying on the retina.

But there are eye defects - myopia or farsightedness. When judging the optical properties of the eye, the concept of refraction is used.

Rice. 4. Refraction of the eye:

A - proportionate; B - farsighted; B - myopic

Biology teacher. Myopia may be caused by a greater distance between the retina and the lens compared to a normal eye (Fig. 4 B).

Physics teacher. This means that an eye that has a focus at calm state The ocular muscle lies inside the eye. Then, if the object is at a distance of 25 cm (the distance of best vision), then the image is not obtained on the retina (as in a normal eye), but closer to the lens, in front of the retina. Therefore, in order for the image to appear on the retina, you need to bring the object closer to the eye. Therefore, in myopic people the distance of best vision is less than 25 cm.

Biology teacher. Myopia may be due to the fact that the retina of the eye is located closer to the lens compared to a normal eye.

Physics teacher. This means that the eye that has focus when at rest is called farsighted. eye muscles lies behind the retina. The image of an object is obtained behind the retina of such an eye. If an object is removed from the eye, the image falls on the retina. Therefore, in farsighted people, the distance of best vision is more than 25 cm.

Biology teacher. A difference in the location of the retina, even within a millimeter, can already lead to noticeable myopia or farsightedness. People who have normal vision in youth become farsighted in old age. This is explained by the fact that the muscles that compress the lens weaken and the ability of accommodation decreases. This also happens due to the compaction of the lens, which loses its ability to shrink in old age.

But myopia and farsightedness can be eliminated by using glasses.

Physics teacher. What glasses should be used to correct these vision defects?

In nearsighted people, images of objects are obtained inside the eye, that is, in front of the retina. In order for it to move to the retina, it is necessary to reduce the optical power of the refractive system of the eye. To do this, use a diverging lens in glasses (Fig. 5 B).

The optical power of the farsighted eye system must be enhanced in order for the image to fall on the retina, so a converging lens is used in glasses (Fig. 5 A).

Rice. 5. Correction of eye refractions:

A - farsighted; B - myopic

Biology teacher. The invention of glasses was a great boon for people with visual impairments. .

Teacher physics. And this benefit appeared a long time ago. In engravings and paintings with ancient scenes you can often see people wearing glasses. Artists (XV-XVII centuries) willingly depicted noble people of the past wearing glasses in order to give them a more impressive, learned appearance. During archaeological excavations in Pompeii and Tire, processed pieces of glass were found that resembled magnifying lenses. There is reason to believe that it was in Italy at the end of the 13th century that the first glasses appeared. Glasses appeared in Russia at the end of the 15th century. At first, only one magnifying glass with a long handle was used. Then double round glasses in a metal frame appeared. They were held in front of the eyes or put on the nose. Gradually they acquired glasses modern look.

So, to correct myopia, glasses with concave, diverging lenses are used. If a person, for example, wears glasses with an optical power of -3 diopters, then he is nearsighted. Glasses for farsighted eyes use convex, converging lenses. Such glasses may have, for example, an optical power of +3 diopters.

Biology teacher. Throughout life, a person sooner or later has to resort to glasses. Glasses allow us to see better, they seem to extend the life of our eyes and enable most people to continue active work in old age.

Physics teacher. Guys, how can you tell which glasses are for nearsighted people and which are for farsighted people? It turns out to be very simple. I take glasses for myopic eyes and the lenses from them, look, they give a shadow, but the far-sighted lenses do not have a shadow. This suggests that diverging lenses have imaginary foci, while converging lenses have real foci.

Biology teacher. Guys, what kind of eyes do representatives of the animal world have? Most arthropods have many eyes, oriented in all directions. Each eye has the shape of a very narrow and deep funnel. Fish eyes have a flat cornea and a spherical lens.

Rice. 6. Eyes various representatives animal world:

A - eye of a fly; B - zebra eye; B - human eye

Physics teacher. Accommodation of the eye in fish is achieved by moving the lens.

Biology teacher. Birds have sharp vision. Vultures and eagles have an elongated eyeball. The eyes of highly organized animals are similar to the human eye, only some animals can rotate them, for example a chameleon. In other cases, for example in the hare, they are located on the sides of the head, which gives a view of over 180°.

Physics teacher. Today in class, guys, you got acquainted with one of the senses - vision. We learned about the structure of the eye, eye defects, and how these defects are corrected by wearing glasses. Refraction is the refractive ability of the eye at rest of accommodation, when the lens is as flattened as possible.

Biology teacher. Let me add that there are three types of eye refraction:

1) proportionate (emmetropic);

2) farsighted (hypermetropic);

3) myopic (myopic).

Physics teacher. You are convinced of the connection between the science of biology and physics. The laws of nature are uniform and can be applied to a living organism. Today in class we applied the laws of physical optics to the eye.