Temat: Oko – narząd wzroku

Autor: Elżbieta Szedzianis

Adresat

Uczeń klasy VII szkoły podstawowej.

Podstawa programowa

10. Narządy zmysłów. Uczeń:

1) rozpoznaje elementy budowy oka (na modelu, rysunku, według opisu itd.) oraz przedstawia ich funkcje w powstawaniu obrazu, dokonuje obserwacji wykazującej obecność tarczy nerwu wzrokowego;

2) przedstawia przyczyny powstawania oraz sposoby korygowania wad wzroku (krótkowzroczność, dalekowzroczność, astygmatyzm).

Cel lekcji

Uczniowie opisują związek budowy i funkcji na przykładzie oka.

Kryteria sukcesu

• opiszesz budowę oka;

• wykażesz na czterech przykładach, że budowa oka ma związek z pełnioną przez nie funkcją;

• omówisz powstawanie wrażeń wzrokowych;

• wyjaśnisz, na czym polega krótkowzroczność, dalekowzroczność i astygmatyzm.

Kompetencje kluczowe

• porozumiewanie się w języku ojczystym;

• porozumiewanie się w językach obcych;

• kompetencje matematyczne i podstawowe kompetencje naukowo‑techniczne;

• kompetencje informatyczne;

• umiejętność uczenia się;

• kompetencje społeczne i obywatelskie.

Metody/formy pracy

Praca z tekstem, obserwacja.

Praca indywidualna oraz praca w grupach.

Środki dydaktyczne

• abstrakt;

• tablica interaktywna lub tradycyjna;

• tablety/komputery;

• rozsypanka – jedna na grupę.

Fazy lekcji

Wstępna

Nauczyciel podaje temat lekcji i kryteria sukcesu oraz omawia przebieg zajęć.

Realizacyjna

1. Nauczyciel dzieli uczniów na grupy. Każda otrzymuje rozsypankę – pocięte na zdania dwa wydrukowane fragmenty abstraktu: „Twardówka, naczyniówka, siatkówka” oraz „Jak powstają obrazy”. Uczniowie w grupach losują zdania i po kolei odczytują je, a następnie układają z nich opis budowy oka oraz opis powstawania wrażeń wzrokowych. Po ułożeniu rozsypanki, rysują schemat przedstawiający budowę oka.

2. Nauczyciel wyświetla ilustrację interaktywną „Budowa oka” i prosi uczniów, żeby porównali
   z nią swoje schematy. W skali od 1 do 5 oceniają podobieństwo swoich rysunków do ilustracji interaktywnej. Korygują ewentualne błędy.

3. Uczniowie na ilustracji interaktywnej (wyświetlonej na tablicy interaktywnej) rysują drogę przebywaną przez promienie świetlne w oku. Omawiają mechanizm powstawania wrażeń wzrokowych.

4. Uczniowie opisują zjawisko adaptacji średnicy źrenicy jako wyniku odruchu bezwarunkowego. Tłumaczą, dlaczego rozpoznawanie obiektów (np. rozpoznanie przyjaciela) jest efektem odruchu warunkowego.

5. Uczniowie prowadzą obserwację, mającą na celu potwierdzenie istnienia plamki ślepej na siatkówce („Obserwacja 1”). Zapisują swoje spostrzeżenia i wyjaśniają wynik obserwacji.

6. Uczniowie czytają fragment pt. „Choroby i wady narządu wzroku” i analizują ilustracje
   z galerii „Wady wzroku i sposoby ich korekty”.

Podsumowująca

7. Uczniowie wykonują ćwiczenia interaktywne.

8. Nauczyciel prosi podopiecznych, żeby dokończyli zdanie: „Na dzisiejszej lekcji nauczyłem się...”.

Praca domowa

Odsłuchaj w domu nagrania abstraktu. Zwróć uwagę na wymowę, akcent i intonację. Naucz się prawidłowo wymawiać poznane na lekcji słówka.

W tej lekcji zostaną użyte m.in. następujące pojęcia oraz nagrania

Pojęcia

Teksty i nagrania

Eye - the organ of sight

An eyeball has a spherical shape. Its outer layer is composed of three membranes. Sclera surrounds the eyeball and protects it from injuries. It also gives it its shape. At the back part of the eyeball it is thick and opaque, whereas in the front of the eyeball, where we call it cornea, it is thin and transmits sun rays.

Under the sclera there is the choroid, which has blood vessels, it surrounds the eye and provides it with oxygen and products of metabolism. In the front part of the eyeball, the choroid converts into the iris, which has the shape of a ring. The opening in that ring is the pupil. In the iris there are smooth muscles, thanks to which it can change the diameter of the pupil and regulate the amount of light transmitted into our eye. Adapting to the intensity of light is reflex. The colour of the iris depends on the amount of the pigment – melanin.

The most internal membrane of the eyeball is the retina. It has 2 different types of sensory cells that are sensitive to light – cone cells and rod cells. Rod cells are sensitive to the intensity of the light – thanks to them our brain differentiates between different shades of gray, but not colours. Cone cells ensure chromatic vision and are active only when the light is bright. This is the reason why we don’t see colours well in semidarkness. Each cone cell is responsible for catching light of different colour (wave lenght). On the retina there is 125 million rod cells and 6 million cone cells, whereas rod cells are found on the outside part of the retina and cone cells are found at the rear part of the eyeball. Its highest concentration (250 thousand per mmIndeks górny 2²) is found in the point called macula lutea. It is the area of the sharpest vision. On the retina there is also a place that has no sensory cells. It is the blind spot, from which departs the optic nerve that transfers neural impulses to the encephalon.

After passing through the cornea, the light reaches the pupil behind which is the lens. It is transparent and its shape can change. Sun rays go through the lens and then through the vitreous humour (vitreous body) that lies directly behind it and that consists in 98% of water. Next, they reach the surface of the retina. On the way, they become refracted by the cornea and by the lens, thanks to which the sharp image is created on the retina.

Light stimulates receptor cells on the retina. Each one of them has photosensitive pigment which, under the influence of the light energy, decomposes and causes the creation of a neural impulse. The impulse from the receptor cells travels to the optic nerve and then, through the optic nerve, to the optic cortex in the brain. There, neural impulses are translated and interpreted (recognized), thanks to which we learn how our surroundings look like.

The most sensitive part of the retina is the macula lutea which consists mainly of cone cells. Image which is created there is sharp, clear and colorful. In complete darkness the cone cells become less sensitive, and the rod cells, situated at some distance from the macula lutea, become stimulated. The image created thanks to the rod cells is less sharp and gray.

Eyes adjust (adapt) to the amounts of light. After leaving a dark place into the light, and from a light room into the dark room, our eyes may be blinded for a short time, but then they begin to send information to our brain. Strong light can damage our eyesight, which is why we should not look directly into the sun without protective lenses. Strong light is a stimulus that causes us to squint and causes our pupil to narrow.

Tracking objects that are approaching or departing is possible thanks to the shape of the lens (curvature). It allows you to adjust the visual acuity. When we look at the image from up close, the lens becomes more convex, whereas when you are looking at the object from a distance, the lens becomes flatter. This phenomenon is called accommodation of the eye.

Seeing on both eyes allows us to judge the distance. Eyeballs are directed towards the front, they are at distance of about 6 cm from each other. Because of that, they receive 2 slightly different images. Optic nerves transfer them to the brain and there, in the optic centre, both information are analyzed and superimposed on each other. This is how the spatial (three dimensional) image is created.

Eyes deliver about 70% of information from the surroundings. Every day many external factors influence them, which is why they require special care and protection. Hygiene of the organ of sight should include those actions, which allow the eyes to function correctly. These are, among other things:

• protecting the eyes from too intense light by using sunglasses with UV filter;

• protecting your eyes from having a contact with chemical substances in water (e.g. in a swimming pool) by using swimming glasses;

• remembering about correct moistening of the eyeball, by drinking around 2.5 l of liquids every day and maintaining adequate humidity in rooms, especially during heating season;

• caring for correct lighting of your work place and positioning the computer screen at a distance not shorter than 50 cm from the eyes, and, when you work longer using a computer – using glasses with anti‑glare lenses;

• limiting time we spend in front of the TV or computer;

• regular eye checks.

Wrong shape of the lens or the eyeball is the cause of myopia or hypermetropia, and wrong curvature of the elements that refract the light leads to astigmatism. Eyesight defects can be corrected using adequate lenses.

The cause of myopia can be the incorrect, too bulgy shape of the lens or too elongated eyeball. As a result, the light is focused before the retina, which causes the person with such defect to see clearly only the objects that are at a short distance from her eyes. In order to correct this defect, we use dispersive lenses, marked with the minus sign. In the case of hypermetropia, the eyeball is shortened or the lens is too flat, which causes the light to focus behind the retina. In order to correct this defect, we use focusing lenses, marked with the plus sign. The ability of the eye to see is expressed in diopters.

The irregular curvature of the cornea or the lens focuses the light in different points of the retina or outside the retina, which causes the image to be blurry. This type of defect is called astigmatism. In order to correct it, we use cylindrical lenses.

Working with a computer requires focusing your eyes on a screen that is at fixed distance, which, in consequence, may lead to weakening of the muscles that are responsible for changing the shape of the lens and problems with eyes’ ability to accommodate. That is why it is recommended to make short breaks while working, during which we should look at something far away. Looking at a computer screen lowers the frequency of blinking, which leads to bad moistening of the eyeball surface. In this situation, you feel your eyes burning, or you have the impression you have sand in your eyes. If this discomfort continues, it can lead to cornea infections.

• Organ of sight consists of the eyeball and the protective and moving apparatus.

• Eyeball is covered by three membranes: sclera, choroid and retina.

• On the retina there are photoreceptor cells - cone cells and rod cells.

• Macula lutea is the place of sharpest vision.

• Light passes through the cornea, lens, vitreous humour (vitreous body) and reaches the retina.

• The image created on the retina is smaller and inverted.

• The phenomenon of accommodation allows us to see sharply objects that are close and far.

• Problems with sight can be caused by eye diseases, genetic conditions or result from wrong construction and shape of the elements of the eye.