Kate

Referát - Optics

Môj ďalší referát, tentokrát na anglický jazyk, preto je aj v angličtine, na tému optics (optika), konkrátne poruchy oka a ich korekcie šošovkami:

Disorders of the eye and its correction by lenses

Hypermetropia- far sight- hyperopia

Hypermetropia, also known as a far sight, is one of the common disorders of a human eye. Person can see clearly objects in the long distance, but blurredly those which are close. The light rays coming through the lens converge not at but behind retina. The main reason why people have this problem is still not clear. It is said, that the generator of this cause is heritability. However, lots of people do have hypermetropia although their parents didn’t have. There are also other factors which participate on the origin of far sight. For instance flatter cornea, lower thickness of lens, shorter anterodorsal size of eye, influence of some medicaments or injuries. The appearance of far sight in higher age is quite frequent. The decrease of refractive index of lens fibers is considered a normal status.

The anterodorsal distance of eye is shorter than it should be at the birth of majority of people. But as the child is growing up, so does the construction of his eye and the distance is corrected.

Symptoms of hypermetropia- person can have problems with reading, he can have a headache or eye ache or he can squint and weep.

Hypometropia- short sight- myopia

This is an opposite of hypermetropia. We can see clearly objects which are close to us, but blurredly those, which are further. The light rays converge in front of the retina. Also here, doctors and scientists can’t say exactly what the origin is and again the most realistic cause is the genetic predisposition. There are three known types of short sight; short sight of the lower level, of the higher level and congenital short sight. The first one is not so horrible and is corrected by proper glasses. The second one is a serious clinical and genetic problem because it can lead to blindness. Only in some cases the increase of short sight could be stopped thanks to an operation. The last one, congenital short sight, is caused by abortive childbirth.

Astigmatism

While the problem of hyper or hypometropia is the wrong size of the lens, here the problem is with the whole eye. Astigmatism is defined as a deformed eye. It means that one part of the eye surface doesn’t have correct shape; the most often is irregular shape of the cornea. We can compare the shape with a spoon or rugby ball. The subject-matter is that a point is not projected into one point at the retina, but between two lines.

Vocabulary

Hypermetropia-far sight-hyperopia= ďalekozrakosť

Blurred= rozmazaný

Converge= zbiehať sa

Heritability= dedičnosť

Cornea= rohovka

Lens= šošovka

Retina= sietnica

Anterodorsal= predozadná

Refractive index= index lomu

Squint= škúliť

Weep= slziť

Congenital= vrodený

Abortive childbirth = predčasný pôrod

Astigmatism= astigmatizmus, nerovnomerné zakrivenie rohovky

Subject-matter= podstata

LENSES

A corrective lens is a lens worn in front of the eye, mainly used to treat myopia, hyperopia, and astigmatism. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract removal. Myopia (near-sightedness) requires a divergent lens, whereas hyperopia (far-sightedness) requires convergent lens.

HYPEROPIA

If the lens is biconvex or plano-convex, a beam of light travelling parallel to the lens axis and passing through the lens will be converged (or focused) to a spot on the axis, at a certain distance behind the lens (known as the focal length). In this case, the lens is called positive or converging lens.

MYOPIA

If the lens is biconcave or plano-concave, a collimated beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens. The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the lens; the distance from this point to the lens is also known as the focal length, although it is negative with respect to the focal length of a converging lens.

ASTIGMATISM

A toric lens is a lens with two different powers in two orientations perpendicular to each other. One of the lens surfaces is shaped like a "cap" from a torus (see picture), while the other one usually is spherical. Toric lenses are primarily used in eyeglasses, contact lenses and intraocular lenses, to correct for astigmatism.

Vocabulary:

Cataract – šedý zákal

Axis – os

Beam of light – lúč svetla

Perpendicular – kolmý

Emanate – vyžarovať