Gli esami per l'occhio sonomolto importanti e complessi. Bisogna pensare infatti che l'occhio non solo è un diottro composto (cioè formato da una camera oscura alla quale sono anteposti m stemi di lenti) di cui bisogna misurare l'indice di rifrazione, ma è anche un organo cavo riempito di liquidi trasparenti (umor acqueo e umor vitreo) che presenta una certa pressione, mantenuta da un continuo ricambio dell'umor vapor, which, therefore, one must know the exact pressure and because of its alterations. You must also review the back of the eye, with special equipment, since it is not visible to the naked eye. In order to examine everything you need different equipment, which of course are not all used in every eye examination, but now one, now another, according to information obtained by history and that the specialist examination in daylight.
examination of refraction - is the examination which serves to establish the functioning of the eye from the visual point of view. We begin by measuring the length of the anterior-posterior eye (We know that in a myopic eye the anterior-posterior axis is longer than normal, while in a hyperopic eye the anterior-posterior axis is shorter), then measuring the refractive index of the cornea on the various axes, for to determine the presence of a possible astigmatism.
The schiascopìa - The word derives from greek and means "examination of the shadow." To implement this test is used a plane mirror with a central hole, a light bulb, at the side of the patient and a straight edge of lenses. If you look at the pupil of the patient through the mirror, the reflected light is uniform. If, however, gives the mirror a movement back and forth, the pupil is invaded by a shadow that starts first, and progressively invades the other end. If the shadow follows its movements in the movement of the mirror, the eye is considered emmetropic or hyperopic, running a reverse movement the eye is myopic.
To determine the refractive index is sufficient to put before the eye lenses of progressively more powerful that will be positive if the shadow follows the movement of the mirror, negative if it goes in the opposite direction, until the shadow reverses the journey. The exact refractive index is determined by the number of diopters of the lens that was less than a diopter reverse the shadow, in the case of positive lenses, and is determined by the number of diopters of the lens which makes the reverse shadow in the case of negative lenses.
The ophthalmometers - By means of this survey measures the curvature of the front surface of the cornea. In some cases, the cornea does not appear as a segment of a sphere, but has different radii of curvature on two perpendicular meridians. This alteration causes the defect that refractive astigmatism. By measuring the curvature of the front surface of the cornea and consequently deterioration of its curvature, is implemented by means of ophthalmometers. These measure the curvature of taking into account the distance at which the two aims should be placed on the support hemispheric light, because their reflection on the cornea can be seen in contact.
Ophthalmoscopy - With this test you can see the back of the eye and appreciate all the changes that may occur against the carpet retinal vessels of the papilla and the macula lutea.
tonometry - The eye is an organ in which it has a continuous supply of a transparent liquid content, ie the aqueous humor. We know that an alteration in the absorption or production of this fluid increases the eye pressure and can lead to serious deterioration of the optic nerve, as occurs in glaucoma. To measure the tone (ie the pressure) of the eye using special devices called tonometry.
The instrument consists of a hollow cylinder, whose lower end is shaped like a cup. Inside this cylinder, it runs another, whose upper end is loaded with weights of known value. The high end is in contact with a lever that controls a lancet. After anesthetized, the eye rests on the cornea cupped portion of the instrument. It is clear that the more the eye pressure is high, much less the inner cylinder can depress the cornea and vice versa. The level of depression is viewed on a graduated scale, this value is, with a specific table, converted to millimeters of mercury. Endobulbare pressure ranges between 18 and 20 mm Hg.
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