Our eyes ‘photograph’ everything around us every day, but sometimes they need help to adjust vision and make it perfect to do so. Not all, in fact, are emmetropic, that is, we have a clear vision without the need to use glasses. Often there can be the classic refractive defects: myopia, hyperopia and astigmatism which can appear at any age causing blurry vision with a serious impact on the quality of daily life. Defects which should be noticed especially now that school and work activities are resumed because sight plays a fundamental role to give the best in every area of our life.
The eye like a camera
The eye can be compared to a camera in which the objective is made up of two lenses, the cornea and the crystalline. “When the distance of the object varies – explains Luigi Mele, ophthalmologist surgeon at the Luigi Vanvitelli University of Naples and President of the Scientific Committee of the Salmoiraghi & Viganò Foundation – focusing occurs automatically not by shifting the lens, as it happens for the camera, but for a change in the curvature of the lens, a complex mechanism that takes the name of accommodation ”. Always imagining the eye as a camera, then we find the diaphragm, the pupil, whose opening / closing is automatically adjusted according to the light intensity. Finally, the film, that is the retina, on which the image arrives and is transformed into a series of nerve impulses that are transmitted to the brain.
What is myopia
Myopia is a refractive defect of the eye that prevents you from focusing on objects from a distance, while you can see them very well up close. “This happens because the myopic does not correctly converge the light rays on the retina and the vision of the images is formed in front of it instead of, as it should, on it, thus becoming blurred as the object moves away”. Depending on its extent, myopia can be mild (up to 3 diopters), medium (between 3 and 6 diopters) or high (over 6 diopters). “Myopia – continues the ophthalmologist – usually arises in school age, progresses rapidly to puberty, and in its mild or benign form stops at the age of 22/24. The progressive form, on the other hand, is characterized by the elongation of the bulb which does not tend to stop but can continue throughout life “. There are also forms of congenital myopia when it is already present at birth. “It is important that when parents have high myopia they take their children to the ophthalmologist already in the very first years of life,” recommends the ophthalmologist.
Hyperopia: when you see badly up close
Farsightedness is the exact opposite of myopia. The sight of nearby objects, in fact, is more blurred than those far away; Very distant objects can sometimes be seen clearly in mild farsightedness, but in the case of high farsightedness these are also blurry. Mild hyperopia does not cause disturbances, but if it reaches a certain extent, visual fatigue may arise due to the accommodative effort to be made when working closely. The most frequent symptoms are: eye pain, a sense of weight in the ciliary arch and headache. “These symptoms – explains Mele – are called accommodative asthenopia and derive from the excess of accommodation because the hypermetropic needs to squint to see clearly. Furthermore, the lens that tends to compensate for the defect is subjected to continuous stress on the ciliary muscle, which is never relaxed “. Even this refractive defect can be corrected with glasses or contact lenses and for this reason it is important to arrive at a diagnosis as soon as possible.
Red eyes and blepharitis: the signs of astigmatism
What about astigmatism? “It is a very common disorder that occurs when the cornea, that is the transparent membrane that covers the front of the eye, does not have the same curvature in all its points”, explains Mele. “In this visual defect, due to the oval shape of the cornea, there is a different refraction along the different meridians which causes the light rays to focus in two points of the eye: in practice, the image will not consist of one point in focus on the retina but from two points and the vision will be blurred ”. Incorrect astigmatism involves visual difficulties and even asthenopia with headache due to the accommodative effort: “The most common signs with which it can occur – continues the ophthalmologist – are blurred vision, headache, pain of the eyeballs”. How is this ailment treated? “For the correction of astigmatism – replies the ophthalmologist – prescription glasses are prescribed whose lenses are designed in such a way as to exert a deviation of the light rays capable of obviating the problem of imperfect corneal curvature, cylindrical lenses”. If, on the other hand, you opt for contact lenses, we are talking about toric lenses, which have a curvature designed to correct different types of astigmatism.
For more information on refractive defects visit the page of the Salmoiraghi & Viganò Foundation.