Short-sightedness

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Symptoms

A typical symptom of short-sightedness is hazy, indistinct distant vision. Therefore, the affected person squints his eyes in order to get an acute image through a narrowed slit - hence the term myopia, which in Latin means “closed eyes.”

Causes

Short-sighted people experience the following: light rays passing through the optical system meet in front of the retina and therefore there is no sharp picture on the retina. In principle, it is caused by the incorrect shape of the eyeball, which is too long. So far, experts have not managed to clarify the exact cause of such eye defects. Its occurrence is probably caused by several factors – notably heritability, as well as disorders in the development and growth of the eye, infectious diseases, excessive eye exertion (e.g. long focus on small details), inappropriate lightening etc. Short-sightedness currently affects approx. one third of the population and is among the most common dioptric defects.

Examination

A routine examination of visual acuity is done by a device called an autorefractometer. The doctor will seat you in front of it and let your chin and forehead lean against a comfortably formed rest. The doctor himself will be seated in front of you. In front of one eye, you will see a defocused fixation point – typically used images are a picture of a house in front of a landscape, a balloon in the sky or a boat sailing in the sea. The point gradually sharpens and blurs again. The device measures the amount of optical power necessary for dioptre corrections. Examining both eyes takes about 5 seconds and is completely painless.

A more precise examination of distant visual acuity is done by optotypes, most often the so-called Snellen charts. These are charts or illuminated boards on the wall in the examination room containing lines with letters of different size. Every line is labelled by a number that equals to the distance from which you should be able to read the letters without difficulties. The doctor will usually seat you or place you 5 meters from the optotypes. You will be asked to cover one eye with your hand – only slightly, without pressure, otherwise you can decrease its ability to distinguish. Afterwards you will be asked to read the chart in lines, or only the letters indicated. The same will be done with the other eye.

To measure eye defects the doctor will use special glasses and a set of corrective lenses. Wearing glasses you will read again from the optotypes and the doctor will add or remove lenses until you see clearly, acutely and sharply. There is no a special preparation needed for this examination. We only recommend not going partying or staying up late– tiredness can distort the visual acuity and the results of the examination.

Conservative treatment

Glasses

Dioptre glasses serve as a visual aid to correct vision. They usually consist of a fixed frame into which optical lenses are attached. The frame should not narrow the visual field and its shape should be adapted to the face. The optical lens is an optical set of two centered areas, in most cases spherical. The lenses of the glasses were initially made of glass, nowadays they are made also from different plastic materials to reduce the risk of breaking and because of their lighter weight compared to glass lenses. The disadvantage is the softness of the material – plastic lenses are exposed to scratches. Nevertheless, the majority of plastic lenses can undergo the so-called “hardening” treatment and can thus provide greater resistance to mechanical damage. Coating of the hydrophobic layer protects the lens against the concentration of the moisture and due to a very smooth surface provides easier cleaning. Lipo-phobia coating means higher resistance against grease, e.g. fingerprints. Anti-glare coating might be also applied on lenses, which prevents creation of glares, reflections on the surface of the glasses. Advantage is also smaller eye tiredness in artificial lighting, while working on a computer or watching TV, as well as better vision while driving (particularly at night) etc.

Short-sightedness can be solved by glasses with diverging lenses (diverging lenses, concave lenses), which transform the collimated beam into divergent. Diverging lens is thinner in the middle than at the edges.

Contact lenses

Contact lenses are a modern optical device intended to be used directly on the cornea. Its curvature replaces the curvature of the anterior corneal surface. It serves mainly to correct short-sightedness, long-sightedness, astigmatism, or presbyopia. They also have therapeutic or protective function in certain eye diseases, for instance, they are used to moisture the cornea when damaged, they are used as a bandage after eye surgery or as a drug carrier etc.

The technology and production of contact lenses was developed by the Czech scientist Otto Wichterle. Since then contact lenses have experienced significant changes due to modern technologies. According to the material used, they can be divided into two main groups – hard and soft lenses. On one hand, due to their non-porosity, hard contact lenses do not adsorb chemicals and other evaporations. They also have the ability to replace the natural shape of the cornea by a new reflecting surface. On the other hand, they are not oxygen permeable and prevent the eye from “breathing.” When applied for the first time, they are usually uncomfortable and it takes some time to get used to them. Correct usage must be checked regularly. They are mostly recommended for long-term wearing, such as yearly. On the contrary, soft contact lenses are highly permeable to oxygen. When applied for the first time, they are immediately comfortable due to their soft material. However, they are made of less durable material, which wears out quickly. It is necessary to change them regularly as sediments from tear film are formed. They are mainly designed for short-term wearing, such as daily, monthly, etc.

Short-sightedness is in most cases corrected by spherical contact lenses (labelled as minus), which replicate the spherical surface of the eye. It is also possible to use aspherical contact lenses, which are not spherical but instead become flatter towards the edge. Images seen through aspherical lenses are not so distorted, unlike spherical lenses, and are perceived as sharper, as aspheric contact lenses have very good imaging abilities even in periphery.

Surgery

Excimer laser correction surgery

For a very long time short-sighted or long-sighted people were entirely dependant on corrective tools – glasses. It was only the development of modern technologies that enabled  procedures to be performed which are now considered routine although until recently would have been considered  sci-fi, procedures for example such as “cutting” or “turning”  the cornea with a laser beam. This means that a laser beam causes evaporation of the cornea when it touches the corneal surface. The depth effect depends on the strength of energy with which the beam was sent. It results in a new shape of the cornea at its center and therefore different refractive power.

The surgery is performed on an outpatient basis. Anesthetic drops will be applied to your eye, and then lying down you will undergo a surgery that lasts on a few minutes. Afterwards, you will be discharged home with your eye covered with a bandage. Because of the heat created by the laser beam, the doctor will cool the eye before and after surgery. Mild pain in the eye or swelling of tissue might occur after surgery. To reduce these, the doctor will prescribe anti-inflammatory drops or an ointment. The surgery takes 10-15 minutes.

Correction surgery LASIK

To solve short-sightedness, long-sightedness or astigmatism an effective method known as LASIK can be also used. It combines the operation technique of the corneal flap with modelling of the cornea with an excimer laser. The surgery is performed on an outpatient basis. Anesthetic drops will be applied to your eye, and then lying down you will undergo LASIK surgery. The surgery takes only a few minutes. Firstly, the doctor will use a special device called a microkeratome to cut off a thin plate of surface corneal tissue, detach it and then the excimer laser will be focused on the exposed site. The laser will remove the precisely selected tissue of the inner part of the cornea and therefore the shape of the cornea will be changed Mild eye pain or swelling of tissue might occur after surgery. To reduce these, the doctor will prescribe anti-inflammatory drops or ointment. The surgery is performed on an outpatient basis under local anesthesia and takes about 15-30 minutes.

Refractive lensectomy and intraocular lens implantation

To treat dioptric defects a method known as refractive lensectomy can be used. Its objective is to correct vision in such a way so that patients no longer need to wear glasses after surgery or at least do not need such “thick” glasses. By means of ultrasound, the original clear lens is emulsified and its remains are aspirated from the eye. An artificial intraocular lens with a pre-calculated dioptric value is implanted into a preserved pouch. Compared to procedures carried out on the cornea only, this procedure requires more intervention.

Initially, artificial, hard (inflexible) intraocular lenses made of plastic (polymethylmethacrylate) were used. The development of delicate surgical methods led to the demand for soft, flexible intraocular lenses, made of biomaterials (silicone, acrylic, collamer etc.) A soft, folded lens is inserted into the eye through a small incision and, once inside the eye, the lens unfolds into the required shape. According to the visual correction needs, it is possible to select monofocal or multifocal lenses. The first provides clear vision of a single focal point in the lens that is either near or far. The latter allows sharp vision at multiple distances. The surgery is performed on an outpatient basis under local anesthesia and takes about 15-30 minutes.

Implantation of phakic lenses

Patients with a higher dioptre defect or with a thin cornea, where laser surgery is not recommended, might have the special, so-called phakic intraocular lenses implanted, which compensate the dioptre defect inside the eye. Through a small incision in the cornea, the lens is inserted into the anterior chamber of the eye and attached to the iris at a safe distance from the human lens or to the posterior chamber, and placed directly on the human lens. After the surgery, there are two lenses present. The advantage of this method is its reversibility into the original condition – if the patient is not satisfied with the phakic lens, it may be removed without problems and replaced with another. The surgery is performed on an outpatient basis under local anesthesia and takes about 15-30 minutes.

Equipment/devices used

Projection optotype

This device projects onto a wall tables with letters, numerals, signs or hooks of various size that help determine visual acuity from various distances. It further allows color vision to be examined – the eye’s ability to recognize colors and lights of different wavelengths. It also contains many tests to determine visual functions. Our clinic uses the projection optotype of the Nidek Company.

LCD optotype

This device uses LCD screens with high-resolution to display letters, numbers, symbols or hooks of various size which function to determine visual acuity from various distances, even under normal day-light conditions. It further allows color vision to be examined – the eye’s ability to recognize colors and lights of different wavelengths. It also contains many tests to determine visual functions. Our clinic uses the projection optotype of the Nidek Company.

Autorefractometer

This device measures dioptric eye defects (short-sightedness, long-sightedness, astigmatism). It performs automatic, fast, and very accurate measurements of eye refraction by the image projected on the retina and then it analyses the number of dioptres necessary to obtain a sharp image.

Keratometer (opthalmometer)

This device uses an optical method for measuring the diameter or the degree of curvature of the cornea (in millimeters or dioptres) and for determining corneal astigmatism.

Contactless pachymeter

This device is designed for ultrasound measurement of the corneal thickness in its entirety without the necessity of attaching (touching) the test probe to the eye. Local eye anesthesia is therefore not necessary and the risk of transmitting infection is reduced. Our clinic uses the contactless pachymeter of the Nidek Company.

Keratotopograph

This device uses an optical method for imaging the color map of the cornea’s curvature. It is mainly used to diagnose keratoconus – a corneal disease characterized by its conical camber.

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