Myopia and Hyperopia
What are myopia and hyperopia?
Both myopia and farsightedness - and also astigmatism - are part of what are known as refractive errors. In a very simplified way, these defects cause that the images do not focus exactly on the retina, but that the approach is done well in front or behind it. The consequence is a blurred vision.
In the case of myopia, the focus is made in front of the retina, so we see well at near distances, but very bad at far distances, and in the case of hipermetropy it is just the other way around, the focus is behind the retina which causes a good far vision and poor near vision.
Astigmatism is also a refractive defect caused by an irregular shape of the cornea, which causes the images not to focus on a single focus. The result is a blurred vision in near and far images too. Astigmatism can appear separately but is usually associated with myopia or hyperopia.
What causes these refractive errors?
The eye has two lenses that are responsible for focusing what we see: the cornea and the crystalline lens. The cornea is the first lens and the one with more power, but it is a fixed lens (it can not change its size or shape). The crystalline lens is a lens that is attached to a muscle that allows to modify its shape and its power. Thanks to these movements our eyes are able to focus at different distances.
For the image to be seen clearly, it must focus just on the retina. If the power of the two lenses (cornea and crystalline lens) does not allow us to reach that exact focus, it is when we speak of a refractive defect, since the image will be projected a little ahead or a little behind, and therefore we will see a blurred image.
How are refractive errors corrected?
The solution to this lack of power is to compensate for the refractive defect of the eye. Classically this has been done through physical devices: glasses or contact lenses that allow adding power (diopters) to correct hyperopia or subtract power in the case of myopia, getting the image to be projected just over the retina.
The glasses, apart from causing discomfort due to the mount, as well as sweating, irritation, etc. also have limited power because of the size and thickness of the crystals. In addition, the greater the power, the greater the crystal must be. This produces a distortion in the size of the images that can cause a feeling of dizziness.
Contact lenses are based on the same corrective principles as glasses with the particularity that they are placed directly on the cornea. Therefore, they should be cleaned and renewed frequently to avoid irritations and infections. In addition, they must be removed before the appearance of any discomfort and not try to endure them.
The option that avoids this dependence on both glasses and lenses and its drawbacks is refractive surgery. Basically there are two surgical techniques: laser correction (Lasik) or correction with ICLtype collagen lenses. Both techniques are totally safe and very fast. So much so that the same day the patient can go home walking and the next day and can begin to make his normal life, without using glasses or contact lenses of any kind. The choice of one surgery or another depends mainly on the anatomical characteristics of the eye, which will be determined by a battery of diagnostic tests.
Laser Correction: This technique consists of altering the anatomical characteristics of the cornea, modifying its curvature, and therefore its dioptric power, permanently. The remodeling is done in a very precise and controlled way by vaporizing the corneal tissue. Laser pulses polish the surface of the cornea with great accuracy until the refractive defect is eliminated. The intervention does not last more than 10 minutes per eye and its effects are permanent and effective from the first moment, although the vision can be altered during the first days due to the processes of regeneration of the treated tissue.
Collagen lenses type ICL: The main difference compared to the laser technique is its reversible character. The surgery consists of introducing a very flexible lens through a small incision of no more than 3.0mm in amplitude. We say that it is reversible because if it is necesary the lens can be removed, and replaced by another without affecting the eye tissues at all. The corneal tissue is not treated directly as in the case of the laser to correct the refractive defect, but this defect is corrected by the implantation of a physical element: the ICL type collagen lens. In this case the intervention lasts only 5 minutes per eye and the patient's vision is almost perfect from the first minute.
Both one technique and the other are ambulatory (do not require hospitalization) and are performed under topical anesthesia (drops), accompanied by a very slight sedation that helps the patient to be calm and relaxed.