Refractive Surgery Unit


What is Refractive Surgery?

Refractive surgery is known as the group of surgical techniques undertaken to eliminate or minimize ocular refractive errors (such as myopia, hyperopia or astigmatism).

The image that passes through the eye from the outside undergoes a process known as refraction. This image is projected on the retina, allowing it to be transmitted to the brain and perceived clearly; this is what occurs in a normal eye.

However, when an eye has a refraction error (myopia, hyperopia or astigmatism), the image is projected anomalously. This implies an altered perception of the image, and therefore blurry vision.

Myopia causes the eye to focus the image in front of the retina, and not directly over it, so the perception of the image is not sharp. In practice this implies having difficulty seeing far objects well.

When it comes to hyperopia, the image is focused behind the retina, which means a person has trouble seeing clearly up close.

Astigmatism is caused by an imperfection in the curvature of the cornea. As a result vision for both near and far objects appears blurry or distorted.

For more than 15 years, at Eye Clinic Dr. Tirado, we have been using and developed various surgical refractive surgery techniques to treat refractive errors.

The use of the excimer laser is nowadays the first choice technique to correct these types of ocular errors. However, when the patient is not a candidate for refractive surgery with excimer laser, there are other surgical alternatives, such as phakic lens implantation or refractive lensectomy.

A detailed analysis of the patient will allow the highly qualified ophthalmologist to decide and use the most appropriate technique for each case.

What is laser eye surgery?

With the laser, we correct myopia, hyperopia, astigmatism and presbyopia, modifying the curvature of the cornea. We remove tissue from the cornea to give the necessary curvature so that the eye can focus perfectly and as a result see well in a natural way.

The cornea has several layers and it is necessary to apply the laser to the central layer (stroma) to shape it. To reach this layer, the superficial layer has to be removed (epithelium) and depending on how this is done, the diverse surgical techniques below are used.

Surgical techniques

There are different methods to remove the corneal epithelium and apply the laser to the immediate layer.

Lasik Technique

95% of the ocular laser surgery that is performed in the world is done with this technique. It is very precise, safe and allows patients to return to normal life very fast.

A superficial layer is lifted and after applying the laser it is replaced back in its position.
This layer can be lifted in two ways:

- Lasik technique with Microkeratome:

It has been the most applied technique in laser surgery. In Eye Clinic Dr. Tirado, we have performed thousands of such interventions due to its precision and safety. We lift and fold back a thin layer of the cornea tissue with a mechanical device called microkeratome. This layer is replaced after the use of the laser, it is an absolutely painless technique. Our microkeratome allows to specify the thickness of the epithelial lamina according to each patient´s corneal thickness. On the next day the patient can go back to completely normal life.

- Lasik technique 100% Laser:

With a very high precision laser, the surface layer of the cornea is separated.

The accuracy in the shape, diameter and thickness of the separated layer make this technique the safest in ocular laser surgery. It is so " gentle " for the eye that in a few hours the patient is already up and about. In Eye Clinic Dr. Tirado, we possess the prestigious LDV Ziemer femtosecond laser.

Surface Techniques:

This method is only used when it is not convenient to perform LASIK because of thickness or corneal curvature.

The corneal epithelium is completely removed (superficial layer of 50 microns thick) and once the laser is applied a lens is adapted to protect the eye during the four days that the corneal epithelium takes to regenerate. In this case it will take the patient four or five days to gain good vision and return to normal life.

Eye Clinic Dr. Tirado applies excimer laser eye surgery, mainly, through LASIK technique.
It is currently the fastest and most precise technique chosen to correct visual problems such as myopia, hyperopia or astigmatism. It is characterized by its high efficiency, safety and predictability, allowing the patient to recover straightaway.

For more than a few years now, we have been performing all surgeries in a customized way, applying technique variations adapted to the patient's needs and the demands of the cornea, with aberrometry guided treatments and choosing the optical treatment areas in virtue of all of the patient´s parameters (pupil size, sclera (white of the eye), etc.).

Only then do we obtain the best results with the lowest corneal detriment.

In few particular situations we choose surface techniques (LASEK or PRK), since it is more annoying and delays the return to normal life or work for at least one week.

Eye Clinic Dr. Tirado, innovator in this kind of surgery, has a significant amount of highly trained professionals, for adequate advice on all the aspects of the intervention.


Myopia is a visual focus error that causes difficulty seeing distant objects clearly, whereas near objects are perceived without any problems.

A person´s eye with this problem focuses the image in front of the retina, not directly on it, so the perception of the image is not clear.

This visual impairment, which both men and women experience in the same way, can begin in childhood and change over the years (stronger prescription). Myopia tends to stabilize from the age of 18, from which ocular laser surgery treatment is recommended.


Hyperopia is a visual focus error that causes blurry and difficult vision at close range, although from a certain age (about 50 years old), far objects are also deficiently seen.

A person´s eye with this problem focuses the image behind the retina, not directly over it.
This visual impairment affects men and women alike. Most children are born with hyperopia, but during the period of growth, this visual error tends to be corrected. When the problem prevails from childhood and is not corrected properly, visual disturbances, lazy eye (amblyopia) or other symptoms can be triggered. Hyperopia can be operated by laser surgery from the age of 18, if it is stable.


Astigmatism is an imperfection in the curvature of the cornea — the clear, round dome covering the eye's iris and pupil — or in the shape of the eye's lens. Normally, the cornea and lens are smooth and curved equally in all directions, helping to focus light rays sharply onto the retina at the back of your eye.

However, if your cornea or lens isn't smooth and evenly curved, light rays aren't refracted properly. This is called a refractive error.

The corneal structure abnormality, responsible for astigmatism, is usually genetically determined or caused by other factors such as eye injury or eye surgery.

There are several kinds of astigmatism: Myopic astigmatism. One or both principal meridians of the eye are near sighted. (If both meridians are near sighted, they are myopic in differing degree.) Hyperopic astigmatism. One or both principal meridians are farsighted. (If both are farsighted, they are hyperopic in differing degree.) Mixed astigmatism. One principal meridian is near sighted, and the other is farsighted.
If Astigmatism in any of its variants is stable, it can be operated from the age of 18, by means of laser eye surgery.

In the Eye Clinic Dr. Tirado besides correcting the most known visual errors (myopia, hyperopia and astigmatism) and modifying asphericity to improve clear vision or the focus, we apply personalized treatments, either guided by an aberrometer or by topography.

Aberrometer guided treatment

The most common human eye errors that most affect eyesight are myopia, hyperopia and astigmatism, but there are other errors that do not affect the focus, but do affect the quality of the image projected by the cornea in the retina, making the vision less sharp, which are called high-order aberrations. When the ocular aberrations are such that the adjustment of the asphericity is not enough to compensate them, we turn to the aberrometer for its correction.

Correcting eye aberrations with wave front technology, we are able to improve aspects such as the quality of night vision, the ability to distinguish colour shades and brightness and resistance to glare.
In the personalised wave front treatment, the use of laser depends on the information we get from the aberrometer.

The human eye is not a perfectly regular lens, whose surface would be like a pool ball or an egg in eyes with astigmatism, however there are small irregularities that have a negative impact on eyesight quality.
In standard correction with glasses, lenses or by traditional laser, the eye is considered to be the same as a perfect surface with just one prescription for all its area of vision. With the aberrometer, we divided the optical area of vision by analysing 64 different areas, achieving a precise prescription of each one of the subzones.

This gives us the possibility to design a specific treatment for each eye, therefore improve patients´ eyesight quality in which the nature of their ocular errors causes them not to be properly corrected with the adjustment of the asphericity.

Treatment guided by topography.

The corneal topographer gives us a three-dimensional image of the cornea allowing us to detect asymmetries or irregularities on its anterior and posterior poles. If these irregularities are such that they stop eyesight from being good with a standard correction, we turn to topography-guided treatment to modify the curvature of the cornea while smoothening or making its surface smooth.

The Wave front Allegretto technology, with which we work in Eye Clinic Dr. Tirado is the latest generation in vision correction through laser surgery.

In Eye Clinic Dr. Tirado we are able to combine optimized laser surgery (Allegretto Wave) with customized wave front treatment (Allegretto Wave front Analyser), F-cat asphericity modification treatments, or Pentacam topographer-guided correction for corneal irregularities, we are always in search of the best results for each patient.

The Allegretto Laser is approved by both the American FDA and the European Union.

Eye Clinic Dr. Tirado has the latest technology to achieve the best results.

The 400hz Allegreto EYE-Q excimer laser, designed by German engineering "Wave Light", is currently the fastest in the world, producing 400 laser pulses per second, with a 9 millimetre diameter. The "Eye Tracker" guiding system monitors the position of the eye at a frequency of 250 times per second thanks to infrared cameras that assist the laser computer, so that throughout the surgical procedure any slight movements of the eye are followed. It allows the treatment to be perfectly centred. The energy it releases in each pulse, makes it ideal for accurately ablating tiny segments of corneal stroma.

Ziemer Femtosecond LDV laser functions by performing tissue photo disruption. Its tiny pulses of energy pass through transparent eye tissues releasing its energy to a certain depth dissipating the tissue and creating tiny, 2-micron diameter, air and carbon dioxide bubbles. The adjacent tissue remains cool and unaltered. Its pulses of energy are so short, that they are measured in femtoseconds, the smallest temporal magnitude, that is to say, pulse that lasts for a quadrillionth of a second to create the flap. However, they are endowed with high energy for their tiny size.

The T-CAT treatment module, unique in the world, allows to perform treatments in which in addition to eliminating the prescription, it is possible to modify the corneal asphericity to improve eyesight quality. The optical aberration analyser, useful both in diagnosis and assisting the laser in the treatment, analyses the refraction of the eye in 64 different points. This achieves a maximum eyesight quality by eliminating optical aberrations and personalizing the treatment for each small area of the corneal surface.

The Pentacam topographer takes a three-dimensional image of the cornea that allows the laser to correct any asymmetry or irregularity achieving a geometrically perfect corneal surface.