After laser eye surgery, the question often arises as to how exactly the procedure affects the various structures of the eye.
What changes occur to the cornea?
Does the natural lens remain untouched?
And why do many patients suffer from dry eyes after laser surgery?
In this article, we shed light on the specific effects of laser eye surgery on the eye structure, highlight possible risks and explain what changes occur after the procedure in terms of visual acuity, tear film and more.
Find out how safe the procedure is and what you can expect – from the cornea to the retina.

Cornea: The heart of laser eye treatment

The
The cornea plays a central role in the correction of short-sightedness, long-sightedness and astigmatism.
As the front, transparent part of the eye, it is largely responsible for the refractive power of the light that enters the eye.
In the case of defective vision such as short-sightedness (myopia), the eye is often too long, causing the light to focus in front of the retina.
With long-sightedness (hyperopia), the eye is too short so that the light is focused behind the retina.
In astigmatism (curvature of the cornea), the cornea is irregularly shaped, which leads to distorted vision.

Role of the cornea in the correction of myopia, hyperopia & astigmatism

Through
Laser eye surgery, especially with modern procedures such as LASIK or Femto-LASIK, precisely changes the shape of the cornea to correct these visual defects.
In the case of short-sightedness, the cornea is flattened in order to direct the light correctly onto the retina.
In the case of long-sightedness, the cornea is made steeper, and in the case of astigmatism, the irregular shape is corrected.
These
laser treatments are particularly safe and effective and offer patients the opportunity to see well again without glasses or contact lenses.

How is the cornea changed during laser eye surgery?

Femto-LASIK:

• Creating a flap: In procedures such as LASIK or Femto-LASIK, a thin, superficial incision is first made in the cornea to create the so-called flap.
  This flap is carefully folded to the side to work on the underlying area of the cornea.
  The flap protects the cornea during the healing process.
• Changing the shape of the cornea: A certain amount of corneal tissue is then removed using an excimer laser.
  Depending on the type of visual defect, the cornea is shaped differently:
  • With short-sightedness, the cornea is flattened in order to refract the light less strongly and focus it on the retina.
  • With long-sightedness, the cornea is shaped more steeply in order to focus the light more strongly.
  • In the case of astigmatism, irregular areas of the cornea are corrected in order to correct distorted vision.
• Healing of the flap: After the procedure, the flap is folded back, where it reattaches and heals on its own.
  This procedure enables rapid healing and a quick recovery of vision.

Trans-PRK:

• Ablation of the epithelium: Unlike LASIK, where a flap is cut, in Trans-PRK the top layer of the cornea (epithelium) is completely ablated with an excimer laser.
  This is done without mechanical incisions, which makes the procedure gentler on the eye.
• Laser treatment of the cornea: Once the epithelium has been removed, the excimer laser is used to ablate targeted tissue from the cornea.
  Depending on the type of visual defect, the cornea is shaped:
  • Myopia: The cornea is flattened to shift the focal point of light to the retina.
  • Farsightedness: The cornea is made steeper in order to focus the light more strongly.
  • Astigmatism: Irregularities of the cornea are compensated to correct distorted vision.
• Healing phase: As the epithelium is removed, the cornea needs several days to regenerate.
  During this time, a special contact lens protects the eye until the cornea has healed again.
  This regeneration takes longer than with procedures such as LASIK, as healing starts from the surface.

Effects on the thickness and shape of the cornea

Effects on corneal thickness:

• Corneal ablation: In procedures such as LASIK, Femto-LASIK or Trans-PRK, a certain amount of corneal tissue is removed in order to achieve the desired correction of visual defects.
  The degree of removal depends on the severity of the visual defect: the more severe the short-sightedness or long-sightedness, the more tissue needs to be removed.
• Permanent thinning: This ablation leads to a permanent thinning of the cornea.
  The corneal thickness remains reduced after the procedure, but this is not a problem for most patients as long as enough tissue remains to ensure the stability of the cornea.

Effects on the shape of the cornea:

• Changing the curvature: The shape of the cornea is changed during treatment so that it refracts light correctly.
  In the case of short-sightedness, the cornea is flattened, while in the case of long-sightedness it is made steeper.
  This new shape remains permanently after the treatment.

Is that dangerous?

• Safety of the procedure: As long as the procedure is performed by an experienced ophthalmologist and the corneal thickness has been thoroughly measured before the operation, the treatment is safe.
  Before the laser treatment, a comprehensive preliminary examination is carried out to ensure that there is sufficient corneal tissue to ensure that the cornea remains stable after ablation.
  If the cornea is too thin, the ophthalmologist may recommend alternative procedures such as lens replacement or other refractive surgery.
• Dangers of excessive thinning: If too much tissue is removed or the cornea is already very thin, this can lead to complications.
  A cornea that is too thin could lose its stability, which in rare cases can lead to ectasia – a protrusion of the cornea that impairs vision.
  Therefore, precise measurement of the corneal thickness in advance is crucial to minimize this risk.

Lens: Does the natural lens remain untouched?

Yes, with most
laser eye procedures such as
LASIK, Femto-LASIK or Trans-PRK, the natural lens of the eye remains untouched.
These procedures focus on the cornea, which is shaped by the laser in such a way that vision defects are corrected.

Why does the lens remain untouched?

Focus on the cornea: Vision defects are corrected by changing the curvature of the cornea in order to better focus the light on the retina.
The natural lens is not affected as it is not changed or replaced in these procedures.

Lens implantation & lens exchange for presbyopia and cataracts

• Presbyopia: In the case of presbyopia, which is caused by the natural hardening and loss of elasticity of the lens, laser eye surgery cannot provide a permanent solution.
  In these cases, lens replacement is oftenthe best option for restoring near and distance vision.
• Lens replacement for cataracts: The clouded natural lens is also replaced with an artificial lens in patients who have cataracts.
  These procedures aim to improve visual acuity by removing the lens completely.

Retina: Indirect effects of laser eye surgery

• Change of focus: By correcting the defective vision, the cornea is shaped so that the light hits the retina correctly.
  This improves visual acuity and the ability to see well, but does not cause any structural changes to the retina itself.
  After treatment, the retina receives the light in betterfocus, resulting in clearer vision.
• Risks associated with high myopia: Patients with high myopia often have an elongated eye axis, which makes the retina more susceptible to retinal detachment or tears.
  Although laser eye surgery itself does not pose a direct threat to the retina, the eye of a highly myopic patient may be more susceptible to complications such as retinal detachment, regardless of the laser treatment.
  Therefore, a thorough preliminary examination is usually performed on these patients to ensure that the retina is stable.
• Indirect complications: If the retina is very thin or already weakened, postoperative complications can occur if, for example, strong eye movements or pressure are exerted on the eye.
  However, these complications are rare and tend to affect very short-sighted patients who are already at increased risk before the procedure.

Tear film: changes and symptoms after laser eye surgery

After laser eye surgery, there may be changes in the tear film that lead to dry eyes in many patients.
The tear film is a thin layer of fluid that protects, moisturizes and nourishes the eye.
In laser procedures such as LASIK, Femto-LASIK or Trans-PRK, the cornea is treated, which can temporarily affect the function of the nerves in the cornea.
This can disrupt the flow of tears and make the eyes appear drier.

Changes in the tear film after laser eye surgery:

1. Reduced tear production: After the procedure, the nerves in the cornea are temporarily impaired, which reduces the signaling for tear production.
   As a result, less tear fluidis produced, which leads to dry eyes.
2. Irregular tear film: Due to the changes to the corneal surface, the tear filmmay be unevenlydistributed over the eye, which can increase the foreign body sensation or a feeling of “sand in the eyes”.

Typical symptoms:

• Dry eyes: Many patients report dry, irritated eyes after laser treatment, especially in the first few weeks after the procedure.
• Foreign body sensation: A common symptom is the feeling of having something in the eye (like grains of sand), which is due to the change in the tear film and the healing of the cornea.
• Fluctuating visual acuity: As the tear film is important for clear vision, an irregular tear film can cause temporary fluctuations in visual acuity.