Laser vision correction — how important is the role of the cornea?

What is the cornea and what functions does it have?

The cornea is a layer covering the eye’s anterior (front) part. It protects the eye from external factors such as mechanical injuries or foreign bodies getting into the eye. The cornea also refracts the rays of light, which enables proper visual acuity. The surface of the cornea allows numerous chemicals to pass into the conjunctival sac in the form of drops, e.g. atropine and pilocarpine.

The layered structure of the cornea

• Tear film – covers the surface of the eye and is responsible for lubricating and nourishing it and hence preventing corneal damage.
• Corneal anterior epithelium – covers the front part of the cornea and consists of a few layers of cells. It is lubricated by the tear film, it quickly regenerates and contains a lot of nerve endings.
• Anterior limiting lamina (Bowman’s membrane) – constitutes the second layer of the cornea, and consists of collagen fibres. Its primary role is to protect the corneal stroma from infections, yet, contrary to the corneal epithelium, it does not have the ability to regenerate after damage.
• Corneal proper substance (corneal stroma) – the thickest of all layers, which makes up 90% of the corneal thickness. It consists of transparent lamellae made of collagen fibres.
• Posterior limiting lamina (Descemet’s membrane) – thick, basement membrane for the endothelial layer. It protects the cells and blood vessels, shielding the deeper structures of the eye.
• Posterior epithelium of the cornea (endothelium) – a single layer of cells linked together into a honeycomb pattern. It helps to maintain the corneal stroma in a slightly dehydrated state (it swells when the fluid builds up inside it, which in turn leads to corneal opacity).

Corneal diseases and damage

Keratitis – caused by bacteria or a viral infection. Most common symptoms include redness of the eye, itching and pain, swollen eyelids, and discharge from the conjunctival sac. Keratitis should be treated pharmacologically, e.g. with antibiotics. More advanced stages of the disease often require additional surgical treatment.

Corneal degeneration – change of the correct shape of the cornea or change of corneal transparency. It may be related to a natural ageing process or result from general diseases or eye diseases. Symptoms characteristic of corneal degeneration usually appear in a more advanced stage and include: visual acuity deterioration, photophobia, lacrimation and a sense of a foreign body in the eye.

Keratoconus – progressing condition of the cornea, in which its central or paracentral part undergoes a thinning and bulging process, eventually taking the shape of a cone, which causes blurry, distorted vision. The treatment of keratoconus may slow down the progression of the disease or stop it at a particular stage. The treatment requires using hard contact lenses, conducting a corneal cross-linking procedure or intracorneal ring segment implantation.

Corneal erosion – damage of the outer layer of the corneal epithelium. Its most common cause is mechanical injuries, e.g. a nail scratch, a scratch caused by an animal or misuse of contact lenses. The symptoms usually include severe eye pain, lacrimation, discharge from the eye, photophobia, and blurry vision. Corneal erosion can be treated pharmacologically with the use of antibiotic ointments, with a laser procedure or surgically.

Corneal scar – may appear as a post-traumatic complication. It requires treatment if it distorts vision. Photo therapeutic keratectomy (PTK), a laser procedure for corneal scar removal, is currently considered to be the safest treatment method.

Laser vision correction – what is the role of the cornea?

Laser vision correction consists in the proper reshaping of the cornea with a laser beam. Such a procedure alters corneal thickness to some extent, depending on the refractive error which needs to be corrected. This value is assessed during a preliminary qualifying examination. If the cornea is too thin, the patients cannot undergo the surgery.

In order to increase the odds of positive qualification results for a greater number of patients, various correction methods are used during the procedure – our clinic offers the following: SBK LASIK, TransPRK and LASEK. What is understood by a correction method is the way of preparing the cornea for the work of a laser beam. A variety of different methods makes it possible for more patients to be eligible for the procedure, even if they have, for instance, thinner cornea.

All kinds of corneal degeneration and corneal diseases, depending on their type and stage, may constitute a temporary or permanent contraindication to a laser vision correction procedure.

Are you tired of wearing glasses or contact lenses? Find out whether laser vision correction is a suitable solution for you! Fill in a preliminary qualification form online, or contact our Centre by phone. If you have any particular questions regarding your refractive error and you need specialist advice, you can submit the questions using the ask a doctor tab.

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