**6. Corneal surgery**

The corneal transplant surgery is useful in the removal and replacement of damaged corneas, replacing it with a clear donor cornea (corneal grafting) in its entirety (penetrating keratoplas‐ ty) or in part (lamellar keratoplasty). Another surgical technique is the deep anterior lamellar keratoplasty (remotion of the anterior layers of the central cornea) if the replacement includes posterior cells: endothelia, stroma and Descemets cells (DSEK) or Descemets/endothelium (DMEK).

Boston keratoprosthesis is a synthetic cornea used since 2008 (Boston KPro), which was developed for the Massachusetts Eye and Ear Infirmary. The AlphaCor, a device that contains a peripheral skirt and a transparent central region, is another artificial cornea. The parts connect interpenetrating polymer network made from poly-2-hydoxyethylmethacrylate (pHEMA). Another model is the osteo-odonto-keratoprosthesis, wherein a lamina of the patient´s tooth New Technologies in Eye Surgery — A Challenge for Clinical, Therapeutic, and Eye Surgeons http://dx.doi.org/10.5772/61072 9

**Figure 5.** Corneal surgery techniques.

**4. Types of eye surgery**

8 Advances in Eye Surgery

**Figure 4.** Classification of the types of eye surgery.

**5. Ocular surgical techniques**

**6. Corneal surgery**

(DMEK).

Today, the classification of eye surgery can be summarized in Figure 4.

In the surgery of myopia, astigmatism, and presbyopia, several techniques have improved since the 80s (See figure 5). And recently, a stromal ring technique has been introduced for keratoconus. Due to the shortage of donors for corneas, the stem cell culture and the devel‐ opment of new biopolymers has increased until the creation of several artificial corneas.

The corneal transplant surgery is useful in the removal and replacement of damaged corneas, replacing it with a clear donor cornea (corneal grafting) in its entirety (penetrating keratoplas‐ ty) or in part (lamellar keratoplasty). Another surgical technique is the deep anterior lamellar keratoplasty (remotion of the anterior layers of the central cornea) if the replacement includes posterior cells: endothelia, stroma and Descemets cells (DSEK) or Descemets/endothelium

Boston keratoprosthesis is a synthetic cornea used since 2008 (Boston KPro), which was developed for the Massachusetts Eye and Ear Infirmary. The AlphaCor, a device that contains a peripheral skirt and a transparent central region, is another artificial cornea. The parts connect interpenetrating polymer network made from poly-2-hydoxyethylmethacrylate (pHEMA). Another model is the osteo-odonto-keratoprosthesis, wherein a lamina of the patient´s tooth

is implanted into the eye using an artificial lens. The porous graphite/PVA hydrogel composite as the skirt of artificial cornea, in the experimental model shows the interconnective porous network. The mechanical properties and water content are similar to nature donor cornea. Water content is another crucial characteristic of hydrogel used as a material for artificial cornea because it will influence the biocompatibility of hydrogel. Experimental studies developed in rabbits in vivo shows that the hydrogel nanocomposite implants of Zn NP were well tolerated in over 3 weeks of study, with no evidence of wound leakage, infection, inflammation, or neovascularization [4].

Corneal cross-linking is a technique used for the treatment of keratoconus. It increases the corneal rigidity by photo polymerization of the stromal collagen fibers with UV light for less than 30 minutes. The standard cross-linking technique, also called Dresden protocol (CXL), requires the removal of the central 9 nm of the corneal epithelium layer followed by 30 minutes of riboflavin administration [5].

In order to make a predictive value pair wing refractive surgery and have a more accurate and useful value for refractive surgery and the stromal rings for keratoconus, sophisticated software have been developed to help surgeons take more precise models before the surgery. Some of them are provided by manufacturers and others have been developed based on sophisticated mathematical models, which are very useful in cases of keratoconus or corneal astigmatism [6].

Nomograms are incisions within the cornea without the need to break the epithelium or Bowman´s, thus avoiding the risk of wound problems and possible overcorrections during refractive surgery. Recently, specialized software products can help surgeons on the different procedures. Some of them are IBRA, Intacs®, and Nomograms (useful for ICRS in keratoconus by the use of a ring base on the type of the cone) [7, 8, 9]. In presbyopia surgery, an optical device as thin as a contact lens is inserted into the cornea to reshape the front surface of the eye in order to improve vision. Corneal inlays are used to improve near vision and reduce the need for reading glasses. This device can be combined with LASIK for nearsightedness, farsightedness, and/or astigmatism.

This procedure is less invasive than phakic IOL (intraocular lenses placed deeper in the eye). So, with the corneal inlays for vision correction, eye surgeons may sometimes be able to avoid complications associated with procedures, such as LASIK and PRK, because no corneal tissue is removed. The Kamra Corneal Inlay, previously called ACI 7000, for presbyopia is now in clinical trials. The device in inserted in a thin flap in the center of the cornea. The flap is then replaced over the inlay to hold it in place in a process of 15 minutes [10].

Its innovation holds a promise to replace reading glasses with good near vision in the near future. The characteristics of Kamra are described as follows: 3.8 millimeters in diameter, 10 microns thick, made of an opaque biocompatible polymer (Kynar), and a thermoplastic material that softens in heat and hardens in cooler conditions.

Corneal inlays and onlays are also called keratophakia. They are implants placed in the corneal stroma for the correction of presbyopia. The procedure is done under topical anesthesia and the implant is done monocularly in the non-dominant eye as a stromal pocket or under the flaps created by the microkeratome or by the femtosecond laser. See Figure 6.

**Figure 6.** Position of the corneal onlay implants.

Other innovations for these techniques have been developed for researchers in Mexico, who are working on Raindrop near Vision Inlay (ReVision Optics) with some variation on diame‐ ters, thickness, and biomaterials.

This inlay is placed in the cornea under a LASIK-style flap. When in position, the inlay changes the curvature of the cornea so the front of the eye acts much like a multifocal contact lens. The other alternative is the Flexivue Microlens (Presbia Cooperatief U.A., Amsterdam), which uses a laser and creates a tiny pocket just below the eye's surface. Currently, it requires developing the instrument to insert the microlens in the pocket that is sealed to hold the lens, and a hydrophilic polymer is irrigated during surgery with a highly moisturizing substance. The synthetic intraocular lens replaces the natural lens during cataract surgery. Its characteristics are as follows: 3 mm in diameter and 20 microns thick at the edges [11].
