Despite its technical difficulty and the limited visual recovery that is usually obtained with classical lamellar keratoplasty, the lower incidence of complications and the simplicity of follow-up and postoperative treatment has made it my technique of choice, for more than 30 years, in certain indications, either by the type of ocular pathology or by the personal characteristics of the patient.

I usually perform the lamellar dissection of the receiver with a blade. The donor one can also be manual or with Castroviejo’s electrokeratome (video 4.3.1.1). Once the patient is under anesthesia, a hummingbird-type speculum, and a fixation suture of the upper rectum are placed, and we evaluate with the surgical slit lamp the depth of the corneal tissue to be resected.

For the trepanation in the receiver I use the motorized trephine of Barraquer-Mateus (Grieshaber), which allows to adjust the depth of its plunger in tenths of a millimeter (Figure 1). After checking the circularity, centering and depth of the trepanation, we start the lamellar dissection with a blade. We place its cutting edge up or slightly inclined. Its non-excessive edge is useful to avoid inadvertent deep cuts or changes in the plane of dissection. When pulling the edge of the trepanation with hummingbird forceps, fine striations or vertical tissue strips are formed: the blade dissects them with a horizontal sweeping motion. This allows us to maintain the constant plane, which we verify is adequate with the slit (Figure 2).

Once the dissection is finished, the disc is just trimmed with Troutman scissors. If we have not obtained the desired transparency, we can dissect another sheet of the bed. We extend the lamellar dissection plane about 0.5 mm outside the edge of the trephination, which allows the donor button to be set and favors coaptation (Figure 3). We protect the bed with a rigid contact lens, to avoid the inclusion of particles while obtaining the donor disk.

The donor tissue for lamellar keratoplasty does not require a viable endothelium, but it is preferable to avoid corneas with a lot of edema, which makes it difficult to obtain the desired thickness. In general, I prefer to use whole eyeballs because they facilitate dissection. If it is a corneoscleral segment, it must be mounted in an artificial anterior chamber and properly pressurized. Maintaining a good tone is important – both in the donor and the recipient – since hypotonia favors inadvertent changes in the plane of dissection and even perforation. It is advisable to have a pair of donor corneas in case there is any complication during this phase.

The dissection of the donor can be done (a) with the same blade technique as in the receiver, (b) by delamination with spatulas of Paufique-Bonet, or (c) with the electrokeratome of Castroviejo¹ (Figure 4). It is advisable to select for the donor a trephine 0.5 mm greater than that of the receiver and obtain a dissection 0.2 mm deeper to compensate for post-mortem edema.

Once the donor button is obtained, we place it in the receiver after removing the protective contact lens and washing the bed profusely with BSS. Before proceeding with the suture, we verify the coincidence of thicknesses and the congruence of its diameters with the slit lamp (Figure 5). If there are traces of materials in the interface (e.g., particles, filaments or viscoelastic) we should insist on washing after the first stitches.

For the temporary fixation of the tissue, we place 8 sutures of 9-0 virgin silk, material that allows a greater traction than the 10-0 nylon. In this phase it is sometimes necessary to hypotonise the eye (decrease the ocular pressure) by means of a paracentesis. The sutures are placed through, transfixing it in the donor and through the plane of dissection that we have prepared in the receiver, peripheral to trepanation. We check again the correct donor-recipient apposition and place the definitive suture, generally a continuous monofilament 10-0 nylon of about 16 turns, removing the silk sutures at the end (Figure 6). The knot of the continuous one is buried in the corneal parenchyma and the tension is adjusted in all the handles to minimize the astigmatism. Before applying the bandage, we proceed with subconjunctival injection of a broad-spectrum antibiotic and a corticoid.

With this technique we have operated more than 450 cases with good results, particularly in tectonic or reconstructive indications, in order to correct thinned areas or in preparation for a second optical procedure². In the cases with optical purpose (N = 203), the results of visual acuity with correction (VACC) were moderately good, with 44.82% of the cases with final VACC greater than 0.5 and 48.76% with VACC between 0.2 and 0.5. 92% had a final residual astigmatism of less than 5 diopters. The pathologies that most frequently recurred were nodular Salzmann’s degeneration (53.33%) and perilimbal melanomas (41.17%). Although the visual results may be better with a penetrating keratoplasty or a deep anterior lamellar one, there are situations in which the classical lamellar technique allows to recover an acceptable vision with less risk of complications.

The surgical technique of superficial anterior lamellar keratoplasty (SALK) that we have employed most often is based on the use of the ACS microkeratome (Automated Corneal Shaper or ALK System) from Chiron Vision Corp., later acquired by Bausch & Lomb. This is a modification by Luis A. Ruiz of the microkeratome devised by José I. Barraquer to carve under applanation corneal discs with parallel faces (Figure 1). Although initially developed for keratomileusis and keratophakia¹, it was found to be very useful for corneal lamellar transplants².

THE ACS MICROKERATOME SYSTEM

The ACS microkeratome of Ruiz supposes a mechanization of the one of Barraquer and its adaptation to perform the technique of keratomileusis «in situ» – second refractive cut in the bed of the first lamellar cut, precursor of the LASIK. The electric motor, which by means of an eccentric shaft generates the oscillation of the "shuttle" piece that supports the blade, acts at the same time on the gears (Figure 2) that allow the head to move forward or backward in a controlled and constant way over the suction ring.

To choose the thickness or depth of the lamellar cut, the ACS system incorporates a whole series of interchangeable plates or gauges (Figure 3A). The suction ring is adjustable in height by means of a thread, which allows adjusting the diameter of the disk that we are going to cut (Figure 3B).

Said diameter is determined by a calibrated applanation lens, which replicates the pressure of the head of the microkeratome on the cornea and is applied when the suction ring is already fixed in the eye. The height of the ring can be adjusted with a special key until the flattened area or the meniscus that delimits it matches the circle engraved on the chosen lens. The system includes a whole set of calibrated lenses for different diameters (Figure 4). When varying the height of the ring, we change the diameter of applanation and therefore of the cut: if we raise it, the applanation decreases and the microkeratome will cut a disc of smaller diameter and vice versa. This allows to choose the diameter of the bed in the receiver and that of the graft in the donor directly by the lamellar cut, without the need to use trephines.

Only the first ACS microkeratome is useful for this technique, since the later models use fixed rings that are not adjustable – since it is not necessary for a LASIK and have a non-removable stop that prevents the complete cutting of the disc (free cap), that we need here. The original Barraquer system also included another set of lenses to measure the radius of the perilimbal sclera (sclerometers) and with that data to choose between different suction rings.

SURGICAL TECHNIQUE

The technique of SALK with microkeratome ACS can be seen in the attached video (video 4.3.2.1). Since it usually does not last more than 20-30 minutes, topical anesthesia is a good option in adult and collaborative patients. With peribulbar we must be careful not to generate conjunctival chemosis, which can prevent the correct fixation of the suction ring. We reserve general anesthesia for pediatric or non-collaborative patients.

Obtaining the donor disk

The diameter and thickness of the cut will have been chosen in the preoperative assessment according to the condition of the receiver. The donor disc or lamina of tissue is usually obtained first, although this rule may vary if we prefer to ensure that the pathology in the recipient has been adequately resected. In the donor, factors such as the presence or absence of epithelium and the degree of edema must be evaluated. When the recipient has epithelium and the donor does not, the cut in it should be about 50 μm finer if we want the graft to be the same thickness as the resected stroma. However, this is usually compensated by post-mortem edema, or it may even be necessary to cut a graft thicker than the resection of the recipient, since it will then thin out when the normal degree of hydration is regained. If we want the graft to be really thicker than the resected tissue (e.g. for reconstructive purposes), we must apply these corrections to the planned difference. In cases of post-PRK scars, it is not important to increase the final thickness since this tends to cause myopia. In any case, ultrasonic pachymetry is performed before and after each cut to determine the real thickness of the donor and resected tissues.

Since this system requires a special suction ring, it is not possible to use it with an artificial anterior chamber and it is necessary to have an entire (fresh) eyeball. Care must be taken that the ring is well centered with the cornea, before and after activating the suction. It is important to check – both in the donor and in the receiver, that the fixation of the ring is adequate, using Maklakov-Barraquer applanation tonometry (Figure 5). The tonometer that accompanies the system has a circular mark that corresponds to about 60 mmHg. A meniscus somewhat smaller than that circle indicates a somewhat higher intraocular pressure, and therefore sufficient suction. If the pressure is low (applanation greater than the circle), the fixation is inadequate and may result in a thin or insufficient diameter cut or be completely released during cutting and render an unusable, irregular or perforated tissue.

It is known that the thickness of the microkeratome cut also depends on the intraocular pressure and the advance rate. The higher the pressure, the thicker the cut. The higher the speed of passage, the finer. However, the ACS system is designed to have a constant speed, thanks to the mechanized advance with gears, and the suction pump does not allow large adjustments.

Before starting the cut, lubricate the corneal surface and, after setting the head of the microkeratome (Figure 6), activate the blade and the motorized advance with the pedal until the complete cut is obtained and the disc or lenticule appears in the groove of the head; we remove it and submerge it in balanced saline solution (BSS) to avoid dehydration.

Procedure in the receiver

The carving with the microkeratome is repeated in the recipient cornea. If the same blade is used, the second cut is usually 20-40 μm thinner than the first. If we do not want this difference, it will be necessary to assemble a new blade – assuming both donor and recipient have epithelium. In practice, we usually use the 160 μm gauge for a fresh donor (with little edema) and the 240 μm gauge in the receiver without changing the blade, which gives us resections of 180-220 μm in the second. If we want other depths, we will select the appropriate applanation gauge considering these corrections. In general, the diameter is adjusted to be the same in the recipient and the donor, but in case of doubt it is preferable that the recipient bed is somewhat larger. It can rarely happen that the resection in the recipient is very thin or incomplete. In this case we perform a second cut with a finer gauge, taking care that it is well centered with the first.

Once the receiver is ready, we place the donor disk on it and check that the apposition is correct, wash the interface and extend it and flatten it on the bed. If the graft is somewhat smaller than the bed, it will suffice to center it well; the epithelium will grow above the created sulcus without causing any alteration. On the other hand, if the donor exceeds the area of ​​the bed, there will be a risk of epithelial invasion of the interface. To avoid this, we can scrape the epithelium in a margin around the bed, so that no cells remain under the edge of the graft. More rarely, in case of a large excess of donor tissue, we can cut a peripheral ring of it with a punch tread, taking care that it is well centered. In this case, the graft will be left with a vertical edge, incongruent with the horizontal cut of the receiving bed. This is solved by means of a partial trepanation of the bed, shallow and of a diameter 0,25 mm smaller, to then suture the donor edge to edge in it with 8 sutures of 10-0 nylon.

If everything is correct, the graft is well extended and centered and, after waiting a few minutes, the test of the stretch marks when compressing the edge with a sponge shows that it is well adhered to the receiving bed (Figure 7), it is possible to leave it without sutures, as is usual in LASIK surgery.

However, in the absence of a hinge and because it is non-autologous tissue – and therefore probably incomplete congruence, there is some risk of graft dislocation. We prefer to place 4 sutures of 10-0 nylon, which are adjusted with the help of the surgical LED keratoscope mounted on the objective of our microscopes. This minimizes astigmatism and, after burying the knots under the edge of the graft and a new washing of the interface, the procedure ends. If it has been done with topical anesthesia, we place a therapeutic contact lens and leave the patient with a simple protective shell; If the anesthesia has been peribulbar or general, we place a semi-compressive bandage.

The day after the operation, we verify again the correct apposition of the graft, the absence of folds or particles in the interface and the state of the epithelium, the minimal inflammatory reaction and the absence of signs of infection. The treatment includes antibiotic eye drops for a week and corticosteroids that are then reduced slowly, as well as frequent lubricants without preservatives. In general, the patients can resume their usual activities immediately, taking care to avoid situations with risk of trauma or exposure to irritants during the first month.

The sutures can be removed after 3 or 4 weeks, depending on the residual astigmatism. They should be drawn into the limbus to avoid tractions on the graft that could even lift it. We warn the patient that the visual recovery is usually slow and progressive, and that one should wait until at least one year before judging the final result.

Our preferred technique of superficial anterior lamellar keratoplasty (SALK) uses the ALTK system – acronym for "Automated Lamellar Therapeutic Keratoplasty" –, produced by Moria S.A. (Antony, France). This system consists of a Carriazo-Barraquer microkeratome, with turbine engine and radial sweep – like the Hansatome, but with manual advance, an artificial anterior chamber (AAC) that integrates the guide for the microkeratome, as well as suction rings, trephines and other auxiliary instruments. Both the microkeratome and the AAC heads are available in reusable and single-use versions (Figures 1 and 2).

Although this system has been applied to treat pathologies of both the anterior stroma¹, and the middle stroma² and even full thickness except for endothelium such as in keratoconus³, the best visual results have been found with grafts no thicker than 200 μm^4,5.

We have indicated SALK in cases of superficial opacities such as post-keratitis leukomas, fibrosis after laser ablation ("haze" post-PRK), replacement of the LASIK flap, anterior corneal dystrophies, and opacities that affected the visual axis after pterygium surgery (Figure 3).

SURGICAL TECHNIQUE

Obtaining the graft

We will ask the eye bank for a donor cornea with healthy anterior stroma, although not necessarily valid for endothelial keratoplasty. The ring of sclera must be wide enough to be mounted on the ALTK AAC. Previously, the corneal thickness to be resected will be determined by assessing the depth of the lesion by optical coherence tomography (OCT, Figure 4).

After mounting the cornea in the AAC, we perform ultrasonic pachymetry before and after removing the epithelium (Figure 5). We will calculate the thickness to obtain considering that we are going to pressurize the chamber to a high value so that the lenticule is of large diameter; this will momentarily increase the edema that the preserved cornea already has. Once transplanted, this tissue will thin by dehydration, which will be partially compensated by the new epithelium. Although it is difficult to accurately predict the final thickness of the donor disk, in our experience it tends to be thicker than the one removed in the receiver if we use the same heads. Although this does not necessarily mean a worse final vision, in general we prefer a slightly thinner head in the donor than in the receiver. For example, for a lesion about 90 μm deep, we will use a head of the same value for the donor and a head of 110 μm for the recipient.

Apart from the nominal cutting thickness according to the selected head, the ALTK system allows to regulate the thickness and diameter of the cut to a certain extent depending on the pressure and the speed of the microkeratome – since the advance is manual. At higher pressure, larger diameter and greater thickness. A very fast advance it will tend to cut thinner. In general, we use an advance at medium speed with the AAC at high pressure. Once completed, the donor disc or lenticule is retrieved from the head (Figure 6). We check that it is complete, and we will keep it in balanced salt solution (BSS) inside a sealed container, to avoid dehydration.

We will measure the diameter of the bed in the donor that corresponds to the diameter of the carved disc, normally between 9 and 10 mm with the ALTK system (Figure 7). The rest of the tissue can be discarded, sent for study or even be used for other grafts if it had the appropriate viability (endothelial keratoplasty).

Carving of the recipient bed (superficial keratectomy)

We prepare the receiving eye with a drop of pilocarpine so that the miosis helps us in the centering of the suction ring. We prefer retrobulbar or sub-Tenon anesthesia by puncture to the peribulbar, in order to avoid the chemosis that could hinder the fixation of the ring. A good exposure is necessary, by means of a Lieberman type speculum, since the microkeratome is rotational, and its stroke is longer to achieve a complete cut without a hinge. To choose the suction ring, we follow the manufacturer's instructions regarding the maximum "K" value in diopters (D). In most cases we use the "0" ring and only in very flat corneas (K<40 D) or very curved corneas (K>50 D) we consider using other rings.

We always mark the surface, in case it is necessary to abort the implantation and replace the receptor tissue in its bed. We center the suction ring on the pupil and activate the microkeratome with an advance at medium speed, constant and without stops. At the end of the cut, the pathological tissue is retrieved from the head and can be sent for study (Figure 8). Once the suction is released and the ring removed, we measure the diameter of the resulting bed, which is usually between 8 and 9 mm (Figure 9).

Implantation and fixation of the donor tissue

If the diameter of the donor disc or lenticule is equal to or slightly smaller than that of the recipient bed (up to 0.5 mm), we can implant it as is. Since the ALTK system usually cuts larger diameters in the donor (9 to 10 mm) than in the receiver (8 to 9 mm), it is necessary to reduce the first to avoid the epithelial invasion of the interface. To do this, we will trepan it, well centered, to a diameter 0.25 mm less than that of the receiver bed, before placing it on this, taking care to maintain the proper orientation with the Bowman’s layer on the anterior surface.

With very thin grafts, up to 120 μm, spontaneous fixation can be obtained as with a LASIK flap. However, in general, we prefer to place transverse containment sutures to avoid possible dislocation (Figure 10). In cases with thicker discs or with marked donor-recipient furrow, we use independent stitches and/or a continuous suture. Before completing the fixation, we wash the interface with BSS and antibiotic solution for intraocular use (cefuroxime or vancomycin). We finish the intervention with the placement of a therapeutic contact lens, instillation of dexamethasone and cyclopentolate eye drops.

POSTOPERATIVE MANAGEMENT

We maintain the contact lens until the epithelialization is complete. We start topical corticosteroids every 6 hours, with progressive reduction over three months. We remove the sutures between 3 and 6 months, depending on their tolerance, the correct epithelization of the peripheral sulcus and the absence of signs of graft ectasia. We measure the residual thicknesses with OCT from the first month. Refraction is usually stable after 6 months (Figure 11).

The SALK with the ALTK system is a simple and reproducible procedure. Regarding the manual technique, it offers a higher quality of surfaces and better visual results. Regarding the ACS microkeratome, it allows to work with preserved donor tissue (corneo-sclera) and obtain larger diameter grafts.

To perform superficial anterior lamellar keratoplasty (SALK) my technique of choice is based on using the ACS/ALK mechanized microkeratome, developed by Luis A. Ruiz in Colombia (described in detail in chapter 4.3.2). This is a simple, elegant technique with good visual results within its known limitations. The advantage of this microkeratome is in having different calibrated applanation plates that allow choosing the depth of lamellar cutting, although it is mandatory to use a whole donor eye globe.

I perform this surgery in two stages, under topical anesthesia and without the need for sutures (Figure 1, video 4.3.4.1). In the first phase, I cut with the ALK microkeratome (model with stop) a flap with nasal hinge – incomplete lamellar cut. I use the applanation plate of 160 microns and a fixed suction ring with which a cut of about 9 mm in diameter is obtained. In general, this microkeratome cuts less deep than the nominal value of the plate used, so I remove the epithelium before getting deeper (about 50 μm). Once obtained, I perform a wash under the flap, reposition it and place a therapeutic contact lens. This procedure lasts only 3-5 minutes and the patient is discharged immediately with antibiotic eye drops and lubricants for a week.

Four weeks later, we obtain the donor disk of a fresh eyeball. In this we repeat the same procedure of incomplete lamellar cutting, after removing the epithelium. The same diameter and depth are used as in the first phase. After replacing the flap, we make a vertical cut of about 200 μm in depth with a single-use pneumatic fixation trephine, 7 mm in diameter. This results in an anterior corneal disc with vertical edges and about 160 μm thick.

We go to the receiver, again under topical anesthesia, and after marking the cornea with a series of cross-points for a good centering, we repeat the trepanning with the diameter and depth. The pathological tissue to be replaced is easily removed by the lamellar cutting plane that we had made 4 weeks before. If the hinge was large, one may need to complete the dissection with a semilunar knife. We wash profusely the receiving bed and apply the graft, which will fit perfectly into it. The adherence that follows, as in LASIK type surgery, and the congruence of the graft-bed dimensions and their vertical edges, obviates the need for sutures. We place a therapeutic contact lens and we discharge the patient with the aforementioned treatment.

I perform SALK in superficial opacities, not very dense but that significantly affect vision, such as those secondary to keratitis, bacterial or adenovirus, trauma, band degeneration, etc. In cases of anterior stromal dystrophies, I notify the patient of the probable recurrence, although it will be easy to replace the graft when required. It is also useful in the recurrences of dystrophies in penetrating keratoplasty, provided they are really superficial. It is a very safe technique, of simple execution and with moderately good visual results in selected cases.

The introduction of the femtosecond laser (FsL) in ocular microsurgery has meant having a tool capable of performing previously unthinkable actions or with a much higher precision and flexibility. The FsL uses ultrashort light pulses (of the order of 10^-13 to 10^-15 seconds) in the near infrared. This allows concentrating energy in space and time in such a way that its photodisruptive effect (analogous to that of a Nd:YAG laser) is confined to a bubble of a few mm. By rapid repetition of the pulses – in the order of tens or hundreds of thousands per second – and their controlled application in space by an electro-optical system, it is possible to make dissection planes within the transparent tissues for that wavelength, of different shapes and orientations and with minimal damage to neighboring structures.

FEMTOSECOND LASER PROPERTIES IN CORNEAL SURGERY

The first use of FsL in ophthalmology was to replace the microkeratome in the realization of the lamellar cuts of the LASIK technique. Although it has been used later in many others, both corneal and in the lens, this first application already augurated its usefulness in keratoplasty, both penetrating and lamellar. The advantages of FsL over other instruments in this field, whether manual or mechanized, include:

- Action at a distance, avoiding the compression and deformation of the tissue induced by mechanical instruments such as trephines. This increases the donor-recipient congruency, although it is limited by the application interface, which often (not in all models) requires corneal applanation.

- High accuracy, of the order of 5-10 mm or less depending on the application and the system. This allows to work with narrower margins, for example, when making a superficial lamellar cut without risk of perforating the corneal surface, or of getting really parallel faces where the microkeratomes produce meniscal cuts.

- Versatility to make cutting planes in almost any direction (vertical, horizontal, oblique) and shape (circular, annular, elliptical, polygonal, etc.), as well as to combine them.

This last property has opened the possibility of trepanations of different profiles, not only far from the classic verticality with conical cuts, but with complex profiles in several planes. The best known are the profiles in mushroom, in top hat or in zig-zag (Figure 1), but the possibilities are very diverse. Having so many options requires a reflection on its possible usefulness.

All complex cuts increase, (with respect to cylindrical trepanation) the contact surface between the edges of the graft and the receiver. This favors a faster healing and allows an earlier removal of the sutures¹. It would also facilitate reinnervation of the graft. The different forms can be better adapted to the needs according to the pathology. For example, the mushroom profile increases the turnover of the superficial layers and that of the top hat of the deep ones.

In principle, any increase in the contact surface would lead to more resistant scarring, but other factors may surely influence this. Thus, it is possible that the junctions of lamellar planes in the cornea (such as the horizontal ring of the mushroom profile) tend to scar little, as we know from experience with LASIK flaps. On the other hand, the profiles in which the receiver moves forward and to the center (a conical profile or the "spur" of the zig-zag), possibly better oppose the intraocular pressure structurally.

The limitations of FsL can be derived from its nature, from its way of application or from the interaction with tissues. Although its nature is the source of its main virtues (accuracy, security, speed, etc.), these properties have their physical limits. More relevant in practice are the limitations derived from its way of application, which varies according to the systems. Those that require applanation induce some deformation of the tissue, which may be more important and irregular if it is already previously deformed (keratoconus). Not all have the same versatility in making cuts of different orientation and shape.

The quality of the surfaces obtained in the lamellar cuts depends on the parameters of the laser, such as the energy and distance between the points of application, in turn limited by the repetition rate. It will also depend on the variable interaction with tissues according to their transparency and their intrinsic properties. The latter would explain the difficulty in obtaining regular surfaces in the deeper planes of the cornea, which for the time being have limited the application of FsL in deep anterior lamellar and endothelial keratoplasties. This does not apply, however, to superficial anterior lamellar keratoplasty (SALK), which is an ideal field for the application of FsL.

TECHNIQUE OF SUPERFICIAL ANTERIOR LAMELLAR KERATOPLASTY WITH FEMTOSECOND LASER

The different FsL systems are coupled to the cornea by optics that can be flat or concave, and by contact or by immersion. Concave optics deform the cornea less when engaged, but calculations to determine cutting surfaces are more complex than when working with the flattened cornea. Because it involves the superficial layers, the deformation by applanation is less relevant in a SALK.

To obtain the donor tissue with FsL, it is most often taken from a corneoscleral segment mounted in an artificial anterior chamber (AAC). Although it is possible to use a whole eyeball mounted on a special base, with the AAC it is easier to control that the pressure is adequate, in general more similar to the physiological than with the microkeratome techniques. Since the tissue is fixed in the AAC, the suction ring is not necessary (Figure 2). In any case it is advisable to make marks on the cornea for a good centering, and the coupling with the optics of the laser must achieve a sufficient contact surface to include the entire desired cutting diameter (video 4.3.5.1).

The dimensions of the cut will have been programmed previously, depending on the tissue to be removed in the donor, in general the minimum necessary to improve vision. However, having intraoperative OCT allows a greater degree of control, including last-minute adjustments. In general, there is less difference between the size in the donor and the receiver than with mechanical instruments, except the compensation for post-mortem edema. To this end, 10-15% (20-30 mm) of thickness is added to the donor^3,4. The epithelium can be respected or removed if it is an obstacle to the laser, in which case it will be preferable to do so in the receiver. The diameter, typically about 8 mm, is also increased 0.2 mm in the donor. Choosing a conical peripheral profile (closed) or complex, when possible, can improve biomechanics and reinnervation, reduce the need for sutures or allow their early removal. The energy for lamellar cutting is similar to that of the LASIK technique, although it should be increased in case of opacities and to ensure good trepanation.

Surgery in the recipient is usually done under topical anesthesia. It is important that the patient is comfortable on the laser stretcher, with his head horizontal and immobile. The eye is held by a suction ring-type device that guides the coupling of the laser optics and keeps it in position. The FsL systems generally have sensors that check that the pressure is correct before allowing the treatment. Otherwise the carving technique is similar to that of the donor (video 4.3.5.2). The pathological disc is then removed, and the stromal surface is washed with BSS. After verifying that the dimensions have been the correct ones, the graft is placed in the receiving bed. We have performed this technique even in a case of autokeratoplasty (video 4.3.5.3).

The great congruence between graft and receptor that can be obtained with the FsL and the vertical or complex edges, allows performing the technique without sutures when it comes to thin grafts⁵. This would result in a lower induction of astigmatism and high order aberrations⁶, as well as a faster visual improvement and greater long-term graft stability⁷. However, when the grafted disc exceeds 200 μm, we still prefer placing 4 to 8 independent sutures under keratoscopic control, which allows us to adjust their tension (Figure 3). The selective removal of these sutures allows to control the astigmatism in the postoperative period and can be done early after a few weeks.