Like other types of corneal transplant, deep anterior lamellar keratoplasty (DALK) can be combined with other eye surgeries. The most common association is with that of cataract and, less frequently, with vitreo-retina, glaucoma or ocular surface procedures.

DALK COMBINED WITH CATARACT SURGERY

Cataract surgery requires a minimal transparency of means. In the presence of corneal opacities that impede it, we can try to solve them previously or by means of combined surgery. Operating the cornea first, either by penetrating keratoplasty (PK) or a DALK, has the advantage of allowing later – when a stable refraction has been reached – the calculation of the intraocular lens (IOL) without the interferences of the corneal pathology – imprecise keratometry because of irregular astigmatism – and with real "K" values ​​instead of theoretical ones. This results in better refractive results, but it prolongs the time to visual rehabilitation, causes a greater endothelial loss¹ and requires at least two entries in the operating room.

The combined surgery of cataract and keratoplasty avoids these inconveniences. Classically, the combination of a PK, cataract extraction and IOL implant was called "triple procedure". Cataract surgery was often performed openly, with risks such as the feared expulsive hemorrhage. And although a temporary keratoprosthesis could be used to operate the cataract “closed sky” and then place the graft², it is a complex procedure and it is not free of risks either. In certain indications – e.g. cataract and corneal edema in the pre-endothelial keratoplasty era –, visibility allowed the cataract to be operated first through limbal incision and then perform a PK, but the refractive results were in any case not very predictable.

When cataract surgery is combined with a non-penetrating corneal technique such as DALK (Figure 1), safety is gained by avoiding the risks of open sky – although not in refractive results. The options are to operate the cornea first and then the cataract or vice versa.

DALK first, followed by cataract

If we start with DALK with a descemetic technique such as "big bubble" (BB), we must bear in mind that, in case of obtaining a BB type 1, the bed will include the Descemet membrane (DM) together with Dua's predescemetic layer (PDL). To produce the rupture of the DM/PDL bed, 1.46 bar (1095 mmHg) was necessary, which means sufficient resistance for phacoemulsification maneuvers. If, on the other hand, a type 2 BB is formed, limited by DM alone, 0.6 bar (450 mmHg) will be enough to break it³. In the second case, it is advisable to postpone cataract extraction until another day⁴ or at least until the graft is fixed in position. BB type 2 would be more frequent in older patients and in those with deep stromal leucomas and fine corneas⁵ (for the characteristics of both types of BB, see chapters 5.2 and 5.4.3). With predescemetic techniques the resistance will probably be higher than BB type 1, so that phacoemulsification can also be carried out immediately.

For this, it is recommended to use a scleral incision, away from the cornea. The visualization through DM/PDL is excellent since leucomas rarely affect them. This may be due to its thinness and lack of response to inflammation due to the absence or scarcity of keratocytes in PDL⁴ (Figure 2). The flows, aspiration and vacuum values should be low to avoid any collapse of the anterior chamber^6,7. Once the IOL is implanted and the viscoelastic is removed, the graft will be placed and sutured.

Cataract surgery followed by DALK

Starting with the cataract is only possible when the corneal opacity is not very marked (Figure 3). If the opacity is important but not very deep, we can first perform a lamellar keratectomy (debulking) of about 300 μm in the partially trephined area. In most cases this provides enough transparency to be able to perform phacoemulsification. If necessary, we will use other aids – especially for capsulorhexis – such as capsular staining, a surgical slit lamp or a fiber-optic endo-illuminator. After completing the lens surgery, and suturing the incision, we will complete the corneal surgery, either with a descemetic technique (BB) or a predescemetic one like that of Melles (video 5.5.1).

DALK ASSOCIATED WITH VITREO-RETINAL SURGERY

The association of vitreo-retinal pathology and corneal opacification is a rare circumstance. They can coexist in certain circumstances, such as after eye trauma or surgery, with detachment or other pathologies of the retina and corneal opacity due to leucomas, scars, calcium impregnation or hematocornea (Figure 4, video 5.5.2).

The conventional approach of combined keratoplasty and vitreo-retinal surgery involved performing first the penetrating trepanation and fixing a temporary Landers⁸ or Eckart type keratoprosthesis^9,10 – or even a non-viable cornea, provisionally – to visualize the posterior segment. Once the vitreo-retinal procedure is completed, the prosthesis is replaced by a PK-type graft.

With the development of DALK techniques, this is simplified by avoiding keratoprosthesis and improving safety by working at all times in a closed eyeball. The necessary transparency can often be obtained with only a deep lamellar keratectomy, before completing the bed dissection¹¹. However, the resistance of the DM/PDL sheet is sufficient to support, at least, the pressure changes produced during the filling maneuvers of the vitreous chamber or exchanges of fluids such as perfluorocarbons, gases or silicone oil.

Once the vitreo-retinal part of the surgery is complete, we proceed to the suture of the full-thickness graft without DM-endothelium¹². In eyes that have suffered major traumas, it is preferable to perform predescemetic techniques. Apart from its greater safety, the greater scarring at the interface improves the biomechanical results with respect to the descemetic techniques¹³.

DALK ASSOCIATED WITH GLAUCOMA SURGERY

The most common indications of DALK (primary or secondary ectasias, leucomas, corneal dystrophies) are not usually associated with primary glaucoma frequently, while secondary glaucoma, relatively frequent after PK – either by anatomical modification of the chamber angle or by the prolonged use of corticosteroids – is rare after DALK^14,15. We prefer, therefore, not to associate DALK with glaucoma procedures except in eyes with previous or aphakic glaucoma.

This type of combined surgery presents difficulties in either surgical sequence. If we start with glaucoma surgery, the hypotonia that we create will make the DALK maneuvers difficult. It will be preferable to employ a non-penetrating filtering technique or to perform a hermetic suture that can be partially removed at the end. If we start with corneal surgery, glaucoma maneuvers may be difficult, such as carving the scleral hatches or placing a valvular implant or filtering devices.

Ocular hypertension as a complication in the early postoperative period of DALK has been observed in some cases with the BB technique, possibly due to air obstruction of the trabecular meshwork¹⁶. On the other hand, some surgeons prefer to leave an air bubble in the anterior chamber at the end of the intervention to promote the application of DM to the stroma, and in particular if a microperforation has occurred – air or even gas¹⁷ – to prevent the formation of a pseudo chamber. In these cases, the patient should be left in pharmacological mydriasis and it is advisable to perform an iridotomy or prophylactic iridectomy to avoid pupillary block. Urrets-Zavalía syndrome has also been described in some cases after the Melles’ technique, possibly due to an excess of operative time with the anterior chamber being pressurized with air¹⁸.

The risk of glaucoma appearing after DALK seems to be low. The majority of postoperative hypertension cases are transient and are related to the use of corticosteroids, they stop when these are withdrawn and respond well in the few cases that even require hypotensive eye drops – 3 out of 69 in a series¹⁹ –. When topical treatment rarely fails to control hypertension, we have found an excellent response to drainage devices (Figure 5).

DALK ASSOCIATED WITH RESTORATION OF THE OCULAR SURFACE

When stromal opacification is accompanied by limbal insufficiency, keratoplasty, either penetrating or anterior lamellar, is usually doomed to failure if we do not add procedures to restore the function of the limbus and the ocular surface. If the contralateral eye is healthy, we can perform a limbal autograft, either prior to or simultaneously²⁰. In these cases, it is common to associate an amniotic membrane implant (see chapter 1.7).