The current indications of anterior chamber (AC) intraocular lenses (IOL) are the correction of aphakia without capsular support and that of certain ametropias. In the first case, AC IOLs are more frequently associated with corneal decompensation and therefore constitute a frequent indication of penetrating keratoplasty (PK). This may be due to the fact that they are usually used after complicated cataract surgeries or severe trauma, or due to their design, position and type of support or occupation of the AC, they favor contact or another type of progressive deleterious influence on the corneal endothelium. In these situations, in addition to aphakia, iridectomies, erosion or other iris defects, chronic inflammation, hyphema or/and glaucoma are usually associated.

These circumstances pose a challenge for any technique of endothelial keratoplasty. However, its advantages over PK in the face of a specific failure of the endothelium make it even preferable (see chapter 6.6.2). And although the challenge seems greater with Descemet-endothelial keratoplasty (DEK or DMEK) than with endothelial lamellar keratoplasty (ELK or DSAEK), the superior visual results of the former make it worthy of reviewing the options for its application in this field.

DIFFICULTIES IN DESCEMET-ENDOTHELIAL KERATOPLASTY IN AN APHAKIC EYE WITH ANTERIOR CHAMBER INTRAOCULAR LENS AND POSSIBLE SOLUTIONS

In these complex situations many surgeons prefer ELK (DSAEK) due to the greater technical difficulty of DEK (DMEK) and greater risk of graft detachment. However, DEK has the advantage over ELK of being the finest graft, so the depth of the AC is not modified, and the risk of angular blockage is lower. The best visual results are those with the DEK and the Melles’ group describes 3 cases in which, after an initially successful ELK (DSAEK), they developed fluctuating or limited vision, were operated on by DEK and recovered a vision similar to those obtained with the primary ELK². As the experience and standardization of the DEK increase, so does the number of surgeons that use it and practicing it in one eye with AC IOL is an option that is contemplated despite its difficulties, which we analyze below.

Limited visibility

A marked corneal edema results in poor visualization of the AC. To improve it, the corneal epithelium must be removed, and it may be useful to instill a few drops of glycerol. It is important to ensure good graft staining, either by repeated applications of 0.06% trypan blue (Vision Blue^®, D.O.R.C.) or with a higher concentration (0.2% Membrane Blue^®) (Figure 1). It also becomes more important to mark the graft to ensure its good orientation.

Lack of space in the AC

The presence of an AC IOL, due to the space it occupies, makes it difficult to practice the descemetorhexis, the injection and the deployment of the graft. This can cause further damage to endothelial cells, especially if the endothelial surface is applied against the plastic of the IOL, which can lead to primary failure or graft detachment (Figure 2). Preference is given to techniques that avoid such contact as much as possible, such as corneal percussion, bimanual or Price’s technique with a small bubble under the donor disc (see chapter 7.2). Other causes of lack of space in the AC that may be associated include the presence of anterior synechiae, vitreous or silicone oil.

Low adherence of the corneal stroma

Chronic edema is associated with a lower imbibition pressure of the corneal stroma, which increases the risk of graft detachment. It is therefore advisable to ensure adequate pressurization of the eyeball at the end of the surgery, first with balanced saline solution (BSS) and then with the AC completely filled with air or, better, with 20% sulphur hexafluoride (SF₆).

Risk of pupillary block

The presence of an AC IOL may favor a pupillary block and postoperative hypertension that will increase endothelial damage. Although these eyes usually have one or more iridectomies, it is important to check that they are not blocked by synechiae or vitreous, silicone, etc., and ensure their permeability, or perform a new iridotomy, inferior and well permeable.

Lack of separation between chambers

Although the AC IOL tends to occlude the pupil, the complete aphakia and the presence of defects in the iris pose a risk of intraoperative dislocation of the graft to the vitreous chamber. This also hinders the permanence of the air in the AC, necessary to press it against the receptor stroma. The subsequent migration of the air or gas has the aggravating factor of moving forward the AC IOL, which can contact the graft and damage it. To avoid it, it is advisable to inject the air carefully and progressively. The intraocular pressure (IOP) must not exceed 25-30 mmHg – measured with an intraoperative tonometer – and, if it is not reached, it must be reformed with BSS and no more air than is possible in the AC, as it will pass backwards. The bubble should be kept longer than usual or even not removed, provided that we have a permeable inferior iridotomy. The miotics are useful if the problem is a large pupil, but they will enlarge a peripheral iris defect, which may be necessary to close with sutures if possible.

Ocular hypotony

In a hypotonic eye, especially after vitrectomy or filtering surgery, the maneuvers of descemetorhexis, the unfolding of the graft and its fixation to the receptor stroma are more difficult. A continuous infusion of air or BSS may be useful depending on the phase of the operation, either via limbus or via pars plana (in vitrectomized). In addition, insufficient IOP is one of the main causes of detachment of endothelial grafts. In order to obtain adequate final pressurization, the same recommendations as in the previous point must be followed (see also chapters 6.5.2, 6.5.3 and 7.3.2).

SURGICAL OPTIONS FOR DESCEMET-ENDOTELIAL KERATOPLASTY IN APHAKIC EYE WITH ANTERIOR CHAMBER INTRAOCULAR LENS

All the above recommendations will have some utility depending on the situations. However, since these can be very variable according to the combination of difficulties in each case, it can happen that the DEK is not the most indicated technique in the presence of an AC IOL. Given this we can choose another form of keratoplasty (ELK or PK) or consider the extraction of the IOL from AC, which in turn raises several options.

Keep the lens in the anterior chamber

In our experience and according to the Melles group⁴, it would be the option with fewer intra- and postoperative complications, whenever feasible. The risk/benefit ratio of the DEK must be weighed; especially the advanced age of many of these patients would support it as the technique of choice.

Lens exchange and Descemet-endothelial keratoplasty in two stages

If the AC IOL has been the cause of corneal decompensation, it is also likely to cause a more or less late failure of any type of keratoplasty. In general, endothelial failure appears early when it is due to surgical trauma; in patients who have had a period of good vision before decompensating, the IOL itself will be suspected of causing progressive endothelial damage. In these cases, it will be preferable to exchange it for a posterior chamber (PC) lens and perform the keratoplasty a few months later.

The type of PC IOL for the exchange can be chosen as discussed in chapter 6.6.2. This phase should be used to perform the other reconstructive maneuvers of the anterior segment, such as releasing synechiae and reconstructing the iris defects, anterior vitrectomy and eventual removal of the silicone oil, replacing the valvular tube in the PC, etc. In this way, at the time of practicing the DEK, many of the difficulties will have been corrected. This option has, however, the drawbacks of requiring 2 surgeries and the delay in visual recovery.

Lens explant and Descemet-endothelial keratoplasty in two stages

We can choose to leave the eye aphakic after explanting the AC IOL and performing a DEK later. In general, it is not desirable to practice this surgery in an aphakic eye and would require a secondary PC IOL implant, except in eyes with high myopia or low visual potential. The most frequent procedure will be to implant the PC IOL in the same time as the DEK, which has been successfully reported, either with an IOL fixed to the sclera⁵ or to the posterior surface of the iris (iris claw)⁶.

Lens exchange and Descemet-endothelial keratoplasty in a single stage

The exchange of an AC IOL for another in PC followed immediately by a DEK presents the drawback of needing a large incision to extract the AC IOL, usually a rigid one. This generates a high risk of complications, so it does not seem advisable and we have not found it in the literature.

RESULTS OF DESCEMET-ENDOTELIAL KERATOPLASTY IN THE PRESENCE OF ANTERIOR CHAMBER INTRAOCULAR LENS

There are not many published data on DEK (DMEK) in complex eyes and with an AC IOL. Kruse's group includes 2 of these cases in a series of 24 with various complications, in which the AC IOL is exchanged for one in the PC sutured to sclera and the DEK is performed 4 months later. They point out that 46% of the eyes (11/24) required air reinjection and 17% (4/24) suffered a secondary failure⁷. The group of Melles describes 11 eyes with IOL fixed to iris in AC, in which they perform 6 DEK and 5 ELK (DSEK) without removing the IOL and with good results. In the cases of DEK, at 6 months the endothelial cell density was between 900 and 2,070 cells/mm², and its visual acuity (VA) between 0.1 and 0.9 decimal⁴.

In our department we performed 9 DEK in 6 eyes with AC IOL, with an endothelial density at the 3^rd month of 1052.67 ± 600.32 cells/mm² (range 538 to 1891) and at one year of 849 ± 438.19 cells/mm² (range 502 to 1719). These values ​​are lower than in the standard DEK (Figure 3). VAs were low, 0.3 decimal on average (range of counting fingers to 0.8), often due to retinal comorbidity (Table 1). Patient No. 4, aged 86 years and single eye with AMD, required 4 DEK in 4 years, 2 due to graft detachment and one due to late endothelial failure 2 years after surgery; currently he has a VA = 0.5 and 1.043 cells/mm². Patient No. 2, who had recovered VA = 1, presented late failure after being treated for a macular edema with intravitreal Ozurdex^® after 48 months and is awaiting a new DEK. The rest remain stable with a follow-up between 5 and 48 months.

DESCEMET-ENDOTELIAL KERATOPLASTY IN PHAKIC EYE WITH ANTERIOR CHAMBER INTRAOCULAR LENS

Corneal decompensation after a refractive AC IOL in the phakic eye – either of angular or iris support – usually occurs in younger patients than in the aphakic group, with greater visual potential – and needs – and a less advanced degree of corneal alteration. Many of the difficulties mentioned above do not occur, – except the narrowness of the AC –, so the DEK would be the technique of choice against the ELK. Since the AC IOL is – more clearly than after cataract surgery – the cause of the endothelial damage, it must be explanted. The Melles’ group withdrew AC IOLs of angular support in 9 out of 10 cases before DEK⁴. If they are young myopic patients (<45 years) and there is no cataract, it is advisable to respect the crystalline lens.

Penetrating keratoplasty (PK) remains the "gold standard" in corneal transplantation for several reasons. However, after the failure of a PK, each new penetrating graft has a lower survival rate¹ (see chapter 3.6). In this context, the lower risk of rejection associated with endothelial keratoplasty is an advantage of special relevance, in addition to the others known – non-penetrating surgery –, avoid problems related to sutures and astigmatism, etc. Descemet-endothelial keratoplasty (DEK or DMEK) provides the least amount of tissue and antigens compared to endothelial lamellar keratoplasty (ELK or DSAEK), which has resulted in a risk of rejection 20 times less than PK and 15 times smaller than ELK² (Figure 1). Therefore, DEK would be the technique of choice after a failure of a PK, despite its greater technical difficulty compared to ELK.

INDICATIONS AND RESULTS

All patients with a failed penetrating graft, with corneal edema but without irreversible stromal opacities and with not very high astigmatism or corneal curvatures will be candidates for DEK (Figure 2). In cases with poor visualization of the anterior chamber due to severe stromal opacity, an ELK or a new PK may be preferable, depending on the case and the experience of the surgeon.

Some ELK series have been published after PK failure (see chapter 6.6.4), but almost none of DEK. However, in the large series of DEK, its indication after the failure of a previous transplant (either PK or ELK in its various modalities) is among the 3 or 4 first indications: 2.8 to 3.6% in Melles’ group³, and as 3^rd indication after Fuchs’ dystrophy and pseudophakic edematous (bullous) keratopathy in Price’s⁴ group. These have published one of the rare series of DEK – although they mix DMEK and DMAEK – after PK failure⁵ and conclude that it is a valid technique but must be performed by surgeons with previous experience in uncomplicated eyes. The use of DEK as a rescue after a failed ELK – not necessarily after PK – has also been reported, with good results^6,7.

SPECIAL ASPECTS OF THE SURGICAL TECHNIQUE

The surgical technique of DEK (DMEK) after failed PK does not vary substantially from the standard (video 7.4.2.1), but we must consider some particularities.

Limited visibility

Frequently, the failed graft presents a lower transparency than in the usual cases of DEK due to Fuchs’ dystrophy (Figure 3). It is advisable to remove the epithelium and it may be helpful to instill a few drops of glycerol. You should also work with a well-stained graft, with trypan blue at a higher than usual concentration of 0.06%, such as 0.2% Membrane Blue^® (D.O.R.C.), or up to 0.4%, as well as mark the graft to check its orientation. For the latter, as well as ruling out the existence of peripheral folds at the end of the intervention, the slit lamp or the optical coherence tomography (OCT) intraoperatively will be especially useful tools.

Intraocular pressure

In general, a hypotonic eye is preferable during DEK (not at the end). Apart from the usual measures – Honan’s balloon, massage, etc. – if after placing the speculum we check that the orbit is "tight" and the intraocular pressure (IOP) is high, especially if it does not allow us to fill the anterior chamber with air, we can resort to a canthotomy or administer 20% iv mannitol.

Descemetorhexis

In addition to limited visibility, it is important to avoid the old graft-graft scar, which we can weaken or slightly open. Due to this and the probable shortage of endothelial cells, as well as the absence of guttae, some authors propose to completely obviate the descemetorhexis in these cases – either with DEK or ELK⁸. In our experience, leaving this layer leads to an increase in optical density in the Descemet’s plane and to some visual limitations, so we recommend its elimination, just inside the old graft (Figure 4).

Graft size

The diameter of the new graft compared to the old one is one of the most controversial aspects. Some authors prefer to make it bigger, others smaller and most of the same size. In order to minimize the detachment of the DEK graft, the most important factor is to avoid possible internal steps from the previous PK. For this, the OCT study is fundamental: if there are such steps, the new graft must remain inside them in order not to compromise its adherence (Figure 5).

Graft fixation

Due to the higher risk of detachment, it may be advisable to use a gas such as sulphur hexafluoride (SF₆) at a non-expandable concentration (20%)⁹ (video 7.4.2.2). As in the standard DEK, we recommend always performing a lower iridotomy, be it preoperative with Nd:YAG laser, if the transparency of the medium allows it, or intraoperative.