In general, endothelial lamellar keratoplasty (ELK) by stripping Descemet’s membrane (DM) – popularly known by the acronym DSAEK of the English term – is indicated in any dysfunction of the corneal endothelium that produces visual alterations and/or discomfort enough to require definitive surgical treatment, in the absence of irreversible opacity in the stroma¹. The growth of endothelial keratoplasty to the detriment of penetrating keratoplasty (PK), as the treatment of choice in these pathologies, is based on the rapid visual recovery, the low induced astigmatism and the lower risk of rejection. This change in practice also assumes that long-term survival is equivalent for both procedures².

GENERAL INDICATIONS

Currently, Fuchs' dystrophy and postoperative edematous (or bullous) keratopathy – pseudophakic or aphakic – are the most frequent indications of KLE (DSAEK). The first would be, in the United States and the United Kingdom, the most frequent cause of endothelial transplantation, above the second^3-5. However, this frequency relationship seems to be the reverse in Spain¹. The distinction between the two entities is not always evident, since a postoperative edema may be the consequence of an undiagnosed endothelial dystrophy.

Isolated cases of other endothelial pathologies treated by ELK in the pediatric age have been reported, such as posterior polymorphous dystrophy and congenital hereditary endothelial dystrophy, with satisfactory results^6-9. Price treated with ELK three cases of iridocorneal endothelial syndrome (ICE) together with peripheral anterior synechiotomy and graft suture in one, with good results¹⁰.

In cases of PK failure due to an endothelial cause and without irreversible alterations in the stroma – particularly if the refractive result was correct –, ELK is preferable for offering faster visual rehabilitation and with a lower risk of rejection than a second PK. The main drawback is graft dislocation, more frequent (4.1% -5.8%) than in other indications^11-12. Similarly, in cases of buphthalmos or megalocornea with edema due to endothelial failure and in the absence of stromal opacities, ELK is a good option. Although they require grafts larger than usual, the great depth of the anterior chamber (AC) allows this technique to be performed and to preserve the phakic state^13-14.

INDICATIONS OF ELK (DSAEK) IN FRONT OF DEK (DMEK)

The introduction of Descemet-endothelial keratoplasty (DEK/DMEK) raises the dilemma with ELK/DSAEK in many indications. Although they have been shown with the first one best visual results and lower risk of rejection compared with the second, this remains the preference of many surgeons, primarily due to the greater technical difficulty of the former. On the other hand, several situations with comorbidity and associated difficulties that reduce the probability of success of the DEK, suppose objective factors to favor the realization of an ELK. Between these some stand out¹⁵:

• Poor visibility. If after removing the epithelium and other maneuvers to reduce edema – such as instilling a drop of glycerin – a sufficient transparency that allows to see with precision the structures in the AC is not obtained, the ELK will have more possibilities to ensure the good placement and adherence of the graft than a DEK.

• Complete aphakia. In these cases, air tamponade will be difficult, due to its tendency to migrate to the posterior segment. Therefore, we believe that ELK improves the likelihood of adherence of the graft, if necessary by placing transfixing sutures (Figure 1).

• In endothelial failures after glaucoma surgery – in particular with drainage devices but not exclusively – the rejection of an ELK is more frequent, as well as the early dislocation of the graft due to failure of the pressurization – e.g. when the air of the bubble migrates through the drainage tube –¹⁶. This favors the ELK before the DEK, but in any case, hypotonia should be prevented in the immediate postoperative period. It must be verified that the correct IOP has been obtained at the end of the surgery – preferably somewhat high; if the state of the optic nerve allows it, about 20-30 mmHg. If necessary, use maneuvers such as clamping the tube of the valve, closing the defects in the iris (iridotomies or iridectomies), making corneal drainage incisions or even fixing the graft with sutures^17-18. On suspicion that a drainage tube has contributed to corneal decompensation, it must be ensured that it is away from the graft and preferably in a retro-iris position.

• Anterior chamber pseudophakia. In this situation, in addition to the considerations in case of aphakia, the easier handling of the ELK disc and the lower risk of endothelial damage due to contact with the intraocular lens (IOL) make it preferable to a DEK (Figures 2 and 3).

• Before malformations or major alterations of the anterior segment, whether they are congenital (megalocornea, microcornea, etc.) or acquired (post-traumatic or post-surgical, etc.) that will hinder air tamponade and adhesion of the graft, an ELK will also be preferable to a DEK

• Limited visual prognosis. In patients with palliative purpose (pain due to bullous keratopathy) or other causes of low visual expectations, the greater experience and reproducibility of ELK – in obtaining the graft and in its probability of surgical success – make it preferable to DEK.

• Failure of the graft after PK, due to rejection or other causes that do not irreversibly affect the stroma. The difficulty of adhesion of the graft that can suppose the irregularity in the posterior face of the cornea with PK makes ELK preferable to a DEK.

• Recurring failure of DEK (DMEK), will make it preferable to opt for an ELK.

SELECTION AND PREPARATION OF THE PATIENT

In a patient in whom endothelial transplantation has been indicated, we must first check that the indication is correct and rule out the presence of other pathologies. To plan for the surgery, we must identify the possible risks that may recommend special precautions or maneuvers. For this, the preoperative study must include the following explorations:

Clinical history. It is an essential part for a correct diagnosis and to decide the best technique (ELK vs. DEK). It is important to specify the age of the process, the form and pattern in which the loss of vision occurred (suspicion of a non-corneal problem), the symptoms, treatments or previous interventions, etc.

Visual acuity (VA). Patients who tend to achieve better VA are those with corneal edema which is not very advanced or in late phases. With the chronicity of edema, the corneal stroma develops irreversible scar opacities that may interfere with VA and limit the possible benefit of an endothelial keratoplasty.

Corneal topography. Cases with high astigmatism, especially if it is irregular, may contraindicate endothelial keratoplasty in favor of a PK¹⁹.

Biomicroscopy with slit lamp. In addition to the condition of the cornea, the depth of the AC should be assessed – if it is narrow or there is an AC IOL, if it may be necessary to explant it – and other conditions that may make surgery more difficult, such as the presence of iridectomies, synechiae, flaccid iris, filtering surgery or drainage tubes.

Crystalline lens state. If the patient is phakic, we need to assess the need to associate cataract surgery, according to their age and the depth of the AC. In practice, the lens is extracted – in the same surgical act or previously – in most cases, because the type of pathologies oftentimes carries a high risk of developing cataract in the postoperative period. The calculation of the IOL should consider the hyperopic change associated with the ELK, in a range of 0.66-1.50 diopters (D)^20-21. IOLs of hydrophilic material should be avoided, since their opacification has been observed, apparently due to contact with the air bubble. In aphakic patients, consider the possible difficulties in obtaining a correct air tamponade.

Optical coherence tomography (OCT) of the anterior segment. It allows to quantitatively specify aspects such as the depth of AC, corneal diameter and angle-angle, in order to decide the diameter of the graft, or aspects not easily visible at the slit lamp such as the arrangement of the synechiae, situation of tubes of drainage or of filtering operations²², or the disposition of the posterior surface of the cornea in case of a previously failed PK²³. The Scheimpflug camera allows a similar study, although with less precision.

Intraocular pressure. We need to assess the risk of hypertension in the early postoperative period and that it may rapidly damage the optic nerve²⁴.

Posterior segment. We also need to assess the condition of the macula, eventually with a macular OCT. The risk of macular edema following cataract procedures combined with ELK, greater than in cases of isolated ELK, can be reduced with the preventive use of non-corticoid anti-inflammatory eye drops²⁵. Likewise, risks of retinal tears and retinal detachment should be ruled out, especially in aphakic cases.

The preparation of the patient for an ELK must consider all available information, so that the surgeon knows the difficulties that may be encountered and be prepared to take the appropriate measures for their correction and thus ensure the success of the intervention.