Although the combined management of corneal pathology requiring penetrating keratoplasty (PK) together with a cataract is complex, currently the anterior segment surgeon has several techniques to cope with it. There are two main options: the "triple procedure" – simultaneous PK and cataract surgery with intraocular lens implant (IOL) – and sequential surgery, that is, performing only the PK first and cataract surgery in a second stage¹, each option with its advantages and disadvantages. In this chapter we will deal with cases of cataract associated with corneal opacity that affects all its layers, where to achieve transparency it is necessary to perform a PK (Figure 1).

Historically, sequential surgery was the only option for the management of a corneal opacification along with cataract. In the year 1966 the combined surgery of cornea and cataract was born, which Katzin and Meltzer² call «double procedure». The classic technique known today as triple procedure was described by Taylor³ in 1976, when associating IOL implantation, at that time of type of fixation to the iris. The introduction of posterior chamber IOLs and the improvement of surgical techniques made the triple procedure the standard for treating corneal pathology in the presence of cataract.

INDICATIONS

The indications of the classic triple procedure are in constant evolution, especially after the emergence of endothelial transplantation. Previously, its main indication was the association of cataract and endothelial decompensating due to Fuchs' dystrophy⁴. And despite not being the main indication today, the classic triple procedure remains a viable and effective option for this situation, especially where endothelial keratoplasty is less established⁵.

Currently the main indications, both for the triple procedure and the sequential surgery of PK and cataract are: corneal leucomas, whether of infectious cause – especially after herpetic keratitis – or post-traumatic, corneal decompensating or failure of a previous transplant, dystrophies – especially stromal – and advanced ectasias with associated hydrops (Figure 1) or antecedents thereof, and chemical injuries, among others. In the literature, there is a transplant survival rate of 60% to 100% according to the studies and the primary corneal pathology⁷. The decision making towards triple or sequential surgery will depend on several factors. Figure 2 schematizes it according to the visualization of the anterior chamber (AC). If this is relatively good, the possibility of performing a lamellar transplant has been previously ruled out. Figure 3 shows a decision-making algorithm according to the personal circumstances of each patient.

ADVANTAGES AND DISADVANTAGES OF THE TRIPLE AND THE SEQUENTIAL PROCEDURES

Among the main advantages of the triple procedure are a good rate of effectiveness, rapid visual recovery, avoids the need for a 2^nd surgery and decreases the risk of endothelial loss due to it⁶. Its main drawback is the difficulty in choosing the dioptric power of the IOL⁷, precisely the main advantage of sequential surgery, since the calculation in the latter is made when the cornea is already refractively stable. This also allows the use of techniques to correct astigmatism, such as toric IOLs, arcuate incisions, etc. However, it has the disadvantage of needing a longer time to achieve visual rehabilitation. Other drawbacks are related to the second procedure, such as the added anesthetic risks, endothelial damage and other complications such as endophthalmitis and expulsive haemorrhage⁷, as well as the additional cost (Table 1).

CALCULATION OF THE IOL

Given the difficulty in predicting the final keratometry of the PK, it is important that at least the axial length be measured with the greatest precision for the calculation of the IOL. Due to the opacity of media, the most reliable method in these patients is with ultrasound, with an error typically <0.2 mm or 0.6 diopters. The keratometry and depth of AC usually change in an unpredictable and sometimes marked manner after this surgery. To compensate for this difficulty and reduce the resulting refractive error we can use: a) the keratometry of the other eye if it is healthy; b) the keratometry of the donor; c) a constant A individualized by regression analysis with the values of the surgeon, or d) a standard fixed value of keratometry, which can be based on the results of the surgeon. None of them is infallible^7-9.

Sometimes the choice of the IOL becomes complicated if the implant in the bag is not possible. If the peripheral capsular support is sufficient, the simplest is to place it in the precapsular position ("in sulcus"). If it is insufficient, an IOL of iris fixation (Artisan) or one sutured to the sclera can be used (see chapter 6.6.2). In cases of complicated cataract and PK surgery, we prefer IOLs of iridian fixation in the retro pupillary position (Figure 4), since it avoids damage to the endothelium that can occur with the anterior implant due to iridodonesis. For this modality, a constant A = 116.8 is used for ultrasound, although the calculation is still complicated when associating a PK.

TRIPLE PROCEDURE TECHNIQUE

Preoperative evaluation

In addition to obtaining a detailed clinical history of the patient, it is important to determine the degree to which cataract and corneal pathology separately contribute to visual impairment¹⁰, both clinically and with imaging tests such as corneal topography to assess corneal irregularities, optical coherence tomography (OCT) to visualize the details of the AC, presence of synechiae, evaluate the endothelium state, intraocular pressure and macular function.

Pre-operative treatment

As prophylaxis, we use topical antibiotics (e.g., a 4th generation quinolone) every 30 minutes, 2 hours prior to surgery. Pupillary dilation is performed with mydriatics (phenylephrine, tropicamide, cyclopentolate) every 15 minutes in the hour prior to surgery, together with topical NSAIDs every 30 minutes in order to minimize intraoperative miosis.

The type of anesthesia that we most use for this procedure is peribulbar with 0.5% bupivacaine and 2% lidocaine, accompanied by facial blockage to ensure complete akinesia and avoid eyelid compressions. General anesthesia is preferable in young or non-cooperative patients, with severe hearing loss or mental retardation, language barrier or rupture of the eyeball.

It is important to ensure the hypotonia of the eye⁵, especially because this is an open-sky procedure. To do this, we perform a digital massage or with the Honan balloon in the 15 minutes prior to the intervention and put the patient in anti-Trendelenburg position to reduce the orbital venous pressure. We can also use an intravenous solution of 250 ml of 20% mannitol in slow drip, one hour before the intervention. In cases with marked orbital pressure, a lateral canthotomy may be necessary.

We prepare the surgical field in the usual way, taking care to ensure maximum sterility. 5% povidone iodine is used in the conjunctiva and 10% in the periocular area. A speculum that fits properly to the eyelids, without compressing the eyeball, should be used. We can use traction palpebral sutures when the pressure should be as low as possible, as in pierced eyes. In cases of aphakia and collapsible sclera it is advisable to suture a Flieringa ring before trepanation, to stabilize the eyeball and prevent its collapse (video 3.3.1.1).

Preparation of the graft

Obtaining the donor button must be done before trepanning the recipient's cornea. The most common way is from the endothelial side with a trephine-die as Barron’s (Katena). In general, it is recommended to choose a nominal diameter 0.25-0.50 greater than that of the trephine for the receiver, to compensate for the disparity of the cut (see chapter 3.2.1). Once obtained, we must keep the corneal button hydrated or protected with viscoelastic.

Open-sky surgical technique

First, we mark the cardinal positions and the center of trepanation in the recipient cornea with a radial marker¹⁰. We practice a paracentesis to introduce a viscoelastic agent into the AC. We thus avoid the contact of the cornea with the iris at the time of trepanation and serve as a way to introduce balanced saline solution (BSS) or for fine instrument maneuvers such as releasing synechiae, etc. after the suture.

At the moment of trepanation of the receiving cornea, we can stabilize the globe by holding the limbal zone with tweezers or through the Flieringa ring. When using a pneumatic fixation trephine (Hessburg-Barron) it is important to ensure its correct centering before fixing it, and then we activate it progressively. We stop as soon as aqueous humor appears, we cease the suction and remove the trephine. We verify the extension of the trepanation along the perimeter and if necessary we expand the penetration with a knife. We lift the corneal button with hummingbird forceps and trim it with corneal scissors.

We continue with the open-sky cataract surgery. In this situation it is more difficult to control the capsulorhexis than in a closed chamber. It may be useful to support ourselves with a sponge or a flat spatula with the other hand to compensate for the "vitreous pressure". Although it is easier to make it continuous if it becomes small, it is necessary that its size allows the removal of the nucleus. It has also been described to leave a capsular flap and complete its resection after the IOL implant. Core extraction is usually easy by injecting BSS behind with a 27G hydrodissection cannula. Sometimes it is necessary to harpoon it with the cannula or with a fine needle (video 3.3.1.2). The irrigation-aspiration of the cortex is done with the usual technique, although with less irrigation or even with manual aspiration.

For the IOL implantation it is necessary to fill the bag, although this is difficult in the open-sky, with a cohesive viscoelastic. Normally you get a certain space that is enough to guide the first haptic – usually the lower one – towards the equator of the bag, and once in position we take the other haptic with fine forceps and accompany it until it passes under the edge of the capsulorhexis, with a movement of rotation assisted by a hook. Since it is not always possible to ensure that the implant is in the bag, in the sulcus, or one haptic in each space, an IOL that is not exclusive for the bag should always be used. The advantages of foldable IOLs are lost in the open-sky situation and those of PMMA offer easier handling and greater stability.

After the implant, we obtain meiosis with 1% acetylcholine and apply viscoelastic on the IOL and AC to keep it formed and protect the endothelium of the graft during suturing. We place the donor button in the window and fix it first with 4 cardinal points, followed by the final suture of our choice (video 3.3.1.3).

SEQUENTIAL SURGERY

The sequential technique consists of first performing a conventional PK^11-13 and later cataract surgery. We usually wait 1 year or the necessary time until the refraction and the keratometric values stabilize and we can calculate the power of the IOL with some reliability. In case of significant residual astigmatism, we can use a toric IOL or previously perform an anti-astigmatic procedure¹⁴. In addition to the advantage in calculating the IOL, with sequential surgery it is easier to ensure that the implant is in the bag.

Glaucoma is one of the most frequent causes of irreversible visual loss in patients undergoing corneal transplantation, and the second cause of graft failure after rejection. We consider ocular hypertension or suspicion of glaucoma after a penetrating keratoplasty (PK), when there is an increase in intraocular pressure (IOP) greater than 21 mmHg, associated or not with losses in the visual field or objective changes in the optic nerve. It is an important clinical problem due to its frequency and the difficulty in diagnosis and monitoring – in the preoperative period due to the opacity of the media and in the postoperative period due to the corneal thickness of the graft or the induced astigmatism that creates artefacts when measuring the IOP. In addition, the appearance or worsening of glaucoma after PK is a risk factor for graft failure and irreversible visual loss¹.

SECONDARY GLAUCOMA AFTER PENETRATING KERATOPLASTY

The appearance of secondary glaucoma after PK depends on multiple factors^1,2, among which are:

- The preoperative diagnosis. It is rarer in keratoconus (0-12%) and in cases of Fuchs’ dystrophy. It is more common in edematous (bullous) aphakic or pseudophakic keratopathy, in re-transplantation or after infectious keratitis (75%)³ (Figure 1).

- The moment of presentation. According to the series, it presents in 9% to 31% in the early postoperative period and in the late postoperative period between 18% and 35% of PK^2-6.

Risk factors for developing glaucoma after PK

● Edematous aphakic or pseudophakic keratopathy

● Dysgeneses of the anterior segment

● Iridocorneal endothelial syndrome

● Pre-existing glaucoma

● Perforated corneal ulcer

● Adherent leukoma

● Re-grafts (previous PK)

● Traumas (as an indication for PK)

● Combined surgery of PK with cataract extraction

● Combined surgery of PK and vitreous-retinal

The most frequently related mechanism is secondary angle closure due to the formation of peripheral anterior synechiae (Figure 2), which may be present in up to 87% of patients undergoing PK^4-6. Less frequently, there are other mechanisms of secondary open angle glaucoma, such as that induced by prolonged treatment with corticosteroids. The diameter of the transplant is related to the likelihood of developing glaucoma. It is advisable that the graft be of real size slightly higher (0.25-0.50 mm) than that of the receiving window. Other possible causes of hypertension that must be considered during surgery and the immediate postoperative period include pupillary block, hemorrhages, viscoelastic retention and malignant glaucoma, among others.

DIAGNOSTIC METHODS FOR GLAUCOMA IN PENETRATING KERATOPLASTY

Despite the difficulty to perform a complete examination, both in the preoperative and in the postoperative period of a PK, we can affirm that the diagnosis of glaucoma after PK is based primarily on the measurement of the IOP and changes in the optic nerve, objectified in functional and structural tests^7-9.

- Tonometry. In the immediate postoperative period, the corneal surface is irregular and makes Goldmann tonometry difficult. An electronic tonometer (Tonopen), a pneumotonometer, or the dynamic contour tonometer (DCT) may be more effective. The measurement with the O.R.A. (Ocular Response Analyzer) provides additional information on corneal biomechanics (see chapter 1.6). When it is possible to use the Goldmann, if there is high astigmatism, two measurements should be taken in the flatter and more curved meridians and averaged. In case of corneal edema, applanation underestimates the IOP. Other conditions such as scars, blood retention, etc., that alter the corneal thickness and elasticity can also distort it. The thickness of the graft possibly alters the IOP measurement, but not in the way it is related to pachymetry in normal corneas, since biomechanics are altered by other factors such as trepanation, sutures, etc.

- Gonioscopy. In general, it is difficult to perform and interpret, in the preoperative period due to corneal opacity and in the postoperative period due to irregularity, apart from the persistent opacity in the peripheral receptor cornea.

- Biomicroscopy and photography of the optic nerve. It is the technique of choice although it requires an adequate learning of the technique and its interpretation.

- Campimetry. It is useful for diagnosis and monitoring if the means are transparent and the patient has reached a sufficient degree of vision. Otherwise, its interpretation becomes difficult.

- Optical coherence tomography (OCT) of the anterior segment. It helps to assess the anatomical condition prior to surgery in the presence of an opaque cornea. After the PK, it allows to study the possible causes of hypertension, including the state of the angle, formation of synechiae or the state of filtering procedures.

- Ultrasonic bio microscopy. Its usefulness is similar to that of the OCT. Although it has lower resolution and its practice is more cumbersome, it allows to visualize structures where opacity blocks the OCT, as in the posterior chamber or behind very dense leukomas.

- Laser polarimetry (GDx). It allows measuring the thickness of the nerve fibber layer of the retina and helps monitoring the progression of the disease.

- Confocal microscopy of the posterior segment (HRT). It allows measuring different anatomical parameters of the optic nerve and differentiating those that are pathological.

- OCT of posterior segment. Apart from monitoring the condition of the macula, it allows to quantify the nerve fibber layer, even detecting early losses, not yet evident in the campimetry.

TREATMENT OF GLAUCOMA IN PENETRATING KERATOPLASTY

Medical treatment

The first therapeutic step in glaucoma after PK, except that it is due to a resolvable mechanical cause (e.g., a pupillary block), remains pharmacological. It is necessary to assess the effectiveness and hypotensive power and to mark an objective IOP, without forgetting the possible side effects on the ocular surface, especially those related to preservatives^6,8,11.

- Beta-blockers and alpha-2 adrenergics are the most frequently used.

- Prostaglandins are effective in hypotensive power, but may promote inflammation, with the consequent risk of rejection, cystic macular edema and recurrence of herpetic keratitis.

- The miotics are usually ineffective as hypotensive in this situation and in the early postoperative period can promote rupture of the blood-aqueous barrier and narrow the anterior chamber (AC), with risk of increasing inflammation and promote the formation of anterior and posterior synechia.

- Inhibitors of carbonic anhydrase. Since this enzyme participates in the function of endothelial pumping, its use is not recommended – especially topically – in grafts at the limit of decompensation. The systemic formulas offer the advantage of respecting the ocular surface more than any topical agent.

- Topical corticosteroids. Its administration should always be monitored and as soon as possible, those with a lower risk of inducing an increase in IOP, such as fluorometholone or similar, should be used. In corticosteroid responders we must consider their substitution by other agents such as topical cyclosporine A (0.5-2%, 4 times a day) or other immunomodulators.

Physical treatments

- Laser trabeculoplasty. It can be performed with argon laser or the "selective" with pulsed green laser (Nd:YAG, frequency doubled at 532 nm). Its indication is limited by the high frequency of anterior synechiae after a PK, as well as by the poor visibility of the trabeculum¹². Graft rejection episodes attributable to the laser have been described, either by hypertensive peaks or by the induced inflammatory reaction, which is why it is reserved for very selected cases.

- Laser Iridotomy (Nd:YAG). Although PK patients are usually carriers of one or more iridotomies or iridectomies, in cases of pupillary block it may be necessary to practice them additionally.

- Iridoplasty (gonioplasty) laser (Ar). It consists of retracting the peripheral impeller of the iris with coagulation points. It may be useful to avoid the formation of anterior synechiae in cases with narrow peripheral AC.

- Cyclodestructive procedures. Ablation of the ciliary body – be it by thermal Nd:YAG laser, diode laser or cryotherapy, either transscleral or by endoscopy – reduces the IOP by decreasing the production of aqueous humor. If an IOP ≤ 21 mmHg is defined as successful, it is achieved in 63% to 97% of cases after a single application, although this can be repeated – and is necessary with some frequency. Although they are sometimes the last measure to control glaucoma refractory to other treatments, they have serious drawbacks such as induced inflammation, which increases the likelihood of rejection up to 17% -44% or the risk of leading to chronic hypotonia^3,9,21,22 (see chapter 3.7.6).

Surgical treatment

- Trabeculectomy. It has long been considered as one of the main procedures to consider for the control of IOP in patients after PK. However, the failure rate in this situation is high, attributable to the limbal alterations and the great tendency of these eyes to fibrosis. The use of antimetabolites (mitomycin C, 5-fluorouracil) improves its efficacy^13,14. The control of IOP after a trabeculectomy with mitomycin C after PK is 67% -91% but decreases to 50% at 2 years. The risk of post-trabeculectomy graft failure has been estimated between 12% and 18%, although in some studies it reaches 60% at 2 years^15,16. Patients who have undergone a trabeculectomy after PK usually require hypotensive treatment in a high percentage of cases to control IOP.

- Non-penetrating deep sclerectomy (NPDS). Its success rate in this situation is high, comparable to trabeculectomy, although its indications are very limited. This is due to the high probability of anterior synechiae. In addition, limited visibility can make a goniopuncture very difficult if necessary. Although the data are not yet conclusive, it is speculated that the NPDS could offer a lower rate of graft failures when compared with trabeculectomy, by reducing the complications related to sudden decompression and a possible flattening of the AC.

- Drainage devices. Nowadays they are the most common treatment for the control of IOP after PK, when the pharmacological treatment is insufficient^3,9,15,17-20. There are two types: valved (Ahmed or Krupin valves) and non-valved (Molteno or Baerveldt implants). The first ones have as advantages the ease of implantation and the low frequency of hypotonia in the immediate postoperative period. Its main drawback is a high rate of increase in IOP in the hypertensive phase at months 1 to 3 of the postoperative period. The non-valved ones have in their favor the large drainage area, with a lower hypertensive phase, and as an inconvenience the greater difficulty in the implantation and the immediate postoperative functionalism. Most publications provide IOP control with these devices between 62% and 96%, as well as a probability of graft failure from 35% to 74% at 2 years. One of the series with the longest follow-up time found a control of IOP in 82% and graft survival of 55% at 36 months¹⁸.

The most appropriate moment to implant the drainage device can be before the PK, simultaneously or later. The published results are very different, but there is consensus that the existence of prior glaucoma constitutes a risk factor for graft failure and poor IOP control. The optimal location of the drainage tube remains controversial. The most frequent is in the AC (Figure 3). Some studies do not find differences between this location and the posterior one (via pars plana) in terms of IOP control, but a better viability of the transplant with the second one (83% per year, versus 48% when in the AC)¹⁷. The placement of the tube by pars plana requires a complete vitrectomy to avoid its occlusion. On the other hand, the situation in AC allows to monitor the state of the tube with the slit lamp.

The cause of graft failure after the implantation of a drainage device would be multifactorial: a) Retrograde passage of inflammatory cells through the tube to AC (no significant differences have been found, however, between valvular and non-valvular in terms of rejection of the graft). b) Chronic inflammation, extensive anterior synechiae, multiple previous surgeries. c) Reduction of the graft endothelial population (up to 60%) in the first 2 years after drainage implantation. d) Complications associated with the implant, such as flattening of the AC, iritis, contact of the tube with the endothelium or its occlusion by blood or vitreous and extrusion (Figure 4). Given the dilemma of which type of implant to use, the current trend favors the valvular one in cases of incipient or moderate glaucoma and reserves the non-valvular one for the most advanced cases.

In the presence of an alteration of the corneal transparency that requires a transplant, together with vitreous-retinal pathology (VR) that must be treated surgically, the problem of the fundus visualization is considered by both the VR surgeon and the corneal surgeon, because of the possible impact of the posterior segment condition and its surgery on graft survival. The first can be solved by means of the combined surgery of penetrating keratoplasty (PK) and VR¹, with the help of a temporary keratoprosthesis (KPT). This constitutes a higher level of complexity, firstly requiring the coordination of two surgical teams. For the corneal surgeon it involves the additional steps of placing and removing the KPT. However, these devices allow VR surgery to be performed under conditions of perfect visualization without compromising the viability of the graft, which will only be applied afterwards².

TYPES OF TEMPORARY KERATOPROSTHESES

The KPT are devices of transparent and cylinder-shaped refractive material that is set in a corneal window of trephination, which will be used at the end to receive a penetrating corneal graft. They are provided with extensions or side skirts on the anterior portion to allow suturing.

Several types of KPT have been developed; the most widespread are those of Landers and Eckardt. The first has gone through several designs, all of polymethyl methacrylate (PMMA). The classic model, first described in 1981 (Figure 1), consists of an optical cylinder with a diameter of 6.2 mm and a threaded profile to improve sealing. The optical zone is 5.0 mm in diameter and a vertical length of 4.0 mm. The anterior surface has 2 lateral projections for its attachment to the sclera. Both the anterior and posterior surfaces are concave with a radius of curvature of 7.8 mm, which increases the visual field. Even so, peripheral visualization with this model is somewhat limited.

Later Eckardt presented a KPT design made of silicone elastomer. The optical cylinder, of 7.0 mm in diameter and 2.8 mm in height, has smooth walls. The anterior side is convex with a radius of curvature of 7.8 mm and a peripheral flap of 1.5 mm radius for the suture. The total diameter of the anterior disc is 10 mm. The posterior side is concave with a radius of curvature of 4.4 mm (Figure 2). This greater amplitude and smaller height of the optical cylinder allow a greater field to it than with the one of Landers. The combination of surfaces gives rise to an effective dioptric power of 35 diopters (D), which allows observing the back of the eye without the need for a contact lens. However, the addition of this or another wide field optical device for VR surgery allows a much better visualization of the retinal periphery.

These features give the Eckardt KPT clear advantages over the classic Landers, especially to deal with complex VR cases that require good visibility of extreme periphery. Later Landers developed new models called "wide field", which follow the general form of Eckardt – with an anterior convex face – but are made of PMMA. They exist in diameters of the cylinder of 7.2 and 8.2 mm, which correspond to visual fields (static) of 28° and 30° respectively, but with a contact lens they allow a peripheral visualization similar or better than with that of Eckardt.

SURGICAL PROCEDURE

The combined surgery of PK and VR involves a minimum of three phases: (1) the preparation of the anterior segment, with the trepanation and the application of the KPT; (2) the VR surgery phase; and (3) the final phase of the anterior segment, with removal of the KPT and its replacement by the corneal graft. To these is usually added a fourth at the end, with exchanges of instrumental fluids by the VR surgeon, and sometimes a previous one – rare nowadays – if a scleral procedure is required.

In the trepanation phase, a Flieringa ring is usually sutured first. The diameter of the trepanation, in addition to the corneal pathology, must consider that of the KPT that is going to be used. With the new ones from Landers, trepanation is recommended 0.2 mm lower, that is, 7.0 or 8.0 mm. If there is a lens, it should be removed, generally leaving the empty bag ready to implant the IOL at the end. This prevents the IOL from interfering with the visualization of the retinal periphery during the VR phase. The KPT of Eckardt is fixed with 6-8 sutures of the preferred material by the surgeon (e.g., 7-0 silk or vicryl), which are given through the material itself in the peripheral flap of the anterior plate. The old Landers KPT was fixed with two sutures that hugged the lateral extensions. The new ones have 6 holes in the anterior skirt for the passage of sutures (Figure 3).

Once the KPT is fixed, we proceed with VR surgery. We use medium concentration cohesive viscoelastic (hyaluronate 14 mg/ml) to ensure a stable optical union of the KPT with wide-field contact lenses. After this phase and with the infusion closed, a tamponade with perfluoro octane is performed as a step prior to the removal of the KPT and placement of the graft by the corneal surgeon. This minimizes the risk of complications such as expulsive hemorrhage. The KPT is exchanged for a donor corneal button with a diameter 0.5-0.75 mm greater than trepanation. After the PK is sutured, the VR operating room is again used for the extraction of perfluoro octane and possible exchange with SF₆ or C₃F₈ gas or with silicone oil³.

EFFECT OF VITREO-RETINAL SURGERY ON THE SURVIVAL OF THE GRAFT

VR surgery is in itself an invasive procedure and many patients have prolonged ocular inflammation after the intervention, which can have adverse effects on the corneal graft^4,5. The likelihood of maintaining the graft transparent is somewhat lower compared to patients subjected to PK alone. When the VR surgery has been of simple type together with the PK, the probability of maintaining a transparent graft is much greater than if it has been complex, especially if it has required a tamponade and especially if this is with silicone oil.

In a study of 34 eyes in 31 patients with severe eye injuries, who underwent combined surgery of PK and VR, the Roters'’ group found that the extensive contact of silicone oil with the endothelium in 22 cases led to failure of the graft in all of them³. In 4 eyes endothelial damage was prevented by implanting artificial iris type diaphragms during the initial procedure. A subsequent study of the same group, in mostly non-traumatic patients, confirmed that the contact of the silicone with the endothelium was the first reason for the failure of PK. During the 1-year follow-up, 29 of 44 eyes (66%) with silicone maintained a transparent graft and 7 of 9 eyes (78%) without silicone did so⁶. However, Khouri et al.² found no such relationship or common factor for graft failures in 24 eyes operated on PK and VR and followed for 36 months; no eye in their series needed extraction of the silicone for graft hazard. Although most authors believe that the risk of graft failure is greater (around 2/3) if the silicone is not extracted, it would be a complex issue, influenced by multiple factors from the cause of the corneal problem to aspects of the VR surgical technique, of the time that the silicone is left in or of the state of the iridian diaphragm.