Filament formation around the incision site can be treated with debridement.

The extrusion of the segment is one of the most common postoperative complications and requires its explantation. Explantation rate varies among studies ranging from 0.98 to 30 % [1]. Colin et al. reported explantation of the segment in 12 % of eyes implanted with Intacs, due to dissatisfaction and visual symptoms [10].

Ideally, an intrastromal implant should not affect the normal physiology of the cornea, as an impermeable implant has the potential to impede fluid and nutrients movement within the cornea. A nutritional deficiency of the stroma anterior to the inlay can result in anterior stromal edema and melting with corneal ulceration and implant extrusion [11].

By determining the stromal depth of the segment during slit lamp evaluation, the surgeon can identify those cases where stromal thinning and extrusion are more likely. Deep implantations allow an adequate nutrition of the overlying stroma and there is less risk of extrusion. The first sign of stromal thinning is usually punctate epithelial staining over the ring. Ultimately the epithelium breaks down, the stroma melts, and the segment extrudes (Fig. 18.2).

The extrusion or removal rate for Intacs SK has been reported at 19.3 %, greater than the one reported for regular Intacs. Nevertheless, Kwitko and Severo et al. reported an extrusion rate for Ferrara rings of 19.6 % [12].

Ferrer et al. evaluated the main causes of intrastromal ring segment extrusion over a 9-year period and its relationship with microscopic findings on the ICRS surface [2]. Intrastromal segments were explanted with a rate of 22.8 %. The main cause was extrusion (48.2 % of explanted segments), followed by unsatisfying refractive outcome (37.9 %) and keratitis (6.8 %).

Shallow implantation is one of the main risk factors of extrusion as it has been associated with ring superficialization, stromal thinning, and epithelial breakdown [13]. Khan et al. suggested as risk factors for extrusion a thin cornea and a history of atopy with eye rubbing [14].

Lai et al. performed an optical coherence tomography (OCT ) between 7 and 43 days after ICRS implantation to study their final stromal depth. They observed that the distal and inferior portions of the segments tended to be placed at a shallower depth. They suggested that a shallower placement of the segments may result in more complications, such as epithelial–stromal breakdown and extrusion, because of the greater anterior stromal tensile strain [15].

Kamburoğlu et al. used Pentacam to assess the depth of Intacs implanted by femtosecond laser, and reported a decreased depth at the end of the first postoperative year in all measured points, being these differences statistically significant at the superior, inferior, and temporal sides of the Intacs [16].

Toroquetti and Ferrara identified two major causes of ICRS extrusion: superficial implantation and the placement of a segment close to the incision [17]. They claimed that, as a general rule, the thickness of the implanted ICRS should not be more than 50 % of the corneal thickness in the ring track. Deeply located ICRS produce better results and also leave a greater amount of corneal stroma between the ICRS and the corneal epithelium, what should theoretically protect from extrusion .

When segment migration brings the end of the implant adjacent to the incision, this represents an unacceptable risk for wound melt. In this scenario, the segment should be repositioned as soon as possible. This can be easily accomplished with a Sinskey hook placed into the corneal tunnel through the entry wound. If after an initial repositioning, the segment continues to migrate to the incision, it will be necessary to remove it (Fig. 18.3).

Infectious keratitis after ICRS implantation is very rare, and culture-proven infections were less than 1 % in several large clinical series [13, 18]. According to the literature, the incidence of infectious keratitis after Intacs implantation for the treatment of myopia is low, ranging from 0.2 to 0.63 % [13].

Bourcier et al. reported a case of late bacterial keratitis after ICRS implantation. Cultures were positive for Clostridium perfringens and Staphylococcus epidermidis, showing the risk of microbial keratitis even months after the implantation [18].

Bilateral infections after uncomplicated ICRS implantation have also been described [19]. An early recognition of the infection, aggressive treatment with antibiotics and, in many cases, removal of the ICRS are critical to prevent serious sight-threatening complications.

Traumatic shattering of intrastromal segments due to blunt trauma is possible [20]. Sharp edges of the shattered segments may compromise the anterior or posterior stroma, so their removal should be assessed in order to avoid the risk of corneal erosions and a subsequent infection.

European multicenter study of Intacs reported 1 case of channel infection that was observed 3 weeks after the implantation [13]. No microorganisms were identified in that case, and the infection resolved with high dose topical antibiotics without requiring the explant of the ICRS. Results of phase II and III of US Food and Drug Administration trials reported 1 case of infectious keratitis among 499 eyes with Intacs [21]. Infectious keratitis should be differentiated from simple deposits of extracellular substance, which accumulates in the lamellar channel around the segments [22].

Several mechanisms can help to explain the presentation of channel infection after ICRS: the incisional keratotomy to create the channel puts the wound perpendicular to the corneal plane, which tends to heal slowly. Also, the presence of an intrastromal foreign body carries an additional risk of postoperative infection because of the possible adhesion of cells, proteins, or microorganisms onto the surface of the biomaterial.

Infectious keratitis has been reported with either implantation technique (manual or femtosecond laser assisted) [23].

If a patient complains of photophobia or aching pain after the surgery an examination to rule out infection should be performed as soon as possible. Signs of infection include edema or an infiltrate involving the stroma adjacent to the segment (Fig. 18.4). A minimal infiltrate may initially be treated with hourly broad-spectrum antibiotic drops. If the infiltrate worsens or the initial stromal reaction is more advanced, removal of the ICRS should be considered.

In all forms of keratorefractive surgery, transitory reduction of corneal sensitivity may occur. With corneal ring segments, all these findings are minor. In most of the cases, in 2–3 months period, corneal sensitivity returns to the preoperative baseline values, without any neurotrophic effects [24].

Minor epithelial cysts or plugs should be considered normal. Very large plugs may indicate excessive wound gape and can induce against-the-rule astigmatism.

An unsutured radial corneal incision alone (without segment implantation) has specific effects on the corneal topography [25, 26]. Flattening of the incised meridian with steepening of the perpendicular meridian is seen. A wound which is too long or too traumatized is prone to excessive gap, and a 12 o’clock wound which gapes too much may induce an against-the-rule (ATR) astigmatism. Nevertheless, as the wound contracts, these effects will resolve by themselves. On the other hand, a tight 12 o’clock wound can be associated with a with-the-rule (WTR) astigmatism. Thus, an overly tight suture will induce steepening in the incised meridian, although due to the coupling created by the presence of the segments there will not be a compensatory flattening of the meridian 90° away, resulting in a WTR cylinder and a myopic shift. Early removal of the tight suture may relax the steep meridian and may allow a shift of the spherical equivalent toward emmetropia.

Patients may complaint of short-term glare or halos. As the tunnels are dissected, the lamellae split and this creates temporary tunnel haze just central to the inner aspect of each implanted segment. This haze will resolve after 30–60 days but may induce glare for a few months in a minority of patients. Patients with large pupils are more prone to develop these visual symptoms.

A small percentage of patients may experience diurnal visual fluctuations, what is observed more frequently with thicker segments [27, 28]. Keratoconus patients experience a morning hyperopic shift and an evening myopic shift. Thus, undercorrected patients see better in the mornings than in the evenings, except emmetropic and overcorrected patients (induced hyperopia) who experience an increase in visual acuity during the day. The reason of the drift is unknown, although it should be related to the effects of the nighttime lid closure, causing metabolic alterations by oxygen deprivation .

As we have already discussed in the previous chapter, due to the abnormal corneal biomechanical response, the precise outcome of an ICRS implantation in a keratoconic eye is not possible to accurately predict, and this should be informed to the patient during the preoperative evaluation [29, 30]. However, the refractive effect of an ICRS is reversible, so a worsened refractive defect after ring implantation may be improved to the preoperative values by simple explantation of the device [31].

Alternatively, ICRS adjustment surgery may be attempted: this adjustment surgery is defined as any combination of removal, exchange, addition, or shifting an ICRS to improve its refractive effect over the cornea. Actually, Alió et al. reported a significant visual and refractive improvement by implanting a new ICRS combination after previous unsuccessful ICRS, which were explanted due to either poor visual results or extrusion [32]. Pokroy et al. reported that approximately 10 % of keratoconic eyes managed with ICRS may require an adjustment surgery, which often has a good outcome [33]. In this study, the indications for ICRS adjustment were increased astigmatism in four eyes, induced hyperopia (overcorrection) in three eyes, and undercorrection in one eye. Induced astigmatism and hyperopia were most often managed by removing the superior segment. The undercorrected eye, having initially received a single inferior segment, was treated by implanting a superior segment.

These infiltrates commonly occur during the second week after surgery and they are usually asymptomatic. If the physician feels that the stromal reaction may be infectious (based on timing, appearance, and clinical presentation), it should be treated immediately with antibiotic drops as we have already seen .