Disclosures: Jacob reports she has a patent pending for special trephines, devices and processes used to create these segments as well as for the CAIRS segments and various types of shaped corneal segments. Agarwal and John report no relevant financial disclosures.
September 22, 2020
7 min read
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CAIRS a reversible, stand-alone option for keratoconus treatment

The risk for complications is lower with corneal allogenic intrastromal ring segments.

Disclosures: Jacob reports she has a patent pending for special trephines, devices and processes used to create these segments as well as for the CAIRS segments and various types of shaped corneal segments. Agarwal and John report no relevant financial disclosures.
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Anterior lamellar keratoplasty continues to evolve, with newer surgical techniques and improved surgical instruments, and this progressive, forward movement is transforming the landscape of corneal surgery.

Thomas "TJ" John
Thomas "TJ" John

Historically, lamellar keratoplasty was performed before full-thickness penetrating keratoplasty, and both procedures have a role in treating select groups of patients.

When glasses and contact lenses have failed to improve vision in keratoconus, surgery becomes the next step for visual rehabilitation. The surgical approach in keratoconus encompasses deep anterior lamellar keratoplasty, penetrating keratoplasty, intrastromal corneal ring segments, topography-guided PRK, Bowman’s layer transplantation and, more recently, corneal allogenic intrastromal ring segments (CAIRS). Collagen cross-linking can be a stand-alone procedure or may be combined with other surgical techniques, especially in progressive keratoconus.

Lamellar keratoplasty in these patients retains the patient’s endothelium and replaces most of the remaining corneal tissue. While eliminating endothelial corneal graft rejection, deep anterior lamellar keratoplasty introduces other challenges including, but not limited to, uniform surgical removal of the diseased corneal tissue, preventing Descemet’s membrane tear during surgery, postoperative interface haze that can be slow to clear, and suture-related issues.

In an attempt to delay or prevent a lamellar keratoplasty or penetrating keratoplasty, intrastromal corneal ring segments have been successfully used in patients with keratoconus globally. This surgical approach is aimed primarily at flattening the cone (ectatic cornea) and improving vision. In the CAIRS procedure, instead of using plastic ring segments, donor corneal tissue strips are inserted intrastromally into the mid-peripheral recipient cornea.

The host corneal tissue would be expected to react somewhat differently with plastic vs. donor corneal tissue. Some of the differences include less rigidity of donor corneal strips in CAIRS as compared with plastic inserts and more tissue integration of recipient cornea to donor cornea in CAIRS as compared with plastic. However, strong tissue integration over time may affect the ease of reversibility of the procedure, and this needs to be studied long term. Further, the volume addition with synthetic material is fixed for the most part, while the volume addition with donor tissue strips can potentially vary and decrease with time, especially after tissue integration, tissue remodeling, and recipient corneal and endothelial pump function.

In this column, Drs. Jacob and Agarwal describe their new CAIRS surgical procedure to treat keratoconus. Larger patient numbers, close monitoring of the postoperative results and long-term follow-up are essential to further understand safety and efficacy of the procedure.

Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor

CAIRS, or corneal allogenic intrastromal ring segments, initially described by Jacob, refers to mid-peripheral intrastromal transplantation of donor cornea stromal segments in patients with keratoconus.

It is a less extensive procedure than deep anterior lamellar keratoplasty. As a stand-alone procedure in nonprogressive cases and together with cross-linking techniques in progressive cases, it has become an advantageous solution that is reversible, and it does not take away the ability to do DALK or any other treatment modality that may become available in the future. Additionally, it can be used synergistically with other treatment modalities such as topography-guided ablation or phakic IOL implantation. CAIRS is a mid-peripheral mid-stromal sutureless variant of anterior lamellar keratoplasty in which donor corneal tissue segments are transplanted into the mid-periphery of the mid-stroma of the patient’s eye in a circular zone that lies outside the line of sight.

Technique

A donor corneoscleral rim is prepared by removing all epithelium and endothelium. The donor cornea is then trephined using the Jacob double-bladed CAIRS trephine. This gives a ring of donor stromal tissue that is cut into segments and transplanted into a circular mid-stromal mid-peripheral channel dissected in the keratoconic eye. The segment could also be precut by the eye bank and provided to the surgeon ready to insert. The channel in the recipient eye could be femtosecond laser dissected or manually dissected using a semicircular dissector and a vacuum-centering guide (Figures 1 and 2).

The Jacob double-bladed CAIRS trephine
Figure 1. The Jacob double-bladed CAIRS trephine (a). The ring of stromal tissue cut by the trephine (b). Two CAIRS segments prepared by cutting the ring in half (c and d).

Source: Soosan Jacob, MS, FRCS, DNB, and Amar Agarwal, MS, FRCS, FRCOphth
The CAIRS segment introduced
Figure 2. The CAIRS segment introduced into either femtosecond or manually dissected intrastromal channels (a and b). Both segments lying within the channel (c). Postoperative image taken on slit lamp (d).

Results

The mid-peripheral position avoids the limbus and the visual axis. CAIRS preserves the patient’s own cornea as much as possible while using localized anterior lamellar transplantation of donor tissue for flattening out the conical protrusion of the cornea and making it more regular. Simultaneously, it also increases mid-peripheral thickness of the thinned-out host cornea. In our published study in the Journal of Refractive Surgery, we had significant improvement in almost all parameters including uncorrected and best corrected visual acuity, spherical equivalent, topographic astigmatism, maximum and steepest keratometric values, anterior and posterior best fit spheres, and mean power in the 3-mm and 5-mm zones. We have done more than 140 CAIRS cases in our center.

Advantages of CAIRS

CAIRS has many advantages over conventional DALK in patients with keratoconus (Figure 3).

Pre- and post-CAIRS curvature maps
Figure 3. Pre- and post-CAIRS curvature maps of an advanced case of keratoconus that would have otherwise undergone DALK. Note the significant flattening and regularization achieved by doing CAIRS instead.

Lack of suture-related issues: DALK is held in place with multiple radial sutures (generally 16, sometimes more) that go close to the limbus and the limbal vasculature. These are long-term sutures that are retained between 6 months to a few years. These sutures often loosen with time and incite neovascularization into the donor graft from the limbus. This results in a higher risk for graft rejection, edema, scarring, lipid keratopathy and opacification of the entire cornea. These complications can eventually necessitate a penetrating keratoplasty, which in the setting of neovascularization results in immediate and long-term risk for graft rejection, intractable secondary glaucoma and even permanent visual loss, while also predisposing the patient to a series of surgeries (Figure 4). Because CAIRS is held securely within the mid-stromal location, it is a sutureless procedure. The patients are off steroids within 1.5 months, the typical regimen being the same as used after cataract surgery.

Postoperative anterior segment OCT
Figure 4. Postoperative anterior segment OCT showing perforation and double anterior chamber after DALK (a). Extensive neovascularization, host stromal thinning and lipid keratopathy after loosening of sutures in a case of DALK (b).

Decreased risk for rejection: DALK involves a large area of transplantation. Typically, a 7.5- to 8-mm DALK graft with an average thickness of 600 µm works out to be between 26.5 mm3 to 35 mm3 of tissue transplanted. In contrast, CAIRS is only a thin sliver of donor corneal tissue that is transplanted, and therefore the volume of tissue transferred varies between 1 mm3 and 6 mm3 only. This tremendous decrease in the volume of donor tissue transplanted makes CAIRS much less antigenic than DALK. The risk for rejection that exists with DALK is yet lower with CAIRS. Added to this is the safety factor that CAIRS are transplanted outside the visual axis.

Decreased surface issues: Unlike the CAIRS procedure, corneal nerves are cut all around while doing DALK, leading to a higher risk for surface issues such as dry eyes, grittiness, foreign body sensation, persistent epithelial defect and neurotrophic keratitis with DALK.

Clear and uninvolved visual axis: Postoperatively, in DALK, the interface of the graft goes across the visual axis of the patient’s eye, and therefore interface haze affects final visual acuity and can sometimes be severe enough to need repeat surgery. In CAIRS, on the other hand, the visual axis is not encroached upon.

Decreased risk for intraoperative complications: DALK has the disadvantage of other possible complications such as Descemet’s membrane perforation or tear during surgery and having to convert to penetrating keratoplasty. Most surgeons keep an additional donor cornea of optical grade as stand-by tissue. A side-port incision is often made in DALK for instillation of air and/or balanced salt solution into the anterior chamber. There is no intraocular entry with CAIRS, and hence, it is a safer surgery especially when compared with DALK.

Easier and faster surgery: The time taken for surgery for CAIRS is much less than for DALK, and the learning curve is also smoother.

Postoperative visual acuity: Both procedures can improve uncorrected and best corrected visual acuity. However, the multiple sutures in DALK can by themselves induce large amounts of irregular astigmatism, which may become difficult to treat. CAIRS, however, decreases irregular astigmatism, thus contributing to an improved final visual acuity.

Reversibility: CAIRS is a reversible procedure, and the transplanted tissue can be taken out. CAIRS does not prevent DALK, penetrating keratoplasty or any future new developments from being performed at a later date.

Combination treatments: CAIRS can easily be combined with cross-linking simultaneously or sequentially. Thin cornea cross-linking techniques such as contact lens-assisted CXL can be applied to cross-link even in advanced cases, and we have thus avoided DALK in many patients. CAIRS thickens the cornea in the mid-periphery and may also help redistribute corneal stress forces by flattening the cone. It can be combined synergistically with a phakic IOL and even with topography-guided PRK, depending on the indication.

An early treatment option: In addition to treatment of advanced keratoconus, CAIRS can also be used to treat earlier stages of keratoconus before patients reach the advanced stage, thereby allowing an earlier and better return to normalization of their disease process.

Conclusion

CAIRS helps patients avoid more invasive, irreversible surgeries such as PK and DALK, which are known to have a much higher risk for complications including graft rejection, visual axis corneal edema and scarring, surface and suture-related complications, neovascularization and lipid exudation. It allows an easy, effective and safe means of visual improvement in patients with keratoconus while maintaining reversibility and the possibility for future treatment options.