Corneal allogenic intrastromal ring segments can be implanted with manual technique
Surgeons who do not have access to a femtosecond laser to dissect the intrastromal channels may use this technique.
Click Here to Manage Email Alerts
Corneal structural and morphologic distortion of any degree usually has a negative impact on quality of vision, and patients can often become symptomatic even at an early stage.
Corneal ectatic disorders cause visual distortion and erode visual quality, the extent of which depends on the degree of corneal ectasia (mild, moderate or severe).
These disorders are usually noninflammatory, bilateral corneal thinning that may be focal or diffuse, with secondary corneal ectasia involving the central, paracentral or peripheral cornea. They encompass keratoconus, keratoglobus, pellucid marginal degeneration, Terrien’s marginal degeneration, and post-LASIK and post-PRK ectasia.
Treatments to improve vision in corneal ectatic disorders include glasses, contact lenses and surgery. Corneal collagen cross-linking is aimed at strengthening the cornea and retarding or preventing progression of keratoconus.
Surgical corneal treatment modalities include corneal transplantation, which ranges from partial-thickness deep anterior lamellar keratoplasty to full-thickness penetrating keratoplasty, intrastromal corneal ring segments, topography-guided PRK, Bowman’s layer transplantation and corneal allogenic intrastromal ring segments (CAIRS). Surgeons now have a choice between plastic intrastromal segments and corneal tissue intrastromal segments to decrease corneal ectasia in patients with keratoconus.
In this column, Drs. Dockery, Parker and Parker describe a manual CAIRS technique for keratoconus. Newer surgical techniques such as CAIRS need to be followed and studied for their long-term safety, efficacy and reproducibility with larger groups of patients.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Superficially, corneal allogenic intrastromal ring segments (CAIRS) are a modified form of intracorneal ring segments (ICRS), with the difference being that the implanted material is composed of corneal tissue instead of synthetic polymer. In reality, CAIRS represents a new form of anterior lamellar keratoplasty, one in which donor corneal tissue is used not to replace the anterior corneal surface but to reshape it. The amount of reshaping far exceeds that typically observed with conventional ICRS, with some corneas experiencing 20 D to 30 D, or even more, of flattening (Figure 1). As a result, CAIRS may potentially supplant not only ICRS but also deep anterior lamellar keratoplasty and penetrating keratoplasty for eyes with visually significant keratoconus.
Source: Philip W. Dockery, MD, MPH, Jack S. Parker, MD, PhD, and John S. Parker, MD
The originally described CAIRS protocol specified the use of a femtosecond laser to dissect the channels into which the donor corneal segments are placed. This may be a problem, however, for surgeons without access to this technology or for patients with limited ability to afford it. Fortunately, a “manual CAIRS” technique is also possible, which appears equally efficacious and perhaps even easier to perform.
Technique
For a manual CAIRS technique, the steps of tissue preparation are the same. Donor corneal buttons are debrided of their epithelium and endothelium using surgical sponges, then trephinated using a dedicated CAIRS trephine (Jacob CAIRS trephine, Madhu Instruments). These trephines are manufactured in two sizes: large (7.75 mm/8.75 mm inner and outer blade diameters), which produces thinner segments, and small (6.5 mm/8 mm), which produces thicker segments. Theoretically, the thicker segments may induce more flattening, but they are also more technically challenging to implant. As a result, starting surgeons may initially opt for the larger size trephine, at least during their learning curve. Trephination yields a circular ring of corneal tissue, which may be split into two semicircular segments. These segments may be stained with 0.06% trypan blue (VisionBlue, DORC International) to enhance their visibility and to assist in distinguishing them from the surrounding recipient corneal stroma during subsequent implantation (Figure 2). An optional step is to air dry the segments for 20 to 30 minutes, which transiently shrinks and stiffens them, rendering them easier to insert into the intrastromal channels in the recipient cornea (Figure 3).
Once the segments are prepared, the surgeon turns his or her attention to the patient.
The anesthesia may be topical or retrobulbar, but for starting surgeons especially, general anesthesia may be advised. This is particularly true because many patients eligible for CAIRS are young (children or young adults), for whom cooperation may be difficult.
The operation begins in a manner identical to manual ICRS implantation. The thickness of the recipient cornea is measured in the location of the planned main incision, approximately 1 mm to 2 mm central to the temporal limbus. The cornea is then dried, and an epithelial impression is created using an 11-mm zone marker (Duckworth & Kent) (Figure 4a), the center of which is marked with an inked Sinskey hook (Figure 4b). An inked 0.9-mm procedure marker (AJL Ophthalmic) is aligned with this central mark and pressed against the corneal surface, establishing purple guidelines for the creation of the main (temporal) incision and the intrastromal channels (Figure 4c).
A diamond micrometer knife (AJL Ophthalmic) is calibrated to 60% of the measured corneal thickness and then used to create a 1-mm radial groove in the temporal cornea, which serves as the main wound (Figure 4d). A vacuum centering guide (AJL Ophthalmic) is fitted over the ocular surface and connected to a vacuum system (AJL Ophthalmic). Suction is engaged to stabilize the eye, and a pocketing hook (AJL Ophthalmic) is inserted into the radial groove and rotated to dissect the space on either side (Figure 4e). Into each of these spaces, a symmetric glide (AJL Ophthalmic) is placed, and a corneal separator (AJL Ophthalmic) is advanced (Figures 4f to 4h). This creates two channels that intersect in the nasal cornea, generating a single 360° tunnel. The micrometer knife is then reset to 100 µm deeper than the temporal incision and used to create a 1-mm incision in the nasal cornea in the area of the channel overlap (Figure 4i).
The ocular surface is then dried, and the CAIRS segments are placed atop the recipient cornea and pushed into the intrastromal channels on either side of the temporal incision using a bent Y-rod (Figures 5a and 5b). After approximately 50% of each segment has been advanced by pushing, a reverse Sinskey hook is introduced via the nasal incision and used to engage the distal end of the CAIRS segments and pull them into final position (Figures 5c and 5d) The nasal and temporal wounds may be sutured if wound gape is evident; otherwise, the operation is concluded.
Discussion
The chief advantage of femtosecond technology vs. manual dissection for intrastromal channel creation is greater precision. Nevertheless, manual dissection is still common globally, particularly where femtosecond technology is either unavailable or unaffordable. In addition, a manual technique may offer some theoretical advantage because femtosecond laser ablation is tissue destructive, which may be counterproductive to the aim of CAIRS (ie, to thicken and strengthen the recipient corneal stroma).
The basic technique for manual CAIRS resembles that of manual implantation of synthetic intracorneal rings. One advantage to this similarity is an intuitive learning curve. However, unlike conventional synthetic rings, CAIRS segments are not sufficiently rigid to insert via a single incision, and a second incision is often needed to pull the segments into final position. In our experience, this nasal incision should be made 100 µm deeper than the temporal incision to guarantee access to the underlying stromal channels.
Evaluation of the long-term results of manual CAIRS, and particularly their comparison to femtosecond CAIRS, awaits further study. Until then, manual CAIRS may be regarded as a technically viable option when femtosecond technology is unavailable or otherwise contraindicated.
- References:
- Jacob S, et al. J Refract Surg. 2018;doi:10.3928/1081597X-20180223-01.
- Parker J, et al. Pre-implantation dehydration for corneal allogenic intrastromal ring segment (CAIRS) implantation. J Cataract Refract Surg. 2020 (submitted).
- Parker J, et al. Trypan blue assisted corneal allogenic intrastromal ring segment (CAIRS) implantation. J Cataract Refract Surg. 2020 (in press).
- Piñero DP, et al. Clin Exp Ophthalmol. 2010;doi:10.1111/j.1442-9071.2010.02197.x.
- Piñero DP, et al. Ophthalmology. 2009;doi:10.1016/j.ophtha.2009.05.016.
- Rabinowitz YS, et al. J Refract Surg. 2006;doi:10.3928/1081-597X-20061001-06.
- Seider MI, et al. J Cataract Refract Surg. 2008;doi:10.1016/j.jcrs.2007.12.043.
- Yoo SH, et al. Ophthalmology. 2008;doi:10.1016/j.ophtha.2007.10.037.
- For more information:
- Jack S. Parker, MD, PhD, can be reached at Parker Cornea, 700 18th St. South, Suite 503, Birmingham, AL 35233; email: jack.parker@gmail.com.
- Edited by Thomas “TJ” John, MD, a clinical associate professor at Loyola University Chicago and in private practice in Oak Brook, Tinley Park and Oak Lawn, Illinois. He can be reached at email: tjconference@gmail.com.
Collapse
Parker J, et al. Trypan blue assisted corneal allogenic intrastromal ring segment (CAIRS) implantation. J Cataract Refract Surg. 2020 (in press).
Read more about
Click Here to Manage Email Alerts