CAIRS can be customized for treatment of keratoconus, other corneal ectasia conditions
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The term corneal allogenic intrastromal ring segments, or CAIRS, refers to the intra-channel placement of allogenic tissue for the treatment of corneal ectasia.
The allogenic tissue can be from any source, including fresh-cut CAIRS, unprocessed or processed CAIRS, and preserved or packaged CAIRS with or without modifications and with or without storage and shelf-life capabilities. The procedure was first described by Soosan Jacob, who has been using it successfully to treat keratoconus since 2015. Since then, it has become popular and is currently performed in more than 12 countries, including the United States, Australia, Canada, Lebanon, Germany, Ireland, Turkey, South Africa and Israel, with some countries, such as the U.S. and India, having multiple centers where it is performed.
CAIRS segments are traditionally standard, longitudinally cut and have a uniform thickness; however, Jacob has also described customized CAIRS to further refine the results of treatment. Customization allows the effect of CAIRS to be tailored to the individual patient with keratoconus, providing better topographic and refractive results.
Uniform-thickness CAIRS
Synthetic symmetric intracorneal ring segments (ICRS) have been used for keratoconus for many years. We have previously described encouraging results for symmetric uniform-thickness CAIRS in keratoconus, with patients showing significant improvement in almost all the parameters studied such as uncorrected and spectacle corrected distance visual acuity, spherical equivalent, topographic astigmatism, maximum and steepest keratometry, and best fit sphere. As described previously, these are longitudinally cut allogenic segments of uniform thickness that are somewhat similar to Intacs (CorneaGen).
Customized CAIRS
We know that keratoconus occurs in a wide variety of phenotypes. There are different classifications for these phenotypes, with a commonly adopted one being the Alfonso classification. Alfonso’s phenotypes include the croissant, bow tie, snowman, duck-type and nipple cones. Although we obtained good results with standard uniform-thickness CAIRS, the possibility of further tweaking the results by customizing CAIRS to the individual patient’s topography and refraction was an exciting one. We therefore used customized CAIRS in patients with asymmetric keratoconus. This was done by shaping CAIRS according to the topographic and refractive needs.
Customized CAIRS includes symmetric or asymmetric specifically shaped CAIRS, which can be of progressive or variable thickness and progressive or variable width. In addition, the transition zone can be created to have a sudden change or gradual taper, and variations in shape or thickness may be along a defined extent or the entire arc length. Customized CAIRS may be prepared by the surgeon or made available by eye banks as preprepared, ready-to-insert segments, preserved, processed or modified with or without storage and shelf-life capabilities. In progressive ectasia, CAIRS is combined with corneal cross-linking to stabilize progression.
Technique for customized CAIRS
We customized CAIRS by first trephining standard CAIRS using a special double-bladed trephine (Jacob CAIRS trephine, Madhu Instruments), placing the standard CAIRS segment on a computer-printed degree-zone marker, followed by marking the required arc length and transition points with a fine-tipped inked marker. This was then placed on a flat cutting surface, for instance, a reversed Teflon block, and cut with a sharp blade using the transition marks as reference points. The degree-zone marker was designed by Jacob, and we found that it gave us excellent predictability with the hand-cut segments matching well to the surgical plan. We also found it easy and quick to customize once the marks were applied to standard CAIRS. For surgeons desiring freedom from preparing customized CAIRS, this could be done by an eye bank technician or, in the future, using the femtosecond laser.
Once the customized segments are prepared, they are inserted into femtosecond or manually dissected channels in the cornea. Just as for standard CAIRS, we continue to use wider tunnel settings together with shallow placement, which, in our opinion, allows a smoothening effect without abrupt shifts. The usual settings we employ are an inner diameter of 4.6 mm and outer diameter of about 7.1 mm to 7.2 mm with tunnel depth programmed to be at 50% of minimum stromal thickness (50% of minimum pachymetry plus 50 µm for presumed standard epithelial thickness) in the implantation zone (Figures 1 and 2).
Source: Soosan Jacob, MS, FRCS, DNB, and Amar Agarwal, MS, FRCS, FRCOphth
Advantages of CAIRS
CAIRS has numerous advantages over synthetic ICRS. For one, the allogenic nature of the tissue decreases the risk for some of the complications associated with synthetic ICRS, such as stromal melting, necrosis, intrusion, extrusion and migration. In addition, CAIRS can be implanted in corneas that are thinner and steeper than the limits defined for synthetic segments and also more superficially, thus potentially giving better results than synthetic segments. The allogenic nature allows wider channels and, as already mentioned, more superficial placement than with synthetic segments while still retaining efficacy. CAIRS also gives the ability to use smaller optic zones because the risk for photic phenomena (glare and halos) from CAIRS is low as compared with ICRS. Progression and eye rubbing can result in inadequate coverage of an initially satisfactorily placed synthetic ICRS, resulting in subsequent increased risk for melt. This risk, too, can be mitigated by the use of CAIRS.
Additional advantages conferred by customized CAIRS
CAIRS takes advantage of customization to provide superior topographical and visual results compared with uniform-thickness segments (Figure 3). Progressive-thickness ICRS have been used for asymmetric keratoconus to elicit a more customized and tailored response. CAIRS, however, has advantages over these progressive-thickness synthetic segments not only with respect to the advantages mentioned above, but also because, unlike synthetic segments, both standard and customized CAIRS do not need large inventories to be maintained, consisting of segments with different thicknesses, arc lengths, optic zones and clockwise/anticlockwise versions. In addition, the arc length and thickness of progressive-thickness ICRS come in a limited number of fixed combinations, which is not the case with CAIRS. The ease of preparation of CAIRS by the surgeon as well as the rapid customizability avoid the need for large inventories while also allowing greater customization and ability for spot customization. For instance, unlike synthetic progressive-thickness ICRS, we did not use uniform end-to-end taper but chose the location to correlate more closely with topographic pattern.
Conclusion
Many topographical characteristics make customization of intrastromal segments more desirable. We have had good results using progressive-thickness CAIRS, just as progressive-thickness synthetic segments have been reported to offer good refractive and topographic results. Different customized shapes can be employed, such as single-side taper, double-side taper, central taper and connecting band shape, among others. Transitions can be sudden or gradual. For instance, for asymmetric bow tie pattern, the segment is created with a thicker inferior part and the superior end tapered. The thicker inferior part is then inserted to be placed under the steep topographic area.
CAIRS are currently becoming popular because they provide an allogenic and more natural way of attaining synthetic segment-like refractive and topographic effects with less risk for complications. The future, we believe, will see more use of CAIRS. Customized CAIRS is another step toward achieving the best possible results for our patients.
- References:
- Jacob S. CAIRS A new technique for keratoconus and corneal ecstasias. https://www.youtube.com/watch?v=qF-9ycSQPq8&ab_channel=Dr.SoosanJacob. Published May 9, 2017. Accessed Feb. 21, 2022.
- Jacob S, et al. J Refract Surg. 2018;doi:10.3928/1081597X-20180223-01.
- Kozhaya K, et al. J Refract Surg. 2022;doi:10.3928/1081597X-20220223-01.
- Learn from the masters – tips & tricks in advanced procedures. https://www.youtube.com/watch?v=qdCTmrbPOso. Published Jan. 28, 2022. Accessed Feb. 21, 2022.
- New keratoconus treatment Australia: CAIRS - corneal allogenic intrastromal ring segment. https://www.drdavidgunn.com.au/blog/cairs-keratoconus-treatment. Accessed Feb. 21, 2022.
- Parker JS, et al. J Cataract Refract Surg. 2021;doi:10.1097/j.jcrs.0000000000000582.
- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre, is the author of several books published by SLACK Books, sister company of Healio publisher Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: aehl19c@gmail.com; website: www.dragarwal.com.
- Soosan Jacob, MS, FRCS, DNB, can be reached at email: dr_soosanj@hotmail.com.
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