Custom-shaped CAIRS for personalized treatment of Keratoconus
Year: 2024
Type: article
Abstract: Corneal allogeneic intrastromal ring segments (CAIRS) refer to intracorneal placement of allogeneic ring segments of any type, e.g., fresh, unprocessed, processed, preserved, or packaged segments with or without shelf-life.[1-10] Both uniform thickness and customized tapered CAIRS segments were first described by the author.[2,9,10] She is also the first to describe custom-shaped CAIRS and is performing them since 2018. Customization allows better individualized profiling for each patient and is made possible by creating custom shapes that match the patient’s tomographic and aberration maps as well as the refractive error. Many topographical characteristics make customization of intrastromal segments more desirable. These include variations even within different known phenotypes of keratoconus. The gradations in the keratometric values along the cone and the extent of gradation, maximum keratometry, extent of cone, and many other characteristics can vary [Fig. 1]. These together with other patient characteristics such as ocular aberrations make every keratoconic eye unique and need individualized custom shaping in segment preparation. Customized variable thickness and variable width CAIRS allow gradation of effect to better match the varying topographic gradients in keratometric values over the cornea of the keratoconic patient. We published results of one of the shapes we use, viz., narrow edge taper. However, our algorithm uses different shape customizations such as double edge taper, centrally tapered, flared CAIRS, and others [Figs. 1-3]. Custom-shaped CAIRS have variations not only in the form of different shapes and sizes, progressive or variable thickness, and progressive or variable width but also as steep or tapered transitions as well as non-linear variations in the extent and location of customization along the arc length, etc. The Jacob CAIRS nomogram thus differs from other CAIRS nomograms such as the Awwad,[5] Istanbul[11] and CTAK[12] nomograms. Customization is based on the tomographic map of the patient, refraction, and a study of the higher order aberrations, and it allows improvement in visual and topographic results with the amount of flattening correlating with the type of customization.Figure 1: Example of keratometric map showing steep values in both superior and inferior quadrants, requiring however different degrees of flatteningFigure 2: Illustration of few examples of custom-shaped CAIRS used in the Jacob CAIRS nomogramFigure 3: A few examples of custom-shaped CAIRS segment used in the Jacob CAIRS nomogramCustom-shaped CAIRSs are created by us using the double-bladed trephines (Jacob CAIRS trephine, Madhu Instruments, India) that come in different sizes and the Jacob CAIRS customizer instrument (Epsilon, USA). The width of the tissue ring cut by the CAIRS trephines varies based on the trephine size from very thin to very thick thus allowing treatment of all grades of keratoconus from mild to advanced. Customization is performed for all trephine sizes. The cut CAIRS segment is flipped on its side with Bowman’s layer facing the visual axis.[7] This gives several distinct advantages – the width now becomes the thickness, and thus, the thickness of the CAIRS segment can be easily varied by changing the gap between the circumferential blades and by changing the optic zone of trephination from central thin to peripheral thick cornea. Marking of the Bowman’s layer allows the graft to be placed Bowman’s layer side facing the visual axis.[7] This allows the more compact anterior cornea to be toward the visual axis, thereby getting a stronger and more consistent effect. The marked Bowman’s layer also allows easy identification of twists and therefore serves as a useful guide to allow proper placement of the CAIRS. Flipping is not done only for the largest trephine size which cuts at a tissue width of 2 mm. The CAIRS customizer helps in further shape customization. It has optic zones from 3 to 12 mm in 0.5 mm steps, and all radial axes marked on a true-to-size template. This therefore allows the surgeon to easily translate the plan marked on the patient’s topographic image to the CAIRS segment. Custom-shaped CAIRS of multiple types can thus be easily and exquisitely cut to shape just by marking the transition points using the CAIRS customizer followed by using a 15-degree blade to simply cut along the marked points. Preparation of any kind of custom-shaped CAIRS is currently easier manually as described above than with femtosecond customization.[13] This is because though the femtosecond laser has been used to cut asymmetric tapered segments,[14] it is difficult to program it to cut to all the different types of custom shapes possible unlike the simple ease of creating manually. In addition, varying hydration of eye bank tissue decreases the advantage of femtosecond precision unlike in refractive surgery. The central disc of tissue left after cutting out the CAIRS ring can be used as a donor graft for deep anterior lamellar keratoplasty. If cut before removing endothelium, it may also be used for a penetrating keratoplasty. The endothelium can then easily be wiped off the CAIRS before use. The peripheral corneo-scleral rim may similarly be used, if desired for limbal stem cell harvesting. Similarly, a DMEK graft may be harvested and the segment cut out after that. Multi-purpose use of the same donor cornea can help extend the usage of one donor cornea for multiple purposes. This helps more efficient utilization of scarce donor tissue while allowing usage of non-edematous and high-quality tissue for CAIRS. Cutting with the double-bladed CAIRS trephine would allow simultaneous cuts, thus allowing one single trephination to prepare both the donor graft tissue and the CAIRS tissue. This may be followed easily by manual customization to extend benefits of custom-shaped CAIRS to keratoconic patients. Glycerine preserved corneas may also be used where donor tissue is difficult to access. Custom-shaped CAIRS have advantages over synthetic asymmetric polymethylmethacrylate (PMMA) intracorneal ring segments (ICRS) which have previously been reported to regularize corneal shape and provide visual improvement in eyes with significant differences between corneal topographic and comatic axes.[15,16] These asymmetric segments are available in different but fixed combinations that vary in a uniform and fixed gradient in arc length, thickness, and width. Clockwise and counterclockwise segments are manufactured for each eye. The PMMA segment is selected as the one that fits best to the overall phenotype of keratoconus and not as one that fits the individual patient’s keratoconic cornea. As an analogy, they are tailored broadly but not bespoke, thus being less than ideal for the individual patient. Customized CAIRS and custom-shaped CAIRS, on the other hand, allow the ability to freely customize on spot to obtain the exactly desired configuration. Moreover, even with only fixed combinations available, asymmetric synthetic segments still need a large inventory of segments to be maintained, with different arc lengths, optic zones, thicknesses, and widths, while these can be easily customized in CAIRS based on the presenting clinical situation. Custom-shaped CAIRS is thus a distinct type of CAIRS, designed based on the individual patient’s topographic phenotype and refractive requirement. It can be symmetric or asymmetric, specially shaped, selectively tapered, or with sharp transitions, with variable/progressive thickness and/or variable/progressive width, with the type, direction, length, and location of change adjusted by the surgeon. We have our own nomogram for custom-shaped CAIRS to enable tailoring the CAIRS according to individual patient characteristics. This is different from the Istanbul nomogram[11], the Awwad nomogram[5] and the CTAK nomogram[12] in various ways, one of which being that it is the only CAIRS nomogram to utilize customized segments and custom shaping. Financial interest statement Dr. Jacob holds a patent for special trephines, devices and processes used to create CAIRS segments as well as for the CAIRS segments and various types of modified, cross-linked as well as shaped corneal segments; Madhu Instruments; Ziemer Ophthalmic Systems.About the authorDr. Soosan Jacob Dr. Soosan Jacob is Director and Chief, Dr. Agarwal's Refractive and Cornea Foundation and Senior Consultant, Cataract/ Glaucoma Services at Dr. Agarwal’s Eye Hospital, Chennai, India. She is a noted surgeon, academician, educator and well-respected innovator. She holds multiple posts in international Ophthalmic Societies and peer-reviewed Journals including being the President-Elect of International Society of Refractive Surgery and Associate Editor of Journal of Refractive Surgery. She has won numerous international awards and delivered many prestigious named orations worldwide. She has been featured as one among Top three most influential female figures in ophthalmology and ranked 17th within the Top 100 Most Influential Ophthalmologists worldwide in the Power List 2024. She has been listed multiple times in the Top 100 Power Lists, is a key opinion leader and listed among the top 2 percentile scientists consecutively in Stanford’s 2021-2024 lists. She has more than 125 peer-reviewed publications, 200 chapters and is editor for 17 Ophthalmology textbooks. She has numerous innovations and techniques to her credit including CAIRS, custom shaped CAIRS, Jacob CAIRS nomogram, Glued Capsular Hook, CACXL, PEARL, SIGS and many others. Her educational YouTube channel is amongst the top-most heavily subscribed Ophthalmic YouTube channels. She has more than 30,000 followers on her social media handles.
Source: Indian Journal of Ophthalmology
Author: Soosan Jacob
Institution: Dr. Agarwal's Eye Hospital
Language: English
Subfield: Radiology, Nuclear Medicine and Imaging
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4405696464