The diary of a cornea that didn’t like plastic

The management of keratoconus has seen a tremendous shift over the last decades from “replacing” the diseased tissue (with full i.e penetrating keratoplasty PKP or partial thickness corneal transplantation i.e Deep Anterior Lamellar Keratoplasty DALK) to “remodelling” the ectatic cornea with the use of corneal collagen cross-linking (CXL) and/or implantation of intracorneal ring segments (ICRS). The last two additions in the armamentarium of non-tissue-replacing options for keratoconus have been welcomed with much enthusiasm by the corneal community, while ongoing evolution and refinement of the relevant techniques have been keeping them in the spotlight of research and scientific talks.

ICRS are small devices made of synthetic material which are implanted deep in the corneal stroma at about 70% to 80% depth, in order to reduce the corneal curvature and regularise the front corneal surface, while improving the refractive power and maintaining the existing biomechanics status of the cornea. Several published articles have reported the benefits of ICRS in corneal ectatic disorder like keratoconus [1-2].

Despite improved outcomes with the use of femtosecond lasers for tunnel creation and the mastery of nomograms allowing for customised treatments, there is an associated risk with implanting a synthetic substance within the cornea. Complication rates can be as high as 30% in some case series making some surgeons sceptical about the long-term compatibility of the artificial ring segments with the corneal collagen, despite the good topographical and visual outcomes [3-6].

Here we present a case of a cornea that ultimately rejected an intracorneal ring segment

• At presentation

A 23 year-old male with progressive keratoconus and floppy eyelid syndrome was referred to our department for further assessment and management. His right eye (RE) uncorrected visual acuity (UCVA) was 6/60, best corrected (BCVA) 6/12, and refraction -16.25 sph / -7.00 x 47⁰ cyl. He underwent corneal collagen cross linking (CXL) as a first step, followed by implantation of a 210⁰ Ferrara-5 intracorneal ring segment (Ferrara Ophthalmics, Belo Horizonte, Brazil) due to contact lens intolerance. His corneal topography prior to ICRS treatment showed an inferior cone with K1 47.2D/ K2 55.4D/ Km 52.0D/ Kmax 66.1D, keratometric astigmatism 8.2D and a Q value of -1.52. The procedure was uneventful. The ring tunnels were created with a femtosecond laser (Ziemer FEMTO LDV Z8, Ziemer Ophthalmic Systems AG, Port, Switzerland) at a 400microns incision depth (80% depth) guided by pachymetric analysis and corneal topography.

• 6 months later

6 months follow-up confirmed a positive effect on refraction (-8.25 sph/-3.25×16⁰ cyl) with  a 10 diopter reduction in spherical equivalent and impressive improvement of topographical values with 6D reduction in Kmax, Km improvement from 51.0D to 48.4D, an improvement of 3.4D of keratometric astigmatism and a less negative Q value (Pre-op -1.52 to post-op -1.19).

Despite the favourable impact on topographic indices, the patient’s UCVA and BCVA remained similar to pre-op, although subjectively quality of vision was better.

• The COVID era

18 months after ICRS implantation

When COVID restrictions were lifted and the patient was able to attend at 18 months after implantation, he reported a gradual reduction of RE vision of recent onset with redness and discomfort. Slit lamp examination revealed migration of the distal end of ICRS inferiorly into the tunnel with Descemet’s membrane/ endothelial perforation and presence of approximately 40% of the segment body into the anterior chamber causing a low grade anterior chamber inflammation and localised corneal oedema. There were no signs of corneal infection nor damage to intraocular structures. There was no history of trauma. The patient denied eye rubbing, however floppy eyelid syndrome was clinically noticeable.

• Next steps

Urgent surgical explantation of the ring segment was arranged. This was initially attempted through the original corneal incision that was femtosecond laser created to insert the ring segment. A reverse Sinskey hook was used to grasp the segment through the positioning hole of the proximal end. However the ring appeared to be slipping further inside the anterior chamber with every move.

After a few attempts to grab the ring segment in that manner, the proximal edge broke off…which meant that there was nowhere to hold  the ring from and so this approach needed to be abandoned.

An anterior chamber approach was then employed. A corneal incision was constructed, the anterior chamber was filled with viscoelastic offering a protective coating in case the ICRS fell into the anterior chamber and then with a reverse Sinskey hook the ring was eventually successfully removed in one piece. The manoeuvres were slow and careful so not to cause any further damage to the endothelium. The proximal end was still in the tunnel which allowed for controlled pulling of the ring.

• 3 weeks after ICRS explantation

At three weeks follow-up the posterior cornea had healed well with no signs

of leakage from the anterior chamber, while inflammation had completely settled. Some scarring along the previous ring tunnel was evident.  The patient was pleased and relieved with the removal of the ring segment. Surprisingly his UCVA was improved to 6/30, while the corneal topography resembled more the post-ICRS insertion one with a Kmax of 60D and topographic astigmatism of 5.7D, rather than the topography before the procedure.

• What does this case tell us?

Femtosecond assisted ICRS implantation is generally considered a safe procedure thanks to more precise and predictable size and depth of ICRS implantation. However, despite the evolution that has taken place in ICRS insertion, the question of whether the cornea tolerates synthetic materials still stands [1-3]. In our practice where we treat a large volume of keratoconic patients and have been using ICRS for many years, we do see cases where the cornea sooner or later “reacts” to the ring segment despite a thorough pre-operative assessment to ensure suitability of treatment and formulation of a customised surgical plan. Our approach to insertion of corneal ring segments is consistent in terms of indication, criteria, surgical procedure, and post-operative monitoring.

Amongst the reported complications of the standard synthetic ICRSs are extrusion, intrusion or migration, neovascularisation, corneal melt, corneal necrosis, epithelial ingrowth, and infection. There is also a number of reports in the literature of reactive “sterile infiltrates” around the rings or sterile anterior chamber hypopyon indicating that the cornea is not as compatible as we think with synthetic material after all. The risk of ring segment complication in particular the chance of failure and ring removal should be an important element in the pre-operative discussion and contenting procedure. We have example of patients who were disappointed to have the rings removed especially when there is not many minimally invasive options or alternative to correct their vision.

It is along these lines that the concept of Corneal allogenic intrastromal ring segment (CAIRS) was born, in an effort to reduce complications related to the insertion and presence of a synthetic plastic material in the cornea especially when these types of implant produce similar benefits to patients. Dr Soosan Jacob was the first to introduce this idea, with the reported outcomes so far showing excellent biocompatibility, with follow-up ranging up to nearly three years [7]. This enhanced tolerance is considered to result from host keratocytes quickly repopulating the small amount of donor stroma, as happens in deep anterior lamellar keratoplasty (DALK) buttons, but quicker due to the much lower volume of tissue transplanted as well as the intrastromal placement. High tolerance also makes CAIRS more flexible than their synthetic counterparts, and allow for implantation at more superficial level of 50% of depth which increases their efficacy in reshaping the cornea [8-9].

Reference:

1. Bautista-Llamas MJ, Sánchez-González MC, López-Izquierdo I, López-Muñoz A, Gargallo-Martínez B, De-Hita-Cantalejo C, Sánchez-González JM. Complications and Explantation Reasons in Intracorneal Ring Segments (ICRS) Implantation: A Systematic Review. J Refract Surg. 2019 Nov 1;35(11):740-747.
2. Park SE, Tseng M, Lee JK. Effectiveness of intracorneal ring segments for keratoconus. Curr Opin Ophthalmol. 2019 Jul;30(4):220-228.
3. Nguyen N, Gelles JD, Greenstein SA, Hersh PS. Incidence and associations of intracorneal ring segment explantation. J Cataract Refract Surg. 2019 Feb;45(2):153-158.
4. Vega-Estrada A, Alio JL. The use of intracorneal ring segments in keratoconus. Eye Vis (Lond). 2016 Mar 15;3:8.
5. Giacomin NT, Mello GR, Medeiros CS, Kiliç A, Serpe CC, Almeida HG, Kara-Junior N, Santhiago MR. Intracorneal Ring Segments Implantation for Corneal Ectasia. J Refract Surg. 2016 Dec 1;32(12):829-839
6. Warrak EL, Serhan HA, Ayash JG, Wahab CH, Baban TA, Daoud RC, Sammouh FK. Long-term follow up of intracorneal ring segment implantation in 932 keratoconus eyes. J Fr Ophtalmol. 2020 Dec;43(10):1020-1024.
7. Jacob S, Patel SR, Agarwal A, Ramalingam A, Saijimol AI, Raj JM. Corneal Allogenic Intrastromal Ring Segments (CAIRS) Combined With Corneal Cross-linking for Keratoconus. J Refract Surg. 2018 May 1;34(5):296-303
8. Daoud RC, Sammouh FK, Baban TA, Warrak JE, Warrak EL. Allogenic corneal tissue transplantation in substitution for extruded intracorneal rings: A case series. J Fr Ophtalmol. 2019 Dec;42(10):1090-1093
9. Parker JS, Dockery PW, Parker JS. Flattening the curve: a manual method for corneal allogenic intrastromal ring segment (CAIRS) implantation. J Cataract Refract Surg. 2020 Dec 14.