ICRS: Extrusion Management
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Intrastromal corneal ring segment or intracorneal ring segment (ICRS) extrusion occurs due to a progressive superficial stromal thinning and epithelial breakdown, subsequently leading to ring protrusion. This is reversible or mitigated with ring explantation. ICRS extrusion is the most common cause requiring ICRS explantation and accounts for 48.2% of all explanted cases. ICRS extrusion is caused most often by ring migration and/or corneal melting and presents with foreign body sensation and photophobia with epithelial defects.
ICRS extrusion results from progressive, stromal thinning, and subsequent ring protrusion through an epithelial defect, the latter of which is required for the diagnosis of ICRS extrusion. ICRS extrusion is often preceded by corneal melting or ring migration but can also occur with deep neovascularization, infectious, and sterile keratitis.
Ring migration and corneal melting are preceding signs of ICRS extrusion resulting from epithelial hypoplasia and stromal thinning with subsequent ring exposure and protrusion through an epithelial defect. Findings in ICRS extrusion resolve with ring explantation.
- Ring migration is an early sign of ring extrusion. Shallow ICRS implantation leads to increased anterior tensile strain, stromal compression, compressed anterior stromal depth, epithelial-stromal breakdown, corneal thinning, and spontaneous extrusion.
- Corneal melting suggests an underlying inflammatory process. Kugler et al. proposed that surgical trauma during incision and tunnel creation results in progressive keratocyte apoptosis, tissue degeneration, and corneal melting. Furthermore, this progressive keratolysis following ICRS implantation can be related to degradation of the corneal matrix by matrix metalloproteinases (MMP), because the introduction of exogenous stimuli and tear film insufficiency often leads to overexpression of MMP-1 and MMP-2, resulting in corneal thinning.
- Ring migration is caused by excessive ICRS width in a thin cornea, shallow tunnel placement, and narrow tunnels.
- A narrow ICRS channel (6.6 mm x 7.6 mm) can result in ring migration with epithelial plugging, tunnel haze, compared to the wide (6.7 mm x 8.2 mm) tunnel group.
- ICRS tip placement close to the incision is the leading risk factor for infection, extrusion, and corneal melting.
- Inflammation caused by infection, trauma, and stromal separation often results in channel deposits or infiltrates and can progress to ring extrusion.
- Simultaneous crosslinking and keratoconus grade 3 with eccentric cones are risk factors for ring migration and corneal melting.
- Patients with a history of vernal conjunctivitis or chronic eye rubbing should be offered ICRS with caution.
- Treatment of vernal conjunctivitis should take place prior to ICRS implantation.
- Cornea and anterior segment ocular coherence topography (CAS-OCT) should be used on the first week and month following ICRS implantation to identify patients at high risk of extrusion.
- Patients at high risk have a mean percentage depth of less than 60% or a tunnel depth of less than 70% and should be followed closely.
Device selection and segment placement
- ICRS implantation should be placed away from the incision site and include a ring thickness that is less than half of the pachymetry thickness at the site of implantation. ICRS extrusion occurs most often in patients with thin stroma and ring placement close to the incision. Furthermore, the incidence of ICRS extrusion decreased significantly after applying this ‘pachymetry law’ to ICRS implantation.
- Lai et al. suggests that superior segment placement may reduce progressive stromal thinning.
- Femtosecond lasers are recommended for tunnel creation because they are faster, easier, more reproducible. Femtosecond lasers also offer greater control and accurate tunnel dimensions. These factors reduce the risk of postoperative complications, such as ring migration and late spontaneous extrusion. Femtosecond lasers also cause minimal epithelial changes, faster recovery, and more precise stromal separation inexperienced surgeons, as compared to mechanical dissection. Other studies have shown no significant difference in extrusion rates between mechanical and femtosecond laser tunnel creations.
- Shallow tunnel creation can be prevented by setting the channel depth to 80% using the femtosecond laser or the diamond blade knife.
- A wide (6.7 mm x 8.2 mm) tunnel can reduce the risk of ring migration and extrusion.
- ICRS implantation in the posterior 2/3 of the stroma has been proposed as a possible way to reduce stromal thinning and ICRS extrusion.
ICRS extrusion is diagnosed clinically with the presence of stromal thinning and ring protrusion through an epithelial defect that resolves with ring explantation.  ICRS extrusion has a mean onset of around 10 years, but cases can occur anywhere from 1 month to 20 years following implantation.
- Foreign body sensation is the most common symptom.
- Other symptoms include photophobia, tearing, itching, and preceding eye rubbing or trauma.
- Diagnostic features include an area of stromal thinning, epithelial defect, and ring protrusion.
- Preceding corneal melt, ring migration, or anterior stromal necrosis are signs of impending extrusion. 
- Epithelial defects resolve with explantation but not with contact lens discontinuation. Punctate, arcuate, or linear staining patterns can occur.
- Tunnel vascularization can occur with superficial corneal vascularization.
- Slit-lamp examination should be used to detect stromal thinning, ring protrusion, and an epithelial defect.
- Corneal staining with fluorescein can confirm the epithelial defect.
- Corneal topography should be used to identify unstable ring positions, as depicted by topographical shifts and keratometric flattening.
- Cornea and anterior segment ocular coherence topography (CAS-OCT) should be used to identify superficial ring placement or focal corneal thinning around the involved ring segment on pachymetry.  A superficial ring placement, defined by Lai et al. as a mean percent depth of 60% or less, increases a patient’s risk for epithelial-stromal breakdown and ring extrusion.
Complications after ICRS implantation
Possible postoperative complications following ICRS implantation:
- Segment migration presents with undesirable refractive outcomes despite the help of scleral contact lenses and unstable segment position on topography.
- Corneal melting is an epithelial breakdown with a defect, which leads to stromal thinning. Lack of corneal integrity would result in worsening irritation with scleral contact lenses.
- Anterior stromal necrosis is stromal thinning and ring exposure with overlying debridable epithelium that precede ring extrusion by about 1 year. Staining occurs after debridement with the use of a cotton sponge applicator. Linear ring exposures without protrusions can be present. Erosions are a rare finding. An inflammatory halo around the tunnel can also be present. Stromal infiltrates may suggest an infectious process.
- Infectious keratitis is one of the four most common causes of ring explantation and usually presents with more acute pain, photophobia, decreased visual acuity, stromal infiltrates stromal necrosis and an epithelial defect that resolves with antibiotics.  Rapidly progressive infectious keratitis can quickly lead to endophthalmitis with hypopyon and fibrin formation.
- Lamellar channel deposits are cellular and protein deposits that are found on the inner curvature of the proximal ring segment near the incision site. Lamellar channel deposits can be confirmed on the slit-lamp exam. Ruckhofer et al. suggests that increased segment thickness and duration increases the incidence of channel deposits and can present with anterior stromal necrosis.
- Tunnel vascularization presents with contact lens intolerance with poor fitting fluctuating vision, halos around lights, crystallized deposits, and stromal vascularization around the ring segments. An epithelial defect without stromal thinning resolves with discontinuation and re-steepening of scleral contact lenses. Contact lens intolerance despite discontinuation and re-steepening should be managed with ring explantation, due to poor visual outcomes.
- Explantation is the surgical removal of ICRS ring segments and is indicated in cases of ICRS extrusion, poor visual quality or fluctuations in vision, corneal melting, culture-positive or negative keratitis, corneal neovascularization with poor contact lens fitting, and corneal perforation.
- Incisions can be made in one of two ways. If the extrusion was proximate to the incision site, the previous entry can be opened with a Sinskey hook. A 10-0 nylon suture should be used to close the defect. If the incision site is completely healed, a diamond blade set to the original depth should be used to make an incision entry beneath the extruded ring. The depth of the ring can be confirmed on CAT-OCT. A circumferential dissector can be used to create a channel beneath the segment. A Sinskey hook is then placed anterior to the segment and pushed down gently to break adhesions between the ring and the stroma and to pull the positioned segment through the new entry site.
- Conjunctival and corneal swab with culture are performed in all suspected infections. Infectious keratitis should be treated aggressively with topical fortified antibiotics and explantation, but fortified antibiotics without explantation are also effective in some cases. Systemic antibiotics can also be used in cases of endophthalmitis,  Hashemi et al. suggests that early penetrating keratoplasty can be alternatively for rapidly progressive keratitis.
- Combination antibiotic-steroid eye drops for 5 days
- Artificial tears for 1-3 months, and are instructed to avoid eye rubbing
- Adjunctive therapy includes an amniotic membrane to fill the virtual gap or bandage contact lenses to aid corneal epithelial healing. The amniotic membrane (glycerin-preserved) maintained transparency by 2 years but does not prevent myopization and increased astigmatism.
- Fortified antibiotics can be continued at a lower frequency for 3 weeks in cases of infectious keratitis, following explantation.
- Topical steroids for at least 10 days following explantation secondary to deep corneal neovascularization to promote ghost vessel regression and improve contact lens tolerance.
Complications after explantation
Clinch et al. reported postoperative data of 46 out of 684 myopic eyes following ring explantation and concluded that ring removal is not associated with decreased BCVA, astigmatism, or myopia.
Complications of ring segment explantation include:
- Tracks of lamellar haze that decreases over time 
- Persistent incision scar without visual impairment 
- Corneal neovascularization
- Partial stromal melt
- Cosmetic complaints from permanent stromal haze
- Corneal leukoma
In most cases of explantation, patient follow-up should occur on the first day postoperatively, 1 month, 3 months, 6 months, and 1 year postoperatively with slit lamp exam, UCVA, BCVA, corneal topography. Visual, refractive, and topographic changes were normal after 3 months. 
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