Myoring (full 360 ring)

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Introduction

Intracorneal ring segments (ICRSs) play a an important role in the management of keratoconus by flattening the central cornea via an “arc-shortening” effect on the corneal lamellae reducing the refractive power of the cornea and shifting cone apex. [1] Suggested by Albert Daxer in 2007, MyoRing is a flexible, polymethylmetacrylate (PMMA) intracorneal implant, that is continuous (360°) ring. Available in diameters ranging from 5 to 6 mm and thickness ranging from 200 to 400 μm in 20 μm increments. The anterior surface is convex, and the posterior surface is concave, with a radius of curvature of 8.00 mm. [2] Moreover, MyoRing implantation is considered as reversible and adjustable surgical procedure.[3]

Indications

1. Keratoconus=

All grades of non-central and central keratoconus and PMD as long as the minimal corneal thickness is larger than 350 microns. According to the long-term results of up to 8 years

2. Post-LASIK keratectasia.[4]

3. Moderate and high myopia

In cases that are not eligible for excimer laser refractive surgery, such as:

thin corneas
irregular corneal surface
forme fruste keratoconus
high myopia
patients who refuse LASIK but want a minimally-invasive and easily reversible myopia treatment [5]

Effect of MyoRing implantation on IOP measurement

Biomechanical changes after MyoRing implantation may affect the measurement of intraocular pressure (IOP), studies show there is slight reduction in the measured IOP when measured using corneal center, when IOP is measured near the implanted ring it will be falsely higher because of localized stiffness as effect of implanted ring.[6]

Technique

Corneal pocket is made in the corneal stroma at a depth or 300 or 250 μm.[7] This can be achieved by one of these methods: 1. Corneal intrastromal implantation system (CISIS) using the Pocket Maker microkeratome (Dioptex, GmbH, Linz, Austria). 2. Femosecond laser created pocket.[8][9]


Complications

It is generally safe procedure with low rate of complications, these may include: segment extrusion, epithelial plug at the initial incision site, corneal neovascularization, segment migration, infectious keratitis, channel deposits, chronic pain, corneal haze, corneal melting, persistent incisional gaping, night halos and focal edema were reported as complications and limitations of ICRS implantation.


Outcomes

Mean improvement in visual acuity (UCVA) of 6 snellen lines, with long-term stability of visual acuity in patients with keratoconus.[10] The mean change in refraction is about 5 diopters less in myopic sphere. And 3 diopters improvement in myopic astigmatism (some studies reported less change)[11] Another study reported an average central K readings reduction by about 11 diopters after implantation.[12]

MyoRing implants have a greater potential for myopic and astigmatic correction in keratoconus than other ICRSs, probably because of the more significant arc-shortening effect achieved with the completely circular mid-peripheral design of the MyoRing implant.[13][14] The main advantages of a full ring are easy implantation, excellent centration, and the postoperative possibility of adjusting the position of the ring, if necessary. The corneal pocket can also be used for the direct application of the riboflavin into the cornea. Bypassing the epithelium by injecting riboflavin directly into an intracorneal pocket seems to be a safe and effective method, preserving the epithelium and avoiding pain and discomfort seen [15][16]



Implantation of MyoRing with cross linking at the same session

Cross linking had been used widely to control the progression of Keratoconus by modulating the biomechanical properties of the cornea using Riboflavin and UV light to polymerize the collagens fibrils, cross linking them together resulting in more stretch-resistant corneal architecture. [17] MyoRing implantation with cross linking altogether appears to be safe method. The implantation of a MyoRing and the combination of MyoRing with CXL have shown efficacy and safety in stabilizing progressive keratoconus, as well as in the correction of concomitant ametropia 3 years after surgery.[18]

References

  1. Frost NA, Wu J, Lai TF, Coster DJ. A review of randomized controlled trials of penetrating keratoplasty techniques. Ophthalmology. 2006;113:942–949.
  2. Mahmood H, Venkateswaran RS, Daxer A. Implantation of a complete corneal ring in an intrastromal pocket for keratoconus. J Refract Surg. 2011;27:63–68.
  3. Jadidi K, Janani L, Mosavi S, Nejat F, Naderi M, Nourijelyani K. MyoRing implantation in keratoconic patients: 3 years follow-up data. Journal of Ophthalmic and Vision Research. 2016;11(1):26. doi:10.4103/2008-322x.180713.
  4. Daxer A, Mahmoud H, Venkateswaran RS. Intracorneal continuous ring implantation for keratoconus: One-year follow-up. J Cataract Refract Surg. 2010;36:1296–1302.
  5. Mahmood H, Venkateswaran RS, Daxer A. Implantation of a complete corneal ring in an intrastromal pocket for keratoconus. J Refract Surg. 2011;27:63–68.
  6. El-Radi M, Saleh M. Effect of continuous intrastromal corneal ring (MyoRing) implantation on intraocular pressure measurements in patients with keratoconus. Delta Journal of Ophthalmology. 2019;20(4):144. doi:10.4103/djo.djo_25_19
  7. Jabbarvand M, Hashemi H, Mohammadpour M, Khojasteh H, Khodaparast M, Hashemian H. Implantation of a complete intrastromal corneal ring at 2 different stromal depths in keratoconus. Cornea. 2014;33(2):141–144.
  8. Daxer A. Adjustable intracorneal ring in a lamellar pocket for keratoconus. J Refract Surg. 2010;26:217–221.
  9. Daxer A. Corneal intrastromal implantation surgery for the treatment of moderate and high myopia. J Cataract Refract Surg. 2008;34:194–198.
  10. Daxer A, Mahmoud HA, Venkateswaran RS. Corneal crosslinking and visual rehabilitation in keratinous in one session without epithelial debridement: new technique. Cornea. 2010;29(10):1176–1179.
  11. Jabbarvand M, Salamatrad A, Hashemian H, Khodaparast M. Continuous corneal intrastromal ring implantation for treatment of keratoconus in an Iranian population. Am J Ophthalmol. 2013;155:837–842.
  12. Daxer A, Mahmoud HA, Venkateswaran RS. Corneal crosslinking and visual rehabilitation in keratoconus in one session without epithelial debridement: new technique. Cornea. 2010;29(10):1176–1179.
  13. Daxer A. Adjustable intracorneal ring in a lamellar pocket for keratoconus. J Refract Surg. 2010;26:217–221. doi: 10.3928/1081597X-20100224-08.
  14. Daxer A, Mahmoud H, Venkateswaran RS. Intracorneal continuous ring implantation for keratoconus: one-year follow-up. J Cataract Refract Surg. 2010;36:1296–1302. doi: 10.1016/j.jcrs.2010.03.039.
  15. Studeny P, Krizova D, Stranak Z. Clinical outcomes after complete intracorneal ring implantation and corneal collagen cross-linking in an intrastromal pocket in one session for keratoconus. J Ophthalmol. 2014;568128:5.
  16. Jabbarvand M, Salamatrad A, Hashemian H, Khodaparast M. Continuous corneal intrastromal ring implantation for treatment of keratoconus in an Iranian population. American Journal of Ophthalmology. 2013;155(5):837–842.
  17. Wollensak G, Spörl E, Mazzotta C, Kalinski T, Sel S. Interlamellar cohesion after corneal crosslinking using riboflavin and ultraviolet A light. British Journal of Ophthalmology. 2011;95(6):876–880.
  18. Kazakbaeva G. MyoRing Implantation in Comparison with MyoRing Implantation Combined with Corneal Collagen Crosslinking for Keratoconus. Ophthalmology in Russia. 2019;16(1S):85-90. doi:10.18008/1816-5095-2019-1s-85-90