Keraring AS allows customized keratoconus treatment
The device is ideal for correcting asymmetrical keratoconus, especially when the topographic flat axis diverges from the coma axis by more than 30°.
Click Here to Manage Email Alerts
By shortening the cornea’s central arc length, flattening its central surface and displacing its peripheral area forward, intrastromal corneal ring segments, or ICRSs, allow the refractive power and geometry of eyes with keratoconus to be changed. However, despite these clear advantages, ICRS devices have one significant shortcoming: Keratoconus affects every eye differently, yet any given ICRS will produce the same effect in all eyes.
This observation has long remained in my thoughts when working with patients with keratoconus. Even after trying several types of ICRS devices, I was always aware that I could not provide the truly customized outcomes I wanted for my patients with existing ICRS devices. However, I recently started using the new asymmetric Keraring (AS, Mediphacos) progressive thickness ICRS in my clinic, and the results have been particularly noteworthy.
The new AS model, which is not available in the U.S., is a PMMA ICRS, designed to enhance vision in low light. The primary difference between the original Keraring ICRS and the asymmetric version is that the former has a uniform thickness that ranges from 150 µm to 350 µm in 50 µm increments with a 5-mm or 6-mm optical zone. In contrast, the AS version offers variable thickness within the same device — it is thin at one end and thicker at the opposite end.
More specifically, the 160° and 330° arc devices have thickness gradual variations of 150 µm to 250 µm and 200 µm to 300 µm, and that is available in a clockwise or counterclockwise direction. There is also the option to use a version of the device that has thin tips and a thicker central arc segment.
These features offer a progressive and tailor-made flattening effect that allows a surgeon to carefully customize each patient’s corneal remodeling to fit their visual needs.
Source: Efekan Çokunseven, MD
Customizing keratoconus management
Research by Alfonso and colleagues has shown keratoconus can be categorized in five phenotypes. This poses a real-life challenge when attempting to correct keratoconus with an ICRS.
The nature of standard ICRS devices means that if you implant a 300 µm ICRS, for example, you will produce a 300 µm flattening effect everywhere. However, topographical examination of any keratoconic eye will typically show various degrees of curvature all over the eye. This means that when you implant a consistent-thickness ICRS into an eye, while ectasia will be reduced, existing discrepancies in refractive power and ectasia will remain in different areas of the eye. As such, the ideal scenario is to produce more flattening in areas of the cornea that need it and less flattening in areas that do not need it. However, with more than 40 different thicknesses, arc lengths and diameter variations of the asymmetric ICRS, I can create the variable flattening effect that most keratoconus patients need. I can also better select and combine segments, allowing me to correct multiple problems at the same time. Implantation is reversible, adjustable and easily combined with cross-linking. In fact, if a patient has a significant risk for progression, I will aim to maximize their results by combining AS implantation with another treatment, such as topography-guided laser treatment.
Indications for use
The Keraring AS is ideal for correcting asymmetrical keratoconus, especially when the topographic flat axis diverges from the coma axis by more than 30°. I have found it to be particularly beneficial for correcting the snowman phenotype — paracentral with noncoincident topographic and coma axes. This type of keratoconus requires more correction inferiorly than superiorly. As such, using a standard ICRS would either provide too much correction superiorly or too little correction inferiorly. With the asymmetrical ICRS, especially the 330° version, the fact that the inferior part is thick and the superior part is thin allows the creation of the exact effect needed to correct the snowman phenotype.
Like the original Keraring, the AS is also indicated for use in keratoconus patients with reduced best corrected visual acuity who cannot tolerate contact lenses. Those with post-LASIK ectasia, pellucid marginal degeneration, and significant regular or irregular astigmatism after penetrating keratoplasty are also good candidates for this ICRS.
Surgical tips
After years of using a standard ICRS, switching to a variable-thickness ICRS can trigger concerns about procedural considerations. However, I have found that the learning curve is mild; the implantation technique required is the same as with a standard ICRS. The main consideration for surgeons using this ring is that it produces better topographic results than the regular ring. This means that it is important to make a few adjustments to prevent complications. For example, when using the AS, you must make the incision far away from the tip. You should also follow the ring’s nomogram carefully to make sure you clearly distinguish the thicker ring from the thinner one before implanting.
The AS has the same low complication rate as the original, and I have yet to see any complications in patients implanted with the ring more than a year ago.
ICRS of the future
I believe that the Keraring AS marks a turning point in ICRS-based treatment of keratoconus. The exemplary results produced, along with the low complication rate and gentle surgical learning curve, all make it an attractive proposition for patients and surgeons alike. Studies into the long-term efficacy and safety of this device are currently ongoing, and if they deliver the outcomes I have witnessed in my own practice, variable thickness ICRSs may become the gold standard treatment option for asymmetric keratoconus.
- References:
- Alfonso J, et al. Biomecánica y arquitectura corneal: Monografías SECOIR. 2014:180-184.
- Liu XL, et al. Int J Ophthalmol. 2015;doi:10.3980/j.issn.2222-3959.2015.04.11.
- For more information:
- Efekan Çokunseven, MD, can be reached at Refractive Surgery Department, Dunya Eye Hospital, Etiler, Istanbul, Turkey; email: efekan.coskunseven@dunyagoz.com.
Disclosure: Çokunseven reports he is a paid consultant for Mediphacos.