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Intacs: Do they work and whatever happened to them?
Intacs with or without cross-linking are an option for patients with keratoconus.
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Originally approved by the FDA in 1999 for the treatment of low myopia ranging between –1 D to –3 D sphere, Intacs segments, now from CorneaGen, were granted a humanitarian device exemption in July 2004 for the treatment of keratoconus, for which they are primarily used today alone and/or in conjunction with collagen cross-linking technology.
A 2007 retrospective evaluation of my Intacs data with 3- to 10-year minimum follow-up in 50 eyes was recently presented at the inaugural Cornea360 meeting in Scottsdale, Arizona. Interestingly, all patients in 2007 underwent the original manual trephination technique, and all patients re-established contact lens tolerance, with 80% gaining at least one line or more of corrected distance visual acuity; 95% of patients had uncorrected distance visual acuity of 20/60 or worse preoperatively that improved to 52% of 20/40 or better postoperatively. The good news is that Intacs have been shown to be effective in improving visual outcomes in patients with keratoconus.
The late Joseph Colin performed the first Intacs procedure for keratoconus in 1997, in which he placed a single superior thin segment 0.25 mm from a temporal approach and a single thicker segment 0.45 mm inferiorly, with the thought that the superior segment flattened the cone and the inferior thicker segment lifted the cone. The FDA study for keratoconus included 74 eyes of 50 patients in which all patients were contact lens intolerant. Forty-five percent of patients gained two or more lines of CDVA, and 72% of patients gained two or more lines of UDVA, with the majority of patients still needing some type of visual correction with contact lenses or glasses postoperatively.
The Intacs keratoconus nomogram, originally created by Addition Technology, is based on symmetric or asymmetric Intacs segment placement determined by if the cone on the posterior float on corneal topography is within or outside the 3- to 5-mm geometric optical center zone. In the symmetric nomogram, a pair of 0.45-mm segments are utilized when the sphere power is –5 D or greater, and in the asymmetric nomogram, a superior 0.25-mm segment and inferior 0.45-mm segment are utilized if the cylinder power is 4 D or greater. The manual trephination technique has been replaced with laser creation of Intacs channels with an inner diameter of 6.8 mm and outer diameter of 8 mm utilizing iFS IntraLase technology (Johnson & Johnson Vision). Pearls for success include a minimal incision entry site of 450 µm or greater, a minimal incision depth of 66% or greater, suturing incision with a single 10-0 nylon suture with removal at 1 to 3 months postoperatively, and contact lens fitting or refitting as soon as 6 weeks postoperatively for best visual rehabilitation purposes.
Intacs with cross-linking has become more popular but is considered off-label use of two FDA-approved devices. The literature is widespread on whether a concurrent/simultaneous or sequential procedure is the best approach, the latter in which Intacs are placed first followed by cross-linking performed 3 months later. Topography-guided PRK and ICL technology (Staar) may also add benefits for refractive error correction associated with keratoconus. Peter Hersh, in a March publication, showed in a randomized study comparing the two approaches in 198 eyes of 198 patients that there was no significant difference in simultaneous vs. sequential approach based on a maximum keratometry decrease of at least 2.5 D, UDVA improvement by two log lines and topographic inferior-superior difference improvement by 3.9 D. What he did find was that both thicker segment size and single segment placement resulted in greater topographic improvement.
In summary, keratoconus really is no longer the bad boy of corneal disease now that Intacs, with or without cross-linking, are available readily with modern techniques.
- References:
- Boxer Wachler BS, et al. Ophthalmology. 2003;doi:10.1016/S0161-6420(03)00094-0.
- Hersh PS, et al. J Cataract Refract Surg. 2019;doi:10.1016/j.jcrs.2019.01.020.
- Yeung SN, et al. J Cataract Refract Surg. 2013;doi:10.1016/j.jcrs.2013.03.022.
- For more information:
- Mitchell A. Jackson, MD, can be reached at Jacksoneye, 300 N. Milwaukee Ave., Suite L, Lake Villa, IL 60046; email: mjlaserdoc@msn.com.
Disclosure: Jackson reports no relevant financial disclosures.