Refractive Surgery Update
Refractive Surgery Update
Here's a look at the latest procedures that may benefit your patients.
Justin Holt, O.D., West Point, Utah
Although the terms “bladeless surgery,” “cornel inlay” and “collagen cross-linking” sound like they belong in an Isaac Asimov novel, in actuality, they represent the latest in refractive surgery technology.
Here, I discuss these, among other technological advances in refractive procedures, so you can educate both yourself and those patients who you think may benefit from them.
Femtosecond lasers are used in more than 50% of LASIK procedures today. The reasons they are used in so many procedures: Research has shown that these lasers allow for predictably thin corneal flaps (that can provide enhanced corneal stability and low epithelial in-growth incidence), they reduce the risk of postoperative dry eye and enhance visual outcome.
One study, in particular, on three femtosecond lasers revealed that all three devices created thin, precise corneal flaps. Also, the patients who underwent these laser procedures experienced both fast visual recoveries and optimum resulting visual acuities.1
This photo shows a retroilluminated eye immediately after the femtosecond laser capsulorhexis. Note the primary and secondary limbal incisions, corneal arcuate incision and four chop nucleus fragmentation.
In addition, laser-created corneal flaps have been shown to have enhanced adhesion to the stromal bed, and, as a result, a decreased incidence of epithelial in-growth. Keep in mind that reducing the risk of dislodged flaps and visually significant epithelial in-growth has resulted in few re-treatments.2
Further, laser-created flaps have resulted in the decreased incidence of postoperative dry eye.
For instance, one prospective randomized study showed that femtosecond laser LASIK was associated with a slightly lower rate of dry eye than photorefractive keratectomy at six months (3% vs. 4%, respectively.)3
Laser-assisted refractive cataract surgery
In this recent procedure, both the primary and secondary incisions are made with the laser. The incisions can be shaped to the surgeon's preference: one-two- or three-planned. This enables extreme precision, in terms of length, width and position of the incisions, to result in an incision that seals well and has an enhanced predictable astigmatic effect.
In addition, the laser cuts the capsulorhexis, eliminating its shape and position variability.4 Because the surgeon can optimize the capsulorhexis' shape and centration, the positioning of the intraocular lens (IOL) becomes predictable and precise. With positioning being the most important factor in achieving the expected power of the IOL, this is paramount.5
Also, fragmentation of the nucleus of the cataract with the laser decreases phaco time and power use, reducing corneal edema, delayed visual recovery, potential loss of endothelial cells and the risk of a capsule rupture.6
Lastly, the femtosecond laser enables precise and reproducible depth and axis positioning of limbal relaxing incisions. This allows the use of incision-spreaders post-operatively, should less correction than expected exist. This precision could lead to more predictable astigmatic reduction. (See “Promising Applications,” below.)
|In addition to changes in refractive and cataract surgery, femtosecond laser surgery also has promising applications in procedures, such as in corneal grafts, glaucoma and retinal surgeries.|
With regard to corneal grafts, the femtosecond laser allows for the exact cutting of the edges of both the diseased cornea and the donor cornea as well as the possibility of avoiding a transplant altogether with the advent of DSEK.
In glaucoma patients, the femtosecond laser enables the creation of more precise tabs with the experimentation of different wavelength settings.
In retinal surgeries, the femtosecond laser may enable the lysing of retino-vitreous adhesions.
Currently, Technolas Perfect Vision (www.technolaspv.com) and Lens AR (www.LensAR.com) offer this treatment. That said, neither procedures are available in the United States, as the FDA has yet to approve them.
The IntraCor procedure, from Technolas Perfect Vision, treats presbyopia in a way that is similar to multifocal contact lenses. Specifically, multiple power zones are created across the corneal surface via femtosecond laser to provide a greater depth of focus for clear vision at all distances.7
The center of the cornea can be shaped to correct the patient's distance vision or their near vision, depending on the type of multifocal ablation pattern created with the laser.
This procedure has been available in both Canada and Europe since 2002.
The LensAR Laser System, from LensAR, Inc., employs femtosecond laser treatment in the crystalline lens to increase lens flexure.
A 2001 study on cadaver eyes revealed that reversing crystalline lens elasticity loss was indeed possible via selective intralenticular photodisruption.8
Corneal implants and corneal inlays are refractive devices, such as tiny lenses, inserted into the cornea to correct vision. Although several of these devices are in development, the only one currently undergoing FDA trials at this time (as we go to print) is the Kamra, from AcuFocus, Inc. (www.acufocus.com).
Formerly known as the ACI 7000, this is a small, donutshaped lens intended for intrastromal placement via a LASIK-like flap.
The technology of this device is based on the concept of small-aperture optics. Specifically, in early “old-fashioned” cameras, the depth of focus was controlled by reducing the aperture through which light entered: The smaller the aperture, the greater the depth of focus. This concept also applies to the human eye. In the eye of a presbyopic emmetrope, the lens cannot accommodate sufficiently to focus the light rays from a near object onto a single point on the retina. Thus, a point object is imaged as a blur circle on the retina, and images of extended objects are degraded as well. If an implantable opaque disc of approximately 2.0mm, with a small aperture in the center is placed in front of the eye, however, the peripheral rays will be obscured while the central rays pass unaffected. Since peripheral rays enter the eye at a larger angle than central rays, they create a larger blur circle at the retinal image plane. Eliminating these peripheral rays reduces the size of the blur circle, improving image resolution.
No doubt you are wondering whether the surgery is a done deal. The answer to this question is no. The surgery is reversible. In other words, the AcuFocus Kamra can be removed, and the cornea can be returned to pre-surgical levels. Or, if the patient desires, the Kamra can be replaced with a different corneal implant/inlay.
Other corneal implants/inlays include the Flexivue Microlens (Presbia, www.presbia.com); the Vue+ (ReVision Optics, www.revisionoptics.com) and the Invue Intracorneal Microlens System (Biovision).
Another promising refractive procedure pertains to strengthening the stroma of the cornea. Specifically, clinical trials are underway on the infusion of riboflavin 0.1% into the corneal stroma via an UV-X light source to create a corneal cross-link (CXL).9 The use of CXL can create a more stable cornea in keratoconic, ectatic and post-radial keratometry eyes. CXL is a procedure that you, the optometrist, can and should embrace because of its non-invasive nature.
Isaac Asminov once said: “No sensible decision can be made any longer without taking into account not only the world as it is, but the world as it will be.” By being aware of the latest refractive procedures and those in the pipeline, we are armed with the information we need to make decisions regarding the best course of action for our patients and our practice. OM
1. Ahn H., Kim JK, Kim CK, et al. Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome. J. Cataract Refract. Surg. 2011 Feb;37(2):349-57.
2. Holladay JT. LASIK with wavefront-guided and femtosecond technology superior: With wavefront-guided LASIK, the goal is to reduce all higher order aberrations. ASCRS EyeWorld The News-magazine of the American Society of Cataract & Refractive Surgery. www.eyeworld.org/ewsupplementarticle.php?id=252&strict=&morphologic=&query=amo (Accessed May 20, 2011.)
3. Krader-Guttman K. Data: Femtosecond laser outperforms microkeratome at multiple levels. Ophthalmology Times. 2010 Mar 15.
4. Nagy Z, Takacs A, Filkorn T, Sarayba M. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg. 2009 Dec;25(12):1053-60.
5. Hill WE. Does the Capsulorrhexis Affect Refractive Outcomes? In Chang D, editor: Cataract Surgery Today, Bryn Mawr Communications, Wayne, Pennsylvania, 2009. p. 78.
6. Nagy Z, Takacs A, Filkorn T, Sarayba M. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg. 2009 Dec;25(12):1053-60.
7. Krueger RR, Sun XK, Stroh J, Myers R. Experimental increase in accommodative potential after neodymium: yttrium-aluminum-garnet laser photodisruption of paired cadaver lenses. Ophthalmology. 2001 Nov;108(11):2122-9.
8. Holzer, MP. Update on intraCOR: At 3 months, results were stable, and patients gained up to six lines of near visual acuity. Cataract & Refractive Surgery Today Europe. www.bmctoday.net/crstodayeurope/2009/01/article.asp?f=0109_10.php (Accessed May 20, 2011. )
9. ClinicalTrials.gov. Corneal Collagen Cross-linking With Hypotonic Riboflavin in Corneas Thinner Than 400 Microns (HypotonicRibo) http://clinicaltrials.gov/ct2/show/NCT00890266?term=collagen+cross&rank=1 (Accessed May 20, 2011.)
|Dr. Holt graduated from the IAUPR and completed a residency at the University of Utah and VA Medical Center. He then worked for more than seven years at Mount Ogden Eye Center. Dr. Holt is now in private practice at West Point Eye Center, in West Point, Utah. He can be reached at firstname.lastname@example.org, or send comments to email@example.com.|
Optometric Management, Issue: June 2011