Advancements in LASIKAn overview of the latest developments in LASIK and corneal refractive surgery.
By Marc R. Bloomenstein, OD, FAAO; Sondra R. Black, OD; and Jim P. Owen, OD, FAAO
December 15, 2017
December 31, 2018
Online CE will be available through February 15, 2018.
On completion of this educational activity, participants should have a foundational knowledge of corneal refractive surgery—from early excimer lasers and microkeratomes to advancements made possible by today’s femtosecond lasers—as well as be aware of strategies to assess surgical candidacy for LASIK and understand what to expect postoperatively.
Marc R. Bloomenstein, OD, FAAO; Sondra R. Black, OD; and Jim P. Owen, OD, FAAO
This course is COPE approved for 2 hours of CE credit. COPE ID is 55763-RS. Please check your state licensing board to see if this approval counts toward your CE requirements for licensure.
This continuing education course is joint sponsored by the University of Alabama School of Optometry.
Dr. Bloomenstein is a consultant for Allergan, Bausch + Lomb, Lunovus, TearLab, and OcuSoft; he receives research support from Allergan and Alcon; is a shareholder of TearLab; and he is on the speaker’s bureaus of Allergan, Alcon, Bausch + Lomb, Johnson & Johnson Vision, and OcuSoft. Dr. Black is a consultant for AcuFocus, Johnson & Johnson Vision, Labtician Ophthalmics and Valeant. Dr. Owen is a consultant for Tear Film Innovations; and has received honorariums from Alcon, Abbott Medical Optics and ScienceBased Health.
Sponsored by Abbott Medical Optics
One of the most satisfying aspects of being an optometrist is simply the fact that we’re part of our patients’ journeys through their visual lives. We see many of our patients grow from small children through their teenage years and then into adulthood and old age. And throughout all this time, we oversee their visual needs by first diagnosing their ametropia and providing them with opportunities to see clearly and later getting them excited about the new levels of freedom they can enjoy away from glasses as they age. Think about the teenager who walked out of your office beaming with new self-confidence when you fit her in her first pair of contact lenses or about the 80-year-old cataract patient who hugs you because the world suddenly looks so much brighter and more distinct. This is why we love optometry.
We have so much to offer patients and can improve their quality of life in incredible ways. Sometimes, though, we hold back vision correction options based on old norms or simply not asking the patient if they may be interested. In particular, LASIK or other forms of corneal refractive surgery seem to be afterthoughts as of late.
This is truly unfortunate because all those years between adolescence and old age are part of the continuum of care that we should guide patients through. Each doctor may have a unique reason why they are less inclined to offer LASIK as an option for their patient. And, yet, if fear of losing a patient to refractive surgery is the main reason, the irony is it’s more likely to happen to the doctor who chose not to be a part of the process.
It may not seem as new and exciting as it did in 1999, but LASIK technology has changed dramatically in the past several years. Much about the procedure today is safer and more precise, providing even better outcomes. And though ODs in this country are not performing the procedure, they guide the preoperative and postoperative care of the patient in collaboration with the patient’s surgical center. The last thing we want is for our patients to select a surgical center on their own without involving us in the dialogue or surrounding care.
In the pages that follow, you’ll learn about the nuances of today’s LASIK platforms and procedures so you can identify and inform your patients. Educating ourselves and our patients about LASIK technology is an important responsibility. It is incumbent upon us as referring optometrists to have in-depth knowledge about the technology used by the surgeons to whom we direct our patients. Motivated patients may turn to friends, advertising and the Internet, but our informed counsel should play the more prominent role in terms of decision-making. Being an informed adviser demonstrates your desire to stay involved in the surgical process.
When a patient comes into your practice and needs vision correction, that patient becomes a potential refractive surgical candidate. We may eventually find clinical reasons why we won’t refer the patient, but LASIK needs to be part of the armamentarium that deserves consideration whenever it’s clinically appropriate. Here, several factors are relevant, including age, corneal thickness and astigmatism.
With regard to age, refractive stability is far more important than age. Very generally speaking, low myopes (<4.00D) typically achieve refractive stability by 18 years of age, whereas high myopes may not stabilize until they’re 21 or older. If a patient is new to your practice and you don’t have a refractive history, consider a second evaluation after six months when patients are near these age thresholds. At the second visit, confirm that there is no more than a 0.50D shift in spherical equivalent (not diopter sphere), a 0.25D shift in astigmatism or more than a 10-degree shift in axis. Also make sure that these changes are not relative to an ocular surface change.
Next, look at corneal thickness. This becomes an import factor when considering the amount of correction needed in a given eye and the thickness of the flap incision—created by the surgeon in the anterior cornea. With the flap open, the surgeon reshapes the stroma to achieve the shape upon which light can reflect off of the retina and produce clear vision. Thin corneas alone are not a significant risk factor for refractive surgery. The prescription plays an equally important role here since a patient’s refractive error dictates the amount of stroma to remove. The surgeon will use a nomogram to determine the ablation depth but you can safely assume 15 to 20 microns of ablation per diopter of prescription. The ideal residual stromal bed has been a shifting value over the years. A standard has been to leave at least 300 microns residual, but each surgeon is different. Therefore, it’s also helpful to know what your surgeon’s cutoff is and understand that it may vary from case to case.
Talk to Contact Lens Wearers about LASIKWhy do people wear contact lenses? It’s because they don’t want to wear glasses. Period. It’s only logical that these same patients might appreciate the added freedom that LASIK can provide.
In particular, contact lens wearers who have struggled with lens intolerance, dry eye, giant papillary conjunctivitis (GPC), allergies, meibomian gland dysfunction, contact lens-induced acute red eye response (CLARE), ulcers or red eyes can often benefit from LASIK. For your sake and the patient’s, you may also want to present LASIK to non-compliant contact lens wearers.
Touch PointsIt’s understandable that you may be stretched thin with a waiting room full of spectacle and contact lens patients. The good news is you don’t have to spend a ton of time getting into specifics about refractive surgery. To start, make sure LASIK has a presence in your waiting room. You could have posters, videos and brochures describing the procedure. Next, include a question about interest on your intake form.
When you do choose to have a discussion with your patient about LASIK, you can keep it fairly brief if you properly train staff on the LASIK conversation.
If a patient presents with normal-thickness corneas (i.e., above 500 microns), they are likely to be a viable surgical candidate especially if the surgery center uses a femtosecond laser for flap creation. For corneas below 500 microns, it’s still a good idea to send the patient to a surgery center for evaluation. In the majority of these cases, photorefractive keratectomy (PRK) would be performed, as less corneal tissue is removed by surface ablation vs. LASIK, but allow the center to make that decision. In cases when corneal thickness is borderline, don’t get the patient too excited about LASIK in particular, but also don’t rule it out. Just frame it differently. For example, you might say, “The numbers are a little tight, so let’s ask the surgeon to do some measurements and further testing to determine the best procedure for you.” Let the patient know you’re on their side and are advocating for what is best for them. This is the same discussion that should be given in the absence of knowing your patient’s pachymetry.
More Myopia Means More Patients in NeedThe incidence of myopia continues to rise in the United States and worldwide. According to a recent study, the prevalence of high myopia is predicted to increase seven-fold from 2000 to 2050.1 Among Caucasians ages 40 to 49, more than 40% are myopic. However, among Caucasians, myopia may remain flat for several years, while in other races, myopia is rising sharply.2 For example, myopia is expected to nearly double in the next 15 to 25 years among Hispanics.2 Overall trends show an increase in myopia across the U.S. population as a whole, with long-term trends showing a much greater growth of the prevalence of myopia in Hispanic and black races compared with Caucasians.2 As more and more patients present in need of vision correction, it will be up to us to offer them with a menu of options that suits their needs and clinical presentations.
Patients with astigmatism have grown accustomed to being excluded from vision correction opportunities, but that’s no longer the case with modern LASIK. We still have patients assuming that their astigmatism can’t be corrected, but that changed in 1998. In fact, the treatment of small amounts of astigmatism has successfully yielded sharper contrast and induced clarity in some patients.
|Microkeratomes—utilizing keratome instruments that incise the cornea—pulled at the corneal nerves in such a way that delayed the healing process after the surgeon put the flap back down.|
|CAA patient exhibits epithelial ingrowth grade 2. Femtosecond lasers help decreased the risk of epithelial ingrowth. Photos: Sondra R. Black, OD|
When evaluating astigmatic patients, it’s important to determine whether the astigmatism is normal or abnormal, and then investigate symmetry by looking at the top and the bottom of the topography. The level of astigmatism between the two eyes, in the absence of any disease or injury, should be relatively the same. For example, a 1D or 2D difference is not common and might be a red flag. Caution should be taken, but do not automatically rule out refractive surgery solution for the patient; a few possibilities might exist. Consider that the asymmetry may be caused by ocular surface disease (OSD). If so, be aggressive with an ocular surface treatment regiment and determine if that is the root of the topographical disparity. If, however, the asymmetric astigmatism is physiologic, the options are fewer and wavefront-guided treatment is a must. In the absence of OSD, if there is more than 1.5D of asymmetry on vertical keratometry readings or in mean keratometry between the eyes, consult with your surgeon prior to referring.
The steepness of the cornea also tells us a lot about who is a good candidate and who isn’t. There is no formal limit to how much a cornea can be flattened, but anything below 35D (or above 48D for hyperopic ablation) requires a conversation with the surgeon. A myope tends to decrease curvature in a three-fourths ratio of their correction and hyperopes tend to steepen one-to-one of the hyperopic diopter. But, again, some of this may only be a sign of surface disease in need of pre-treatment.
Pupil size is much less of a concern than it used to be. With custom, wavefront-guided ablations and optical blend zones, pupil size has become an insignificant factor for assessing LASIK candidacy. However, if a patient has a very large pupil, you should counsel them about increased likelihood of some glare and halo. Essentially, the surgeon needs to take extra precautions with larger pupils, which is where wavefront-guided LASIK becomes especially important.
In the last 10 years, with the release of DEWS II, so much more has been discovered, and our understanding of diagnostics and new therapeutic approaches is significantly more evolved. Instead of sending patients on their way with nothing more than a boatload of artificial tears, optometrists now recognize that more can be done. We are proactively treating dry eye and are making real headway in understanding how the disease works.
From Microkeratome to Femto
It seems like yesterday that microkeratomes were synonymous with LASIK surgery, and many of the complications we saw were directly related to microkeratome use. For example, surgeons struggled to control flap thickness and sometimes made the cornea too thin. Microkeratome flaps by design were thinner in the center and thicker in the periphery, which made consistency a problem and also lessened flap stability, resulting in complications such as partial flaps, button-holes and free caps.
To minimize these challenges, we had to carefully consider keratometry, pachymetry and more. Although these factors need to be considered, the use of a laser to create the flap has made them less important.
Femtosecond lasers can be focused to a specific depth, creating virtually any flap thickness the surgeon requires. The many benefits to using a femtosecond laser include:
A dislodged flap with striae post-LASIK is depicted in this photo. In the past, microkeratome design lessened flap stability, resulting in a variety of flap complications.
|Prior to femtosecond lasers, flap striae were a common consequence of LASIK.|
- Fewer flap creation complications
- The ability to vary the size and thickness of the flap
- Greater precision
- No moving parts
- Stronger flaps3
- Increased contrast sensitivity4
- Decreased risk of epithelial ingrowth
- Less IOP rise during procedure5
- Less induced dry eye6
Many of these benefits can be attributed to the inverted bevel-in side cut up to 150 degrees. Microkeratomes used to shear the cornea and pull at the corneal nerves such that, when you put the flap back down, they didn’t heal as quickly.
On the other hand, the femtosecond angle can have a significant impact on healing, minimizing postoperative complaints such as dry eye.6 You’ll likely see increased flap adhesion postoperatively, which translates into optimal wound healing and three times more flap stability compared to a microkeratome-created flap. This also improves severed nerve apposition and results in less reduction in corneal sensitivity.
LASIK used to be performed using a standard laser pattern that was based on a single measurement. This method relied solely on refraction results and the same type of patient preference methodology that we use to compare corrective lens options. The prescription was generated from a phoropter and was then entered into the laser for the treatment. From there, a theoretical curve, similar to that of glasses, determined the spot pattern that was applied to the eye.
Every patient with the same prescription received the same laser treatment. But, because the eye’s curvature varies and the compensation for the steepness of the curvature is based on averages, some spherical and other aberrations were often induced. For example, the induction of spherical aberration often resulted in the night vision disturbances associated with traditional LASIK procedures.
The Road to a More Exact Prescription
When wavefront-optimized LASIK was introduced, surgeons could use special software to reduce LASIK-induced spherical aberration. Using wavefront modeling, surgeons can administer extra pulses in the periphery of the ablation zone to manage the induced spherical aberration.
However, as with conventional LASIK, the same number of laser pulses is used for every patient with the same prescription. In other words, the procedure is customized to be prescription-specific, but it is not specific to the individual aberrations of each eye. Furthermore, “optimized” simply implies that adjustments have been made to treatments to minimize induction of spherical aberration; it does not mean you can correct aberration that already exists. In some patients, depending on their unique curvatures, optimized LASIK can actually make the aberrations worse and the patients symptomatic. For example, for patients who have neutral or negative spherical aberrations (approximately 10% of the population), wavefront-optimized laser treatment can be less favorable since the extra peripheral pulses induce additional negative spherical aberrations.
A Perfect Match
They say no two snowflakes are the same, and the same rule applies to eyes. We want to make the surgical treatment as precise as it can be. The introduction of wavefront-guided technology allows us to achieve this. Wavefront-guided treatment platforms appear to offer significant advantages in terms of reducing residual refractive error, uncorrected distance acuity and contrast sensitivity.7 They also provide distinct benefits in terms of night vision performance and low contrast acuity.8
With wavefront-guided LASIK, the goal is to reduce all higher-order aberrations. This is achieved by introducing a grid of infrared laser light into the eye. The wavefront aberrometer captures and measures each ray of light as it reflects off the retina and determines the aberrations of the entire eye based upon the deflection of the light from its ideal path. This technique can measure hundreds of individualized light rays and goes beyond the ability of the standard phoropter.
After this wavefront map is determined, the treatment software calculates the number and diameter of laser pulses to reshape the cornea so that the light from objects will focus perfectly on the fovea.
The Benefits of Wavefront Aberrometers
Wavefront refraction measures patients’ objective refractive error and is designed to be more reproducible and precise than the subjective manifest refraction. Wavefront aberrometry measures refractive aberrations of the eye, detecting the higher-order aberrations. Higher-order aberrations include distortions such as coma, trefoil and spherical aberration, as well as numerous others that cannot be adequately corrected through spectacle lenses. Spheres and cylinders, measured at the phoropter, are called lower-order aberrations.
Your preoperative measurements play a big role in your treatment plan. A variety of systems exist to measure refractive errors of the patient, including the iDesign, KR‐1W and WaveLight Analyzer. We are now able to capture the shape of the cornea, its curvature/power, the ocular wavefront, the patient’s refraction and pupil diameter under different lighting conditions, and to calculate keratometry and pupil size. It’s incredible that we can now achieve this with a single scan of the eye from a device no bigger than an autorefractor.
By providing more high-quality measurements, advanced new systems can improve iris registration, maximizing the chances for successful eye tracking during the surgery. They can take an image of the patient’s iris and note up to 24 identifying marks. This image is transferred with the treatment plan to the excimer laser. Since the patient’s eye rotates when moving from prone to supine, the excimer laser rotates the treatment to ensure it is positioned correctly.
But this advanced technology doesn’t merely make surgery more precise, it also often makes it available to a wider segment of patients. Now, many more patients may be eligible for LASIK—even those who previously did not qualify. That’s because these kinds of systems can provide a detailed map of the eye, making it possible to treat patients with higher levels of astigmatism, a wider range of pupil sizes and even mixed astigmatism.
Although it is true that LASIK can be performed using many different technologies and techniques, not all will meet your needs. We don’t want to confuse patients by overwhelming them with details, but it is our responsibility to help them recognize value vs. cost. Aligning yourself with surgeons and centers that are congruent with your practice philosophy will narrow down the details. When you and the surgery clinic are speaking as a single voice, there is little confusion left for the patient.
As technology evolves, so too must our patient conversations. Indeed, as vision correction options expand, patients will still rely on us to educate and guide them to appropriate procedures as well as surgeons who are equipped with the tools necessary to deliver the best possible outcomes. LASIK surgery, over the last 20 years, has earned a rightful place in your refractive management plan.
|1. Holden BA, Fricke TR, Wilson DA. et al. Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology 2016;123(5):1036-42.|
2. Myopia. National Eye Institute. Available at: https://nei.nih.gov/eyedata/myopia (last accessed November 9, 2017).
3. Kim JY, Kim MJ, Kim TI, et al. A femtosecond laser creates a stronger flap than a mechanical microkeratome. Invest Ophthalmol Vis Sci. 2006;47(2):599-604.
4. Montés-Micó R, Rodríguez-Galietero A, Alió JL. Femtosecond laser versus mechanical keratome LASIK for myopia. Ophthalmology 2007;114(1):62-8.
5. Vetter JM, Faust M, Gericke A, et al. Intraocular pressure measurements during flap preparation using 2 femtosecond lasers and 1 microkeratome in human donor eyes. J Cataract Refract Surg 2012;38(11):2011-8.
6. Salomão MQ, Ambrósio R Jr, Wilson SE. Dry eye associated with laser in situ keratomileusis: Mechanical microkeratome versus femtosecond laser. J Cataract Refract Surg 2009;35(10):1756-60.
7. He L, Liu A, Manche EE. Wavefront-guided versus wavefront-optimized laser in situ keratomileusis for patients with myopia: A prospective randomized contralateral eye study. Am J Ophthalmol 2014;157(6):1170-8.
8. Bower K, Peppers L, Sia R, et al. Visual performance comparison of wavefront-optimized and wavefront-guided laser in situ keratomileusis (LASIK). Invest Ophthalmol Vis Sci 2013;54(15):3125.