The Clinical Benefits
Of Custom LASIK
The clinical studies of wavefront-guided laser vision
correction reflect the promise of this advanced technology in improving visual outcomes.
Thimons, O.D., F.A.A.O., Fairfield, Conn.
Refractive surgery has seen numerous advances in recent years, but none with more potential to positively impact our practices than wavefront technology. Our responsibility as clinicians is to ascertain the scientific and clinical capabilities of the various wavefront systems and ensure that they meet the rigorous standards we've developed for our refractive patients.
One of the best ways to get started is to take the time to review the literature. While there's a significant body of information in the public domain, the phase III clinical trials provide a relatively equal playing field of information that we can use to start the process.
Custom LASIK systems
Three lasers have received FDA approval, Alcon's LADARVision 4000 Excimer Laser System
(CustomCornea), the VISX Star 4 (CustomVue) and Bausch & Lomb's Technolas 217
(Zyoptix). The manufacturers have conducted extensive clinical trials, and results have been published in refereed journals. On the whole, these results are impressive compared with previous technologies, and they
represent significant progress in this highly competitive arena.
To understand these studies, we should review the protocols and criteria that were used to recruit patients. Although the studies were similar in structure, there were significant variations to take into account when interpreting the data. The most important of these is refractive power, both sphere and cylinder.
1. Alcon LADARVision
CustomCornea: Up to 7.00D of myopia and 0.50D of astigmatism.
CustomVue: Up to 6.00D of mean corrected spherical equivalent (myopia) with up to 3.00D of astigmatism.
3. Bausch & Lomb Technolas 217
Zyoptix: Up to 7.50D manifest refraction spherical equivalent (myopia) with up to 3.00D of astigmatism.
As you can see, the trials were limited to myopic patients in the mild-to-moderate range. They excluded hyperopic patients and those with mixed cylinder.
These differences in patient cohorts make comparisons somewhat complicated, but the systems share some common elements that we can compare, namely:
- Uncorrected visual acuity (UCVA)
- Predictability (intended vs. achieved)
- Higher-order aberrations analysis
- Subjective questionnaires
- Contrast sensitivity.
Let's take a closer look.
Uncorrected visual acuity
UCVA measurement has been a standard assessment in all the FDA trials involving laser vision correction. It gives us one way to compare wavefront with other laser systems as well as contrast it to the traditional vision correction methods, spectacles and contact lenses.
The studies showed that all three lasers produced remarkable outcomes at 6 months compared with traditional laser vision correction.
The acuity measurement was stratified into three general levels:
- Greater than 20/20
- Greater than 20/16
- Greater than 20/12.5.
The VISX and B&L systems had a slight edge over the Alcon laser at the 20/12.5 level, achieving over 35% for the Technolas and 27% for the
VISX. This compares with less than 10% of patients who saw this well preoperatively. Part of these differences may be attributable to differences in study inclusion criteria.
Predictability and stability
The concept behind assessment of the intended vs. achieved correction is to give a sense of the initial predictability of the procedure and its long-term stability, or drift. This is a key factor in analyzing the algorithm used to create the ablation and to assess whether the program is an improvement over current technology.
The analytic method was to measure the sensitivity at +/- 1.00D. All three lasers performed well, but the Alcon LADARVision 4000 Excimer Laser showed the highest level (100%) of predictability and stability at 6 months. Both VISX and B&L were at the mid-90% level.
Our experience with refractive surgery showed that LASIK and PRK produced significant alterations of
non-Snellen visual function, including contrast sensitivity and night-vision symptoms. The studies assessed these issues and the data show remarkable results relative to our experience with traditional refractive systems.
Aberrations are divided into two general levels: Lower-order and higher-order. Lower-order aberrations are the more traditional elements, such as sphere and cylinder. Higher-order aberrations include components such as coma, trefoil and spherical aberration. One of the essential goals of wavefront technology is to address the issue of aberrations and their impact on visual outcomes.
The Alcon studies showed that 38% of patients had fewer aberrations postoperatively with custom treatment versus 8% with conventional treatment.
The studies also showed a significant subjective improvement with wavefront vs. traditional laser regarding patient symptoms. This applied to both routine patients and patients with existing optical dysfunction, such as glare, halos and contrast sensitivity loss.
The data from the VISX trials reflects the performance of each of the systems and represents a real step forward in this arena. The data show that more than 70% of patients had either no change or an improvement in higher-order aberrations. What's more, in the area of trefoil, 84% showed an improvement or no change. This is a significant advance over standard LASIK systems and is comparable to or better than spectacles and contact lenses.
One forgotten aspect of visual performance in the early days of laser refractive surgery was contrast sensitivity. This was an unfortunate oversight because it created many patients who had excellent Snellen acuities but didn't feel their vision was as good as before the procedure. Evaluating these patients, we found that contrast sensitivity played a significant role in their dissatisfaction with the procedure. In theory, wavefront could address this issue, and one of the goals of the trials was to measure this outcome.
In this category, each of the three systems performed admirably, with all systems showing greater than 95% of patients demonstrating either an improvement or no change from preoperative data. This is a marked improvement from prior algorithms and one of the reasons that patient satisfaction showed significant gains in the wavefront studies vs. traditional laser refractive surgery.
Another useful segment of the studies was patient satisfaction surveys pre- and post-treatment. Two of the most important issues they covered from a clinical perspective were night driving and glare.
In both categories, all three lasers produced a net improvement over preoperative assessment that was significant both in the percentage of patients who were extremely satisfied (65% pre-op vs. 85% post-op) as well as a net decrease in the number who were either somewhat or very dissatisfied (25% pre-op vs. 9% post-op). The change demonstrated in this analysis is very significant and reflects the promise of wavefront for our patients in all categories.
Tradition gives way to a new era
As you can see from the data presented, wavefront is a significant advance over traditional laser systems. It gives clinicians a new paradigm for treating refractive conditions that will complement traditional therapy and expand the horizons of laser refractive therapy.
Dr. Thimons is medical director at Ophthalmic Consultants of Connecticut in Fairfield, Conn.
Alcon's FDA Labeling Data
In November 2002, the FDA approved
wavefront-guided treatment using the Alcon LADARVision 4000 Excimer Laser and the LADARWave CustomCornea wavefront aberrometer to treat myopia up to -7.00D sphere with less than -0.50D of astigmatism in patients 21 or older with a stable refraction (<0.50D of change per year).
The approval was based on clinical data compiled by the CustomCornea Study Group involving 139 patients in an effectiveness cohort (mean pre-op spherical equivalent:
-3.23D) and a safety cohort of 426 (mean pre-op spherical equivalent: -3.48D).
At 6 months, 79.9% of patients saw 20/20 or better uncorrected while 98.6% saw 20/40 or better. At 6 months, 37.0% of patients gained at least one line of best spectacle-corrected visual acuity vs. 9.4% who lost one or more lines. The mean relative spherical equivalent
(MRSE) was accurate to within 0.50D of emmetropia in 74.8% of patients and within 1.00D in 95.7%.
Complications were minimal. In the 426-patient safety cohort, 3.5% experienced diffuse lamellar keratitis
(DLK), 3.3% had epithelium in the interface, 2.1% had a double or ghost image and 1.9% developed corneal edema. Smaller numbers of patients experienced a foreign body sensation (0.5%), striae (0.5%) and other complications.
related adverse events included recalcitrant DLK with blepharitis (0.5%) and a
microkeratome-related miscreated flap (0.2%).
Comparing CustomCornea with conventional
LASIK, the wavefront-guided procedure offered slightly superior optical quality in terms of reduced monochromatic aberrations. CustomCornea also provided minor improvements in visual acuity compared with conventional
LASIK. Yet, there is no data to support improved functional performance or increased satisfaction in patients receiving CustomCornea vs. the conventional procedure.
Optometric Management, Issue: February 2004