The Road to “Super Vision”: Where Are We Now?

In 1978, the debate in ophthalmology included whether healthy eyes should undergo surgery to correct refractive error and whether refractive errors could be considered a disease or if correction was merely cosmetic, not functional.

In 2005, refractive surgery is the second most common surgical procedure performed in the world and approximately 60% of ophthalmic surgeons currently perform refractive procedures of some kind.

The goals of refractive surgery have changed over time as well. While just 30 years ago ophthalmologists were pleased with making the lenses in eyeglasses thinner, the refractive goals have advanced from achieving 20/20 or better vision for 50% of patients in 2000 to today’s goal of achieving better quality of vision without glasses or contact lenses for all patients at all distances.

What is “super vision”?

Without knowing the definition of super vision, refractive surgeons are grasping at straws to achieve it. Super vision goes beyond the basic Snellen acuity charts to different endpoints in high-contrast, low-contrast and subjective conditions. In high-contrast situations, super vision can be defined as an improvement in best-corrected visual acuity (BCVA) and better postoperative uncorrected visual acuity (UCVA) than preoperative BCVA. For low-contrast situations, super vision would be defined as better postoperative contrast sensitivity or low-contrast visual acuity than preoperative. The third category where super vision can be defined is where the subjective perception of quality of vision is better postoperatively than preoperatively.

In my opinion, if 50% of eyes meet the high-contrast test for super vision and 25% of eyes meet the criteria for low-contrast and subjective super vision, the market for such quality results in refractive surgery will thrive.

Testing and equipment for super vision

Can our testing equipment and lasers help achieve super vision? The standard phoropters that are currently used in refractive surgery measure to 0.25 D. The potential level of accuracy for the excimer laser (0.25 µm/pulse) is 12 times greater than the traditional methods of measuring refraction (3 µm or 0.25 D). Wavefront analysis can measure refraction down to 0.05 µm (or 0.005 D). Thus, wavefront measurements are five times more accurate than an excimer laser can correct (0.05 µm vs. 0.25 µm) and 50 times more accurate than standard refractive techniques can measure (0.005 D vs. 0.25 D). Based on this information, I believe that the tools ophthalmologists are using are capable of superior visual results, but that a need exists to further process the available data and develop the nomograms and algorithms to achieve super vision.

Clinical trials for customized ablation

With the new algorithm, our postoperative results improved so that 100% of patients were 20/25 or better and 88% of patients were 20/20 or better at 1 month (Figure 1). However, when looking at the numbers, we realized that we were still undercorrecting slightly by approximately -0.2 D, so improvements still could be made on that algorithm.

We also performed an extended range study once CustomCornea was approved on eyes up to -8 D with -4 D of astigmatism, which represent fairly high ranges of error. With the improvements in the algorithm and adjustments to our nomogram, 92.9% of patients achieved 20/20 with no enhancement and 69.4% achieved 20/16 at 6 months postoperatively.

What is interesting to note is that all 15 of these patients had high refractive errors between -7 D to -9.25 D with high rates of astigmatism and 100% of these patients achieved 20/20 with customized ablation.

At 6 months, 63.5% of all patients had no change in BCVA when compared with preoperative measures, and 27.1% gained one or more lines of vision. Of the patients who had high myopia, 40% gained at least one line of vision from preoperative measurements and no patients lost any lines of vision.

A net improvement in low-contrast sensitivity was seen at 6 months for 26.7% of patients. Additionally, symptoms of glare improved after surgery for 25.9% of patients and the incidence of halos improved for 17.7%. Night driving improved for 27.1% of patients. These numbers are excellent, but did not meet my definition of super vision.

Comparative results

While the extended range results are better than with standard LASIK, we saw even better results with using a laser vs. microkeratome to create a flap.

In a study using the IntraLase femtosecond laser (Irvine, Ca.) and comparing CustomCornea with Zyoptix (Bausch & Lomb), we found that the CustomCornea outperformed the Zyoptix, but even more importantly, patients who underwent LASIK with CustomCornea were achieving postoperative UCVAs of 20/12 to 20/10 at 1 day, 1 week and 1 month, which was not previously experienced with other patient groups. At 3 months, more patients in the CustomCornea group had UCVAs of 20/16 and better (Figure 2). The accuracy of the two systems was the same, proving that this was not related to nomogram adjustments.¹

In regard to BCVA, 70% of patients treated with CustomCornea gained one or more lines and no patients lost lines of visual acuity at 3 months.

Furthermore, in 3-month postoperative mesopic contrast sensitivity comparisons, 100% of the eyes treated with CustomCornea improved or stayed the same (Figure 3). This improvement from preoperative mesopic contrast sensitivity is statistically significantly better than the changes seen in the patients treated with Zyoptix (Figure 4). Finally, the incidence of double-vision was significantly lower with CustomCornea than with Zyoptix from preoperative rates to 1 month and 3 months postoperative (Figure 5).

In my opinion, the reason that CustomCornea has these advantages over other systems is its unique registration capabilities.

Refining the definition of super vision

As refractive technology moves forward, ophthalmologists and patients will require better definitions of super vision. Currently, the available CustomCornea technology has the capability for achieving the goals of super vision. Patients now expect better quality of vision and once consistent results that reflect the goals of super vision can be provided, I believe that refractive surgery will expand from the numbers of procedures performed in 2005 to exceeding 3 million procedures per year.

Reference

1. Durrie DS, Stahl J. Randomized comparison of custom laser in situ keratomileusis with the Alcon CustomCornea and the Bausch & Lomb Zyoptix systems: One-month results. J Refract Surg. 2004;20(5):S614-S618.