Even though wavefront-optimized LASIK has produced excellent visual acuity for patients, U.S. Army ophthalmologists are investigating whether phakic intraocular lenses might be better option for myopic soldiers, given their special visual needs, particularly at night.
Phakic IOLs are known to have minimal impact on higher-order aberrations of the optical wavefront. Might this characteristic give soldiers with phakic IOLs a visual advantage in combat, compared to wavefront-optimized LASIK?
U.S. Army Maj. Gregory D. Parkhurst, MD, chief of refractive surgery at the Darnall Army Medical Center at Fort Hood, Tex., has been investigating this question. He says early hints suggest the answer might be yes.
(Dr. Parkhurst agreed to talk about his early results, but he emphasized in his interview with Refractive Surgery Outlook that he was giving his personal opinions as a physician, and was not speaking for the military.)
"Today, excimer lasers with wavefront-corrected ablation profiles produce excellent visual acuity for patients. We're hitting 20/20 post-op acuities almost all the time. So now the issue is quality of vision, an area where phakic IOLs excel," said U.S. Army Maj. Gregory D. Parkhurst, MD, chief of refractive surgery at the Darnall Army Medical Center at Fort Hood, Tex.
Early Verdict: Safe for Soldiers
Based on a retrospective study of results in 104 active-duty military personnel (206 eyes), Dr. Parkhurst concluded earlier this year that the Visian Implantable Collamer Lens (ICL, Staar) is a safe, predictable refractive surgery option for military personnel who are not candidates for laser vision correction.
In the fall, he hopes to present the results of a Fort Hood study that tested soldiers' visual acuities with a tool that mimics the low luminance of "night vision goggles" (Rabin Super Vision Test, Premiere Vision). Although he could not give specific details, Dr. Parkhurst spoke generally about the prospective study's results.
In 25 carefully matched pairs of patients (pre-op sphere: -3D to -9D), a preliminary analysis suggests that the subjects with bilateral ICLs had better low-contrast UCVA than patients who had undergone wavefront-optimized LASIK (Allegretto Wave Eye-Q Excimer Laser, Alcon). This appeared to be the case with and without the simulated night vision goggles.
The differences in low-contrast acuity were small—approximately two to three letters on a logMAR chart. They were detectable and statistically significant, but their visual significance to soldiers on the battle field and other professionals requiring excellent quality of vision, such as police officers and professional athletes, remains to be shown, he said.
Small Differences in HOAs
"These are very small differences in HOAs between the ICL and LASIK eyes," Dr. Parkhurst said. "The highest bar on my chart shows 0.45 microns of induced higher-order aberrations. That is a really low number. For example, in LASIK we don't usually consider doing a custom ablation on a patient if pre-op HOAs are 0.4 microns or less.
"There's something about the quality of vision with this lens that is much better than laser vision correction," Dr. Parkhurst said. "Due to word of mouth we're getting to the point that soldiers are now asking for ICLs as their first option, even when their corneas have no extra risk factors from LASIK or PRK. An OR nurse last week told me he was approached when he was out shopping at the commissary and asked about how to get on the list for a collamer lens."
Dr. Parkhurst and other Army refractive surgeons at bases around the country are discussing the possibility of larger, multicenter clinical trials to investigate the quality of vision with ICLs further.
Abundance of Caution
"We're going slowly, trying not to be too aggressive," he said. "The next study needs to be a randomized, multicenter, controlled study in patients with normal eyes that could have LASIK if they chose. We need this to reassure us that if someone gets an ICL instead of LASIK, they're not subject to greater complications."
Dr. Parkhurst's department is on pace this year to perform about 6,000 refractive surgeries on military personnel for whom lost or broken eyeglasses can be a life-or-death situation.
Concerns about flap displacement during combat have made PRK the most common procedure (60 percent). About 25 percent have LASIK and the rest opt for a single type of phakic IOL, the Visian ICL, because of its small incision size and position in the posterior chamber, he said.
Key Concern: Globe Trauma
The U.S. Army has been cautious about embracing phakic IOLs for its soldiers out of concern that the lens might not be stable or safe during combat trauma. Then in 2008, McCauley et al. reported on a soldier whose phakic IOL remained stable despite a grenade attack, orbital shrapnel and blunt globe trauma. 
"That case was considered evidence that the ICL would be stable despite traumatic globe injuries," Dr. Parkhurst said. "So the Army okayed a program of using the ICL in candidates with thin corneas or other contraindications to laser vision correction. Our program at Fort Hood was one of the first."
His department's initial study on 206 eyes of 104 patients found that 100 percent of eyes with three months follow-up (n=139) were within 1.0 D of the refractive target; 89 percent were within 0.5 D.
ICL Safety in 104 Patients
UCVA was at least 20/15 in 67percent of patients and at least 20/20 in 96 percent (with the remaining refractive error caused by uncorrected astigmatism). Preoperative sphere was between -2.50 D and -11.00 D (mean -5.86; SD 2.92). BCVA declined by one line in a single eye; the patient subsequently was referred for investigation of nyctalopia and possible retinal dystrophy.
Among eyes with nearly two years follow-up, no incidence of cataract or any other significant complication has been observed, Dr. Parkhurst said.
"We do still worry, though, about the longer term risk of cataract and of endothelial cell loss because these patients are mostly very young," he said. "The FDA age frame for the ICL is 21 to 45, and in this study the average age was 30."
Complications included: 4.8 percent occasional glare or haloes, none causing functional impairment; one case of iritis; one case of nyctalopia; and three explants (one for excessive vault, two for wrong IOL power.
Dr. Parkhurst said he believes these initial results support use of the ICL, at minimum, to correct myopia in the 10 to 12 percent of soldiers he sees who are not candidates for excimer laser correction. But he expects more and more patients with lower levels of refractive error to choose the ICL, especially after a toric version becomes available.
"We're in an environment where out-of-pocket cost to the patient is not an issue. The active-duty personnel who come in here pay for their surgery with service to their country," he said. "There's no financial incentive here to use one technology over another. A surprising number of them choose the ICL, because they like the idea of a technology that's more reversible."
CONFLICT OF INTEREST DECLARATION:
Dr. Parkhurst has no financial interest in any of the products mentioned in this article.
1. McCauley MB, Anderson DM, Johnson AJ. Posterior chamber Visian implantable collamer lens: stability and evaluation following traumatic grenade explosion. J Refract Surg. 2008 Jun;24(6):648-51.