Phakic Refractive IOLs Gaining Popularity

By Cheryl Guttman

Asymmetric Irregular Astigmatism

New Orleans - The positive refractive results and lack of severe complications achieved with current phakic IOLs have allayed initial concerns about the lenses and greatly boosted their popularity, said Joseph Colin, MD, in a presentation at the 105th annual meeting of the American Academy of Ophthalmology.

“All of the current phakic IOLs provide very good refractive and visual results and are accompanied by few severe complications. Based on those features along with the ease of implantation and potential for reversibility, phakic refractive IOL surgery is gaining popularity. At the same time, this field is advancing with the introduction of foldable materials, toric IOLs to correct astigmatism, aspherical optics to improve quality of vision, and multifocal optics to allow presbyopes to see better,” said Dr. Colin, professor and chairman, department of ophthalmology, University of Bordeaux, France.

Light reflected on the edges of the optical portion of a Nuvita IOL, explaining the patient’s visual side effects.

“Perhaps in the future we will also have phakic IOLs with customised correction based on wavefront technology. Clearly, further studies are needed to determine what location, design, and material will offer the best long-term success. In addition, we must also remember that all the phakic IOLs we implant will have to be removed some time in the future when these eyes develop a cataract or other complications. Cataracts occur 10 to 15 years earlier in myopes compared with emmetropes, and it remains to be seen how easy it will be to remove these IOLs and if that is affected by different IOL biomaterials.”

New Designs Reduce Endothelial Cell Loss
Dr. Colin noted that progressive endothelial cell loss caused by IOL contact with the cornea was a major issue with the ZB IOL, the first design of the Baikoff angle-supported anterior chamber lens. However, more recent studies with the newer ZB5M, a modified design featuring a lower vault and a thinner optical edge, show that the problem has been reduced to some extent, with reported cell loss rates less than 10% during two-to-seven years of follow-up.

 

Nuvita anterior chamber IOL : The length of the implant is too short , and the lens is moving agressively in the anterior chamber inducing a severe progressive endothelial cell loss.

Similarly, endothelial cell loss has been an issue with the iris-fixated IOL. In one series, it was associated with a less than 17% cell loss rate during two years of follow-up, and other authors report endothelial cell loss rates of 9.6% to 13.4% over three-to-four years after surgery.

“The question, however, remains whether that effect is related to trauma during surgery or arises from intermittent contact between the IOL and the cornea,” noted Dr. Colin.
Pupil ovalisation has also been a predominant concern with the angle-supported anterior chamber phakic IOLs. It can develop secondary to IOL oversizing or from pressure of the haptic loop on the angle inducing ischaemia of the iris root. However, <accurate IOL sizing continues to present a challenge because of the difficulty of precisely measuring the anterior chamber.

The possibility of cataract formation is the main concern associated with implantation of posterior chamber phakic IOLs. Lenticular changes may occur through several possible mechanisms - they may be induced by surgical trauma, result from direct IOL contact with the natural lens, or be a consequence of IOL-associated metabolic alterations. Although data from the FDA ICL study show an incidence of opacities of only 2.3%, Dr. Colin noted that his personal experience along with that of other surgeons, reveals an increasing number of cases of cataract formation in eyes implanted with that device. Onset is usually not until 18 months after surgery, but the opacity worsens and results in progressive vision loss, he said.

Visual Function Favourable
The visual and refractive results of phakic IOL surgery are good, although comparisons of predictability outcomes show this modality is less accurate than laser surgery. Notably, however, as reported in various series, all of the different models of phakic IOLs have been associated with very low rates of loss of two or more lines of BCVA - 2.1% for the angle-supported anterior chamber IOLs, 0 to 2.9% for the iris-fixated IOL, and 0 to 7% for the posterior chamber IOLs.

In addition, visual symptoms in eyes with phakic IOLs have been infrequent during the day, but these devices can be associated with complaints of halos and glare at night that can even interfere with driving ability. The aetiology of these problems is multifactorial and may relate to IOL centration, the relation between pupil and optic size, development of progressive pupil deformity, optic design, and refractive index.
Dr. Colin noted that halos have occurred most frequently in eyes implanted with posterior chamber IOLs, for which a rate of 55% has been reported. Iris-fixated IOLs have been associated with halos in 23-44% of eyes while about 28% of patients with angle-supported anterior chamber IOLs complain of halos.

He emphasised that careful selection of patients for refractive phakic IOL surgery may help minimise the risk of many of the above complications. Dr. Colin recommended appropriate candidates should have an anterior chamber depth of at least 3 mm along with a cornea diameter of at least 11 mm, and that the screening evaluation should also include determination of pupil size and measurement of the ciliary sulcus.