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By Cheryl Guttman

New Orleans- Angle-supported anterior chamber phakic IOLs are easy to implant and offer effective, predictable, and stable refractive correction. However, this technology has suffered from its potential to produce complications, particularly pupil ovalization, endothelial cell loss, and glare, reported Thomas Kohnen, MD, at a session of the 105th annual meeting of the American Academy of Ophthalmology.

“Myopic anterior chamber phakic IOLs have been around for a number of years and advances in design have helped to reduce some of the problems of the early generation devices. Yet, we must be conservative in our judgment of these newer models as long-term results are still needed, and particularly welcome would be studies comparing phakic IOLs with LASIK for treatment of higher myopia,” said Dr. Kohnen, during "Refractive Surgery 2001: New Options and New Horizons".

The angle-supported phakic IOLs include three rigid PMMA devices - NuVita MA20 (Bausch & Lomb), ZSAL-4 (Morcher), and Phakic 6 (M&C), and a foldable hydrophilic acrylic IOL - Vivarte/GBR (CibaVision/IOLTECH). All are presently marketed in Europe except for the NuVita.

These IOLs differ in their dimensions, including overall lengths, as well as in their power ranges and dioptric increments. For all of the angle-supported phakic IOLs, optical diameters range from 4.5 mm to 6.0 mm, and their myopic power range is from -2.0 D to -25.0 D with steps of 0.5 D or 1.0 D. A hyperopic version in powers of +2.0 D to +12.0 D is available only for the Phakic 6. Overall lengths for all of the products range from 12.0 mm to 14.0 mm, and except for the ZSAL-4, which is marketed in a single 13.0 mm length, the other devices offer three to five different options for length.

“Size for these phakic IOLs is chosen according to the horizontal white-to-white measurement, but the fact that anterior chamber depth cannot be precisely measured with current techniques makes accurate sizing difficult,” noted Dr. Kohnen, Johann Wolfgang Goethe-Universitat, Frankfurt, Germany, and visiting associate professor of ophthalmology, Baylor College of Medicine, Houston.

Recent publications reporting two-year postoperative results for 21 eyes implanted with the NuVita [Alleman et al. Ophthalmology 2000;107:1549-1554] and for 23 eyes implanted with the ZSAL-4 [Perez-Santojna et al. J Cataract Refract Surg 2000;26:1288-1302] highlight the potential for these devices to provide good refractive and visual outcomes in high myopes.

In both studies, UCVA outcomes were good, and BCVA benefits occurred as well, due to magnification of the visual image. Mean BCVA increased about two lines, and no patients lost two or more lines of BCVA.

Safety Questions Highlighted
But these studies also highlight the disadvantages of these lenses. Those studies along with data from Alio et al., show the incidences of halos and glare as well as rates of endothelial cell loss have decreased compared with earlier generation angle-supported phakic IOLs. However, haptic-related problems, including progressive pupil ovalization, IOL rotation, and low-grade postoperative inflammation, continue to occur relatively frequently. German results from a study of the NuVita phakic IOL are also consistent with those published data, reported Dr. Kohnen.

At two German investigational sites, 34 eyes were implanted with the NuVita MA20 for high myopia (-7.0 to -20.0 D). UCVA at three months after surgery was better than 20/40 in 33% of eyes whereas no eye had that level of uncorrected vision preoperatively. In addition, predictability was very satisfactory, with almost all cases within 1.0 D of intended refraction, the refractive outcomes were maintained, and almost 65% of eyes gained one or more lines of BCVA.

The safety endpoints showed no increases in IOP over time or significant problems with glare. The IOL did not appear to rotate significantly, and its intraocular position was found stable as well using Scheimpflug photography to measure the distances between the IOL and both the cornea and natural lens at one week, one month, and three months.

However, among 23 eyes seen at one year after surgery, 16 (70%) showed pupil ovalization <10%, while morphological changes of 10%-20% and 20%-30% occurred in five (22%) and two (8%) eyes, respectively.

“We have examined the surface quality of this IOL and determined that it is not a major factor in the change in pupil morphology. Instead, it appears to be a function of its design - if the IOL is too large it can cause some fibrosis in the anterior chamber that leads to pupil ovalization,” commented Dr. Kohnen.

Looking to the future, Dr. Kohnen described the “ideal” anterior chamber phakic IOL. That lens will need to be foldable and will have to avoid surgically-induced astigmatism. It should be constructed of a biocompatible material, and be without long-term potential for decentration or endothelial cell loss, pupil ovalization, or chronic inflammation.