Letter to the Editor - Hydrophilic Acrylic IOLs

Gerd U Auffarth MD, PhD, FEBO and Ben Lahood MD, PhD, MBChB(DIST), PGDipOphth(dist), FRANZCO

Previously, this publication asked “IOL Calcification. Are hydrophilic IOLs more trouble than they are worth?”¹ This question was addressed by Professor Gerd U Auffarth at the 40th meeting of the ESCRS in September 2022,² as well as during a podcast with Doctor Ben LaHood in which they discussed the pros and cons of hydrophilic acrylic intraocular lenses (IOLs).³ Altogether the answer was a resounding “No!” According to both surgeons, hydrophilic acrylic IOLs play an important role in optimizing cataract surgery, for the patient and the surgeon.^{2, 3}

Hydrophilic acrylic IOLs have been in use for more than 40 years. Their continued popularity (they account for approximately 29% of IOLs implanted worldwide) is due to characteristics provided by their higher water content and lower refractive index compared to other IOL materials. Usually 18–38% water compared to ≤ 5% for hydrophobic acrylic or silicone IOLs.⁴

Hydrophilic acrylic IOLs unfold within the eye effortlessly to assume their final position quickly.⁵ This is especially beneficial when implanting toric IOLs where the slower unfolding or self-adherence seen with some hydrophobic acrylic IOLs can be time-consuming and may lead to rotation if the surgeon is impatient.^{2, 23} If necessary, rotating or explanting a hydrophilic IOL is easier than with hydrophobic acrylic IOLs due to their greater flexibility. This gives surgeons more confidence to use advanced technology IOLs, as potential problems can be more safely managed. Although hydrophilic acrylic IOLs are highly flexible, with proper haptic design, they resist displacement or rotation as the capsular bag contracts.⁶ The hydrophilic material is also more resistant to forceps damage or fold marks, which Prof Auffarth noted makes these lenses a good choice when training residents.²

Further, the flexibility and compressibility of hydrophilic acrylic IOLs make them an excellent choice for microincision cataract surgery, minimizing surgically induced astigmatism and improving the predictability of post-surgical unaided visual function.⁷ As Dr LaHood notes: “If you can minimize the impact on refractive outcomes of factors we can’t currently predict—such as surgically induced astigmatism—then that’s one area where you can improve your overall predictability.”³

Hydrophilic acrylic IOLs are also highly biocompatible, a benefit for patients with uveitis or diabetes.^{8, 9} In these patients, implantation of hydrophilic acrylic IOLs results in “quieter” eyes and excellent visual outcomes.³

When compared to hydrophobic acrylic IOLs, hydrophilic acrylic IOL implants, with a higher ABBE number, show less light dispersion resulting in minimized chromatic aberration¹⁰ and glare.¹¹ Unlike some of the most frequently implanted hydrophobic acrylic IOLs²², hydrophilic acrylic IOLs are significantly less likely to develop glistenings.¹² These fluid-filled microvacuoles in hydrophobic acrylic IOLs can scatter light resulting in dysphotopsia, decreased contrast sensitivity, and other photic phenomena that interfere with vision.^{4, 13-15} In severe cases, they require explantation.^{13, 16}

The impetus for the suggestion that hydrophilic acrylic IOLs be removed from the cataract surgeon’s armamentarium originated in reports of calcification of hydrophilic acrylic IOLs in patients who underwent procedures using intracameral instillation of air or gas, such as Descemet membrane endothelial keratoplasty, pars plana vitrectomy, or Descemet stripping (automated) endothelial keratoplasty.¹⁷ Since surgeons cannot predict perfectly which patients may need keratoplasty or pars plana vitrectomy surgeries in the future, the suggestion was made that surgeons should just stop using hydrophilic acrylic IOLs. Both Professor Auffarth and Dr LaHood disagree with this suggestion and feel the issue of opacification has been blown out of proportion.

We do not yet have a perfect IOL. However, given the advantages of hydrophilic acrylic IOLs, perhaps a less drastic approach than banning them is available. As Dr LaHood says, “We are dealing with a risk of a risk of opacification” so adaptive techniques may be a suitable option for certain eyes at higher risk. Adaptive techniques have been developed that can safeguard IOLs against exposure to air/gas^18–20 that may increase the risk of excessive calcium buildup. De Cock and colleagues propose that prior to air/gas exposure, the anterior chamber should be irrigated with saline left in place for at least 8 minutes. The presence of the saline removes excess calcium ions from the IOL via passive diffusion.¹⁸ Ahad and colleagues also suggest minimizing the anterior chamber air fill from 1 hour to 10 minutes when performing endothelial transplant surgery. They identified the rebubbling of the endothelial graft as a major risk factor for opacification.¹⁹ Sise and colleagues demonstrated that a modified technique using a reduced volume air bubble (to reduce the total time of contact with the IOL) can significantly reduce IOL opacification even in cases when rebubbling was necessary.²⁰

Further, researchers are developing IOL tests that can help identify a material’s susceptibility to calcification in the eye.²¹

It is inappropriate to recommend the removal of all hydrophilic IOLs from the surgeons’ armamentarium. It is up to the individual surgeon to determine the appropriate IOL to use for an individual patient, taking into consideration risks, benefits, and their patients’ overall ocular and health conditions. It is also incumbent upon companies manufacturing hydrophilic acrylic IOLs to extensively test their product before entering the marketplace.

Citations can be found on page 46 of EuroTimes.