With the increasing use of phacoemulsification and small incision cataract surgery, there is growing interest in the use of foldable intraocular lenses (IOLs).1,2 Biomaterials used in modern foldable IOLs include silicone elastomers and hydrophobic and hydrophilic acrylate–methacrylate polymers.3
Intraocular lens biocompatibility is related to several factors such as postoperative breakdown of the blood–aqueous barrier, cellular reaction to the IOL, and biomaterial factors, the most important being the physical and surface properties.4–12 Ocular pathology and surgical technique also influence local tissue response to the IOL.13–20 Furthermore, foldable materials may be subject to mechanical problems such as scratches, tearing, cracking, or marking caused by their folding. In addition, the appearance of glistenings on some IOLs after implantation and lens pitting after neodymium:YAG laser treatment may occur.21–28
We present an observation made when 15 patients had implantation of a foldable hydrophilic IOL (model ACR6D, Corneal) during a study designed to assess the lens' biocompatibility. Four patients developed a previously unreported defect: a series of pits on the anterior IOL surface.
Four patients with no history of ocular pathology or intraocular surgery had uneventful small incision phacoemulsification with IOL implantation in the capsular bag. The IOL was a single-piece hydrophilic and hydrophobic acrylic copolymer with a 6.0 mm optic and a 13.0 mm overall length (ACR6D, Corneal).
Postoperative therapy consisted of dexamethasone 0.2% eyedrops 4 times daily for 2 weeks followed by sodium diclofenac 0.1% eyedrops 4 times daily for 2 months.
Seven days postoperatively, examination of an 80-year-old woman showed a best corrected visual acuity (BCVA) of 0.9 and an intraocular pressure (IOP) of 19 mm Hg. Slitlamp biomicroscopy showed a low Tyndall effect and a few cells in the aqueous humor, both of which resolved after 1 month. The study of the anterior IOL surface using the specular technique did not reveal the presence of inflammatory cells; a small scratch on the optic was noted, however. Pits of varying size and depth in some areas of the IOL were observed.
During the first postoperative month, moderate anterior capsule fibrosis over the IOL optic and mild posterior capsule fibrosis appeared. Best corrected visual acuity was 0.8. There was no inflammatory cell reaction on the anterior IOL surface. The pits on the IOL remained unmodified (Figure 1,A). By 3 months, the pits were slightly larger but remained unchanged at 6 months (Figure 1,B,C,D).
One year after surgery, BCVA was 0.8 and the pits remained stable. The patient did not report glare, halos, or other visual disturbances. Contrast sensitivity, measured using the Vistech 6500 test chart, was below normal at high spatial frequencies and normal at other spatial frequencies in both eyes; the difference was not significant.
Seven days after surgery, examination of a 73-year-old man revealed a BCVA of 0.8 and an IOP of 15 mm Hg. The anterior segment had low-grade postoperative inflammation, which resolved by 1 month. Specular microscopy of the anterior IOL surface showed a moderate degree of small inflammatory cell reaction. Small pits were observed on the anterior IOL surface, especially on the peripheral IOL optic.
At 1 month, several epithelioid cells were seen on the IOL surface; they disappeared after 6 months. The pits had grown slightly in size but not in number. At 3 months, anterior capsule fibrosis was observed.
The appearance of the pits remained unchanged up to the 1 year follow-up. The patient reported no visual disturbances. Contrast sensitivity, measured with a Vistech 6500 test chart, was bilaterally decreased at high spatial frequencies and normal at all other spatial frequencies; there was no significant difference between the 2 eyes.
Seven days after surgery, examination of a 72-year-old man showed a BCVA of 1.0 and an IOP of 18 mm Hg. The anterior segment examination showed a low Tyndall effect and a moderate number of inflammatory cells in the aqueous humor. Specular microscopy of the anterior IOL surface showed an absence of inflammatory cells. Pits were seen throughout the anterior IOL surface, and they increased modestly by 30 days postoperatively. After 3 months, anterior capsule fibrosis appeared, becoming more pronounced after 6 months (Figure 2, A,B).
By 1 year, visual acuity was the same as at the first examination. No cells were visible on the IOL surface, and the anterior capsule fibrosis and pits remained unmodified. The patient did not report visual disturbances. Evaluation of contrast sensitivity with a Vistech 6500 test chart showed normal values at different spatial frequencies.
Seven days after surgery, examination of a 79-year-old man showed a BCVA of 0.7 and an IOP of 17 mm Hg. Specular microscopy showed small inflammatory cells and pits on the anterior IOL surface. The pits were localized, especially on the peripheral IOL optic (Figure 3,A). By the following examination, the inflammatory cells had resolved. At 1 month, anterior capsule fibrosis developed, becoming more severe after 3 months and stabilizing around 6 months. Pit defects maintained the same appearance during the entire follow-up (Figure 3,B). Quality of vision was described as good. Contrast sensitivity, evaluated with a Vistech 6500 test chart, was normal at all spatial frequencies.
In this series, we report a previously undescribed postoperative complication: pits on the anterior surface of implanted IOLs. These multiple localized depressions, occurring in the immediate postoperative period, were spread over the anterior IOL surface; some increased slightly in size but not in number. There are several possible explanations for these defects.
Mechanical damage (eg, scratches, tears, and cracks) can be directly attributed to poor handling of the IOL during its implantation. We believe that the pits we noted were not caused during surgery (eg, during folding, inserting, or positioning) because these maneuvers were done correctly without complications. In addition, we have not seen this defect in any other type of foldable IOL, all of which we have implanted using the same technique, including the methods of folding the IOL and holding the forceps.
If the IOLs were of the same production lot, the pitting could be a result of a manufacturing defect. However, the IOLs with pits came from different lots. Furthermore, the surgeons did not noticed alterations of the IOL surface before implantation. This suggests that the pits were caused after implantation during in the early postoperative period; they were seen at the 7 day follow-up.
These findings indicate that the pits on the anterior IOL surface might be related to biomaterial properties. Lens hydration is an important physical characteristic of hydrophilic IOLs.29,30 The water content of different IOLs varies from 18% to 40%, according to the model. The Corneal ACR6D has a hydration of 26% (data from Corneal files). This is similar to that of other hydrophilic IOLs. Nevertheless, we think that the pit formation could be related to a modification in hydration after the IOL is implanted. In our study, some pits increased in size during the early postoperative period and then stabilized.
Alteration in IOL hydration is believed to be the cause of the well-known glistening phenomenon in some AcrySof IOLs.24,25 This phenomenon is produced by microbubbles of water inside the IOL. It has been suggested that the glistenings could be related to modifications in the composition of the aqueous humor (B. Dick, MD, G. Magdowski, MD, N. Pfeiffer, MD, “Vacuoles in the AcrySof Intraocular Lens Are Dependent on Aqueous Humor Components,” presented at the XVth Congress of the European Society of Cataract & Refractive Surgeons, Prague, Czech Republic, September 1997). Increased postoperative inflammation might contribute to the appearance of glistenings. This condition might also be responsible for the appearance of the pits we observed.
The pits in our cases were not related to postoperative inflammation. In all eyes, the inflammatory response and cell reaction on the IOL surface were low.
The pits on the IOL seemed to have no clinical effect. They did not impair visual performance. Visual acuity was good in all 4 cases, and no patient reported visual disturbance such as glare or halos. In addition, contrast sensitivity was normal in 2 of the patients. The other 2 had a bilateral reduction in sensitivity at high spatial frequencies. The difference between the 2 eyes was not significant, and the decrease in contrast was probably age related rather than caused by the IOL pitting.
The small number of cases we observed does not allow us to reach a definitive conclusion on the cause of IOL surface pitting. A follow-up with more patients with the same IOL and with other hydrophilic IOLs will provide the information required to reach further conclusions about this phenomenon.
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