Comparison of PCO Between a 1-piece and 3-piece MICS IOL
The present study demonstrates that the modification of the IOL haptic design of an acrylic hydrophobic IOL from a 3-piece to a 1-piece haptic design caused no significant change in PCO, but resulted in a significant decrease in capsular folds rate at 1 year follow-up.
Since both IOLs are made of the same hydrophobic acrylic material and have a similar design (optic size, sharp edge, haptic angulation), any possible differences in PCO rate and capsular bag performance could be explained only by the variation of haptic design.
The possible impact of haptic design on PCO prevention is controversial. Wallin et al reported a significant increase of PCO rate with a 1-piece AcrySof IOL compared with a 3-piece AcrySof IOL. Another study group, comparing the same IOLs in short and long term follow-up, found a significantly higher PCO rate in the 1-piece IOL group after 1 year follow-up. However, the long term follow-up showed that the PCO and Nd:YAG rate was comparable for both IOLs. The authors suggested that, due to the haptic–optic angulation of the three piece IOL, the better barrier effect was given only in an early postoperative period, but disappeared during the following years.
In contrast to this initially higher PCO incidence of the 1-piece AcrySof IOL, other studies reported a comparable low PCO for both IOLs within the short term follow-up. The stronger binding of fibronectin and laminin to acrylate IOL, as previously reported by Linnola et al, may be an explanation for the improved adhesion to the haptics of a 1-piece IOL and, thus, for the comparable rate of PCO.
Except for haptic material, the two IOL types are identical. At the short term follow-up, there was no statistical significance either in severity or in type of PCO between the IOLs. A possible explanation for this might be that IOL haptic design does not play a key role in PCO prevention, once a continuous sharp optic edge is given. Another possible explanation is that a unique combination of monoblock open loop haptic design with supplementary PMMA haptic optic protectors of the 1-piece IOL comprises the mentioned benefit from the same strong fibronectin reaction to the optic and haptics and additionally allows an enhanced contact pressure between the optic edge and posterior capsule, inducing a mechanical barrier that prevents cell migration.
A complete overlap of the capsulorhexis edge with the IOL optic is prone to be an important factor in the prevention of PCO postoperatively. Although a complete rhexis-IOL overlap was created at the end of the surgery, we found at 1 year follow-up a relatively high incidence of buttonholing in both IOL groups that caused a significantly greater wrinkling and higher PCO rates in these eyes.
Concerning capsular bag performance of both IOLs, the 1-piece IOL group showed significantly less capsular folds than the 3-piece IOL group. The likely reason for this may be that PMMA haptics are stiffer and less compressible than the single piece IOL haptics and therefore produce a greater pressure force towards the equator of the capsule, leading to a capsular over-tension. In addition capsular folds may produce a scaffold for LEC growth along the fold onto the posterior capsule. In fact our results showed that a slightly higher PCO rate was associated with presence of capsular folds. However this had no influence on VA, likely because the PCO proceeded from the peripheral area behind the IOL optic–haptic junction and had not yet reached the central region around the visual axis in most cases.
There are some limitations of this study that need to be pointed out. Because of short follow-up (only 12 months), relatively low PCO rates associated with hydrophobic IOL material and a small sample size, a definitive PCO comparison cannot be made. Hence, further follow-up is necessary to prove whether the designs are equally protective against PCO.
In conclusion, modification of the MICS IOL from a 3-piece to a 1-piece haptic design caused comparable PCO and Nd:YAG laser treatment rates in the short term follow-up. Compared with the 3-piece IOL, the 1-piece IOL led to significantly less capsular folds 1 year after surgery.
The authors have no proprietary interest in any of the materials or equipment mentioned in this study. The trial was supported by an unrestricted grant from Hoya.
The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd to permit this article (if accepted) to be published in BJO and any other BMJPGL products and sublicences such use and exploit all subsidiary rights, as set out in our licence.
Discussion
The present study demonstrates that the modification of the IOL haptic design of an acrylic hydrophobic IOL from a 3-piece to a 1-piece haptic design caused no significant change in PCO, but resulted in a significant decrease in capsular folds rate at 1 year follow-up.
Since both IOLs are made of the same hydrophobic acrylic material and have a similar design (optic size, sharp edge, haptic angulation), any possible differences in PCO rate and capsular bag performance could be explained only by the variation of haptic design.
The possible impact of haptic design on PCO prevention is controversial. Wallin et al reported a significant increase of PCO rate with a 1-piece AcrySof IOL compared with a 3-piece AcrySof IOL. Another study group, comparing the same IOLs in short and long term follow-up, found a significantly higher PCO rate in the 1-piece IOL group after 1 year follow-up. However, the long term follow-up showed that the PCO and Nd:YAG rate was comparable for both IOLs. The authors suggested that, due to the haptic–optic angulation of the three piece IOL, the better barrier effect was given only in an early postoperative period, but disappeared during the following years.
In contrast to this initially higher PCO incidence of the 1-piece AcrySof IOL, other studies reported a comparable low PCO for both IOLs within the short term follow-up. The stronger binding of fibronectin and laminin to acrylate IOL, as previously reported by Linnola et al, may be an explanation for the improved adhesion to the haptics of a 1-piece IOL and, thus, for the comparable rate of PCO.
Except for haptic material, the two IOL types are identical. At the short term follow-up, there was no statistical significance either in severity or in type of PCO between the IOLs. A possible explanation for this might be that IOL haptic design does not play a key role in PCO prevention, once a continuous sharp optic edge is given. Another possible explanation is that a unique combination of monoblock open loop haptic design with supplementary PMMA haptic optic protectors of the 1-piece IOL comprises the mentioned benefit from the same strong fibronectin reaction to the optic and haptics and additionally allows an enhanced contact pressure between the optic edge and posterior capsule, inducing a mechanical barrier that prevents cell migration.
A complete overlap of the capsulorhexis edge with the IOL optic is prone to be an important factor in the prevention of PCO postoperatively. Although a complete rhexis-IOL overlap was created at the end of the surgery, we found at 1 year follow-up a relatively high incidence of buttonholing in both IOL groups that caused a significantly greater wrinkling and higher PCO rates in these eyes.
Concerning capsular bag performance of both IOLs, the 1-piece IOL group showed significantly less capsular folds than the 3-piece IOL group. The likely reason for this may be that PMMA haptics are stiffer and less compressible than the single piece IOL haptics and therefore produce a greater pressure force towards the equator of the capsule, leading to a capsular over-tension. In addition capsular folds may produce a scaffold for LEC growth along the fold onto the posterior capsule. In fact our results showed that a slightly higher PCO rate was associated with presence of capsular folds. However this had no influence on VA, likely because the PCO proceeded from the peripheral area behind the IOL optic–haptic junction and had not yet reached the central region around the visual axis in most cases.
There are some limitations of this study that need to be pointed out. Because of short follow-up (only 12 months), relatively low PCO rates associated with hydrophobic IOL material and a small sample size, a definitive PCO comparison cannot be made. Hence, further follow-up is necessary to prove whether the designs are equally protective against PCO.
In conclusion, modification of the MICS IOL from a 3-piece to a 1-piece haptic design caused comparable PCO and Nd:YAG laser treatment rates in the short term follow-up. Compared with the 3-piece IOL, the 1-piece IOL led to significantly less capsular folds 1 year after surgery.
The authors have no proprietary interest in any of the materials or equipment mentioned in this study. The trial was supported by an unrestricted grant from Hoya.
The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non-exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd to permit this article (if accepted) to be published in BJO and any other BMJPGL products and sublicences such use and exploit all subsidiary rights, as set out in our licence.
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