PCO with two aspheric microincision IOLs

As the techniques of cataract surgery are getting refined with smaller incision sizes, so is intraocular lens (IOL) technology. Smaller incision sizes have led to the development of microincision IOLs, which can be implanted through sub-2 mm incisions.

It is already known that spherical microincision IOLs do not match the posterior capsule opacification (PCO) standards of conventional IOLs. We conducted a prospective, randomized, fellow eye comparative study to evaluate the difference in PCO performance between two aspheric hydrophilic acrylic microincision IOLs and these results were further compared with those of a conventional spherical hydrophobic acrylic non-microincision IOL.

Comparative study

Both IOLs included in our study can be implanted through a 1.8 mm incision. The data gathered was also compared with that of a conventional single piece hydrophobic acrylic IOL (AcrySof SN60AT Alcon Fort Worth, Texas, USA) using information from our old database.

The inclusion criteria were uncomplicated age-related bilateral cataract with the potential to see 20/40 or better in each eye. Exclusion criteria were any concurrent medication apart from ocular lubricants, any coexisting ocular pathology, unilateral amblyopia, previous intraocular surgery or laser treatment, retinal complications, pupil dilatation less than 7 mm, any surgical complications or inability to co-operate or maintain follow-up.

A single surgeon performed all surgeries with a standardized phacoemulsification procedure using a 'stop and chop' technique with total cover of anterior capsulorhexis on the IOL optic edge. Patients underwent unilateral surgeries on each eye within 3 weeks. Corrected distance visual acuty and PCO data (using POCO software) was collected.

Results

Eighty four eyes of 42 patients were recruited in this study. The mean age was 72.2 ± 11.4 years. At 12 months, eyes implanted with the AcriSmart 36A IOL were found to have better 100% corrected distance visual acuity (CDVA) than eyes implanted with the old Akreos MI60. The AcrySof SN60AT was also found to offer significantly better 100% CDVA compared to both the microincion IOLs. Additionally, 9% CDVA was significantly better with the AcriSmart 36A at 6, 12 and 24 months but the AcrySof SN60AT had significantly better 9% CDVA at 6 and 12 months compared to both the microincison IOLs.

In our study,¹ the CDVA with both microincision IOLs was comparable to reports already published in the literature. However, the faster development of PCO with the hydrophilic acrylic microincision IOLs in comparison to a conventional hydrophobic IOL (AcrySof SN60AT), was a factor leading to the differences in 100% and 9% CDVA between the 3 IOLs at various follow-up visits.¹ Obviously, other influences included IOL design and material on the visual performance.

Mean percentage PCO score was significantly less with the AcriSmart 36A at 1, 3 and 12 months compared to the old Akreos MI60. On comparing percentage PCO scores between the AcriSmart 36A, the old Akreos MI60 and AcrySof SN60AT IOLs, at one month, AcrySof SN60AT showed more PCO, whereas at 12 months Akreos MI60 IOL showed more PCO. At 2 years, mean PCO score remained under 11% with AcrySof SN60AT whereas, mean PCO score increased linearly with time in both the AcriSmart 36A and the old Akreos MI60 groups with a maximum of up to 16% and 23% respectively. The mean difference in PCO increased until 12 months with the old Akreos MI60 eyes showing more PCO. At 12 months, the mean difference in PCO score was –11.63 ±30.5%. Seven eyes with an old Akreos MI60 needed Nd:YAG laser posterior capsulotomy, which dropped the mean difference in PCO score to –6.85 ± 32.69% at 24 months.

In both groups no eyes were noted to have decentration or luxation of IOLs before or after Nd:YAG capsulotomy.¹ We reported that at 3 months, 2.3% of eyes implanted with a microincision IOL demonstrated capsular bag contraction and phimosis,¹ whereas other authors have described this outcome in 3% of patients implanted with old Akreos IOL model.²

The old Akreos MI60 IOL had 4 haptics with a 10-degree anglulation and 360-degree square-edged design, which were intended to prevent PCO. At two-year follow-up we found an average PCO score of 22.57 ± 25.56% and 8 eyes (19%) required Nd:YAG capsulotomy for visually significant PCO whereas Can et al.² reported 20 eyes (20%) with PCO, which did not require Nd:YAG capsulotomy at 1 year follow up. With the old Akreos MI60 IOL, Alió et al.³ reported PCO incidence of 36% (9 eyes out of 25 required Nd:YAG capsulotomy) after 1 year of follow-up. In our study the conventional AcrySof SN60AT IOLs had a mean PCO score <11% at 2 years in comparison to the old Akreos MI60 (mean PCO score = 23%).¹ Previous studies have demonstrated a capsulotomy rate between 2% and 4.5% a year with conventional AcrySof IOLs.^4–7 The PCO with the hydrophilic acrylic microincision IOLs showed a trend to progression over the 2 year follow-up.¹ This may be because of the difference in material characteristics, design or the posterior optic edge profile.

We scanned the optic-haptic junctions of AcriSmart 36A, the old Akreos MI60 IOL and the new Akreos MI60 with environmental scanning electron microscopy.¹ Since our study, the design of the Akreos MI60 has changed with a sharper posterior edge profile which may improve the PCO performance.

Summary

In summary, our prospective, randomized fellow eye controlled study comparing 2 mcroincision IOLs, found that the AcriSmart 36A IOL had a better 9% CDVA and PCO performance in comparison to the old Akreos MI60 IOL but at 2 years follow-up a conventional hydrophobic acrylic IOL has a better PCO performance compared to both of these microincision IOLs.

References

1. M.A. Nanavaty et al., J. Cataract Refract. Surg., 2013;39(5):705–711.

2. I. Can et al., J. Cataract Refract. Surg., 2010;36(11):1905–1911.

3. J.L. Alió et al., J. Cataract Refract. Surg., 2009;35:1548–1554.

4. S.I. Mian et al., Br. J. Ophthalmol., 2005;89(11):1453–1457.

5. P.B. Stordahl and L. Drolsum, Acta Ophthalmol. Scand., 2003;81(4):326–330.

6. J.A. Davison, J. Cataract Refract. Surg., 2004;30(7):1492–1500.

7. L. Vock et al., J. Cataract Refract. Surg., 2009;35(3):459–465.