Cataract surgery is associated with numerous postoperative complications, including hypopyon/endophthalmitis, lens dislocation from the anterior chamber, pupillary block and secondary surgical intervention.1 By far the most common complication, however, is posterior capsule opacification (PCO),2 which reduces vision and requires treatment with Nd:YAG laser capsulotomy. Fortunately, improvements in surgical techniques, instrumentation and IOL design have helped to reduce PCO rates.
Lens design and visual outcomes
Lens design plays an important role in visual outcomes. Studies have shown that the design of the lens edge influences the migration of lens epithelial cells (LECs). Square edges act as a barrier to LEC migration more than round-edged designs, thus reducing the occurrence of PCO.3,4
The material from which the lenses are made may also influence the degree of opacification: it is higher in lenses made from poly(methyl methacrylate) than other polymers.2,5,6 Studies have also shown that aspheric IOLs lead to better visual outcomes, particularly in terms of contrast sensitivity and night vision and especially in patients with large pupils.7,8
In short, IOL design is a complex but vital factor in achieving optimal outcomes. New IOL designs seek to improve quality of vision9,10 and eliminate the formation of glistenings11,12 within the aqueous medium of the IOL because these reduce visual acuity.11
Glistening-free hydrophobic IOL
The glistening-free, hydrophobic acrylic IOL known as the enVista (Bausch and Lomb Inc.) is a single-piece, monofocal, hydrophobic acrylic, aspherically neutral IOL. The lens optic and haptics of the IOL are composed of a hydroxyethyl methacrylate-polyethylene glycol phenyl ether acrylate-styrene copolymer that is cross-linked with ethylene glycol dimethacrylate.
The lens avoids glistenings through pre-hydration and packing in 0.9% saline. It is 4% water, ensuring it remains in equilibrium with the environment in saline; there is no water movement in or out of the IOL.
This lens, which is the only FDA-approved glistening-free, hydrophobic IOL, also has a 360° square edge in order to minimise PCO. Additional design features include step-vaulted haptics, designed to vault the optic posteriorly for direct contact with the capsular bag and prevent LEC migration, and modified-C fenestrated haptics designed to evenly transmit forces to the optic, thus promoting uniform pressure on the posterior edge.
The enVista IOL label states that no glistenings of any grade were reported for any subject at any visit.13,14 However, published studies evaluating clinical outcomes (in particular, the incidence of PCO) with this lens are limited.
Consequently, we undertook a single-centre, prospective, observational clinical study to assess postoperative visual acuity and the incidence of PCO associated with this IOL in a group of pseudophakic patients.
Patients with against-the-rule or oblique astigmatism over 1.25 D, or with-the-rule astigmatism over 1.5 D, were implanted with a toric monofocal IOL. All other patients received an aspheric monofocal IOL.
In all cases, the IOL was implanted through a 2.2-mm clear corneal incision. All patients underwent at least four postoperative visits, at 24 hours, 1 week, 1 month and 12 months post-surgery.
Ninety-four eyes of 63 patients (mean age 74.5 ± 8.1 years) were included in the analysis. Of the 94 implanted lenses, 82 were aspheric monofocal and 12 were toric monofocal IOLs.
At a mean follow-up of 555.20 ± 34.04 days, there were statistically significant improvements in mean corrected distance visual acuity (CDVA) and spherical equivalent (all patients, P=0.000 and P=0.027, respectively). Overall, 92% of patients reached a postoperative CDVA of 0.1 logMAR (20/25 Snellen) or better. In the toric and aspheric groups, respectively, 100% and 88.6% of patients had a visual acuity of 0.1 logMAR (20/25 Snellen) or better.
Glistenings were not observed via slit lamp imaging or following an analysis of retroillumination images in any of the implanted lenses in any patient or at any follow-up visit. Capsulotomy was performed when vision was insufficient for patients and following image analyses.
Overall, 5.3% eyes implanted with the lens required Nd:YAG laser posterior capsulotomy. Of these patients, 80% reported a progressive loss of vision, whereas 20% reported no symptoms but chose to undergo capsulotomy due to the presence of Elschnig pearls in the visual axis. Nd:YAG capsulotomy was required at 9 months postoperatively in 20% of eyes and at 18 months postoperatively in 40% of eyes; 40% of eyes showed opacification at 25 months postoperatively and were treated with Nd:YAG at this time.
The mean CDVA (logMAR) in patients requiring Nd:YAG laser posterior capsulotomy was 0.10 ± 0.08 (range 0.05–0.22) before the procedure and 0.01 ± 0.04 (range 0.0–0.09) after the procedure – a statistically significant improvement in visual acuity (P=0.0021).
The toric lens also had good rotational stability: the mean rotation of the toric IOL during the first 24 hours post-surgery (versus preoperative calculated IOL position) was 2.0 ± 1.3Ë (range 0–5). The mean IOL rotation was 2.1 ± 1.03Ë (range 0–4) and 2.0 ± 0.95Ë (range 0–4) 1 week and 30 days post-surgery, respectively.
Ideally, our study would have compared the results obtained with the glistening-free lens with those of other IOLs by means of a randomised trial. Additionally, 28.7% of the eyes included in the study presented no ocular pathology, whereas 71.3% had pathology of some form including macular degeneration, glaucoma, epiretinal membrane, diabetic retinopathy and previous vitrectomy. Some of these diseases have been associated with a greater rate of posterior capsule opacification, which may have induced some selection bias.
As mentioned previously, there is a paucity of data describing clinical outcomes following enVista IOL implantation. Nevertheless, the lens appears to compare favourably with other lenses on the market.
Previously, we undertook a 91-patient prospective study in which patients were implanted with one of three monofocal toric IOLs: the Lentis LT (Oculentis), the enVista or the AcrySof IQ (Alcon Laboratories Inc.) or a multifocal toric IOL (the AcrySof IQ ReSTOR, Alcon Laboratories Inc.).
Patients implanted with the glistening-free toric IOL achieved the best uncorrected distance visual acuity compared with the other monofocal IOLs, with 81% of eyes having 0.1 logMAR or better.15 Previous studies have demonstrated that the incidence of PCO following uncomplicated cataract surgery ranges from 50% to <5%;16-19 in the current study, only 5.3% of eyes required Nd:YAG laser posterior capsulotomy.
Overall, findings from our study clearly indicate that implantation of the glistening-free IOL leads to good visual outcomes with a low incidence of PCO. These data also highlight the effect of IOL design on vision quality.
1. Irvine SR. A newly defined vitreous syndrome following cataract surgery. Am J Ophthalmol. 1953;36:599-619.
2. Vasavada AR, et al. Prospective evaluation of posterior capsule opacification in myopic eyes 4 years after implantation of a single-piece acrylic IOL. J Cataract Refract Surg. 2009;35:1532-1539.
3. Nanavaty MA, et al. Edge profile of commercially available square-edged intraocular lenses. J Cataract Refract Surg. 2008;34:677-686.
4. Nishi O, et al. The inhibition of lens epithelial cell migration by a discontinuous capsular bend created by a band-shaped circular loop or a capsule-bending ring. Ophthalmic Surg Lasers 1998;29:119-125.
5. Rönbeck M, et al. Comparison of posterior capsule opacification development with 3 intraocular lens types: five-year prospective study. J Cataract Refract Surg. 2009;35:1935-1940.
6. Rønbeck M, Kugelberg M. Posterior capsule opacification with 3 intraocular lenses: 12-year prospective study. J Cataract Refract Surg. 2014;40:70-76.
7. Schuster AK, Tesarz J, Vossmerbaeumer U. The impact on vision of aspheric to spherical monofocal intraocular lenses in cataract surgery: a systematic review with meta-analysis. Ophthalmology 2013;120:2166-2175.
8. Nanavaty MA, et al. Wavefront aberrations, depth of focus, and contrast sensitivity with aspheric and spherical intraocular lenses: fellow-eye study. J Cataract Refract Surg. 2009;35:663-671.
9. Sandoval HP, et al. Comparison of visual outcomes, photopic contrast sensitivity, wavefront analysis, and patient satisfaction following cataract extraction and IOL implantation: aspheric vs spherical acrylic lenses. Eye (Lond). 2008;22:1469-1475.
10. Packer M, et al. Prospective randomized trial of an anterior surface modified prolate intraocular lens. J Refract Surg. 2002;18:692-696.
11. Werner L, et al. Unusual pattern of glistening formation on a 3-piece hydrophobic acrylic intraocular lens. J Cataract Refract Surg. 2008;34:1604-1609.
12. Gregori NZ, et al. In vitro comparison of glistening formation among hydrophobic acrylic intraocular lenses (1). J Cataract Refract Surg. 2002;28:1262-1268.
13. Bausch & Lomb Incorporated Study #658. A prospective multicenter clinical study to evaluate the safety and effectiveness of a Bausch + Lomb one piece hydrophobic acrylic intraocular lens in subjects undergoing cataract extraction. Final Clinical Study Report, 24 Aug 2011.
14. Tetz MR, et al. A prospective clinical study to quantify glistenings in a new hydrophobic acrylic IOL. Presented at American Society of Cataract and Refractive Surgery Symposium & Congress, 3–8 April 2009; San Francisco, CA.
15. Garzón N, et al. Evaluation of rotation and visual outcomes after implantation of monofocal and multifocal toric intraocular lenses. J Refract Surg. 2015;31:90-97.
16. Schmidbauer JM, et al. Evaluation of neodymium:yttrium-aluminum-garnet capsulotomies in eyes implanted with AcrySof intraocular lenses. Ophthalmology 2002;109:1421-1426.
17. Dholakia SA, Vasavada AR. Intraoperative performance and longterm outcome of phacoemulsification in age-related cataract. Indian J Ophthalmol. 2004;52:311-317.
18. Thompson AM, et al. The Auckland Cataract Study: 2 year postoperative assessment of aspects of clinical, visual, corneal topographic and satisfaction outcomes. Br J Ophthalmol. 2004;88:1042-1048.
19. Schaumberg DA, et al. A systematic overview of the incidence of posterior capsule opacification. Ophthalmology. 1998;105:1213-1221.