The 50th anniversary of the intraocular lens and a quiet revolution

Modern cataract surgery: unfinished business and unanswered questions

We summarize information, based on clinicopathologic studies over the past decade, on various cataract intraocular lens (IOL) procedures and modern "specialized" IOLs, that will help surgeons continuously improve long-term results for cataract patients. Although most operations do initially provide excellent refractive correction and visual rehabilitation, late complications occur. These sometimes are missed because they are outside of the routine period of follow-up care. We have tried to determine if the various techniques and IOLs truly deliver the long-term results that we desire. Most safety and efficacy information is derived from the manufacturer and is passed through the U.S. Food and Drug Administration (FDA). This is often based on limited, relatively short-term observations made by the manufacturer. After a lens receives FDA approval, there are few means to assess the outcome of each procedure and lens years later. We rarely hear of a 10- or 20-year follow-up study. We have found that one of the best means to assess long-term results is pathologic analyses. We discuss recently studied aspects of pathologic reactions, such as posterior capsule opacification, intracapsular fibrosis, glistenings, intralenticular opacification, and other issues with the various IOL platforms; we then present a clinicopathological overview of tissues and IOLs from our database. These include hydrophobic and hydrophilic acrylic designs, plate lenses, and a dual optic lens.

Theoretical evaluation of the cataract extraction-refraction-implantation techniques for intraocular lens power calculation

PURPOSE

To evaluate theoretically three previously published formulae that use intra-operative aphakic refractive error to calculate intraocular lens (IOL) power, not necessitating pre-operative biometry. The formulae are as follows: IOL power (D) = Aphakic refraction x 2.01 [Ianchulev et al., J. Cataract Refract. Surg.31 (2005) 1530]; IOL power (D) = Aphakic refraction x 1.75 [Mackool et al., J. Cataract Refract. Surg.32 (2006) 435]; IOL power (D) = 0.07x(2) + 1.27x + 1.22, where x = aphakic refraction [Leccisotti, Graefes Arch. Clin. Exp. Ophthalmol.246 (2008) 729].

METHODS

Gaussian first order calculations were used to determine the relationship between intra-operative aphakic refractive error and the IOL power required for emmetropia in a series of schematic eyes incorporating varying corneal powers, pre-operative crystalline lens powers, axial lengths and post-operative IOL positions. The three previously published formulae, based on empirical data, were then compared in terms of IOL power errors that arose in the same schematic eye variants.

RESULTS

An inverse relationship exists between theoretical ratio and axial length. Corneal power and initial lens power have little effect on calculated ratios, whilst final IOL position has a significant impact. None of the three empirically derived formulae are universally accurate but each is able to predict IOL power precisely in certain theoretical scenarios. The formulae derived by Ianchulev et al. and Leccisotti are most accurate for posterior IOL positions, whereas the Mackool et al. formula is most reliable when the IOL is located more anteriorly.

CONCLUSION

Final IOL position was found to be the chief determinant of IOL power errors. Although the A-constants of IOLs are known and may be accurate, a variety of factors can still influence the final IOL position and lead to undesirable refractive errors. Optimum results using these novel formulae would be achieved in myopic eyes.

Anterior capsule relationship of the AcryS of intraocular lens optic and posterior capsule opacification

OBJECTIVE

To evaluate the relationship of the anterior capsule and the AcrySof MA30BA intraocular lens (IOL) and its impact on the development of central posterior capsule opacification (PCO).

DESIGN

Prospective, randomized, controlled trial.

PARTICIPANTS

Two hundred two patients with senile cataracts received an AcrySof IOL between July and December 1998 at Iladevi Cataract and IOL Research Center, Ahmedabad, India.

INTERVENTION

Patients were randomized prospectively to receive 1 of the 3 possibilities of anterior capsule and IOL optic relationship: group 1, total anterior capsule cover (360 degrees ) of the optic; group 2, no anterior capsule cover (360 degrees ) of the optic; group 3, partial anterior capsule cover (<360 degrees ) of the optic. After surgery, slit-lamp video photography was performed every 6 months for 3 years. Analyses of variance and chi-square tests were used to compare treatment groups.

MAIN OUTCOME MEASURES

Incidence of PCO in the 3 groups. The posterior capsule was divided into 3 zones: peripheral, central 3 mm, and midperipheral (the space between the peripheral and the central zones).

RESULTS

The average follow-up was 35.3 +/- 1.52 months in all the groups. At 3 years, the rate of central PCO was 6.4% in group 1, 7.1% in group 2, and 5.9% in group 3 (P = 0.9). Midperipheral PCO was present in 24.2% in group 1, 16% in group 2, and 20.6% in group 3 (P = 0.9). Peripheral PCO was seen in 100% of patients in all groups. The neodynium:yttrium-aluminum-garnet laser (Nd:YAG) posterior capsulotomy rate was 0% in all groups.

CONCLUSIONS

There was no significant difference in the incidence of development of central PCO among the 3 groups. No patient experienced central PCO that required Nd:YAG capsulotomy. When using the AcrySof IOL model MA30BA, the relationship of the anterior capsule and the IOL does not seem to be a factor that relates to the development of central PCO.

Effect of haptic angulation on posterior capsule opacification in modern foldable lenses with a square, truncated optic edge

PURPOSE

To analyze the effect of different haptic angulations on posterior capsule opacification (PCO) in a modern foldable intraocular lens (IOL) with a square-edged optic designed to reduce the incidence of PCO.

SETTING

Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

Ten Dutch Belted, serum Pasteurella-free pigmented rabbits of the same age and sex had bilateral phacoemulsification with endocapsular IOL implantation. The eyes were implanted with Centerflex IOLs (Rayner) with haptic angulations of 0 degree (n = 8), 5 degrees (n = 4), 10 degrees (n = 4), or 15 degrees (n = 4).

RESULTS

There was no statistical difference in central PCO, peripheral PCO, and measured IOL decentration among the angulation groups.

CONCLUSION

With the Centerflex IOL, haptic angulation did not seem to be a significant factor influencing PCO. It appears that the barrier effect of the IOL's truncated, square-edged optic overrides the angulation factor in preventing PCO.

Effect of in-the-bag intraocular lens fixation on the prevention of posterior capsule opacification

PURPOSE

To compare the incidence of posterior capsule opacification (PCO) after extracapsular cataract extraction (ECCE) and phacoemulsification and to evaluate the role of posterior chamber intraocular lens (PC IOL) haptic fixation and biomaterial/design in reducing the incidence.

SETTING

Postgraduate Institute of Medical Education and Research, Chandigarh, India; Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

This study comprised 278 eyes of 263 patients having ECCE and 318 eyes of 297 patients having phacoemulsification with PC IOL implantation. Posterior capsule opacification leading to a decrease in Snellen visual acuity of 2 or more lines was considered visually significant. The presence of PCO and IOL haptic fixation were evaluated postoperatively using slitlamp biomicroscopy. Haptic position was noted as in-the-bag (B-B), 1 haptic in the bag and 1 in the sulcus (bag-sulcus [B-S]), or both haptics out of the bag (sulcus-sulcus [S-S]). In addition, the rate of visually significant PCO was compared among 3 IOL biomaterials: poly(methyl methacrylate), silicone, and hydrophobic acrylic.

RESULTS

Visually significant PCO occurred in 42.45% of eyes having ECCE and 19.18% of eyes having phacoemulsification (P <.001, chi-square test) after a mean follow-up of 2.4 years +/- 0.7 (SD). In both groups, visually significant PCO was significantly less in eyes with B-B fixation than in those with B-S or S-S fixation (P <.001). The rate of visually significant PCO in all eyes in the phacoemulsification group with B-B fixation was low (11.90%) and was significantly lower in eyes with a hydrophobic acrylic IOL (2.22%; P <.05, chi-square test).

CONCLUSIONS

In-the-bag PC IOL fixation is required to consistently reduce the incidence of PCO. Thorough removal of lens substance, including hydrodissection-assisted cortical cleanup, and in-the-bag PC IOL fixation seem to be the most important factors in reducing PCO, regardless of surgical procedure or IOL type used. Intraocular lens biomaterial and design also help prevent PCO.

Eradication of posterior capsule opacification: documentation of a marked decrease in Nd:YAG laser posterior capsulotomy rates noted in an analysis of 5416 pseudophakic human eyes obtained postmortem

OBJECTIVE

(1) To report the neodymium:yttrium-aluminum-garnet (Nd:YAG) laser posterior capsulotomy rate (%) of eight rigid and foldable intraocular lens (IOL) designs in a series of 5416 pseudophakic human eyes obtained postmortem, accessioned in our center between January 1988 and January 2000. (2) To identify factors that are instrumental in reducing the incidence of posterior capsule opacification, (PCO, secondary cataract) and hence the need for Nd:YAG laser posterior capsulotomy.

DESIGN

Comparative autopsy tissue analysis.

PARTICIPANTS

A total of 5416 globes with posterior chamber intraocular lens (PC-IOLs) obtained postmortem received from Lions Eye Banks between 1988 and 2000.

METHODS

Miyake-Apple posterior photographic technique. Special reference was given to the presence or absence of Nd:YAG laser posterior capsulotomy orifice on the posterior capsule of each eye.

MAIN OUTCOME MEASURES

The Nd:YAG laser posterior capsulotomy rate (%) as of January 2000 was documented. In addition, the Nd:YAG laser posterior capsulotomy rate for each lens was plotted on a monthly basis for the same period, creating a computerized trend or "timeline" for each IOL style.

RESULTS

Relatively high Nd:YAG laser posterior capsulotomy rates ranging from 20.3% to 33.4% were noted with four relatively older designs (high incidence of implantation between 1988 and the early 1990s). Four modern foldable IOLs manufactured from silicone and acrylic materials had significantly lower Nd:YAG laser posterior capsulotomy rates ranging from 0.9% (Alcon Acrysof) to 17.1%. The difference in Nd:YAG rates among the eight IOL designs was found to be significant (P < 0.0001, chi-square test). Comparing foldable versus rigid designs, the foldable IOLs were associated with a much lower Nd:YAG laser posterior capsulotomy rate (14.1% vs. 31.1%).

CONCLUSIONS

By use of the six factors regarding surgical technique and IOL choice described in this article, we strongly believe that the overall incidence of PCO and hence the incidence of Nd:YAG laser posterior capsulotomy is now rapidly decreasing from rates as high as 50% in the 1980s to early 1990s. Surgical tools and IOLs are now available to bring these rates down to single digits. Careful application and use of these tools by surgeons can genuinely lead in the direction of virtual eradication of secondary cataract, the second most common cause of visual loss worldwide.

Intraocular lens glucose sensor

Ocular spectroscopy, which is the use of the eye to monitor optically the concentration of metabolites in the body, has been successfully applied to monitor aqueous humor glucose concentration. In the United States, 1.7 million intraocular lenses are currently implanted yearly. Because patients with diabetes are more likely to develop cataracts at an earlier age, a relatively high proportion of the patients receiving intraocular lenses have diabetes. Last year, 110,000 patients with diabetes received intraocular lens implants of various materials. We have successfully polymerized a fluorescent complex within a hydrogel intraocular lens that responds well to glucose concentration.