Refractive aspects of cataract surgery

The refractive aspects of cataract or lens surgery has formed a new field of operations. To reduce astigmatism and high myopia, surgeons are looking into alternatives and using various incision techniques as well as phakic intraocular lenses or clear lens extraction to achieve emmetropia. High hyperopia with short axial length and high required intraocular lens power are corrected by piggyback intraocular lens implantation. The use of multifocal intraocular lenses compensates for the loss of accommodation after lens extraction.     

Surgical management of posteriorly dislocated silicone plate intraocular lenses

Silicone plate intraocular lenses do not adhere to the lens capsule and are placed under tension by postoperative contraction of the capsular bag. Recent reports suggest that a defect anywhere in the capsular bag can potentially lead to delayed posterior dislocation of silicone plate intraocular lenses. These implants are more difficult to grasp and manipulate inside the eye than traditional polymethylmethacrylate lenses and therefore, require special microsurgical techniques. Given sufficient anterior capsular support, posteriorly dislocated silicone plate implants can be repositioned in the ciliary sulcus and do not necessarily require intraocular lens exchange. With proper vitreoretinal surgical techniques, posteriorly dislocated silicone plate intraocular lenses can be repositioned or exchanged with excellent visual results and an acceptably low complication rate.     

Dislocated posterior chamber intraocular lens scleral fixation technique through 23-gauge vitrectomy cannulas

A scleral fixation technique for posterior dislocated intraocular lens performed through 23-gauge vitrectomy cannulas is presented. It is based on the creation of polypropylene loops at opposite meridians through which haptics are engaged and placed in the sulcus. Repositioning of the intraocular lens (as opposed to substitution that requires new or reopening of corneal incisions) associated with microincisional vitrectomy techniques (23 gauge) allows for faster patient recovery. Free rotation of haptics through the loops aids in providing spontaneous good intraocular lens centering. The technique provides a minimally invasive solution for dislocated intraocular lenses after the unavoidable vitrectomy procedure to liberate the lens from the vitreous chamber.     

Bioptics: where do things stand?

PURPOSE OF REVIEW: Bioptics treats complex refractive errors by combining refractive techniques with different mechanisms of action, usually using an intraocular implant (a phakic or pseudophakic intraocular lens) followed by a corneal procedure (laser ablation, intrastromal implant). RECENT FINDINGS: In myopia and hyperopia, bioptics with phakic intraocular lenses or refractive lens exchange and subsequent excimer laser yields improved predictability and unchanged safety, compared with sole intraocular lens surgery. Complications are related mainly to intraocular lenses. In keratoconus and pellucid marginal degeneration, intracorneal rings have been successfully combined with phacoemulsification or with phakic intraocular lenses in a limited number of eyes. In the author's series, angle-supported phakic intraocular lenses were implanted in 12 eyes to correct a mean regression of -8 D after excimer laser (reverse bioptics), achieving a mean spherical equivalent of -0.3 D, mean best spectacle-corrected visual acuity of 0.7, and mean uncorrected visual acuity of 0.5, with 83% of eyes within 0.5 D of spherical equivalent. SUMMARY: Bioptics improves vision and halos and adds no particular risks to phakic or pseudophakic intraocular lens implantation in either myopia or hyperopia. Reverse bioptics, with phakic intraocular lenses or refractive lens exchange, can be used to correct regressed corneal surgery.     

Difficult lens power calculations

PURPOSE OF REVIEW: Although cataract extraction seems to be feasible without major technical obstacles, the surgical technique has changed completely, and patients are no longer satisfied with good spectacle-corrected vision but anticipate complete visual rehabilitation after cataract surgery, without correction. To fulfill this desire, toric or accommodative intraocular lenses are of increasing popularity, and the intraocular lens power calculation after keratorefractive surgery has been improved. RECENT FINDINGS: In this review article, we provide an overview of different mathematical strategies of calculating the intraocular lens power with standard formulas and with new algorithms, such as paraxial or numeric ray-tracing. These enhanced techniques may improve the validity of lens power calculation due to reduction of the prediction error, especially in cases with high or excessive corneal astigmatism and after refractive laser surgery. Furthermore, a new calculation scheme for the determination of bitoric eikonic intraocular lenses allows a distortion-free imaging in astigmatic eyes. The biometric determinants for the different formulas and calculation schemes are discussed in detail. SUMMARY: In difficult cases, standard calculation schemes are overemployed and new mathematical algorithms are necessary to adequately address these problems. Ray-tracing algorithms and other complex mathematical computation schemes are of increasing interest and will more and more replace conventional calculation formulas for determination of intraocular lens power.     

Explantation of intraocular lenses

Cataract surgery has evolved recently along with the development of intraocular lenses. With this evolution of intraocular lenses from anterior chamber and iris-fixated lenses to more modern foldable posterior intraocular lenses has come an evolution in the complications that necessitate removal of the intraocular lens. Early generations of anterior chamber and iris-fixated intraocular lenses often had severe complications associated with them, such as pseudophakic bullous keratopathy, uveitis-glaucoma-hyphema syndrome, and chronic cystoid macular edema. With modern foldable intraocular lenses, decentration-dislocation and incorrect lens power, and glare and optical aberrations are leading indications for explantation. Some complications appear to be unique to particular styles of modern intraocular lenses, with incidence of glare and optical aberrations increasing, especially in acrylic and multifocal intraocular lenses. The clinical outcomes after an intraocular lens explantation or exchange have also improved markedly with the advent of modern foldable intraocular lenses. Postoperative visual acuity results are dependent on the preoperative complications associated with the explanted intraocular lens. Final visual results after exchange of modern foldable intraocular lenses have been uniformly good. This is probably because of fewer severe complications that lead to explantation of the intraocular lens.     

New techniques and instruments for lens implantation.

Although no major breakthroughs have emerged in the area of lens insertion techniques and technology, small incremental advancements continue to take place for the placement of foldable intraocular lenses through small incisions. Folders have become more innovative in their ability to fold lenses effectively, and inserters have been downsized and enhanced to allow insertion through smaller incisions with more effective purchase of the lens. New cartridge injectors are increasing in popularity because of their ease of use and ability to pass through smaller incisions, especially with modifications. In addition, knowledge regarding techniques and complications of noncapsular supported intraocular lenses continues to increase, adding to our ability to choose the proper technique for secondary lens insertion in these selected patients.     

New techniques and instruments for lens implantation

Although no major breakthroughs have recently emerged in the area of lens insertion techniques and technology, small incremental advancements continue to take place for the placement of foldable intraocular lenses through small incisions. Folders have become more innovative in their ability to effectively fold lenses, and inserters have been downsized and enhanced to allow insertion through smaller incisions with more effective purchase of the lens. New cartridge injectors are increasing in popularity because of their ease of use and ability to pass through smaller incisions, especially with modifications. In addition, increased knowledge regarding techniques and complications of noncapsular supported intraocular lenses continues to be gained, adding to our ability to choose the proper technique for secondary lens insertion in these selected patients.     

Removal of anterior chamber intraocular lenses: a surgical technique

With the increasing trend toward intraocular lens implantation we are finding more cases in which explantation is indicated. The criteria and surgical techniques for explanation should be individualized depending on the type of lens. We describe removal of anterior chamber intraocular lenses.     

Biocompatibility of intraocular lens materials

PURPOSE OF REVIEW: To provide an update on currently available materials used in the manufacture of intraocular lenses, as well as new materials under development, especially with regard to their uveal and capsular biocompatibility. RECENT FINDINGS: The biocompatibility of intraocular lens materials should be assessed in terms of uveal biocompatibility, related to the inflammatory foreign-body reaction of the eye against the implant, as well as in terms of capsular biocompatibility, determined by the relationship of the intraocular lens with remaining lens epithelial cells within the capsular bag. This situation may result in different entities, e.g. anterior capsule opacification, interlenticular opacification (between piggyback intraocular lenses), posterior capsule opacification and lens epithelial cell ongrowth. Reports on intraocular lens opacification suggest that the potential to calcify should also be taken into consideration when evaluating the long-term biocompatibility of a new material. SUMMARY: Intraocular lenses are being progressively implanted in much earlier stages of life (refractive lens exchange, pediatric implantation) and are expected to remain in the intraocular environment for many decades. Materials used in intraocular lens manufacture should, therefore, insure long-term uveal and capsular biocompatibility, as well as ultimate transparency after implantation.     

人工晶状体材料的研究进展

随着白内障超声乳化吸除联合人工晶状体植入术的广泛应用，许多白内障患者都恢复了有效视力。术后人工晶状体混浊是评价生物相容性的重要指标，它会影响患者的视觉质量，不同材料人工晶状体混浊的表现及危险因素是不同的。然而，获得较好的视觉质量不是由单一因素决定的，人工晶状体的材料、患者对人工晶状体的反应等都是影响术后视觉质量的因素。随着科技的不断进步，越来越多的新材料在人工晶状体领域得到应用，充分了解不同人工晶状体材料的特性，为患者选择合适的人工晶状体，减少材料导致的并发症，将为患者带来福音。本文就不同人工晶状体材料的特性与人工晶状体植入术后发生混浊的表现及危险因素进行探讨。     

Late surface opacification of Hydroview intraocular lenses

PURPOSE: To describe clinical and pathological features of Hydroview intraocular lenses undergoing delayed surface opacification resulting in visual deterioration. METHODS: Twenty one eyes which underwent uncomplicated phacoemulsification and Hydroview lens implantation with good visual recovery, presenting at 46-146 weeks post-surgery with visual deterioration and glare symptoms resulting from opacification of the implants, were included in the study. Twelve eyes had severe opacification, of which nine underwent intraocular lens exchange and three more are still awaiting surgery. The method of explantation is described. The explanted intraocular lenses were examined using light microscopy, scanning electron microscopy and x-ray microanalysis using a light element detector. RESULTS: Light microscopy and scanning electron microscopy revealed diffuse granular deposits of approximately 5 microm diameter covering the optic surfaces but sparing the lens haptics. Light microscopic staining techniques and x-ray microanalysis confirm the major component of the deposits to be calcium phosphate salts. CONCLUSIONS: Late opacification of Hydroview intraocular lens implants is uncommon and aetiology seems to be multifactorial. Implant exchange is necessary to restore sight in some cases. As new materials are increasingly used it is important to highlight such unusual occurrences.     

The cornea in cataract and intraocular lens surgery

Advances in cataract surgery and intraocular lens implantation techniques continue to allow improved safety for the cornea. Complications can include mechanical or toxic injury of the endothelium, stripped Descemet's membrane, epithelial toxicity and disruption, infectious keratitis, or epithelial ingrowth. Most of the recent work has addressed endothelial cell survival after cataract extraction and lens implantation or in cases following secondary lens implantation. A great deal of controversy has been raised over the past year as to whether flexible open-loop anterior chamber lenses, iris-fixated posterior chamber lenses, or transsclerally sutured posterior chamber lenses are safest for the cornea. Even with additional data accumulating, it still is not clear which type of implant provides the best degree of safety in cases requiring secondary implantation. Certainly, both flexible open-loop anterior chamber lenses and bag-fixated posterior chamber lenses placed at the time of cataract surgery have a good record of safety for the cornea. Patients with keratoconjunctivitis sicca require extra lubrication to prevent epithelial toxicity at the time of surgery and also postoperatively. Methylcellulose-containing lubricants appear to be most protective of the corneal epithelium. Overall, cataract surgery and intraocular lens implantation is extremely safe with modern techniques.     

Status of toric intraocular lenses

PURPOSE OF REVIEW: To provide an update on the status of toric intraocular lenses. These lenses can be used as an alternative or adjunct to corneal astigmatic incisions for correcting preexisting astigmatism in patients with cataracts. They are a particularly attractive option in those cases where limbal-relaxing incisions are not powerful or predictable enough. Other toric lenses may correct astigmatism in addition to spherical refractive errors in phakic patients. RECENT FINDINGS: Toric lenses have continued to gain popularity with the US Food and Drugs Administration (FDA) approval of the Acrysof Toric intraocular lenses. This lens is designed to be implanted in patients undergoing cataract removal and who have significant preexisting corneal astigmatism. In the FDA clinical trial, study patients received one of the three cylindrical powers, and control patients received a standard monofocal intraocular lenses. The study found that the Acrysof Toric intraocular lenses provided excellent visual outcomes and exhibited excellent rotational stability. With the Acrysof Toric intraocular lenses, the average lens rotation was less than 4 degrees from the lens' initial placement at 6 months after surgery. SUMMARY: Toric intraocular lenses provide excellent vision for astigmatic cataract patients, and new designs are significantly improving visual acuity by minimizing the risk of rotation.     

Ultraviolet light absorption in intraocular lenses

Implantation of ultraviolet (UV) light-absorbing intraocular lenses and the manufacturers developing these lenses has significantly increased over the past few years. In this paper, the need for filtration of UV light by intraocular lens implants is briefly examined and various new product development aspects of a UV-absorbing IOL are discussed. Two general approaches, additive and chemical bonding, to incorporating a UV-absorbing chromophore into polymethylmethacrylate lens material are described. Different UV-absorbing compounds that are being used in implants and the mechanism by which they absorb light and its dissipation is discussed. The extent of preclinical testing required to establish the biocompatibility, stability, and overall safety of new materials is summarized. Finally, a relative comparison of the extent of UV absorption by various commercially available UV intraocular lenses is presented.     

Lensectomy, vitrectomy indications, and techniques in cataract surgery

Removal of a cataract during a vitrectomy can be performed to improve visualization for the surgeon or to facilitate visual rehabilitation for the patient. Because aphakic eyeglasses or contact lenses are often poor options to correct aphakia, placement of an intraocular lens during or after a vitrectomy is becoming increasingly common. A cataractous lens can be removed by pars plana lensectomy, phacoemulsification, or extracapsular cataract extraction. Options for intraocular lens placement include no intraocular lens, anterior chamber lens or sutured posterior capsular lens in the absence of capsular support, "in-the-bag" posterior capsular lens, or sulcus-fixated posterior capsular lens. This article reviews the current indications and techniques for cataract removal with or without intraocular lens placement in patients undergoing vitrectomy.     

Continuous-tear capsulotomy and insertion of a silicone bag lens

Opacification of the posterior capsule and lack of intraocular lens fixation have been recurring problems and have resulted in a gradual shift from sulcus-fixated silicone lenses to bag-fixated silicone lenses. Postoperative capsular contraction, however, can cause capsular tearing in the periphery and intraocular lens decentration. A new method of combining a small circular capsulotomy, cataract removal without anterior capsular rim tearing, and meticulous bag placement of the silicone lens seems to allow centering and secure fixation of the silicone lens.     

"Special" intraocular lens designs: why do they sometimes fail?

A variety of new "special" intraocular lens models to optimize the visual performance after cataract surgery have been introduced. The majority of these new intraocular lens designs require a good centration within the capsular bag and/or capsular elasticity. Today, the main post-operative complications after cataract surgery still arise from retained lens epithelial cells within the capsular bag, resulting mainly in anterior and posterior capsule opacification. Some special intraocular lenses are not designed to be effective against proliferating lens epithelial cells. Although lens epithelial cells can never be completely removed from the capsular bag, surgical quality is a major factor for success or failure of these intraocular lens designs.     

New techniques and technologies for pediatric cataract surgery

PURPOSE OF REVIEW: This paper surveys the literature from April 2004 to April 2005 and addresses trends in pediatric cataract surgery techniques. RECENT FINDINGS: The evolution of pediatric cataract surgery continues, with many adult cataract surgical techniques being applied to children with minor technical adjustments. More and more, surgeons are implanting intraocular lenses in younger children. One of the most widely reported technologic advances in 2004-2005 was the use of hydrophobic acrylic intraocular lenses in children. Predicting axial growth, and refractive change that accompanies it, is one of the major remaining challenges for the long-term care of children who have had cataract surgery. SUMMARY: Automation and intraocular lenses have helped to provide better anatomic and functional outcome for cataract surgery in children. Two major challenges in the coming years will be to find a way to obviate invasive procedures like posterior capsulotomy and vitrectomy and to study the growth of eyes in a well designed prospective study that will help to design new intraocular lens power calculation formulas specifically suited for children's eyes.     

Wavefront-customized intraocular lenses

PURPOSE OF REVIEW: Recent advances in ocular wavefront measurement and in intraocular lens materials and manufacturing methods have brought cataract surgery to the brink of a period in which customized correction of higher-order aberrations with intraocular lenses may become standard practice. RECENT FINDINGS: Retinal image quality in pseudophakic eyes is limited by the wavefront aberrations of the cornea and the intraocular lens. The Tecnis Z9000 is the first commercially available intraocular lens designed to account for the wavefront aberrations of the cornea, specifically spherical aberration. Clinical findings with the Tecnis Z9000 intraocular lens show improved contrast sensitivity at low and mid spatial frequencies. However, if the lens decenters or tilts modestly, higher-order aberrations are created, and the lens may underperform relative to standard intraocular lenses. At present, one firm is developing an intraocular lens that may be modified in vivo with near ultraviolet energy. Such a technology offers tremendous potential for a fully customized intraocular lens. SUMMARY: Wavefront-customized intraocular lenses offer the promise of near perfect retinal image quality, such that only diffraction, chromatic aberration, retinal sampling and neural factors will limit vision in pseudophakic eyes.