Posterior capsule opacification

Posterior Capsule Opacification (PCO) is the most common complication of cataract surgery. At present the only means of treating cataract is by surgical intervention, and this initially restores high visual quality. Unfortunately, PCO develops in a significant proportion of patients to such an extent that a secondary loss of vision occurs. A modern cataract operation generates a capsular bag, which comprises a proportion of the anterior and the entire posterior capsule. The bag remains in situ, partitions the aqueous and vitreous humours, and in the majority of cases, houses an intraocular lens. The production of a capsular bag following surgery permits a free passage of light along the visual axis through the transparent intraocular lens and thin acellular posterior capsule. However, on the remaining anterior capsule, lens epithelial cells stubbornly reside despite enduring the rigours of surgical trauma. This resilient group of cells then begin to re-colonise the denuded regions of the anterior capsule, encroach onto the intraocular lens surface, occupy regions of the outer anterior capsule and most importantly of all begin to colonise the previously cell-free posterior capsule. Cells continue to divide, begin to cover the posterior capsule and can ultimately encroach on the visual axis resulting in changes to the matrix and cell organization that can give rise to light scatter. This review will describe the biological mechanisms driving PCO progression and discuss the influence of IOL design, surgical techniques and putative drug therapies in regulating the rate and severity of PCO.     

Posterior capsule opacification

PURPOSE OF REVIEW: This paper assesses the factors that contribute to the formation of an effective capsular bend as a deterrent to posterior capsule opacification. Its goal is to assist the practicing ophthalmologist in separating current understanding of this process from various working models previously proposed. RECENT FINDINGS: While a square-edge design appreciably improves resistance to posterior capsule opacification, significant factors remain under the control of the surgeon. These factors combine to form the physical and psychological barrier of a capsular bend. Innovative digital imaging has shown lens epithelial cell migration, allowing for a more rapid assessment of posterior capsule opacification resistance. A three-piece intraocular lens allows for full 360 degree capsular bend formation surrounding the optic edge; some single-piece designs may inhibit capsular bend formation. Decreasing, but not eliminating, the surviving lens epithelial cell population may diminish capsular bend strength, which may decrease resistance to posterior capsule opacification in the face of a regenerating cortex. All demographic features of clear/refractive lens exchange suggest higher rates of posterior capsule opacification than with standard cataract surgery. SUMMARY: The quality of capsular bend formation will determine how resistant an intraocular lens will be to posterior capsule opacification as a consequence of regenerating cortex. As refractive lens exchange and new accommodating intraocular lens designs become more popular, the problems of regenerating cortex will increase in magnitude.     

Posterior capsule opacification

Posterior capsule opacification (PCO) is the most common complication following primary cataract surgery. Advances in intraocular lens (IOL) designs that have reduced the amount of PCO following surgery have been made. The understanding of how the IOL design effects PCO has also advanced. Lenses that provide a mechanical barrier between it and the posterior lens capsule seem to inhibit PCO to a greater degree. Intracapsular rings are now being explored to test and enhance this barrier effect. Major advances in the elimination of lens epithelial cells at the time of surgery especially by pharmacologic means have also been made. An immunotoxin specific for human lens epithelial cells shows promise and is under latter phase clinical development.     

Posterior capsule striae

PURPOSE: To find the incidence, contributing factors, outcomes, and clinical impact of intraoperative posterior capsule striae. SETTING: Iladevi Cataract & IOL Research Centre, Ahmedabad, India. METHODS: In a prospective study, 100 consecutive eyes had phacoemulsification and intraocular lens (IOL) (AcrySof MA30BA) implantation. The presence of striae was noted at the end of the operation, and factors contributing to their development were identified. Follow-up was done at regular intervals, and the clinical impact of striae on patients' vision was evaluated. RESULTS: Striae were observed in 56 eyes (Group 1) but were absent in 44 (Group 2). Mean age in Group 1 was 65.96 years +/- 9.15 (SD) and in Group 2, 59.20 +/- 10.36 years (P = .0012). Mean axial lengths were 23.47 +/- 1.63 and 24.12 +/- 1.49 mm, respectively (P = .0419). Average lens thickness was greater in Group 1 (4.50 +/- 0.43 mm) than in Group 2 (4.13 +/- 0.41 mm) (P = .0001). The sex of patient, capsulorhexis size and centration, grade of cataract hardness, scleral rigidity, and IOL centration were not found to contribute to striae development. The striae disappeared by 5 months postoperatively and did not show a positive Maddox rod phenomenon. CONCLUSION: Intraoperative striae observed in many patients were associated with relatively older age, greater lens thickness, and shorter axial length. The striae eventually disappeared and had no effect on vision.     

Posterior capsule opacification: experimental analyses

The lenses of New Zealand White and Flemish Giant rabbits were removed using five techniques representative of the different clinical approaches to extracapsular cataract extraction currently employed. Posterior capsule opacification developed in all experimental animals within 6 weeks of the operation. None of the techniques reduced the incidence of the capsular opacification. Histological analyses including immunofluorescent and tritiated thymidine labelling were used to determine the nature of the cellular constitutents of the secondary membrane. The evidence indicates that the opacity is due not only to lens cells remaining after the operation but also consists of cells of nonlenticular origin. The data strongly implicate the anterior uvea as the source of those cells. Furthermore, the findings suggest that posterior capsule opacification is the product of a migration and a proliferation of both cell populations.     

Posterior capsule opacification and anterior capsule opacification

Posterior capsule opacification (PCO) is still the most frequent complication of cataract surgery. A variety of studies has led to a better understanding of the pathogenesis of PCO, and strategies of molecular biology have produced new therapeutic options, such as immunological techniques or gene therapeutic approaches. Surgical strategies and intra-ocular lens-dependent factors also are capable to reduce the rate of PCO. In-the-bag implantation of intra-ocular lenses with a sharp optic edge seems to be effective in inhibiting equatorial lens epithelial cell migration to the center of the posterior capsule. Several PCO documentation systems have been developed that will lead to more exact and better comparable recording of PCO rates. In the year 2000, PCO or secondary cataract is still the most frequent complication after extracapsular cataract surgery. In a 1998 meta-analysis, PCO rates of 11.8% 1 year after extracapsular cataract surgery with intraocular lens implantation, 20.7% after 3 years, and 28.4 % after 5 years have been reported. For the United States, it has been estimated that the overall expenses for treatment of PCO are only exceeded by the costs for cataract treatment itself. In the past decade, a lot of experimental and clinical studies have been performed on this topic. They have led to 1) to a better understanding of the pathogenesis of the development of anterior and posterior capsule opacification; 2) more objective and better comparable systems of documentation and analysis of PCO; and a number of 3) surgical and 4) pharmaceutical strategies to prevent PCO.     

Posterior capsule opacification.

A complication of extracapsular cataract extraction with or without posterior chamber intraocular lens (PC-IOL) implantation is posterior capsule opacification. This condition is usually secondary to a proliferation and migration of residual lens epithelial cells. Opacification may be reduced by atraumatic surgery and thorough cortical clean-up. Clinical, pathological and experimental studies have shown that use of hydrodissection, the continuous curvilinear capsulorhexis and specific IOL designs may help reduce the incidence of this complication. Capsular-fixated, one-piece all-polymethylmethacrylate PC-IOLs with a C-shaped loop configuration and a posterior convexity of the optic are effective. Polymethylmethacrylate loops that retain "memory" create a symmetric, radial stretch on the posterior capsule after in-the-bag placement, leading to a more complete contact between the posterior surface of the IOL optic and the taut capsule. This may help form a barrier against central migration of epithelial cells into the visual axis. Various pharmacological and immunological methods are being investigated but conclusive data on these modalities are not yet available.     

Posterior capsule opacification: a specular microscopic study

Posterior capsule opacification following extracapsular cataract extraction is a manifestation of migration of lens epithelial cells onto the posterior capsule. Collagen production by these epithelial cells results in white "fibrotic" opacities. These cells have myoblastic features and their contraction produces wrinkling of the posterior capsule resulting in visual distortion. A high magnification, in vivo specular microscopic study of human posterior capsules following extracapsular cataract extraction is described. In vivo findings correlate with histopathologic observations made on opacified posterior capsules. Lens epithelial cells migrate onto the posterior capsule and produce basement membrane and collagen. Collagen production is associated with a spindle-shaped appearance of the hyperplastic cells. This technique is useful for clinical research on posterior capsule opacification, including the evaluation of interventions designed to treat or prevent this complication.     

Posterior capsule opacification. Part 2: Clinical findings

The incidence of posterior capsule opacification (PCO), the most common complication of modern cataract surgery with intraocular lens implantation, seems to have decreased slightly as a result of improved surgical and cortical cleanup techniques. However, the reported incidence is still significant. The diverse findings on PCO are the result in part of studies using different criteria to clinically judge and quantify the condition. In addition, the influence of intraocular and systemic factors are only now being identified. This second of a 2-part review of PCO focuses on (1) less subjective morphological and patient-dependent means to evaluate and quantify PCO; (2) the influence of ocular factors on PCO; (3) the influence of systemic factors on PCO; (4) available means and approaches to prevent or delay PCO.     

Posterior capsule opacification in myopic eyes

PURPOSE: To determine whether posterior capsule opacification (PCO) is extensive in eyes with myopia or long axial length when an intraocular lens (IOL) of low-power, zero-power, or minus-power, is implanted. SETTING: Hayashi Eye Hospital, Fukuoka, Japan. METHODS: Ninety eyes of 90 patients scheduled for phacoemulsification surgery were recruited. These consisted of 30 eyes with high (> or =-8 diopters [D]) myopia, 30 eyes with moderate (<-8 D and > or =-3 D) myopia, and 30 eyes with low (<-3 D) myopia. All eyes had implantation of an acrylic IOL-low-power, zero-power, or minus-power-with a sharp optic edge (AcrySof MA60BM or MA60MA, Alcon Surgical). The PCO in these eyes was measured using a Scheimpflug videophotography system (EAS-1000, Nidek) 1, 3, 6, 12, 18, and 24 months after surgery. Visual acuity and the incidence of neodymium:YAG (Nd:YAG) laser posterior capsulotomy were also examined. RESULTS: No significant difference was observed in the mean PCO value or in the Nd:YAG capsulotomy rate between the high myopia, moderate myopia, or low myopia groups throughout the follow-up period. There was also no significant correlation between PCO value and the actual spherical power or axial length of the eye. Furthermore, although mean visual acuity tended to be worse in proportion to the degree of myopia, the difference was not statistically significant. CONCLUSION: When an acrylic IOL of low-power, zero-power, or minus-power with a sharp optic edge was implanted, high myopia and long axial length were not associated with the degree of PCO.