Everything You Always Wanted to Know About...

Everything you always wanted to know about… Posterior Capsular Opacification (PCO)

Dr Soosan Jacob MS, FRCS, DNB

Posterior capsular opacification (PCO), also called aftercataract or secondary cataract, is the most common postoperative complication of cataract surgery. The previously reported incidence ranges between a quarter to half of patients developing PCO within a few months to five years of surgery. A better understanding of risk factors and better techniques and technology have helped decrease PCO formation in recent times. Newer thinking attributes some advantage to limited capsular fibrosis in helping stabilise the IOL within the bag.

MECHANISM Extra-capsular cataract surgery retains anterior and equatorial capsular areas harbouring the lens epithelial cells (LEC) as well as the posterior capsule. LECs undergo proliferation to form monolayers, and some undergo abnormal differentiation and migration onto the posterior capsule to result in PCO. Various growth factors and cytokines such as transforming growth factor-β and fibroblast growth factor-2 stimulate myofibroblastic differentiation and cell-mediated capsular contraction. These and others such as hepatocyte growth factor and matrix metalloproteinases contribute to cell proliferation, migration, and cell-mediated contraction and thereby PCO formation.

CLINICAL FEATURES PCO causes decreased vision, decreased contrast sensitivity ranging from mild to severe, and glare and halos. Broad opacities may be visually insignificant, but fine opacities and wrinkles can cause significant visual degradation. Patients with multifocal IOLs may have earlier onset of PCO and may also present visual dissatisfaction earlier.

IOL exchange after YAG laser posterior capsulotomy is difficult, so it’s therefore before IOL explantation. It is important to verify dissatisfaction is due to PCO and not the multifocal optics. PCO can also cause loss of effect of accommodative IOLs, Z-syndrome with Crystalens, and visual dysphotopsia. A small rhexis can cause anterior capsular contracture or phimosis and IOL dislocation.

PCO is easily identified on slit-lamp examination as opacification of varying degrees of the anterior and posterior capsules. Using retro-illumination alone can underestimate PCO and should be combined with reflected light examination. Fibrotic and proliferative forms of PCO exist and Scheimpflug image densitometry-based grading, slit-lamp photographs in reflected light and retro-illumination, OCT analysis, computerised analysis, and subjective grading can be used to grade PCO based on area as well as density.

PCO can also be seen as Elschnig’s pearls. These are round pearls seen on retro-illumination. They are graded as none, trace, mild, moderate, and severe based on appearance ranging from none to thick sheets of epithelial pearls.

PCO may also present with Soemmering rings—a peripherally placed ring of cortical fibres proliferates from equatorial LECs retained between the posterior capsule and the edges of the anterior capsular remnant. Soemmering rings are usually asymptomatic, but they can cause tilt or IOL dislocation and glare if thick. They can get dislodged during secondary surgeries and drop into the vitreous, where they may incite inflammation. They may be removed using glued IOL scaffold technique to decrease chances of fragment drop from the ring.

RISK FACTORS A knowledge of risk factors is important, as PCO can result in patient dissatisfaction, more postoperative visits, increased costs, and risks from additional procedures. Senile mature cataracts have a lower risk than immature cataracts. Paediatric cataracts have almost a 100% rate of PCO, resulting not only in decreased vision but amblyopia. Diabetes, uveitis, myotonic dystrophy, retinitis pigmentosa, and traumatic cataract are other risk factors.

Certain surgeries such as extracapsular cataract extraction and poor techniques such as incomplete cortical removal, wholly or partially sulcal-fixated IOLs, and incomplete overlap of the rhexis all around the IOL optic also increase risk.

The design of IOL affects the incidence of PCO. Square, sharpedge IOLs create a capsular bend, hindering the migration of LECs when compared to round-edge IOLs. Other design features such as slim haptic-optic junction also help. IOL material, too, has a role in decreasing PCO. Hydrophobic material is superior, but this effect may occur only by creating a sharp capsular bend. No difference has been seen between three-piece and one-piece hydrophobic acrylic IOLs. Certain OVD—e.g., those containing exogenous hyaluronic acid—may induce lenticular migration.

PREVENTIVE MEASURES Various surgical techniques have been tried to decrease PCO. These include cortical cleaving hydrodissection, thorough cortical wash, capsule polishing, OVD removal, in-the-bag IOL placement, and 0.25 to 0.5 mm circumferential optic coverage by the anterior capsular rim (shrink-wrap effect). Other approaches include using phaco instead of ECCE, primary posterior capsulorhexis (PPCC) with optic capture, or posterior capsulotomy with vitrector in paediatric patients. Other strategies include primary laser capsulotomy with optic capture in adults and special IOLs—such as bag-in-lens IOL or bulky IOLs that keep the anterior and posterior capsules separated and allow aqueous circulation within the bag.

Therapeutic agents are also employed, such as antimetabolites, anti-inflammatory agents, hypo-osmolar drugs, and heparin. Others use devices as sealed capsule irrigation devices that temporarily seal the capsule with a suction device and irrigate with a pharmacological agent to prevent PCO. A capsular bending ring that decreased ACO and PCO is in clinical trials. Dodick phacolysis can remove the laminin layer of posterior capsule. Newer approaches include Zepto capsulotomy and gene therapy.

Though anterior capsular polishing removes LECs, a study by Liu et al did not see a decrease in residual cell growth but rather an increase in cell proliferation in capsular bag cultures. It decreases anterior capsular opacification (ACO) but also delays the fusion of anterior and posterior capsules, allowing LECs to go past the square edge of the IOL. Since some capsular fibrosis helps stabilise the bag and thereby the IOL, complete removal of all LECs by any means results in a “dead bag syndrome”, causing excessive bag floppiness, subluxation, etc. A fine balance is therefore required in leaving some LECs behind sufficient to stabilise the bag but not cause PCO. New research aims at modulation and not complete removal of LECs.

MANAGEMENT Nd:YAG laser capsulotomy is a simple and effective treatment, but it can add to expense and is unavailable in developing countries. Successful YAG capsulotomy is challenging in patients with poor fixation or poor cooperation as well as those with media opacities such as corneal oedema or scarring that degrade the laser beam or make the aiming beam difficult to visualise. Nd:YAG is relatively contraindicated with glass IOLs as they may crack. It also is possibly contraindicated in the presence of inflammation, increased IOP, cystoid macular oedema, or a high risk of retinal detachment. The function of filtering blebs may be compromised post-YAG, and it is therefore a relative contraindication.

In case endothelial keratoplasty, vitreoretinal surgery, or an IOL exchange is required, the surgery should be avoided or at least delayed till the need for maintaining the capsular barrier is over. Cruciate and circular patterns are preferred, and the capsulotomy opening should be the size of the scotopic pupil but may have to be larger for multifocal optics—though there are no studies to verify this. In addition, the size may increase slightly postoperatively. IOL pitting may occur following YAG and can be avoided using posterior laser offset. Extensive pitting can cause image degradation, even necessitating IOL exchange. It is less seen now with better IOL material, better laser machines, more experience, and better techniques.

YAG anterior capsulotomy in a cruciate spoke like pattern around the edges is used for capsular contraction syndrome.

It is preferable to wait about three months and confirm the cause of symptoms before YAG capsulotomy, as IOL exchange is difficult to perform with an open posterior capsule. This also allows stabilisation of IOL within the bag and prevents vitreous prolapse around the optic. Topical steroids and anti-glaucoma medications may be given for a week after YAG. Complications of Nd:YAG capsulotomy include retinal detachment, cystoid macular oedema, rise in IOP, IOL pitting, bleeding from the iris, and corneal oedema.

Dense membranes or media opacities may necessitate surgical capsulotomy with needle or capsulectomy with vitrector. Pharmacological and immunological methods for the prevention of PCO under research include pharmacological agents such as anti-inflammatories, immuno-modulators, antiproliferative, antiadhering, anti-transdifferentiating agents.

Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India, and can be reached at dr_soosanj@hotmail.com.