PCO formation is an attempt by the eye to make a new lens from remaining lens material.
One form of PCO is a fibrosis that forms inside the capsule by lens epithelial (covering) cells that migrate from the anterior capsule to the posterior capsule when the anterior lens capsule is opened to remove the primary cataract and insert the IOL.
Opacification is also be formed by residual lens cortex cells. The epithelial cells can transform into myofibroblasts and proliferate; myofibroblasts are precursors to muscle cells and capable of contraction. The deposit of collagen on these cells leaves the posterior lens capsule with a white, fibrous appearance. This type of opacification can appear within days of cataract surgery. The greatest capsule opacification is found around the edges of the IOL, where the anterior and posterior lens capsules adhere and form a seam, called Soemmering's ring.
Elschnig's pearls are a proliferation of cells on the outside of the capsule. This type of PCO can be several layers thick and develops months to years after cataract surgery. Elschnig's pearls can also appear along the margins of a previously performed laser capsulotomy.
A secondary cataract will also form from wrinkling of the lens capsule, either secondary to contraction of the myofibroblasts on the capsule or because of stretching of the capsule by haptics, or hooks, used to hold the IOL in place.
One risk of laser capsulotomy is damage to the intraocular implant. Factors that determine the extent of damage to the IOL include the inherent resistance of a particular IOL to damage by the laser, the amount of energy used in the procedure, the position of the IOL within the lens capsule, and the focusing accuracy of the surgeon. The thicker the opacification of the lens capsule, the greater the amount of energy needed to remove it. The accuracy of the surgeon is improved when there is less opacification on the lens capsule.
In addition, during laser capsulotomy the IOL can be displaced into the eye's vitreous. This happens more often in eyes with a rigid implant, rather than with acrylic or silicone IOLs, and also if a larger implant is used.
If the posterior capsule ruptures during extraction of the primary cataract, risk of lens displacement is also increased. Displacement risk is also increased if the area over which the laser capsulotomy is done is large. The most serious complication of a capsulotomy would be IOL damage so extensive that extraction would be required. This is a rare complication.
Another risk of this surgery is the re-formation of Elschnig's pearls over the opening created by the capsulotomy. This occurs in up to 80% of patients within two years of laser capsulotomy. Most of time, these PCOs will resolve over time without treatment, but 20% of patients will require a second laser capsulotomy. This secondary opacification by Elschnig pearls represents a spatial progression of the opacification that caused the initial secondary cataract.
Other risks to take into account when considering a posterior capsulotomy are macular edema, macular holes, corneal edema, inflammation of the iris, retinal detachment, and increased pressure in the eye, as well as glaucoma.
These risks escalate with increased laser energy and with increased size of the capsulotomy area. Retinal detachments are usually treated with removal of the vitreous behind the lens capsule. Macular edema is treated by application of topical anti-inflammatory drops or intraocular steroid injections. Steroids control iritis (inflammation of the iris), either topically or intraocularly. Macular holes are also treated by removal of the vitreous (the substance that fills the main area of the eyeball), followed by one to three weeks of facedown positioning. Elevated intraocular pressure and glaucoma are treated with anti-glaucoma drops or glaucoma surgery, if necessary.
Finally, increased glare at night may result when the size of the capsulotomy is smaller than the diameter of the pupil during dark conditions.
Within one to two days after surgery, maximum visual acuity will be attained by almost 99% of patients. Once the opacification is removed, most patients will not need a change in spectacle prescription. However, patients who have undergone implantation of a rigid IOL may experience an increase in hyperopia, or far-sightedness, after a capsulotomy. For a few weeks after surgery, the presence of visual floaters, which are pieces of the excised capsule, is normal. But, the presence of floaters months after this timeframe, especially if accompanied by flashes of light, may signal a retinal tear or detachment and require immediate attention. Also, if vision suddenly or gradually worsens after an initial improvement, further follow-up to determine the cause of a decrease in visual function is imperative.
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