Laser posterior capsulotomy, or YAG laser capsulotomy, is a noninvasive procedure performed on the eye to remove the opacification (cloudiness) that develops on the posterior capsule of the lens of the eye after extraction of a cataract. This differs from the anterior capsulotomy that the surgeon makes during cataract extraction to remove a cataract and implant an intraocular lens (IOL). Laser posterior capsulotomy is performed with Nd:YAG laser, which uses a wavelength to disrupt the opacification on the posterior lens capsule. The energy emitted from the laser forms a hole in the lens capsule, removing a central area of the opacification. This posterior capsule opacification (PCO) is also referred to as a secondary cataract.
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.
Posterior capsule opacification is the most common complication of cataract removal or extraction. It does not occur when an anterior chamber lens is implanted, because in this procedure the capsule is usually extracted along with the cataract, and a lens is attached to the iris in the front part of the eye, called the anterior chamber. This technique for cataract removal is not often performed.
The purpose of a laser capsulotomy is to remove a PCO. This procedure dramatically improves visual acuity and contrast sensitivity and decreases glare. The visual acuity before capsulotomy can be as poor as 20/400, but barring any other visual or ophthalmologic conditions, the patient will see as well after a laser posterior capsulotomy as after removal of the original cataract. Laser capsulotomies are usually performed once a patient's vision is 20/30.
Approximately 20% of patients who undergo cataract extraction with placement of an intraocular lens into the posterior lens capsule will eventually undergo a laser capsulotomy, although a PCO may appear in up to 50% of patients who have undergone cataract surgery. The average time after cataract extraction for this procedure to be performed is two years, but it may be performed as early as three months after cataract removal, or as late as five years afterward.
Patients who fall into groups with an increased incidence of a secondary cataract formation have an increased rate of YAG capsulotomy. Patients who are younger when undergoing cataract removal are more likely to develop a PCO than are geriatric patients. This is particularly true of pediatric patients who are experiencing ocular growth. The incidence of PCO is higher in women than in men. Fifty percent of patients who experience papillary, or iris capture, of the IOL, which occurs if the IOL moves through the pupil (a hole in the iris) from its position in the posterior chamber of the eye to the anterior chamber, will form a PCO and benefit from laser capsulotomy.
The degree and incidence of capsule opacification also varies with the type of implant used in the initial cataract operation. Larger implants are associated with decreased opacification, and round-edged silicone implants are associated with a greater incidence of opacification than are acrylic implants, which have a square-edged design. These two types of IOLs are called foldable implants because they unfold after being placed in the eye, allowing for a smaller incision on the front of the eye during cataract surgery. Also, the incidence of PCO is less with a silicone IOL than with a rigid IOL. The greater the amount of remaining lens material after extraction, especially in the area of Soemmering's ring, the greater the probability of PCO formation and laser capsulotomy. Also, diabetic patients are more likely to require a YAG capsulotomy than are non-diabetic patients. This is especially true for YAG capsulotomies performed on diabetics 18 months or later after cataract removal. The extent of diabetic retinopathy does not correlate with incidence of PCO or laser capsulotomy. Finally, insufficient dilation of the pupil during cataract surgery and inexperience of the surgeon doing cataract removal contribute to an increased risk of secondary cataract formation.
Laser capsulotomy is usually performed in an ophthalmologist's office as an outpatient procedure. Before beginning the capsulotomy, the patient is given an informed consent for the procedure. An hour before the laser capsulotomy, a drop of a pressure-lowering drug such as timoptic or apraclonidine is administered. A weak dilating drop to enlarge the pupil is applied to the eye. The eye may be anesthetized locally if the doctor uses a special contact lens for the procedure.
The patient then puts the head in the chinrest of a slit lamp microscope, to which a laser is attached. The doctor then may place a special lens on the front of the eye. It is important that the patient remain still as the doctor focuses on the posterior capsule. A head strap to help keep the patient's head in place may be used. While focusing on the posterior capsule, the doctor, with repeated bursts from the Nd:Yag laser in a circular manner, disrupts the PCO. An opening forms on the posterior part of the lens capsule as part of the PCO falls off of the posterior capsule and into the vitreous. Another drop of apraclonidine, or other pressure-lowering eyedrop, is applied to the eye as a preventative measure for increased pressure in the eye, which is experienced by most patients after the procedure. This is a brief procedure lasting only a few minutes and is not associated with pain.
Prior to performing a posterior capsulotomy, the doctor will perform a thorough ophthalmic examination and review any systemic medical problems. The ophthalmologic includes evaluation of visual acuity, slit-lamp biomicroscope examination of the eye to assess the extent and type of opacification and rule out inflammation or swelling in the front of the eye, measurement of intraocular pressure, and a thorough evaluation of the fundus or back of the eye to check for retinal detachments and macular problems, which would limit the extent to which the YAG capsulotomy could improve vision. A potential acuity meter (PAM) may be used to ascertain best expected visual acuity after YAG capsulotomy, and brightness acuity testing will determine the extent of glare experienced by the patient. Contrast sensitivity testing is employed by some doctors.
This procedure cannot be performed in the presence of certain preexisting ophthalmologic conditions. For example, irregularities of the cornea would interfere with the ability of the doctor to see the posterior capsule. Also, a laser capsulotomy could not be performed if there is ongoing inflammation in the eye, or if swelling of the macula (a part of the retina) is present. A laser capsulotomy would be contraindicated with glass IOLs. If macular edema is suspected, which can occur in up to 30% of patients who have undergone cataract surgery, a test called a fluoroscein angiography may also be performed.
After a laser capsulotomy, the patient will remain in the office for one to four hours so that the pressure in the eye can be evaluated. The patient can then resume normal everyday activities. After surgery, pressure-lowering eyedrops may be used for a week, if the intraocular pressure is raised significantly after the procedure. Cycloplegic agents to keep the pupil dilated and to prevent spasm of the muscles in the iris, and steroids to reduce inflammation may also be prescribed for up to a week. Follow-up visits are scheduled at one day, one week, one month, three months, and six months after capsulotomy.
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.
The probability of a retinal detachment after capsulotomy is 1.6–1.9%. This represents a two-fold increase of retinal detachment over the rate for all patients undergoing cataract surgery, regardless if a posterior capsulotomy was done or not. Macular edema occurs in up to 2.5% of patients who undergo a laser capsulotomy and is more likely to occur when the capsulotomy is performed soon after cataract extraction, or in younger individuals. Rarely does glaucoma develop after laser capsulotomy, although as many as two-thirds of patients will experience transient increased intraocular pressure.
The alternative to laser capsulotomy is surgical capsulotomy of the PCO and the adjacent anterior vitreous. There is an increased risk of retinal detachment when this invasive intraocular surgery is employed. The other alternative is to leave the PCO in place. This leaves the patient with permanent decreased visual acuity.
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Martha Reilly, OD
The procedure is usually performed in the office of an ophthalmologist or an osteopathic physician. The training of an ophthalmologist includes a year of internship and at least three years of residency training in the treatment of eye diseases and in eye surgery after graduation from medical school. In states where doctors of optometry are permitted by law to use lasers, and if trained in laser surgery , an optometrist may do the laser capsulotomy. A co-managing optometrist may perform some of the preoperative testing and postoperative follow-up.