Zonulolysis is a surgical procedure where a zonulolytic agent, an enzyme, is used to facilitate the extraction of intracapsular cataract. Examples of zonulolytic agents include Quimotrase (Pevya) and alpha-chymotrypsin (ACT). Age is a factor in deciding which enzyme to use because some work best on juvenile cataracts, while others may function well in senile cataracts.
Research has shown that some proteolytic enzymes can weaken the zonular fibers but may not be strong enough to dissolve them completely. The enzyme is supposed to work selectively so that it dissolves the zonular fibers without affecting the healing of the corneal wound or attacking the vitreous body. While it breaks down the zonular fibers, the enzyme should leave the internal limiting membrane and ciliary epithelium intact. An effective enzyme can also work on unusually resistant zonular fibers.
The human eye’s anterior lens capsule consists of three distinct layers with the outer layer consisting of the zonular fibers. It is this layer that the enzyme is designed to dissolve. The enzyme breaks the zonules into fragments and clusters so that they appear comparatively even in their length and arrangement. The key to successfully breaking down the zonular fibers is to ensure the enzyme has a sufficient concentration, and that it has been left to act long enough.
For example, the enzyme ACT is best under the following conditions:
- In cases where a patient loses one eye due to retinal detachment
- In patients aged 20 and over with traumatic and congenital cataracts
- In one-eyed patients due to the ease and safety of conducting a zonulolysis
- In juvenile and moderately young cataracts with a relatively strong suspensory ligament
- In patients with high myopia because of the reduced risk of subsequent retinal detachment
Also Known As
- Enzymatic Zonulolysis
Before the Procedure
The patient will discuss the procedure with the ophthalmologist. The benefits and risks of the procedure are explained. The patient's medical and ocular history is also taken. S/he also undergoes an extensive ophthalmic examination, including slit-lamp examination, visual acuity tests, imaging tests, etc. The patient will be admitted to the hospital for about three days or more.
The patient is put under local or general anesthesia. This is followed by the pupil's moderate dilatation to enable the enzyme’s injection well behind the iris to access the zonular fibers. The surgeon will:
- Pre-place a conjunctivo-episclero-limbal suture. If vitreous loss or iris prolapse is likely to occur, the surgeon can supplement with two or more additional stitches. Additional sutures can also be used in the case of uncooperative patients
- Create a conjunctival frill with an incision by a von Graefe knife while avoiding cutting the pre-placed suture. The surgeon can use a keratome and scissors where the anterior chamber is shallow or where enophthalmic eyes are deeply set
- Inject a freshly prepared enzyme solution into the posterior chamber (all round). S/he uses a light syringe containing a cannula or long lacrimal blunt needle (some prefer a curved rounded cannulae with multiple holes)
- In case there is posterior synechiae (because the enzyme does not affect it), the surgeon uses an iris repositor to deal with them
- Wait for at least three minutes to allow the weakening of the zonule and for the lens to demonstrate increased sphericity
- A peripheral iridectomy or two can be performed during this waiting time if there is a need, particularly in young patients
- Can further inject in the enzyme behind the iris via an iris coloboma
- Wash the anterior chamber with saline solution after the three minutes' expiry to eliminate any excessive active enzyme
- The cataract can then be removed using the surgeon’s method of choice such as Smith’s methods, suction method, Arruga's intracapsular forceps, etc
- Replace the iris and ties the pre-placed suture
- Smooth the conjunctival frill over the suture lines
- Inject penicillin in the subconjunctival and instill eserine (an inhibitor) and pilocarpine (to reduce eye pressure) drops
- Bandage the eye and send the patient to the ward
Risks & Complications
Several risks and complications can arise following a zonulolysis procedure. They may include:
- Secondary glaucoma
- Temporary elevation of intraocular pressure, which is controlled by medication
- Fragmentation of iris pigment epithelium, which occurs more often with Quimotrase
- Hyphema may occur, but it may not be severe and usually occurs after about five days
- Non-formation of the anterior chamber which occurs within the first eight days after surgery
- Capsule rupture, perhaps due to pressure at the time of the injection but is not a serious complication
- Loss of vitreous, which may be caused by lens subluxation or uncontrolled cannula pressure, and is less common among the younger population
- Retinal detachment, which can be mild and subside on its own. Others may be severe and require further surgical treatment such as scleral buckling
- Iris prolapse, which manifests from between two to seven days following the procedure. It can sometimes be accompanied by marked hyphema. The prolapse is usually excised.
- Keratitis and corneal vascularization, which should disappear in eight to ten days. The inflammation is notably worse if accompanied by loss of vitreous. It can persist in some patients for six weeks and take longer to clear up
Aftercare & Recovery
Zonulolysis patients are admitted to the hospital for several days, depending on their response to treatment. Most of the complications occur several days after the procedure; hence, close monitoring is imperative. The patient is prescribed antibiotics to deal with infection; anti-inflammatory drugs to deal with inflammation; while anti-pain medications help with pain and discomfort.
The patient is observed on the same day of surgery and in the following two days. The surgeon will use a loupe, direct or indirect ophthalmoscope, and a flashlight. Intraocular pressure is taken, eyes photographed, and patients with displaced lens prescribed cataract spectacles. The surgeon estimates vision using the illiterate E test. Refraction tests are also performed.
At the time of discharge, the patient is examined under a slit lamp examination to check whether the anterior vitreous surface is intact. After discharge from the hospital, the patient will require follow up visits to check for more complications like a severe retinal detachment that can happen even seven months after the procedure. Patients can be followed up for seven years and beyond.
With the right concentration of the enzyme of choice, zonulolysis can help make cataract removal more manageable, and with minimal complications. If vision is 20/200, it is considered good while less than 20/200 is poor.