If the anterior capsule tears toward the equator when creating the capsulorhexis, it is usually due to posterior positive pressure, which pushes anteriorly on the lens during the creation of the capsular tear. The resultant “downhill” vector force causes the tear to change from a circular to a radial direction (Figure 1). Under these circumstances, with quick action, the cataract surgeon may be able to bring the tear back toward the center. If the tear has reached the equator or gone beyond it, however, the integrity of the posterior capsule is in question, and vitreous loss may ensue.
PREVENTION
In order to prevent the capsulorhexis from tearing outward, the surgeon must be careful to equalize the pressures in the anterior segment so that no positive posterior pressure develops. The first step is to ensure that the speculum is loose when performing the capsulorhexis. Frequently, we insert the speculum and tighten it to create more working room. Then, we forget the negative impact on the capsulorhexis that results.
The second step is to confirm that the anterior chamber is adequately filled with viscoelastic so that the anterior capsular surface is actually flat. These are probably the most important factors in preventing an errant tear. Third, always keep the vector forces of the tearing capsule close to the actual point of the tear. This requires frequent repositioning of the forceps or needle, so that the instrument is not too far from the point of the tear.
MANAGEMENTPupil
A surgeon cannot perform the capsulorhexis if he cannot see where it is tearing. The capsulorhexis should be located at, or within, the pupillary margin. If the pupil is so small that it prevents visualization of the tear, then the surgeon must enlarge the pupil.
Redirecting the Tear
In the typical scenario of tear misdirection, the capsulorhexis begins to tear circumferentially, and then starts to shoot out toward the periphery. Upon recognition, the surgeon must immediately stop the capsulorhexis. Next, he loosens the speculum and deepens the anterior chamber with viscoelastic. This will neutralize the vector forces that propel the tear peripherally.
At this point, the surgeon uses a forceps to grasp the tearing capsule close to, but just ahead of, the end of the tear. To turn the tear, it is crucial to redirect it directly toward the center of the nucleus. With luck, this new vector direction will pull the tear back. It is critical not to allow the tear to progress too far toward the periphery, which will make redirection exceedingly difficult.
The surgeon must determine the new direction of the vector that is redirecting the capsulorhexis. When the tear has progressed to the equator, it may be difficult to redirect by pulling directly toward the center. This may do nothing more than tear the zonular insertions. In this setting, a technique I have found helpful is to tear slightly circumferentially to initiate the redirection of the tear, and then to pull straight toward the center of the nucleus in order to turn the tear away from the periphery and allow a continuous tear.
Completing the Capsulorhexis
Some tears cannot be redirected. They may have progressed too far into the periphery. Alternatively, they may have collided with and could not circumvent a zonule with an anterior insertion on the capsule. This will cause the tear to follow the path of the anterior zonular origin—directly to the equator!
Incomplete Capsulorhexis
When the tear cannot be redirected, completing the capsulotomy depends upon finishing the capsulorhexis from the opposite side. To perform this maneuver, the surgeon should grasp the tear near its origin and gently tear in the direction opposite to the original direction to begin a new capsulorhexis. If the surgeon cannot initiate the tear, he may use a Vannas Scissor to make a small cut in the capsule. The size and direction of the capsulotomy, once begun, may be maintained in the usual manner (Figure 2).
The capsulorhexis will now be complete, but there will be a radial tear where both the initial and opposite tears meet. This is, by definition, not a continuous capsulotomy. The surgeon must take into account that the radial tear may perhaps extend around the equator and into the posterior capsule. This occurs when, during phacoemulsification, anterior chamber fluid pressure and the posterior pressure of the phaco tip generate a new vector force at the equator that now propels the radial tear posteriorally.
In reality, this complication does not occur often, but prevention is obviously important. The basis of prevention is the performance of gentle hydrodissection (or even gentle viscodissection), which mobilizes the entire nucleus into the anterior chamber. This step can be accomplished without difficulty, because the capsulorhexis is usually large and will not act as a barrier to the anterior movement of the cataract, as the capsulorhexis might when small and intact.
I will then perform phacoemulsification anterior to the plane of the iris using what I call a “visco-sandwich.” This technique requires inserting a dispersive viscoelastic behind the lens nucleus to secure it, as well as placing a dispersive viscoelastic between the nucleus and cornea. The surgeon should then use his preferred technique to emulsify the nucleus in the anterior chamber. No pressure is transmitted to the posterior capsule due to the buffer of viscoelastic, which reduces the possibility of an extension of the radial tear around the equator and into the posterior capsule.
CAPSULORHEXIS SIZE
The size of the capsulorhexis may be a causal factor in the development of capsulotomy complications. As a rule, I make the capsulorhexis approximately 0.25 mm smaller than the intended size of the lens implant's optic. When the capsulotomy is centered, the anterior capsule will overlap the IOL optic. Furthermore, if I happen to tear the posterior capsule, I have the option of placing the optic in the capsular bag with sulcus fixation of the haptic.
Capsulotomy size is not as important if the nucleus is small or soft. However, a small capsulorhexis in the presence of a hard nucleus may generate problems in the course of hydrodissection. Complications occur when BSS (Alcon Laboratories, Fort Worth, TX) collects in the posterior part of the capsular bag and drives the lens anteriorly. The stretching of the bag produces a seal of the anterior capsular edge against the nucleus. The outcome is the equivalent of a pupillary block, but, in this case, aqueous flow is halted by the nucleus' pressing against the capsule. This obstructs fluid egress anteriorly. Consequently, fluid pressure builds up posteriorly and leads to a posterior capsular rupture (Figure 3). A larger capsulorhexis will prevent this problem, but it causes a tearing capsule to extend closer to the equator and leaves less room for errant tears.
FORCEPS CHOICE
I favor the Masket Capsulorrhexis Forceps (Katena Products, Inc., Denville, NJ), which has arced blades. As a result of the blades' curvature, the forceps arch over the nucleus when I am performing the capsulorhexis. This provides an easier grasp of the tearing capsule, without placing pressure on the nucleus, especially when I am tearing the capsule opposite to the incision.
MICROSCOPE MANAGEMENT
The surgeon must focus the microscope carefully in order to visualize the tearing capsule. He must be able to focus through any corneal opacity and distinguish the anterior capsule. If he cannot see the capsule as a result of a dense lens nucleus, he must turn to capsular dyes to enhance visualization of the capsular tear. Without this aid, the threat of an errant capsulorhexis skyrockets.
Suggested reading: Fishkind, WJ, ed. Complications in Phacoemulsification: Avoidance, Recognition, and Management. 1st ed. New York, NY: Thieme Medical Publishers; 2002.
