Displacement of nuclear fragments into the vitreous, commonly referred to as dropped nucleus, is a rare but potentially serious complication of cataract surgery. A recently published study reported results after 1 year of prospective national surveillance through the British Ophthalmological Surveillance Unit (BOSU). In that study, the incidence of dropped nucleus in the United Kingdom was 2 to 3 per 1,000 phacoemulsification operations.1
Despite the fact that 97% of these cases proceeded to vitrectomy—68% within 1 week of the original procedure—at final follow-up only 67% of cases had a BCVA of 6/12 or better. In 14% of cases, a visual acuity of 6/60 or less was reported.2
Many ophthalmic units offer phacoemulsification cataract surgery but do not have facilities within the department to manage this complication. Therefore, it is important to understand the potential risk factors to try to reduce the risk of this complication to as low a level as possible.
The BOSU study established potential risk factors for dropped nucleus using a case-control methodology. The strongest risk factors confirmed on multivariate analysis (odds ratio >5.0) included eyes that had previously undergone vitrectomy surgery, eyes with pseudoexfoliation, and cases in which the nature of the cataract required staining with trypan blue (Vision Blue; DORC International BV, Zuidland, Netherlands) to visualize the capsulorrhexis.
There was also a smaller but statistically significant added risk in patients who had topical or sub-Tenon's anesthesia as opposed to peribulbar or general anesthesia. Risk was also increased in male patients and cases operated on by relatively inexperienced surgeons.
The higher risk in men may be due to intraoperative floppy iris syndrome (IFIS). In patients with IFIS, there is characteristic billowing of the iris stroma during surgery and increased tendency for iris prolapse. A posterior capsular rupture rate of 7% to 12.5% has been reported.3
Incomplete pupil dilation and posterior synechiae were additional risk factors identified in univariate analysis of the study data. Increased age of the patient was also a risk factor. This may be due to denser nuclear sclerosis with age and increased tendency for zonular weakness.
REDUCING RISK
Based on the risk factors identified, we advise taking the following practical steps to reduce the risk of dropped nucleus.
Preoperative. The added risk of this complication for relatively inexperienced surgeons may be mitigated through careful case selection. By keeping in mind the risk factors identified above, exposure to more difficult cases may be gradually increased as a surgeon in training develops greater expertise in lower-risk cases.
Use of tamsulosin and other alpha-receptor blockers should be documented in the patient's medical history and highlighted before surgery, as well as risk factors such as pseudoexfoliation and previous vitrectomy. When preparing the patient, maximal pupil dilation should be ensured by allowing adequate time on the day of surgery for mydriatic drops to take effect, or by providing patients with an additional dose to be administered at home before attending the ophthalmic unit.
Anesthesia. Topical and sub-Tenon's anesthesia are increasingly becoming the methods of choice for most cataract surgeons. A factor that may increase the risk of complications with these methods is the reduced level of akinesia. This factor should be considered for high-risk cases and when training junior surgeons on more difficult cases. In such cases, peribulbar or general anesthesia may be preferred, unless the surgeon routinely obtains adequate akinesia with sub-Tenon's anesthesia.
Intraoperative. Eyes that have undergone previous vitrectomy pose a challenge because of the absence of support from the vitreous and the increased mobility of the lens-iris diaphragm. Deepening of the anterior chamber causes zonular stress and increased difficulty of access for the surgeon. The pathologic anterior chamber deepening is caused by the reverse pupil-block phenomenon and the increased effect of pressure from the irrigation fluid in the anterior chamber with a lack of posterior resistance in the absence of vitreous.4 The pupil block may be alleviated by separating the iris from the lens capsule during surgery with a second instrument, or the whole procedure may be facilitated by the use of a single iris retractor placed at the beginning of surgery.5
In patients identified before surgery as at increased risk for IFIS, an effective method of improving iris tone and dilatation is the administration of diluted intracameral phenylephrine at the beginning of surgery. We have achieved good results from the regime reported by Gurbaxani and colleagues: 0.25 mL of minims phenylephrine HCl 2.5% mixed with 1.0 mL balanced salt solution.6 Others have documented good results from combining this with the administration of preoperative topical atropine 1%.7 A high-viscosity cohesive ophthalmic viscosurgical device may help mechanically enlarge the pupil. In cases in which the pupil remains small, iris retractors may be used.
Pseudoexfoliation is a known risk factor for capsular rupture and lens displacement due to pathologic weakness of the zonular fibers that keep the lens in place.8 Anticipation of this weakness at all steps during surgery will help reduce complications. Care is required during hydrodissection to limit zonular stress, and higher power may be required during phacoemulsification to limit movement of the lens as the probe tip advances through the nucleus. Use of chopping maneuvers to break up the nucleus may also cause less zonular stress. When aspirating soft lens material, excessive pull and stress on the capsular bag should be avoided.
Trypan blue is used to visualize the capsulorrhexis in cases with advanced nuclear sclerosis and also in significant cortical cataracts that impair the red reflex. The use of trypan blue as a risk factor for dropped nucleus is most likely related to the increased difficulty of surgery in eyes with denser nuclear sclerosis. Steps to reduce this risk should be judged by individual surgeons depending on the ability of their phaco machine to handle dense nuclei, their individual experience with such cases, and their experience with large-incision manual extracapsular cataract extraction, which could be considered as an alternative.
Finally, if the nucleus drops despite all precautions, attempts to retrieve it via the anterior segment should be avoided. The BOSU study showed that 77% of primary IOLs were either removed or replaced at the time of a secondary procedure, so leaving the eye aphakic may be preferable. There is an immediate risk of inflammation and raised intraocular pressure that must be managed medically. Urgent referral for vitreoretinal intervention gives the patient the best chance of achieving useful vision.
Stephen J. Charles, MA, MD, FRCOphth, is a consultant ophthalmologist at Torbay Hospital, Torquay, England. Dr. Charles states that he has no financial interest in the products or companies mentioned.
Michael D. Cole, FRCOphth, is a consultant ophthalmologist at Torbay Hospital, Torquay, England. Dr. Cole states that he has no financial interest in the products or companies mentioned.
Charles R.H. James, MRCP, FRCOphth, is a consultant ophthalmologist at Torbay Hospital, Torquay, England. Dr. James states that he has no financial interest in the products or companies mentioned.
Sajjad Mahmood, MA, FRCOphth, is a consultant ophthalmologist at Manchester Royal Eye Hospital, Manchester, England. Dr. Mahmood states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +44 161 276 8044; e-mail: saj@eyebase.co.uk.
Hirut von Lany, FRCS(Ed), FRCOphth, is a consultant ophthalmologist at Torbay Hospital, Torquay, England. Dr. von Lany states that he has no financial interest in the products or companies mentioned.
