Learn how to handle a miotic pupil and the various intraoperative complications to which it can lead.
Samuel Masket, MD Los Angeles
By compromising the cataract surgeon's ability to see what he is doing, a miotic pupil dramatically increases the risk of intraoperative complications. In fact, a study of 1,000 consecutive extracapsular cataract extractions showed that a small pupil was the most common factor associated with vitreous loss and capsular rupture.1
A miotic pupil can cause the surgeon to damage the patient's pupil, emulsify or otherwise damage the iris, or cause collateral damage to the capsule or zonules. Unfortunately, it is a common, as well as a significant, obstacle to a successful surgical outcome. For this reason, surgeons need to know in advance the best methods for handling a miotic pupil. These techniques not only create adequate work space for the surgeon, but they also maintain a pupil of normal function and aesthetics. Problems with pupillary function can result in iatrogenic induced glare dysfunction,2 and, of course, a misshapen pupil is highly dissatisfactory to the patient, especially in the case of light-colored irides (See Figure 1).
Figure 1. Extensive iatrogenic damage to the pupil sphincter
due to large sphincterotomies. This method for managing the pupil
resulted in an aesthetically deformed pupil and an unhappy patient
suffering from postoperative glare symptoms.
(Images reprinted from Masket S., "Cataract Surgery Complicated
by the Miotic Pupil," Cataract Surgery in Complicated Cases,
2000, with permission from SLACK Incorporated.)
In this article, I will describe how to deal with a small pupil and with various resultant surgical complications, should they arise.
Background
Oftentimes, small pupils simply result from the aging process, which can cause the dilator muscle of the pupil to atrophy. Elderly blue-eyed individuals are particularly prone to this problem.
Pseudoexfoliation is commonly associated with small pupils, and this condition significantly increases the risk of complications. In addition, a host of inflammatory conditions, like previous uveitis or iritis, may cause posterior synechia to form, which in turn will inhibit pupil dilation. Diabetes and the long-term use of anti-glaucoma medications can result in a small pupil. There are also some very unusual instances of congenitally abnormal pupils.
Preoperatively
A dilated preoperative examination should alert you if a patient is likely to have a pupillary problem during surgery. Your next step is to define the cause of the small pupil and any associations that may exist. If a patient has pseudoexfoliation, for instance, there may well be an associated looseness of the lens, which will cause other problems.
If your preoperative examination reveals an old inflammatory membrane holding down the patient's pupil, you will want to peel this membrane away during the cataract procedure. Similarly, if you discern the existence of posterior synechia, you will need to plan to lyse those adhesions during surgery. Synechiolysis alone frequently achieves an adequate pupil diameter for cataract surgery.
For patients whose medications have induced miosis, stop the use of these agents for a safe interval prior to surgery. You may need to prescribe alternate drugs to manage intraocular pressure.
Three topical agents will work best when dilating the patient's pupil just prior to surgery: a cycloplegic; mydriatic and non-steroidal anti-inflammatory drug.
* Cycloplegics. The most commonly used cycloplegic agent is cyclopentolate hydrochloride 1%. It provides good cycloplegia and pupil dilation, the latter of which can last as long as 36 hours. Tropicamide hydrochloride 1% also does well with pupil dilation but for a shorter duration and without the same degree of cycloplegia. Finally, atropine sulfate 1% provides long-lasting mydriasis, up to a week postoperatively. Consider this agent in cases of chronic uveitis.
* Mydriatics. The most commonly used agent, phenylephrine hydrochloride 2.5%, delivers excellent pupil dilation when combined with a cycloplegic. Though frequently used, particularly in cases of poorly dilating pupils, phenylephrine hydrochloride 10% may cause a significant increase in blood pressure in some patients. It can also result in punctate keratopathy. Cyclomydril and other combination agents work well for examinations, but they may not be adequate for all surgical cases, especially as they are ineffective at cycloplegia.
* NSAIDs. Combined with mydriatics and cycloplegics, presurgical drops of non-steroidal anti-inflammatory drugs reduce the likelihood of the pupil's constricting intraoperatively. Keep this option in mind particularly for cases that run long and for patients who are diabetic or have had prior surgery. Researchers have investigated suprofen 1% and flurbiprofen sodium 0.03% specifically as intraoperative antimiotics.
Intraoperatively
The pupil size that will allow you to operate comfortably depends both on each individual case and on your personal preference. If I am operating on someone with a small pupil but no other problems, I may be comfortable with a 3.5-mm or 4.0-mm pupil. In a patient likely to have problems, I may need a larger pupil. Generally, if you can create an adequate capsulorhexis, you can complete the surgery.
Naturally, you will want to dilate the pupil with a minimum of damage, expense and time. Following are the steps, from first to last resort, for achieving this goal.
* Viscodilation. Assuming that, if necessary, you have already lysed any adhesions and peeled any pupillary membrane, place a cohesive viscoelastic agent in the pupillary space. This step alone may dilate the pupil an extra millimeter or two and enable you to perform an adequately sized capsulorhexis. You're going to use a viscoelastic anyway, so this step doesn't entail any extra time or expense.
* Pupil stretch. Popularized by Garden City, Kans., surgeon Luther Fry, pupil stretch is an inexpensive and time-efficient method for enlarging a pupil that did not dilate adequately with the placement of a viscoelastic agent.
This technique involves two hooks, one pushing and one pulling, to stretch the pupil in one, two or more meridia. The viscoelastic will keep the anterior chamber deep and will thereby protect anterior-segment structures. Done in a slow, controlled fashion, this method usually achieves an adequately sized pupil that postoperatively will still react and behave normally and will have an aesthetically acceptable appearance. Instruments like Katena's Keuch two-pronged pupil stretcher or Rhein Medical's Beehler four-pronged pupil stretcher are one-time purchases that add little expense to surgery. I happen to prefer the former.
* Mini-sphincterotomies. Should pupil stretch fail to achieve the desired pupil diameter, your next option is to use a small scissors to make a series of very fine partial cuts to the iris sphincter. You may then perform additional stretching maneuvers, which should be more successful than previously. Provided you keep incisions very small, the postoperative pupil should function normally and appear as it did before surgery (See Figure 2).
Figure 2. Postoperative view of a patient who had miotic pupil surgery. In this case, a series of mini-sphincterotomies was formed using retinal scissors. Intraoperatively, it was necessary to lyse previous synechiae and employ pupil stretch in combination with mini-sphincterotomies. Note a superiorly placed laser iridotomy. This patient had sustained an attack of angle closure glaucoma several years earlier.
* Iris hooks. If the patient's pupil is still too small for you to make an adequate capsulorhexis, you will need to consider placing iris hooks. These instruments require particular caution on your part. They can anteroplace the iris diaphragm, which will result in thermal damage during phacoemulsification. To avoid this complication, be sure to position the hooks parallel to the iris plane and release the hooks after the capsulorhexis but before emulsification. Remember, too, that an adequate, not a very large, pupil is your goal.
* Pupil ring expanders. These devices were designed to enlarge a pupil without sphincter damage. They do add significant expense to surgery and can be difficult and time-consuming to place. For that reason, they are my last choice. Three expanders are the Grather, Siepser and Morcher.
Complications
As with any surgical intervention, methods for enlarging the pupil can cause complications. Here are more tips for reducing the risk of complications and for managing them if they do occur.
* Atonic pupil. Irreparable tears to the iris sphincter can result in a pupil that, postoperatively, is enlarged and does not react . As I mentioned earlier, all dilation methods must be done slowly and gradually in order to minimize the tearing effect on this muscle.
Also, be sure to dilate or stretch the patient's pupil only as much as needed. At the close of surgery, bring the pupil back down pharmacologically with an intraocular miotic. If necessary, stroke the pupil with a blunt, gentle instrument to reduce its size. This measure will help keep the pupil from becoming fixated.
Lastly, using a large amount of topical anti-inflammatory agents will prevent adhesions between the iris and the underlying capsule.
* Bleeding. Pupil stretch or any cut or tear of the sphincter muscle could result in bleeding (See Figure 3). Generally, time alone will be enough in these cases. If you encounter significant bleeding, transiently elevate eye pressure by adding a balanced salt solution, a viscoelastic agent or air to the eye. This should slow the flow of blood, and then you can irrigate or aspirate the blood from the eye before proceeding with surgery.
Figure 3. Satisfactory aesthetic and functional outcome following an inferior sphincterotomy with a pre-placed suture in an eye with a miotic pupil. Stretching the pupil or any cut or tear of the sphincter muscle can result in bleeding. The iris hematoma noted above is only a minor aesthetic deformity. Major bleeds within the eye are highly unlikely.
A patient receiving anticoagulants or one who has a natural coagulopathy may require a longer interval of elevated pressure until the blood flow is slowed. You will need to balance the degree of pressure elevation against the need for circulation at the back of the eye.
It is extremely unlikely that enlarging the pupil will create a major bleed within the eye. If it does, however, you may add fibrin.
* Instrument-related damage. Be especially careful if you use a four-pronged pupil stretcher. I have seen patients who sustained damage to the corneal endothelium because one of the prongs was not in the pupillary space but up against the inner surface of the cornea (See Figure 4). Bleeding is another potential complication.
Figure 4. Postoperative view of a patient who sustained thermal damage to the superior iris during phacoemulsification of an extremely dense, brunescent nuclear cataract. Iris hooks were used during the procedure. The hooks tented the iris anteriorly, bringing it in contact with the emulsification tip. Fortunately, given the superior location of the iris damage, the patient was asymptomatic.
With this instrument, the prong closest to you is fixed, while the other three move away from you. Be certain these remain parallel to the iris plane and have not slipped out into the pupil margin. Pay particular attention to their position when you are starting to depress the plunger to create the pupil stretch.
Dr. Masket specializes in anterior segment surgery and is in private practice. He is a clinical professor at the Jules Stein Eye Institute, University of California at Los Angeles.
1. Guzek JP, Holm M, Cotter JB, et al. Risk factors for intraoperative
complications in 1000 extracapsular cataract cases. Ophthalmology
1987;94:46-466.
2. Masket S. Relationship between postoperative pupil size and
disability glare. J Cataract Refract Surg 1992;18:506-507.
Further Reading
De Juan E Jr., Hickingbotham D. Flexible iris retractors. Am J
Ophthalmol 1991;111:766-777.
Fine IH. Pupilloplasty for small pupil phacoemulsification. J
Cataract Refract Surg 1994;20:192-196.
Masket S. Avoiding complications associated with iris retractor
use in small pupil cataract extraction. J Cataract Refract Surg
1996;22:168-171.
Nichamin LD. Enlarging the pupil for cataract extractions using
flexible nylon iris retractors. J Cataract Refract Surg 1993;19:793-796.
Shephard DM. The pupil stretch technique for miotic pupils in
cataract surgery. Ophthalmic Surg 1994;24:851-852.
Methods for Enlarging the Pupil
| DO NOT INVOLVE THE IRIS SPHINCTER |
| Synechiolysis |
| Pupil Membrane Peeling |
| Viscodilation |
| INVOLVE THE IRIS SPHINCTER |
| Pupil Stretch |
| Mini-sphincterotomies |
| Iris Hooks |
| Pupil Ring Expanders |