Retinal Detachment After Laser Capsulotomy

LEITERS

Reference 1. Anderson q. Circumferential perilimbal anesthesia. ] Cataract Refract Surg 1996; 22:1009-1012 .

Reply: I appreciate the comments made by Dr. Bernstein regarding circumferential perilimbal anesthesia (CPA). Dr. Bernstein asks whether the CPA technique is necessary since the topical anesthesia seemed adequate. The answer is that the topical is adequate for superficial pain associated with making incisions, puncturing conjunctiva, injecting lidocaine, and otherwise handling the eye tissue. However, there is a second type of pain that is a deep pressure sensation that patients experience when the eye is distended by fluid during phacoemulsification or other intraocular procedures. This type of pain has been called zonular or ciliary stretch. It has been my experience that approximately 20% of patients will have zonular stretch with the use of topical anesthesia as the only anesthetic. Two examples from my practice exemplify zonular stretch in patients receiving topical anesthesia. One patient was a 67-year-old woman who developed a pressure sensation during the phacoemulsification procedure. The pain required an interruption of surgery. The surgeon gave a subconjunctival injection to relieve her discomfort. The second patient had more severe pressure during phacoemulsification that required a retrobulbar anesthetic injection to continue the surgery. Interestingly, the patient had uneventful phacoemulsification using topical with CPA 6 weeks later in the other eye. The troublesome occurrence of this type of zonular stretch pain was the major reason for the development of techniques such as CPA or intraocular anesthesia. The CPA technique is a specialized adjunct conjunctival injection that is given after the topical. I believe the two anesthesia techniques complement each other. The topical anesthesia provides a superficial anesthesia to the cornea and conjunctiva that provides enough anesthesia to give the subconjunctival injection and to make incisions. The CPA provides a deeper 360 degree treatment that blocks the corneal limbal nerve plexus and the long ciliary nerves that branch in the sclera at the horizontal meridians. Many of these nerves may cause zonular stretch because they enervate and anastomose with the perilimbal sclera, iris, and ciliary body. In my experience in over 1000 cases, CPA does effectively block zonular stretch and I have not had to convert to other types of anesthesia. The second issue is what to do in the event of increasing and intolerable patient discomfort during cataract surgery under topical anesthesia. I agree that retrobulbar or peribulbar in an open eye is a last resort. I would first lower the infusion bottle and gently increase sedation with the assistance of the anesthetist. Second, one could administer either CPA or give an intraocular anesthesia injection. Recently, I have had good success using a 0.5 cc intraoc-

ular 50:50 mixture of preservative-free 1% lidocaine and 0.5% bupivacaine hydrochloride (Marcaine®j diluted 1:4 with balanced salt solution (BSS
Retinal Detachment After Laser Capsulotomy

T

he rate of postoperative retinal detachment (RD) is an important consideration for cataract surgeons. The journal published Olsen and Olson's paper entitled "Prospective Study of Cataract Surgery, Capsulotomy, and Retinal Detachment" in March 1995. 1 The topic remains of great interest throughout the ophthalmic literature, as evidenced by the recent work by Tielsch et al. 2 in which Olsen and Olson's work is recognized. Olsen and Olson's article is one of the more important in the literature relating neodymium:YAG (Nd: YAG) capsulotomy to RD, but there were flaws that affect their conclusions. The most important correction to be made is the conclusion drawn from Table 2; namely, that there is no statistically significant increase in the rate of RD after capsulotomy when all patients, regardless of risk factors, are considered as a whole. Their data support just the opposite conclusion. The t-test is used for analysis of continuous data (e.g., to compare means). The chi-square test is used for analysis of binomial outcomes (e.g., yes or no, black or white, detachment or no detachment). The chi-square test is the appropriate test to determine whether RDs are distributed similarly between groups. The t-test was used to analyze this set of discrete binomial data and led to an invalid and incorrect conclusion. In fact, when the appropriate statistical test, the chi-square test for discrete binomial data, is applied, a significant difference is noted, with a chi square value of 4.59 and a P-value ofless than 0.05.

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LEITERS

Suboptimal statistical tests are applied elsewhere to otherwise excellent data, but without impacting conclusions. For example, nonparametric tests comparing discrete outcomes should be used to interpret Table 3, rather than a t-test for continuous numeric data. The Olsen and Olson study presents very helpful information. Appreciation of the apparent increased risk ofRD in patients with longer axial lengths is buttressed. Critical review of the article emphasizes the importance of proper statistical treatment of data that are painstakingly obtained. Without great care, statistics are as likely to lead as mislead, undermining the value of the work. Based on the information in this article, as well as other information in the literature, higher rates of postcataract surgery RD are associated with Nd:YAG capsulotomy in all patients having the procedure. The risk in some patients may be greater than in others, but the data indicate that some increased risk is conferred on any patient having the procedure. This suggests that we maintain a high threshold for performing Nd:YAG capsulotomy on all patients and continue to strive to identifY and minimize controllable factors contributing to opacification of the posterior capsule. BRADLEY ROSEN, MO

Los Angeles, California

References 1. Olsen GM, Olson RJ. Prospective study of cataract surgery, capsulotomy, and retinal detachment. J Cataract Refract Surg 1995; 21: 136-139 2. TielschJM, Legro MW, Cassard SO, et al. Risk factors for retinal detachment after cataract surgery: a population-based case-control study. Ophthalmology 1996; 103:1537-1545 3. Javitt JC, Tielsch JM, Canner JK, et al. National Outcomes of Cataract Extraction: increased risk of retinal complications associated with Nd:YAG caps ulotomy. Ophthalmology 1992; 99: 1487-1497 4. Javitt JC, Vitale 5, Canner JK, et al. National Outcomes of Cataract Extraction I: retinal detachment after inpatient surgery. Ophthalmology 1991; 98:895-902

Reply: We appreciate the comments of Dr. Rosen in pointing out the importance of statistical analysis truly evaluating the information provided. He has provided additional insight confirming neodymium:YAG capsulotomy as a risk factor for retinal detachment. While the difference seemed apparent to us, our analysis failed to show statistical significance. This instance should impress upon all of us that a test is only as good as it is appropriately used.Randall J. Olson, MD 8

Additional Thoughts on Polysulfone Corneal Inlays

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would like to make the following comments about a recently published article on polysulfone intracorneal lenses. l The concept of correcting refractive errors by altering the refractive index of the cornea in preference to altering its shape, or of the the eyeball itself, is an elegant one. I pioneered the use of polysulfone, with its high refractive index of 1.633, and published my results. 2 These 44 operations were performed shortly before I retired from the National Health Service (NHS) in 1984, following which it became impossible for me to summon the patients for examination or even to pursue the hospital notes without obtaining the written permission of my successor at the Southend General Hospital, Mr. Leslie Alexander, with respect to each and every case. So, after my retirement, I virtually lost control over what happened to these patients, but none of the penetrating keratoplasties referred to in the paper was done in my time and probably was not necessary anyway. The paper is actually more or less correct and is based on material supplied by me to Mr. Horgan, the first named author. It does not, however, give the reason why I stopped using those inlays, which was because of the small number (three) of cases that showed marked diurnal variation in refraction. That is to say, when the patients got up in the morning they could see 20/20 unaided. By lunch time, they needed + 2 to see 20/20 and by late afternoon, they needed +4. Serial K-readings showed that this was due to flattening of the cornea, presumably caused by dehydration of the cornea overlying the inlay as the day wore on. I never could understand why this phenomenon occurred in only three cases and not in the rest of them. Perhaps it had something to do with the tear film. I discussed this phenomenon with Dr. Richard Lindstrom, who had examined many of my patients around 1981 and who published his own results of that survey. We both agreed that it was indicative of the fact (brought out in Mr. Horgan's paper) that polysulfone was impermeable and providing the inlays with microperforations should eliminate the problem. I did, in fact, use two more inlays equipped with macroperforations surrounding the central 3.0 mm unperforated central zone on private patients after I left the NHS. These

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