Origin of the Scleral Tunnel Method

letters to the editor Evaluating Astigmatic Results To the Editor: I read with interest the article by Dr. Masket on his one year astigmatic results for a 4.0 mm scleral pocket incision. 1His observation that introducing a radial component into a tangential suture technique fails in the long term to prevent against-the-rule decay agrees with my own findings with a 5.1 mm incision (Ocular Surgery News, January 1, 1993, page 41). However, the scientific value of Dr. Masket's conclusions would be enhanced by employing vector analysis using Naeser's formula for polar values to which he refers in the text and references. The simple subtraction method used in this paper is useful but only as a "rule of thumb" guide to incision performance. The deficiencies of this method are obviously recognized by Dr. Masket as, in this series, he attempts to "vectorize" his results by excluding all patients whose preoperative axis lies obliquely between 20 and 70 degrees and 110 and 160 degrees. This omission makes it necessary for a significant but unquoted proportion of the population sample to be excluded from the study. Using Naeser's formula for studying the effects of incisions and suture techniques in a polar orientation would enable the inclusion of all eyes regardless of astigmatic orientation, thereby providing valid comparisons of incision and closure techniques. These data are complementary to the information provided by calculating surgically induced astigmatism as described by Jaffe and Clayman, also referred to in the article. Both analyses together provide the comprehensive but essential information required for the analysis of cataract incisions when the surgeon's goal, as in Dr. Masket's series, is astigmatic neutrality. Noel Alpins, F.R.A.CO., F.COphth., F.A.CS. Melbourne, Australia REFERENCE 1. Masket S. One year postoperative astigmatic comparison

of suturedand unsutured 4.0 mm scleral pocket incisions.

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Samuel Masket, M.D., replies: Dr. Alpins and I are in full agreement regarding the astigmatic behavior of sutured incisions. Additionally, we agree that the analysis of induced changes in astigmatism must account for alteration of cylinder axis. 812

Unfortunately, however, Dr. Alpins misinterprets the method of astigmatic analysis used in the study. 1 He suggests that the method is one of "simple subtraction." The subtraction method compares the magnitude of preoperative and postoperative astigmatism without regard to cylinder axis. As an example, using the subtraction method, an eye with 1.0 diopter (D) of preoperative with-the-rule (WTR) cylinder that develops 1.0 D of against-the-rule (A TR) cylinder postoperatively would have no net change in corneal astigmatism. However, in the system used in the study,1 a method that I refer to as algebraic analysis, the same case example would be reported as having 2.0 D of induced ATR cylinder, more appropriate to the surgical outcome. Similar to polar analysis, 2 the algebraic system is designed to discern induced WTR and ATR changes. It assumes an equal value for all positive cylinder between 70 and 110 degrees as being WTR; likewise all positive cylinder between 20 and 160 degrees is treated equally as ATR cylinder. In simple terms, the method evaluates changes in corneal cylinder as an algebraic rather than as a trigonometric function. Nevertheless, it is wholly unrelated to the "simple subtraction method," an arithmetic system. Cases with oblique cylinder are avoided since the incisions (placed superiorly in the study) would be off axis. It should be apparent that Dr. Alpins and I share similar thoughts regarding the objectives for the evaluation and study of postoperative astigmatism. REFERENCES 1. Masket S. One year postoperative astigmatic comparison

of suturedand unsutured 4.0 mm scleral pocket incisions. J Cataract Refract Surg 1993; 19:453-456

2. Naeser K. Conversion of keratometer readings to polar values. J Cataract Refract Surg 1990; 16:741-745

Origin of the Scleral Tunnel Method To the Editor: I congratulate Dr. Masket on his article "One Year Postoperative Astigmatic Comparison of Sutured and Unsutured 4.0 mm Scleral Pocket Incisions." This is a subject about which I spoke at the Welsh Cataract Congress in September 1992. The scleral tunnel incision was first described by Girard and Hofmann in 1982 at the Welsh Cataract Congress and published in 1984. 1 The incision, actually a sclero-corneal tunnel, has become a

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standard approach for phacoemulsification and intraocular lens implantation. In a prospective study, 2 the scleral tunnel incision sutured with absorbable interrupted sutures produced only an average of 0.34 diopter of induced astigmatism after all sutures had absorbed. It is interesting that neither Dr. Masket nor any ofthe other authors who have written about the scleral tunnel incision acknowledge the origin of the incision. It is also interesting that, in addition to various suggested modifications of the shape of the scleral tunnel incision, the trend is to a sutureless scleral tunnel incision. The rationale for the sutureless scleral tunnel incision is not clear. Not suturing the incision does not reduce the amount of induced astigmatism; it leaves the patient with the possibility of a ruptured wound (S.P. Thornton, M.D., "Total Iris Dehiscence Following IOL Implant," Ocular Surgery News, August 1, 1992), and the possibility of endophthalmitis. 3,4,5

randomized, and controlled study. Nevertheless, the 1992 ASCRS survey 1 indicated that 35% of respondent members are using a sutureless method. Poorly constructed wounds that demonstrate leakage at surgery or hypotony in the early postoperative period potentiate infection and should be sutured to create a proper seal. Sutures may be eliminated only when the incision is appropriately constructed to guarantee a hermetic seal. In my study that was cited by Dr. Girard, no benefit was gained from suturing and I reported that mean preoperative and one day postoperative intraocular pressures were statistically indistinguishable for patients with sutured and un sutured incisions; no cases were noted to have hypotony or leakage. Given those circumstances, I believe that a self-sealing internal corneal valve in combination with a reduced dimension sclero-corneal tunnel incision allows sutureless surgery to be safe and effective.

Louis J. Girard, M.D.

REFERENCES

Houston, Texas REFERENCES 1. Girard LJ, Hofmann RF. Scleral tunnel to prevent in-

2. 3. 4. 5.

duced astigmatism. In: Emery JM, Jacobson AC, eds, Current Concepts in Cataract Surgery; Proceedings of the Eighth Biennial Cataract Surgical Congress. Norwalk, CT, Appleton-Century-Crofts, 1984; 101-102 Girard LJ, Hofmann RF. Scleral tunnel to prevent induced astigmatism. Am J Ophthalmol 1984; 97:450-456 Stonecipher KG, Parmley VC, Jensen H, Rowsey 11. Infectious endophthalmitis following sutureless cataract surgery. Arch Ophthalmol1991; 109:1562-1563 Miller KM, Glasgow BJ. Bacterial endophthalmitis following sutureless cataract surgery. Arch Ophthalmol 1993; 111:377-379 Nelson DB, Donnenfeld ED, Perry HD. Sterile endophthalmitis after sutureless cataract surgery. Ophthalmology 1992; 99:1655-1657

Samuel Masket, M.D., replies: Dr. Girard correctly indicates that the scleral tunnel ("pocket") method has become the standard for small incision cataract surgery. While clear corneal incisions are increasing in popularity, 54 % of respondents to the 1992 ASCRS member survey indicated a preference for the incision to be placed 2 mm posterior to the limbus. 1 However, the origin of the scleral tunnel method is generally attributed to Richard Kratz. In a 1980 publication,2 the combination of a scleral tunnel incision with keratometrically controlled running suture tension was reported. Colvard, lead author of the publication, credits the origin of the method to Kratz (personal communication, 1983). Indeed, Kratz has been cited in numerous reports from many authors, including me, in reference to the scleral tunnel method. The question regarding safety and efficacy of selfsealing incisions is difficult to answer without a large,

1. Learning DV. Practice styles and preferences of ASCRS members-1992 survey. J Cataract Refract Surg 1993; 19:600-606 2. Colvard DM, Kratz RP, Mazzocco TR, Davidson B. Clinical evaluation of the Terry surgical keratometer. Am Intra-Ocular Implant Soc J 1980; 6:249-251

Acute Intraoperative Suprachoroidal Hemorrhage To the Editor: James Davison has contributed another useful insight to the anterior segment surgeon in his paper "Acute Intraoperative Suprachoroidal Hemorrhage in Capsular Bag Phacoemulsification."l Dr. Davison reported that with his capsular bag phacoemulsification technique, his incidence of AISH has decreased from 0.9% to 0.06%. I would like to expand on several of his points. My AISH study of2,523 consecutive eyes operated on between 1988 and 1990 (published in this journal although not cited in his paper) showed an AISH incidence of 0.6%, closer to his initial finding. 2 I emphasized that I used a posterior chamber, in-the-bag phacoemulsification technique in 96% of these patients expressly to decrease intracameral pressure fluctuations. 3 I have also noticed a decreasing incidence of AISH in my patient population as I have moved to an ever more watertight incision. I do not use a paracentesis for a second instrument, and I use a 2.5 mm keratome to accommodate insertion of the phaco tip in a snug fashion. I believe this leads to "improved containment," as Dr. Davison mentions. This will decrease the intraocular pressure fluctuations and, therefore, decrease the shear mechanism at work in the suprachoroidal space during cataract surgery. I also presented a method of surgical management of

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